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Electric Stunt => Gettin all AMP'ed up! => Topic started by: Tim Wescott on July 25, 2019, 10:46:16 PM
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Finally decided to pull the trigger on going electric. I'm starting with el-cheapo batteries and a Cobra motor (inexpensive, but some folks seem to like it). I have an old Shultze ESC that was given to me, and should work, and, of course, I'm friends with the wife of a guy who makes timers.
Comments from the peanut gallery on how to mount that motor are welcome. If it was all fresh dry wood I'd put a ring mount in the front, and front-mount the motor -- unless someone speaks up and tells me that Cobras don't like that. Part of me wants to machine a mount that'll catch the existing motor mounts and rear-mount the motor. That'll both give me something that's drop-in, and it'll be drop-out in the event that I decide I hate electrics after all.
Hopefully I've done my math/guessing right. For reference the plane is around 690 squares, and weighed 64 ounces empty with a 46LA. The starting setup is:
Cobra 2826-12 motor
Turnigy 3300mAh 5S battery (I got one 3300mAh and one 3000mAh, to figure out which is best)
Shultze ESC: fut-18.46K-F2B.gra (mit F2B Programm, es müssen kuhl sein!)
Some TUT or other.
I'll want to make room for a Recording TUT, even if I don't have the @#$% recording part working yet. I'll probably use Howard's AMA program, to go with the Shultze's F2B governing mode. Should have quite Hubin-esque flight characteristics, except for the Rushian slow take off.
I'm not sure what prop to use to start -- I'm thinking a 12-6, although the very first run may be a 12-6 cut down to 11-6, for ground clearance. Suggestions welcome...
The ESC has no BEC, so I'll have to tuck a voltage regulator in there somewhere. The TUT draws little enough current that I can probably get by with a 78L05 in some heat shrink.
Look at all the room in that equipment bay! Those things always look so sparse before you try to jam the last little bit-o-kit in there. Like the ESC. And the timer. And all the wires. Omigod, I'm doomed.
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Glad to hear you are going electrical. K2R spot remover (probably Cab-o-sil and a solvent) is good for sopping up oil.
People have had more success mounting the Cobra on the same side of the motor as the prop than on the opposite side from the prop ("front" and "back" definitions may vary).
I have some extra props. The APC is cheap and good, but you'll probably want one that goes the same way as your old engine.
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I have some extra props. The APC is cheap and good, but you'll probably want one that goes the same way as your old engine.
I got "tractor" props. More props to experiment with would be good.
Should I stick with 12" and lengthen my landing gear, or is it even remotely sensible to hold the diameter to 11"?
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How much do you figure will be the final weight? Depending on the weight, I think you have too much battery. I'm flying on a 5S 2450mah battery with a weight of 52 ounces. I'm using @ 75% of the battery.
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How much do you figure will be the final weight? Depending on the weight, I think you have too much battery. I'm flying on a 5S 2450mah battery with a weight of 52 ounces. I'm using @ 75% of the battery.
It's 64 ounces with the 46LA and all the slimer equipment. I'm assuming it'll be the same or slightly more with electrons.
If I just scale your figures by weight I get 3000mAh -- and that's what I would have bought across the board except that I chickened out and got a 3300mAh to try the first time, on the theory that an overweight plane in testing is better than a nice light pile of balsa trash after pooping out at the end of the pattern.
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Welcome to the madness.
XOAR PJN-E or PJM-E 12x6 works great.
https://www.amazon.com/XOAR-Electric-Airplane-Propeller-Blade/dp/B07B9WQVMP/ref=sr_1_2_sspa?keywords=XOAR+12x6&qid=1564158946&s=toys-and-games&sr=1-2-spons&psc=1&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUEyQkpNOVBLMk1IUEM4JmVuY3J5cHRlZElkPUEwMDAxOTUyMUIxS01POTZETzFHQyZlbmNyeXB0ZWRBZElkPUEwNTY3NTc5OTY4SjhQSk02WDVKJndpZGdldE5hbWU9c3BfYXRmJmFjdGlvbj1jbGlja1JlZGlyZWN0JmRvTm90TG9nQ2xpY2s9dHJ1ZQ==
https://www.ebay.com/itm/XOAR-PJM-E-12x6-3-Pack-Black-RC-Electric-Airplane-Propeller-12-Inch-Wood-Prop/372525591771?epid=17026781507&hash=item56bc416cdb:g:dzgAAOSwvwRcCHWo
Perhaps Cobra 3520-14 is a better option for the prop chosen and I assume it looks like it is a 60 size ship.
I would cut out everything out that used to hold the motor or fuel tank out, the engine crutch the fuel tank floor etc. Make sure you have airflow around the battery ESC and motor. A undersized spinner works great and looks pretty cool. With the larger motor I do not expect the system to run hot at all but cooling always helps.
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I use an 11” prop for a similar airplane at 73 oz. The CA 11” prop is inefficient, hence it takes more battery, but the performance improvement is worth it.
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It's 64 ounces with the 46LA and all the slimer equipment. I'm assuming it'll be the same or slightly more with electrons.
If I just scale your figures by weight I get 3000mAh -- and that's what I would have bought across the board except that I chickened out and got a 3300mAh to try the first time, on the theory that an overweight plane in testing is better than a nice light pile of balsa trash after pooping out at the end of the pattern.
Yeah, 2700mah to 3000mah is all you need.
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Yeah, 2700mah to 3000mah is all you need.
With the 3300mAh battery and the motor set into place (but no ESC, motor mount, etc.) it balances just about the same place that it does with the 46LA installed, dry.
So (A) the battery is going to get slid forward, and (B) I may just stick with the bigger battery for balance! (Because a tungsten motor mount would be silly, and I can't cut tungsten anyway).
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The CA 11” prop is inefficient, hence it takes more battery, but the performance improvement is worth it.
CA?
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How much do you figure will be the final weight? Depending on the weight, I think you have too much battery. I'm flying on a 5S 2450mah battery with a weight of 52 ounces. I'm using @ 75% of the battery.
I agree with Crist - I fly a 2820/12 on a 4s 2800 with 35% remaining and I have flown my 2826 on a 4s 2200 with 18%. With the right prop a 3300 is almost enough for 2 flights but I wouldn't try it. The 5s is better but if size and weight are an issue a 4s will work just fine. If your ESC keeps the rpm's constant then they will fly nearly the same and your only issues will be heat and battery ware.
The COBRA's seem to fare better with a front mount. I am using both and I have yet to have an issue because of the way it was mounted. They do exert a tremendous amount of torque when changing speeds and they do it quickly. Make sure you have adequate space beside the rear of the motor if you front mount it.
What are you doing for cooling? The pictures don't show any. The esc and motor will heat up a bit and both need good ventilation. The COBRA's need a gap between the fuselage and spinner to vent if you rear mount them. 1/16 is plenty. Air will actually draw through the motor to cool it. Outside of the rotating housing you just need to be able to move the heated air out but you will not get much cooling from airflow on the outside the motor. Also put a hole somewhere in the top, sort of like that little hole we put over an IC. They will stay hot and need a place to vent after the flight. The ESC and battery need the wind so keep the airscoop from the IC and try and put the battery and esc in it's path. If you had a pipe in there and still have the tunnel then you have a great place to put them. On one of my conversions I mounted all of that stuff on the bottom of the IC Cowl and cut some humongous vent holes at the back. Just keep it cool. The bigger the "S" values of the battery, the cooler they run. One more point on heat. An IC can be cooled by restarting it making back to back flights safe. IMHO this is not true with electric. They need to cool down a bit before going up again for a full pattern.
The clips are a rear "through the mount" where the motor uses the rear mount and prop adapter. This one currently has a 2826 on it. The nose views are to illustrate how you can use the pipe tunnel to advantage. I have moved the ESC to mount over the wing so that I can fit a 6s battery. The one in there now is a 5s 3000 Turnegy. I mount them skinny side down to get as much airflow around the battery as possible and give me room for all of those wires and crud. I mount the timer on the side of the fuselage with all of the pins pointing up. Biggest mistakes I made at first were locating the timer where it was difficult to hook up the programmer and putting the safety plug too close to the esc so that the wires wouldn't bend. Finally, when you locate stuff do it with everything connected (except the battery of course). The connectors don't bend and it really sucks when you have finally found the perfect place for the timer only to find out after you mounted it that the ESC cable won't attach or you can't get to the starting switch connector.
Have fun and you are doing the right thing asking. I just blundered into it a couple of years ago and made a whole bunch of really dumb mistakes. Like most IC types, I was focused on the motor, With electric it all starts with the prop. I don't think I will ever fully understand what changes what in electric but there are a whole lot of people here that do, so ASK, they will only occasionally bite your head off or call you an idiot.
Ken
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I agree with Crist - I fly a 2820/12 on a 4s 2800 with 35% remaining and I have flown my 2826 on a 4s 2200 with 18%.
With a steady-speed timer a pattern consumes an average of 7 watts per ounce of airplane weight (somewhere I have a spreadsheet where I worked that out from all of the then-extant planes on the "list your setup" thread). So you cannot just say "this battery + this motor = works" -- the motor supplies what energy it needs to keep the plane going, and keeps some for itself to keep warm at night. That's why I took Crist's 52 ounce weight and used it to scale up his battery usage.
The COBRA's seem to fare better with a front mount.
Thanks for that. The consensus seems to be that the best mount varies by motor brand. I certainly like a front mount better, although it means ripping into the plane more.
What are you doing for cooling? The pictures don't show any.
The current project plans say "TBD". I'm aware of the need, and will be doing (and verifying) something. I'm hoping to keep the look of the airplane, so I'm going to try to get enough air flowing through all the right places without messing with the outside envelope.
Have fun and you are doing the right thing asking.
Thanks.
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Perhaps Cobra 3520-14 is a better option for the prop chosen and I assume it looks like it is a 60 size ship.
Check out the pictures above. The 2826 barely fits that nose. If you want to put in a 3820 you are going to have to rear mount it. The 2820 will easily match the LA46 and the 2826 is a tad stronger. If you can rebuild the nose then I would say go for the 3520. I really don't like the battery that close to the sides but I also don't see any other way. Also while we are in the nose, if that exit ramp at the end of the cowl is all there is then he needs to cut a whole bunch of slots in the back of it. About 4sq" worth. Exit area has to be greater than input area on an electric.
Ken
Sorry, I hadn't seen your last post before posting this. Glad you are keeping cooling in mind. It is really very different than IC. Just a couple of shots of how slots do not distort the look of the plane, especially if they are on the bottom. Some of the guys I fly with have twice that many.
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It's 64 ounces with the 46LA and all the slimer equipment. I'm assuming it'll be the same or slightly more with the electrons.
Unfortunately, not slightly more, but significantly more. You are probably looking at total up weight of north of 70 oz. That’s with 5S battery and 6” prop (more efficient, less battery consumption). 6S and 5” pitch prop, add another 2-3 oz.
Maybe better to leave the poor Atlantis alone and throw together something purpose built?
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Howard's 73 ounce Impact is quite similar in size to the Atlantis, so I suspect I'll be OK if it's not too far north of 70 ounces.
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Howard's 73 ounce Impact is quite similar in size to the Atlantis, so I suspect I'll be OK if it's not too far north of 70 ounces.
I think you are looking at about a 6 oz gain overall with a 10oz battery. Don't know of any 6s that light but there are 5s available. Fuel for a 46LA is about 4 so overall take off weight difference about 2. I have one that is 70oz but it has a 3520 in it. You are going to be under powered but in a different way. It will pull it OK but you are probably going to get hotter than you should be. You need something to get your feet wet and find what works for you. They do fly different and it takes a bit to get used to the constant CG and not having to think about the engine. If the plane was trimmed IC then I would use a normal rotation prop.
Ken
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Probably unnecessary advice but make sure nothing is rubbing agents the motor. Wires or anything touching the motor will cause drag, high current draw and smoke coming out of the motor. Also I have had good luck with the KR timer. It has built in safety featured that protects agents equipment failure. I have used them from the start and they have save more than one motor from my stupid actions. Also you can not run an electric setup on the ground for the full 5 minutes. It will more often than not fry the motor. In flight the motor unloads and the current goes down. Most working setups are running the motor near it's max power. This true because one want's the smallest, lightest setup that has the power to fly the pattern. Another concept to keep in mind is maxim prop size rules are different for electric and fuel motors. For the fuel engines too small of a prop will allow the motor to over rev and destroy itself. With an electric motors it will try and turn the same rpm regardless of the prop. If fact you can run an electric motor no-load (no prop) and it is happy. Put on too big of a prop and it will try and turn the no-load RPMs. This requires more power (more current) then the motor can handle resulting is smoke. The good news is that spare parts for the Cobra are readily available at a reasonable cost and you don't need $10 glow plugs. Glow power has it's problems. Electric has it's problems. Whatever you use there is a learning curve. But once you get electric to work it pretty much works the same every time you turn it on. Electric's two big advantages are no greasy clean ups and consistency in performance and run time.
By the way Cobra has some good prop charts. Once you pick a prop size and required RPMs make sure it is in the safe range of the motor you have chosen. https://innov8tivedesigns.com/
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.... This requires more power (more current) then the motor can handle resulting is smoke. The good news is that spare parts for the Cobra are readily available at a reasonable cost...
I’m sure Tim knows this, but for the benefit of others starting in electrics: if the motor emits smoke due to overload, spare parts will not help, unless you know how to rewind the stator.
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I’m sure Tim knows this, but for the benefit of others starting in electrics: if the motor emits smoke due to overload, spare parts will not help, unless you know how to rewind the stator.
I think the spare part he was referring to was a new motor. With electric, when there is smoke, there is an internet order about to happen.
Ken
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... Fuel for a 46LA is about 4 so overall take off weight difference about 2. ...
The 46LA is an amazing engine. Fuel for a 46LA that's nicely adjusted to fly a 45 ounce plane is about 3 3/4 ounces. It's more like 4 and a tad for a 54 ounce plane, and for the 64-ounce Atlantis, it's just shy of 6 ounces. More power = more fuel, and the 46LA has an incredible range of adjustability for more or less power.
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I forgot to order one. And I'm kind of out of cash until the next paycheck. So I made one from stuff lying around. I expect it'll work, even if it's ugly.
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Probably unnecessary advice but ...
By the way Cobra has some good prop charts. Once you pick a prop size and required RPMs make sure it is in the safe range of the motor you have chosen. https://innov8tivedesigns.com/
Maybe, maybe not. But it is appreciated. I design motorized control systems for a living, or at least I have in the past. So I have made many of those mistakes with the boss's money.
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I generated this post and it didn't show up even after waiting 15 minutes. So I added the second post. Once the second was up, this first one appeared. Go figure.
Tim,
Before you do anything irreversible to the plane, get ALL the pieces together and weigh them. Generally conversions that start from an IC build come out heavy. Make sure you will not exceed about 70 ounces with that plane.
I would opt for a mount to fit the existing beam mount holes for the IC motor. That way you could go back to IC if the electric doesn't work out.
It also looks like you are somewhat limited for battery space, and room For the ESC and timer. It should be interesting to see what you come up with.
Good luck
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Tim,
Before cutting ANYTHING I suggest that you weigh EVERYTHING you will put in that plane and that includes the battery. IC to electric conversions usually come out heavy. Make sure you are not building a 75 ounce pig before you start.
If you can keep it at 70 or less, it might fly fine. I say 70 as opposed to the 73 you mentioned because there is less flap area on the Atlantis than the Impact. It will need the area.
The battery you show there looks massive. I don't use those, and can't read the number of cells, but it looks heavy. If it is a 5S, it might be about the right size depending on the prop used. As HR mentioned, the "CA" prop is the cat's meow for that plane. You are essentially wasting your time working with anything else. Your motor will need to spin it around 11,000 rpm.
I also would make a mount for the electric to mount to the IC beams and holes in case the electric does not work out. That is a possibility.
Others have talked about cooling. If there is space around all the components, precious little is necessary.
Good luck!
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It also looks like you are somewhat limited for battery space, and room For the ESC and timer. It should be interesting to see what you come up with.
Good luck
I find that a bit of an understatement. I converted a stock Nobler and had the same problem.
Just an FYI - I run a 5s 3000 of the same brand as yours and only use 65% on a 70oz pig. I have flown it on the same size Thunder Power which is lighter and about 3/4" shorter. Also you don't need a huge "C" value. Anything 25c or over is going to work. Over 35c and you are adding weight for no reason.
You are going to have to cut some rather large holes in the top of the fuselage if you even think of putting the ESC above that battery with no side clearance. Fortunately for me the Nobler nose is pretty deep and I could mount the battery upright. Yours doesn't seem to have that luxury.
The motor is not going to get "hot" if it is not over worked and with a front mount, which you are pretty much stuck with, it will vent through the spinner gap ( make the gap a tad larger than IC. 1/16 - 3/32 is enough) The airflow you need is over the battery and ESC. The ESC will get hotter than the battery, again by how hard it has to work. Smaller motor, heavy plane = more heat. It looks like your setup is going to have plenty of air coming in under the motor and battery but I don't see any exits over the battery. The openings for air to go out need to equal or exceed where it comes in.
Personally I would be putting a couple of about 1x1/2" vents in the fuselage side just aft of the battery, hollow out the cowl as much as possible and open it up at the back so that you have sort of a tunnel. I would put at least 4 more vent holes of the same size near the end of the cowl itself then I would mount the ESC and timer on the inside of the cowl.
If you have a better way, I am all ears. I am always looking for ways to make cooling these toys better.
Let me add to something Paul said. When you are gathering up all the stuff and weighing it, do your self a favor and hook it all up just like it will be in the plane. This is not just to test it, which is a good idea, but it is to let yourself ask what we all did the first time we did this - where am I going to put all of these (*&*^@) wires. And the good news is that the connectors don't bend!
Keep at it, it is worth it once you figure it out.
Ken
PS: I just read Paul's last post before I saved this and he is absolutely correct. If you have space around components you don't heed much cooling but I want to add to that - AFTER YOU KNOW WHAT YOU ARE DOING. It is very easy to make an innocent mistake, like using a prop the motor doesn't like and get things really hot. Until you learn these things, and I am still very early into that curve, it doesn't hurt to have more cooling. Properly matched components don't generate much heat, mismatched ones can fry eggs.
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Tim,
Before cutting ANYTHING I suggest that you weigh EVERYTHING you will put in that plane and that includes the battery. IC to electric conversions usually come out heavy. Make sure you are not building a 75 ounce pig before you start.
If you can keep it at 70 or less, it might fly fine. I say 70 as opposed to the 73 you mentioned because there is less flap area on the Atlantis than the Impact. It will need the area.
The battery you show there looks massive. I don't use those, and can't read the number of cells, but it looks heavy. If it is a 5S, it might be about the right size depending on the prop used. As HR mentioned, the "CA" prop is the cat's meow for that plane. You are essentially wasting your time working with anything else. Your motor will need to spin it around 11,000 rpm.
I also would make a mount for the electric to mount to the IC beams and holes in case the electric does not work out. That is a possibility.
Others have talked about cooling. If there is space around all the components, precious little is necessary.
Good luck!
Thank you, thank you. Yes, this should have been obvious to me. No, it didn't occur to me -- and I'd been worried about final weight, because as it stands, when things are put roughly where they'll go (not as pictured here) the CG is about the same as with the 46LA and no fuel in the tank -- so the thing may well trim out with some lead in the nose (and, ultimately, a heavier motor, but for now, lead).
Currently at 60 ounces, to my astonishment. This is plane, battery, ESC, timer (a big TUT), motor, prop adaptor, an APC 13x4, arming plug, and the little baggie of connector goodies that came with the motor, just to add weight.
Even given that the final weight is just about certainly going to be more than this, it'd have to really grow to get over 70 ounces.
My current plan is to make a front-mount disk similar to the ones that Bob Hunt sells, only out of phenolic ('cuz I have some). Installation should be pretty low impact (as it were), requiring little or no wood removal, and being easy to chip out in the event that I don't like electric.
The motor has a Kv of 760, the battery is a 3300mAh 5S, which works out to the same Joules as Howard's 2800mAh 6S pack. This leaves me a bit marginal on the overhead for the CA prop (I'd run my numbers assuming 10000 RPM max). The battery is a near-perfect fit between the motor rails (thank you -- I'm glad that you had the forethought in 1990 to arrange that). So I don't want to change batteries -- but if I feel the lack of oomph at the end of a flight, I can switch to a 2826-10, and pick up some Kv.
Just an FYI - I run a 5s 3000 of the same brand as yours and only use 65% on a 70oz pig.
The CA prop that Howard Rush and Paul are suggesting is inefficient, I'm told to expect more battery usage. Howard uses a 6S 2800mAh pack (224kJ); I'm using a 5S 3300mAh pack (220kJ). So aside from the fact that a ThunderPower pack may actually have more energy storage than advertised, while a Turnigy probably has less, I suspect I'm OK.
You are going to have to cut some rather large holes in the top of the fuselage if you even think of putting the ESC above that battery with no side clearance. ...
There's a beautiful spot for the ESC and timer under the battery. I could use it as-is and the ESC cooling fins would go right where the engine's head was. There's even an equipment tray in there when I was using the Atlantis for software verification for Howard's TUT program.
The motor is not going to get "hot" if it is not over worked and with a front mount, which you are pretty much stuck with, it will vent through the spinner gap ( make the gap a tad larger than IC. 1/16 - 3/32 is enough) The airflow you need is over the battery and ESC. The ESC will get hotter than the battery, again by how hard it has to work. Smaller motor, heavy plane = more heat. It looks like your setup is going to have plenty of air coming in under the motor and battery but I don't see any exits over the battery. The openings for air to go out need to equal or exceed where it comes in.
Personally I would be putting a couple of about 1x1/2" vents in the fuselage side just aft of the battery, hollow out the cowl as much as possible and open it up at the back so that you have sort of a tunnel. I would put at least 4 more vent holes of the same size near the end of the cowl itself then I would mount the ESC and timer on the inside of the cowl.
At the moment I'm planning on vents on the sides of the battery compartment, just ahead of the wing LE. That ends up routing the air right along the battery. For the ESC air I'll open up the back of the cowl. I'll probably put a bit of a scoop where the opening is for the motor now -- I need to think about that.
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At the moment I'm planning on vents on the sides of the battery compartment, just ahead of the wing LE. That ends up routing the air right along the battery. Fo
r the ESC air I'll open up the back of the cowl. I'll probably put a bit of a scoop where the opening is for the motor now -- I need to think about that.
If you open up the sides a bit then you won't need the scoop but it would add to the looks. It might reduce, of all things, the amount of air entering the nose which would reduce the amount of area you need for it to exit!
Looks like you are almost there. One cool thing about electric is that you can fly it before spending all those hours making it look pretty. I have given to doing very basic wings level c/g right trimming before I even add primer. Much easier to hide major surgery marks before you put on the finish and nice to know much finish you can put on.
ken
ken
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Something seems wrong Tim..it started at 64, you removed an eight ounce motor, two ounce muffler, one ounce tank. That's eleven ounces. The battery alone weighs more than that.
How can it now weigh 60?? No battery???
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With your 670 KV motor with a 5S pack, you could uneasily have a slowdown in overheads and on. Dang, that's a good prop.
The APC 13x4.5 is a great flying prop, but is very hard on bearings as it buzzes badly in hard corners.
Now what prop can you use?
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Something seems wrong Tim..it started at 64, you removed an eight ounce motor, two ounce muffler, one ounce tank. That's eleven ounces. The battery alone weighs more than that.
How can it now weigh 60?? No battery???
My scale was topping out and not telling me. The electric stuff, not yet hooked up, is 5.2 ounces more than the slimer stuff it replaces. So, technically still under 70 ounces total, if I manage to add less than 0.8 ounces...
With your 670 KV motor with a 5S pack, you could uneasily have a slowdown in overheads and on. Dang, that's a good prop.
The APC 13x4.5 is a great flying prop, but is very hard on bearings as it buzzes badly in hard corners.
Now what prop can you use?
I tossed that one on the pile as my probably-heaviest-prop. I've got a bunch to try, starting with an 11x5.5 or something like that.
I may be getting some CA props.
If the motor poops out late in the flight then I'll get a 2826-10, which has a Kv=930.
I'm not expecting this to be ideal -- but I've been meaning to get into electric anyway, and while the 46LA is a really good motor, it seems to run just a bit different every time I fly it. I actually got Randy Smith to price out everything I needed for a pipe conversion, but that plus my next case of fuel from Powermaster was more than the anticipated price of an electric conversion using cheap parts -- so cheap-parts electric it is!
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What is a CA prop?
Just guessing by going off of the props that have been mentioned favorably in the past, Igor's 3 blade hollow carbon, Cox-Resinger 3 blade carbon, ect, ?
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What is a CA prop?
Just guessing by going off of the props that have been mentioned favorably in the past, Igor's 3 blade hollow carbon, Cox-Resinger 3 blade carbon, ect, ?
It's Howard's name for a Cox-Resinger (Chris-Alan, also CAnada).
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If the motor poops out late in the flight then I'll get a 2826-10, which has a Kv=930.
If you're prop and battery are at peace with each other it should not want to poop till about a minute after the pattern is done and you are changing batteries for the next flight. But when it poops overhead......whew
I am using a MA flat back 11-6 three blade on both my 2820-12 and 2826-10. 32% left on a 4s 2800 but the plane is only 52oz. Does just fine on an APC 12-6 two blade but the Whoosh, whuum, waaaa in the corners drives me nuts. Uses a bit more battery too. I tried a CA three blade and it was clearly better than the MA but not enough better to make me want to pay the price (cheap rules) especially when on our bumpy circles an 11-6 is usually a 10 3/4-6 after a couple of flights.
ken
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If you are prop and battery are at peace with each other it should not want to poop till about a minute after the pattern is done and you are changing batteries for the next flight. But when it poops overhead......whew
I think Paul is referring to the voltage sagging to the point where the motor speed comes out of regulation, not the battery voltage sagging to the point of the ESC cutting out (although that certainly would be exciting!).
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I think Paul is referring to the voltage sagging to the point where the motor speed comes out of regulation, not the battery voltage sagging to the point of the ESC cutting out (although that certainly would be exciting!).
He was, and so am I. First time it happens to you, and it will as batteries get old, it really catches you off guard. Rarely fatal. LL~
Ken
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Fitting the el-cheapo used Hanger 9 spinner to the collet adapter. I managed to achieve a sliding fit on the collet (I was hoping for somewhere between a sliding fit and a tight fit, I achieved tight, I'm happy).
Note the mix of ancient tools, tools improvised from hardware-store fittings, and el-cheapo import tools. The indicator is a Starrett #64, everything else is, well, found art. My shop is an adventure.
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Hoo, boy, it's been a while. I've been busy both working a day job and taking care of my one remaining customer from Wescott Design Services, and fixing our cool-looking custom-made but poorly designed gate (it's better designed now, and the dog won't get out), and looking for a new day job (www.preact-tech -- I've done gone to work for a startup, oh my).
So I actually managed a couple of hours on the Atlantis today. It's the first time I've even touched the plane other than moving it out of the way of the gate project for months.
I shortened the shaft on the motor so that I can get it as far forward as possible in the fuse. I've made a phenolic front mounting plate (which will hopefully work!) that I need to trim down to fit into the fuse. That should be a pretty secure mount.
A test balance of the plane with the flight prop, spinner, etc., shows that I should have the CG at least sorta-kinda more forward than it is with the nitro setup. My sekrit plan if that doesn't work and if I don't want to add weight to the motor is to just let the motor stick out of the front of the plane by as much as it has to, with the battery that much farther forward. It's not like I'll lose out on appearance points...
Note the Bandaid on a couple of the pictures -- note to self, don't try to saw off your thumbnail with a coping saw...
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Do you need a spinner for the 3-blade prop? I can print you one like Fred's that goes on that backplate.
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Do you need a spinner for the 3-blade prop? I can print you one like Fred's that goes on that backplate.
Oooh, yes, please.
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A bit of progress, two days in a row. Wow. Motor mount taking shape; I'm fitting it into the available space, so it's a bit more work. I need to think about cooling holes soon.
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Tim-- for what it's worth I have been flying the higher kv version of the motor you have and spinning the APC 13X4.5 cut to 12in. at about 9600 RPM with very good results for a few years now. About 2300mah used on 5 min 35 sec flight with 63 ft lines. :) Airplane is a Pathfinder profile 525 sq in wing for reference.
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Thanks Dan. The Atlantis is a much bigger airplane, so I may find out that the motor isn't enough -- in which case I'll get more nose weight in a "useful" way, so that's OK.
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Tim--You are well on your way to figuring it out and you are allowing for "contingencies" so I'm sure you'll be in good shape.!
Best regards
Dan
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Tim, where do you anticipate placing the CG?
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Tim, where do you anticipate placing the CG?
I think "place" makes me sound much more astute than I am. The first time around, I was going to keep the prop in the same place with respect to the nose (i.e., no 1 inch gaps between spinner and nose ring) and allow the CG to fall where it does -- then I was going to fly the thing and see what I thought.
With the plane fully assembled as a slimer and the tank empty, the CG sits somewhere around the back of the LE sheeting or maybe 1/8" forward. I remember you making a comment that with the muffler I was using and all you felt the CG was forward of where you had it. At the moment my test balances, without ESC, timer, or wiring, are putting the CG about 1/4" ahead of that point. The ESC and timer will move it forward even more (I'm planning on shoving the ESC as far forward as I can; I'll probably put an air scoop on the cowl and put the ESC well forward in that). I think the CG is going to land about 1/4 to 1/2" ahead of where it was with the 46LA.
So I think I'm going to hit the "put the CG forward of where it goes in a slimer" rule of thumb, but initially perhaps not as much as I'd like.
Speaking of which -- do you recall if the empennage is solid on that airplane, or built up? And would it be too weird to sand off the finish off of it, drill it full of lightening holes, and cover it with some lightweight plastic covering? (Oh, the humanity, I know -- but the horizontal surfaces are all just white anyway, and the dope is peeling).
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The HT is built up. I would not suggest cutting holes in it.
1/2 inch farther forward is a good place to start.
Look forward to seeing it fly.
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Tim, I’m afraid the thin metal spinner backplate won’t suffice as part of a collet prop mount... and the worst part is that you will likely discover that once the plane is in flight. Throwing a prop on reverse wingover might result in an unfortunate demise of the Atlantis. I would recommend installing a commercial unit.
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Tim, I’m afraid the thin metal spinner backplate won’t suffice as part of a collet prop mount... and the worst part is that you will likely discover that once the plane is in flight. Throwing a prop on reverse wingover might result in an unfortunate demise of the Atlantis. I would recommend installing a commercial unit.
Uh, what? It's not part of the collet -- it gets sandwiched between the prop and the collet mount. Or is that what you're warning me about?
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Tim,
sorry for the delayed reply; life got in the way...
I think I need to clarify some terminology, then clarify what I meant. The way prop shafts are typically mounted on the smooth end of the motor axle(shaft) is by using a collet mount system, consisting of the split collet itself (the part that slips over the motor shaft and has threads for prop nut) and the collet chuck (the knurled part that also serves as the prop driver washer, which has the reciprocal cone machined on the inside surface to compress the collet).
It was my understanding, based on the couple of pictures you posted, that it was your intention to replace the stock collet chuck/prop driver with a spinner backplate, with its center hole machined to match the collet cone. If that is NOT the case, never mind. But if that IS the case, my warning still applies - I do not believe that the thin spinner backplate will adequately replace the standard collet chuck/prop driver.
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Nope. The machined hole in the spinner matches the step on the prop drive half of the collet, so the full collet is still being used. The only real sin I'm committing is to index the prop on the threaded shaft rather than the step on the prop drive.
You're now tempting me to machine an integrated backplate/collet. I intend to resist, but it'll be hard.
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Something like this, Tim..?
L
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Something like that. Only if I did it then it wouldn't look as nice!
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Getting some work done today, on the mount for the sensor pickoff, which I'm leaving in so I can capture telemetry with the TUT. This is a matter of building a bracket (which mounts using the motor mount screws), gluing a Hall sensor to the bracket in line with the magnet on the spinner, and then hoping that it doesn't fall apart from vibration.
The pictures, more or less in order, are the pickoff mount on the motor mount, with the position of the pickoff dummied up. Then there's a view of the pickoff mount and its relation to the spinner backplate. The next two are the pickoff mount alone. Final two pictures are the pickoff mount ready for gluing, and everything clamped up.
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Lauri,
would his be an alternative for your backplate construction?
(https://myalbum.com/photo/HXMkeEnff5iA/360.jpg)
Regards,
Wolfgang
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Do the words "overly complicated" mean anything at all to you?
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Lauri,
would his be an alternative for your backplate construction?
(https://myalbum.com/photo/HXMkeEnff5iA/360.jpg)
Regards,
Wolfgang
No, unless I misunderstood the drawing, that’s a little silly.
How do you keep the assembly centric when tightening those 3 screws?
My solution is elegant because most machining operations are made with one mounting, thus perfect centricity.
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Once I got the mount done I had to figure out how to get the dang thing in straight. It's not entirely perfect to key off of the existing motor mounts, because that area isn't perfectly flat -- but it's pretty good, and I can shim things to perfection later.
It's probably not apparent, but there's about one degree of right offset built in -- I should do more, but that's kinda what came out of the sanding block. As soon as I post this I'll glue it all up and see if things actually stick together or if there's been too much mold release soaked into the wood over the years.
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Well, that was almost a disaster. My nice square jig bolted nice and squarely to the engine mounts ended up with the electric motor mount getting glued in with two or three degrees of downthrust.
Fortunately I discovered the problem before the glue was fully cured, so I could pull the mount out without damage. I've got a new improved jig (more rigid, and for some inexplicable reason I needed to sand a bit of a wedge into the nose piece), and more importantly I've verified that the dang thing actually is square to the airframe.
Glue again, and this time check before the glue starts getting hard...
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Lauri,
you probably misunderstood the drawing. There are only 2 parts. By tightening the 3 screws equally, the backplate is perfectly centered. The big advantage is, that you don't have to block the motor when tightening. Also, you can use it with wooden props, because the propnut only has to fix the prop tight enough.
Regards,
Wolfgang
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Lauri,
you probably misunderstood the drawing. There are only 2 parts. By tightening the 3 screws equally, the backplate is perfectly centered. The big advantage is, that you don't have to block the motor when tightening. Also, you can use it with wooden props, because the propnut only has to fix the prop tight enough.
Regards,
Wolfgang
Screws are parts, too, and there's no positive way to make sure the screws are tightened evenly. I'm not sure that your suggestion wouldn't work, but I'm sure that it'd be subject to getting cocked over if it wasn't assembled carefully by someone of skill.
If you really wanted to spare a wooden prop, you could make a recess in the backplate part to hold a nut that tightened the collet (presumably using a pin wrench or some such), then hold the prop on separately -- but that's getting to an awful lot of parts for a problem that's already solved.
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OK. Second time was a charm. And everything fits! I've now officially decommissioned this thing as a slimer -- I've sawn off the fill and overflow tubes inside the engine bay, and I've taken out a cross-piece that prevents the battery from sliding forward. So there's no going back.
I'm planning on putting all of the electronics into the cowl, so the pits procedure will be (usually) to leave the cowl dangling on the motor wires while I'm strapping the battery in, then plug in the battery (with arming plug left unplugged), then attach the cowl (two easy screws). On the flight line I'll plug in the battery, push the "start" button, and go.
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I'm planning on putting all of the electronics into the cowl, so the pits procedure will be (usually) to leave the cowl dangling on the motor wires while I'm strapping the battery in, then plug in the battery (with arming plug left unplugged), then attach the cowl (two easy screws). On the flight line I'll plug in the battery, push the "start" button, and go.
Did it that way on my last two. Added benefit is that all that expensive stuff is smack in the middle of the airflow.
Ken
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Did it that way on my last two. Added benefit is that all that expensive stuff is smack in the middle of the airflow.
Ken
Yes, that's a happy side-effect. I started out by trying to get the battery mounted as high in the fuselage as I can, but getting airflow around the ESC is a strong secondary point.
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ESC & arming switch, although I muffed the heat shrink on the arming switch. I can't see how to solder such a short wire together without shrinking the tubing; I think I'll get some of that tool handle dip stuff and try it out.
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ESC & arming switch, although I muffed the heat shrink on the arming switch. I can't see how to solder such a short wire together without shrinking the tubing; I think I'll get some of that tool handle dip stuff and try it out.
Just put a larger piece of heatsrhink over the whole thing its just a jumper anyway. I'll post a picture later when I get home. Doesn't matter if its a deans or an XT60 Its the same principle.
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T'oh (that's French for d'oh, so it's classy).
Thank you, of course that'll work well.
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I forgot to order one. And I'm kind of out of cash until the next paycheck. So I made one from stuff lying around. I expect it'll work, even if it's ugly.
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E-Bay sells them for E- Cars and Drones battery connectors
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Making sure the SD card fits in the TUT. This may have to be revised a bit for the ESC fit, but it's what's on there now...
https://youtu.be/qsfhBmOHIXE
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I just realized that I didn't post the pictures of the sensor pickoff mount in its completed form. Here it is.
The wire goes above the motor (under in this pic, because the plane's laying on its back).
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Tim,
would it not be easier to measure the rpm electronically? You would get more pulses per revolution, (npolepairs/2).
Regards,
Wolfgang
(https://myalbum.com/photo/Rs7TspRSoDoj/360.jpg)
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Wolfgang: I'm supporting someone who doesn't want to mess with their motor or ESC wiring. And that method works with a slime motor (in fact, I was using it in that plane with a 46LA).
But yes, if you're willing to touch the motor wires you can, and probably with less circuitry than that.
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Tim,
To avoid to touch motor wires, I made a simple adapter:
(https://myalbum.com/photo/Nu3XjYjTwnNz/360.jpg)
Regards,
Wolfgang
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I'm putting an air scoop on, to replace the big hole for the engine.
The cowl's gonna get a coat of paint before I fly, I think...
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I'm putting an air scoop on, to replace the big hole for the engine.
The cowl's gonna get a coat of paint before I fly, I think...
Love that scoop. Now it is starting to look like one of mine! I cram as much of that electronic junk into the wind as I can. Just make sure you have enough holes to let it out.
Ken
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The cowl's gonna get a coat of paint before I fly, I think...
[/quote]
That's one the good things about electric. Can fly before paint. Don't need fuel proofing. y1
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The cowl's gonna get a coat of paint before I fly, I think...
That's one the good things about electric. Can fly before paint. Don't need fuel proofing. y1
This is Oregon. It needs at least one coat of dope for water resistance, or I have to wait until August.
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With your ESC in the cowl does that mean you have to disconnect the leads to the motor each battery change?
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With your ESC in the cowl does that mean you have to disconnect the leads to the motor each battery change?
Only if I messed up! My plan is that there'll be enough slack in the motor wires so the ESC (and cowl) will remain plugged in to the motor, but off to the side, when the battery comes out.
You'll see it at a contest -- eventually.
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Cowl sanded down everywhere, silkspanned, and I'm starting to build up primer.
It doesn't appear that Paul used silkspan or other material to fill the grain of the wood, yet those parts of the cowl that survived our various modifications were glass-smooth. I'd like to know how he did that.
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Only if I messed up! My plan is that there'll be enough slack in the motor wires so the ESC (and cowl) will remain plugged in to the motor, but off to the side, when the battery comes out.
You'll see it at a contest -- eventually.
It is not a problem at all once you get used to it. Just be careful not to put pressure on the connectors. Also keeps the cowl from getting stepped on.
Ken
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Ultra boring, but it's getting there -- prime, sand, prime, work, sand, prime, all work, sand, prime, all work and no, sand, prime, all work and no play, sand, prime, all work and no play makes, sand,
all work and no play makes Jack a dull boy.
all work and no play makes Jack a dull boy.
Oh, man, even though I'm working this isolation is getting to me...
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Well, I screwed up -- I started with "I'm gonna make it shiny no matter how bumpy it is" to "I'm going to make it shiny and smooth". That led to sanding through the silkspan, which led to fuzzies that would not go away (see Silkspan (yes -- silkspan) fuzzies?!? (http://"https://stunthanger.com/smf/paint-and-finishing/silkspan-(yes-silkspan)-fuzzies!/msg578868/#msg578868")).
So I stripped as much as I could off of the cowl (including some dope that felt like wax because of all the castor impregnated in it) and started over. I think it's going to be better this time -- I took down the bumps that were under the first try, so if anything they are now slight dips to be filled, and I'm certainly not going to get too ambitious with the sandpaper this time around.
I'm also using tissue paper, which seems to be easier to finish on solid wood than silkspan. It's probably not as strong -- but it's also definitely just a cowl, so it won't be a load-bearing member unless I have a really unfortunate landing "event".
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Stripped & recovered the cowl -- I've been screwing with it for weeks, only to see the same problems. It's coming out in spots & bumps in all the places you'd expect if it was leaking oil out of the wood.
I'm giving up -- it's not like I'm losing appearance points.
These past few days I got the wiring done to the point where the motor turns. I still haven't turned a prop, I need to install a timer switch, there's various bits (not least of which is the battery) that need to be fastened in properly, but I'm close to flying.
Now I need to get time to fly; I may just shorten the lines to 60' so I can fly in my field.
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Stripped & recovered the cowl -- I've been screwing with it for weeks, only to see the same problems. It's coming out in spots & bumps in all the places you'd expect if it was leaking oil out of the wood.
I'm giving up -- it's not like I'm losing appearance points.
These past few days I got the wiring done to the point where the motor turns. I still haven't turned a prop, I need to install a timer switch, there's various bits (not least of which is the battery) that need to be fastened in properly, but I'm close to flying.
Now I need to get time to fly; I may just shorten the lines to 60' so I can fly in my field.
I think you did a great job. Looks like everything's in place and you managed a front mount.
With luck I'll be doing the same but with a rear mount.
Charles
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Timer switch.
It's a 2.5mm audio jack with a disconnect feature. Plugging in the plug (with the "remove before flight" ribbon) turns the timer off; unplugging it turns it on.
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Timer switch.
It's a 2.5mm audio jack with a disconnect feature. Plugging in the plug (with the "remove before flight" ribbon) turns the timer off; unplugging it turns it on.
What happens if you forget to put that pin in and plug in a battery. Does the system automatically arm when you plug in your arming plug?
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Timer switch.
It's a 2.5mm audio jack with a disconnect feature. Plugging in the plug (with the "remove before flight" ribbon) turns the timer off; unplugging it turns it on.
Putting 40 pounds of stuff in a 30 pound bag can be fun! Good job. Nobody that has never done an IC-Electric conversion on a Classic size can appreciate how challenging it can become. HB~> mw~
I see a potential cooling problem on the top ~^ You have plenty of cooling on the bottom but there is no outlet for the battery heat that will be coming from the top. My Nobler convert looked much like yours. I cut two exhaust holes at the rear of the nose and angled them to create suction (attached) just like the nose hole on the front over the case on an IC. I also added a baffle to keep the area behind the battery from creating a pocket and hindering the air from flowing out the aft exit. Problem solved no more hot battery.
Good Luck - Hope it gets to fly soon.
Ken
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What happens if you forget to put that pin in and plug in a battery. Does the system automatically arm when you plug in your arming plug?
Yes. But that's pretty much what an Igor system does, just with a different switch.
I see a potential cooling problem on the top ~^ You have plenty of cooling on the bottom but there is no outlet for the battery heat that will be coming from the top.
Message received! I still need to take out a couple of posts that used to locate a battery hold-down and electronics bay mounting board (I had the TUT in there to record flights), and I've certainly considered holes. I'm a bit reluctant, because it's a sorta-kinda historical plane, and I can't replicate that blue without a lot of work and help (I'm partially color-blind, so just because a paint color matches to me, doesn't mean it matches to any other human). So I'm going to see if I can make it work with baffles. If that doesn't work, holes will be cut (you can sit back and wait; holes are probably inevitable. But I'm going to try).
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If that doesn't work, holes will be cut (you can sit back and wait; holes are probably inevitable. But I'm going to try).
I feel your pain. Check those batteries as soon as you get down It they are uncomfortable to hold you have issues. Issues are not fun. Remember cutouts do not have to be fuel proof.
Ken
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Battery hold-down strap hold-down straps.
I don't know what current practice is for retrofits, but these will screw into the engine mount bearers with #4 sheet metal screws, probably backed with epoxy because I can't imagine ever taking them out. I'll loop a velcro dingus of some sort around them (I see cuss words in my future) and over the battery.
This should hold the battery in nicely during maneuvering, while making it easy to take out to feel its temperature, per Ken's last comment!
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And, they work!
Some fanatic must have drilled lightening holes in the motor mount rails, because there were voids behind my holes. I'm not going to worry -- I expect that if it isn't working I'll have warning.
I just need to machine a bushing to locate the Cox-Resinger prop that Howard was nice enough to give me, and then this thing will be ready to fly.
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And, they work!
Some fanatic must have drilled lightening holes in the motor mount rails, because there were voids behind my holes. I'm not going to worry -- I expect that if it isn't working I'll have warning.
I just need to machine a bushing to locate the Cox-Resinger prop that Howard was nice enough to give me, and then this thing will be ready to fly.
Excellent - Same straps I use. Never had one fail or a battery go looking for a way out!
Ken
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Tim here is something I noticed. It regards the motor mount cooling. It night not be a problem but better safe than sorry. Most time you have a spinner that has cooling through to cool motors and you must allow the air to pass through the core of the motor. I facilitate this.
Another thing I was looking at was the old motor mounts that can be hacked off.
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I agree that it is not good to block the air flow through the motor. Typical motor mount has cut out for cooling. See photo.
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I agree that it is not good to block the air flow through the motor. Typical motor mount has cut out for cooling. See photo.
Anyone with better knowledg PLEASE play the BS card on me if this is not right. I have been told that the Cobra motors have their own internal cooling and what you need to do is not block it. Depending on the front/rear mount the motor may be venting out the front through the spinner gap. Since virtually nobody seems to use fans anymore I tend to believe this.
Ken
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I agree that it is not good to block the air flow through the motor. Typical motor mount has cut out for cooling. See photo.
John,
Nice mount. I'm guessing they are not universal? Vendor?
Charles
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John,
Nice mount. I'm guessing they are not universal? Vendor?
Charles
Bob Hunt. Vendors corner. Robin's View Productions : https://stunthanger.com/smf/robin's-view-productions/new-product-hardnose-electric-front-mount/
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Anyone with better knowledg PLEASE play the BS card on me if this is not right. I have been told that the Cobra motors have their own internal cooling and what you need to do is not block it. Depending on the front/rear mount the motor may be venting out the front through the spinner gap. Since virtually nobody seems to use fans anymore I tend to believe this.
Ken
I'm going to do some experimenting to verify this. If not, there will be baffling from the scoop down to the motor front end. I don't like holes in the spinner, so I'll avoid them if I can.
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Every time I go to work on the Atlantis there's this other project sitting on my bench -- and it's at the paintin' and sandin' phase, and since work has gotten mentally taxing now that I'm working for a startup, I can do with sanding -- it's relaxing, and doesn't require me to do any math.
A little bit because of sociable distancing, but mostly because of the startup job, I'm just not getting a chance to get out to Delta Park and fly. I made it out Monday, but that was a special case -- and I forgot my JetiBox, and the timer wasn't set up how I wanted it to be for testing. So I ended up chatting with folks and then going home.
But I can fly in my back yard if the lines, handle to canopy, are no more than sixty feet. And my current set of lines is getting a bit long in the tooth. So -- I'm going to shorten them by exactly ten feet and I'm @#$% well going to fly my airplane. If I don't get it done tonight, then tomorrow.
This is my impediment, with a story over in the Scale forum:
(https://stunthanger.com/smf/scale-models/ercoupe-build-(slow)/?action=dlattach;attach=313959;image)
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Excellent - Same straps I use. Never had one fail or a battery go looking for a way out!
Ken
I hve, at the NATS on my first official,, launched my battery through the pits,,, not a happy day, you will NEVER see me holding a pound of battery into an aerobatic airplane,, ELVER
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I hve, at the NATS on my first official,, launched my battery through the pits,,, not a happy day, you will NEVER see me holding a pound of battery into an aerobatic airplane,, ELVER
Let me guess - you used magnets for the hatch cover. ??? Don't use magnets for the hatch cover. n1 If you bolt on the cover the battery can't get out even if the straps slip. It is worth the extra 30 seconds pit time to pull the screws. Was it real Velcro or that cheap Chinese stuff. I have never had any real Velcro slip on anything if put on right.
Just goes to show you that there are "gotcha's" in electric just like IC. Hope that didn't make you switch back. Did the plane survive? Losing one at the Nats really sucks.
Ken
Ken
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I hve, at the NATS on my first official,, launched my battery through the pits,,, not a happy day, you will NEVER see me holding a pound of battery into an aerobatic airplane,, ELVER
You're saying with similar velcro straps?
What do you use now? It's probably not too late for me to change!
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First flight today -- 15 days short of a year since I tore the thing apart to convert it, which is actually pretty good by my standards of "speedy building".
I'm now running on 60' 3" lines, handle to canopy (not quite exactly 60', because I'd have had to put another nail into my line-making jig, and if I'm nearly as likely to hit a tree branch at 60' 3" than 60').
I'm going with a conservative test program, so it was only in the air for 60 seconds or so -- during which time the motor got pretty darned hot, and the battery not discernibly warm at all. So I can stop worrying about the battery for the moment, but now I have to puzzle out how to guide some air from the scoop to the motor.
It has me baffled.
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Let me guess - you used magnets for the hatch cover. ??? Don't use magnets for the hatch cover. n1 If you bolt on the cover the battery can't get out even if the straps slip. It is worth the extra 30 seconds pit time to pull the screws. Was it real Velcro or that cheap Chinese stuff. I have never had any real Velcro slip on anything if put on right.
Just goes to show you that there are "gotcha's" in electric just like IC. Hope that didn't make you switch back. Did the plane survive? Losing one at the Nats really sucks.
Ken
Ken
Nope the cowling was screwed on. The battery went through the cowling ( which was carved balsa), I recall it was on the first corner of the inside square, but I dont recall now. I did not go back to glow, I still fly electric, The plane sort of survived, it fluttered around and I managed to get and keep it sort of upright then it stalled and landed flat, it broke the fuse clean right behind the flap hingeline, it got repaired and flew until Salem contest a year later when I got bad air inverted and slapped the ground , then she was toast, though I still have the carcas for memorits LOL
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So I can stop worrying about the battery for the moment, but now I have to puzzle out how to guide some air from the scoop to the motor.
It has me baffled.
Check the spinner gap. Depending on how it is mounted it will draw air through the motor and vent through the spinner gap. Look for pockets of dead air that can't escape. Don't worry too much about the air over the can. It is the flow through the core that needs to be cool. If the air can't get out it will heat up fast no matter the source. Mine was a battery, yours is the motor. Put some suction vents on the top. We used to put a hole over the top of the case on an IC to let the heat out. Most folks just angled it but it turns into a suction vent if you put a little trough behind it.
Now all of that assumes that you have the right prop. The wrong prop will heat up the motor fast. You are not under powered. My 3520 ran best and cool on a carbon fiber 11-6 three blade around 9,000 rpm give or take. They also run cooler with a higher voltage but I don't see any way you could cram a 6s into that small space.
Good Luck - FYI, I used 2 straps.
Ken
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The plane has those crankcase cooling vents in the cowl, in just the right spot, from when they were used for cooling a crankcase. I just didn't make any real effort to insure cooling air to the front of the engine, because the baffles that I had envisioned making didn't have holes for the motor wires to pass, and when I tried to think of baffles with wire slots my head exploded.
I'm really trying to not do the sub-spinner induction thing. I know it's How it's Done, but I want this thing to look "stock" (although I resisted the urge to make a fake cylinder head for an ST 60).
I think I know what to do now. When you look into the scoop, you'll see it divided by a baffle that takes up maybe the upper 1/3 area of the scoop. This will direct air to the intake holes in the motor. I'll put a baffle around the bottom half of the motor so that the air for the most part has to go through the motor. It should exit from the existing crankcase cooling vents. We'll see how that works -- and if it doesn't, I'll try again.
Howard Rush gave me a couple of Resinger-Cox props, which are known to work well on Impact-sized aircraft but are also known to be kind of inefficient. So we'll see how that impacts motor cooling. If worse comes to worst, I'll see if I can bump up the motor size and keep the same Kv; that should lead to less motor losses and more cooling area, just at the cost of more airplane weight.
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I may have to make a retraction. I was guessing you had a 35xx motor in there but looking at your earlier postings it appears to be a 2826 which, by the way is plenty big but it is not rated for a 6x battery.
I was not suggesting a recessed spinner earlier. I was referring to the gap between the spinner and the nose ring. We make them as tiny as possible for an IC but electric needs a gap for cooling of about 1/16". When I am using a collet I slip a scrap if 1/16" between the spinner & nose ring when tightening it. Personally, when I design one I recess the spinner to provide that gap but not for a classic.
Ken
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I may have to make a retraction. I was guessing you had a 35xx motor in there but looking at your earlier postings it appears to be a 2826 which, by the way is plenty big but it is not rated for a 6x battery.
It's a 5S system, because I'm using a donated ESC to keep costs down.
And if I can't keep this motor cool it'll be a bear to go up a size -- I've just about used up the available space in the front of this fuselage.
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So, I'm not sure how it'll work, but I'm making a baffle to direct air to the front of the motor, which is sitting behind a solid phenolic motor mount. In theory the ram air into the scoop will be directed to the front of the motor, where it doesn't really have much room to go anywhere but through the motor. If that works, then my motor will stay cool.
If it doesn't, then I'll stop trying to be too clever and I'll just look at what a lot of other people are doing, and do that.
It's of composite construction so it's cool. And it's made from a bunch of different stuff, so with luck it'll be light and strong. There's a 1/32" balsa core, with two layers of 1/4 oz fiberglass cloth on the inside and outside. I made no attempt to epoxy-proof the wood, so it'll probably soak up more than not (I could have used Bob Hunt's trick of spraying lacquer on it, but frankly -- I'm lazy). I'm hoping I get something light and stiff -- and it doesn't need much strength in the first place, so strength wise I'm already in overkill-land.
The dry ingredients going in weighed 1.4g, I mixed up 3g of resin and had 2g of resin left over (that's why I tared the scale with my brush and mixing stick included -- I wanted to get the weight of stuff stuck to them so I knew how much resin I used). So raw out of the mold (less any extraneous bits of waxed paper or plug stuck to it -- see below) it should weigh 2.4g, and then I'll trim it.
I didn't have any fancier material on hand, so I used waxed paper as a release agent. I've got my fingers crossed that this thing will pull, because I had epoxy weeping out of the paper as I wrapped it. So there may be a mess involved when it's cured. As long as it separates from the plug without breaking I'll be reasonably happy -- I'm going for usable, not a show-winning finish. If worse comes to worst I'll cut the plug out from the part, but that will be tedious.
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I put it up for another 75-second motor run -- the motor ran distinctly cooler this time. The motor can was well over 50C last time (I touched it and said "ouch!"), and it warmed up for the first minute or two after I landed -- which is a sign that the stator (which is where the wire is, and where the heat is generated) was hotter yet.
This time the motor can was warm enough to be a bit uncomfortable, but I could hang on to it, and after landing it just kept cooling down. Then the wind kicked up, and since my backyard is basically a hole in the trees I stopped.
I hope that this'll be enough -- next time I'll do a two and a half minutes, and if that doesn't seem to overheat anything, I'll go for a full five minutes, and maybe start thinking about trimming (and about whether I can fly on 60 foot lines).
Pics show the rest of the baffle construction, and where I believe the airflow is going -- hopefully the air has read the same books and articles about aerodynamics.
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Mark Scarborough: you spoke, I listened. But I'm still using velcro straps because I'm at a loss of what else to hold my battery in with. I did double them up, which should put a lot less strain on each strap.
So if you can tell me what you did, I'm listening.
The 3.3A-h battery weighs 14 ounces -- if I hang an 8-lb weight that'll stress the thing to 10g (which is about four times less than the acceleration needed to hold a 5-foot radius corner; but that's been discussed).
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Good luck. I've learned, like Mark, to stay away from Velcro. Far away.
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Good luck. I've learned, like Mark, to stay away from Velcro. Far away.
So far two people have told me not to use it. No one has said what to use.
Help me out, here!
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So far two people have told me not to use it. No one has said what to use.
Help me out, here!
If you use those straps in that manner, the battery will probably be ejaculated from the aircraft. You need to pass the strap through a loop, then fold it back against itself. Thus the shear on the connection is half what it is in the configuration in your picture. The loops on the wimpy cable ties in your picture are probably inadequate. I have used straps like this https://www.amazon.com/gp/product/B079BCYDDB/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1 for many years without failure in flight. I use two. I change them every couple years.
If one is in a situation where there are not many flights and the flights are important, it would probably be prudent to use a more secure method of holding the battery.
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I should note that I haven't used those particular Amazon straps. The ones I use came from REI.
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So far two people have told me not to use it. No one has said what to use.
Help me out, here!
Good luck. I've learned, like Mark, to stay away from Velcro. Far away.
You have to build a box with a removable cover that is bolted on. I have seen a couple of them on here but don't give up on the Velcro. What I see in your pictures, it is not installed properly. The end needs to go through the hole in the end then you tighten the strap and pull that little tab and lock it down. Then stick the rest of the strip. I would send you a video but my ships are all gone. I have used those straps on uncovered profiles and never had a battery even slip. Velcro Cable Ties. The Colored Chinese knockoff's are crap. I like Velcro because it gives me a simple adjustable battery. No argument that the latched cover is better, just not necessary.
How is your hatch held on? I hold mine on with 4 4/40 blinds into blind nuts. A crossbar sits on top of the battery. Even without the Velcro it can't get out.
Ken
Howard, you scooped me again but you explained it better. I also like yours better. Have to get some.
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You have to build a box with a removable cover that is bolted on. I have seen a couple of them on here but don't give up on the Velcro. What I see in your pictures, it is not installed properly. The end needs to go through the hole in the end then you tighten the strap and pull that little tab and lock it down. Then stick the rest of the strip. I would send you a video but my ships are all gone. I have used those straps on uncovered profiles and never had a battery even slip. Velcro Cable Ties. The Colored Chinese knockoff's are crap. I like Velcro because it gives me a simple adjustable battery. No argument that the latched cover is better, just not necessary.
How is your hatch held on? I hold mine on with 4 4/40 blinds into blind nuts. A crossbar sits on top of the battery. Even without the Velcro it can't get out.
Ken
Howard, you scooped me again but you explained it better. I also like yours better. Have to get some.
Given the confines of the space I'm in, I'm going to have to do something like make aluminum straps to go over the battery. I hadn't considered the fact that it's pretty lame velcro -- but yes, it's pretty lame velcro. I think the good stuff (Velcro) will be too thick.
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Given the confines of the space I'm in, I'm going to have to do something like make aluminum straps to go over the battery. I hadn't considered the fact that it's pretty lame velcro -- but yes, it's pretty lame velcro. I think the good stuff (Velcro) will be too thick.
Before you throw in the towel, check out the Velcro Brand Cable Ties at the Box Stores. They are very thin and very strong.
Ken
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Before you throw in the towel, check out the Velcro Brand Cable Ties at the Box Stores. They are very thin and very strong.
Ken
Well, yes, but I compete with Randy and Mark, and they helped me get from Beginner to Expert. So they don't hesitate to tell me what to do -- I need to silence them somehow, and compliance works.
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Tim, I use two ply straps across the batteries about a half inch wide held in place with two 2-56 cap screws and washers
they screw into little rails on the fuse side, essentially just like Paul does it but he makes his rails by machining them from bass wood I believe, I have mine laser cut from 1/64 ply and laminate several together... My building room is in a state of flux currently so I cant really show you.. I will look for a picture somewhere,,
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Tim, I use two ply straps across the batteries about a half inch wide held in place with two 2-56 cap screws and washers
they screw into little rails on the fuse side, essentially just like Paul does it but he makes his rails by machining them from bass wood I believe, I have mine laser cut from 1/64 ply and laminate several together... My building room is in a state of flux currently so I cant really show you.. I will look for a picture somewhere,,
Thanks Mark -- that gives me the picture.
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Still using velcro -- I pull-tested a couple of straps. One was a strap that had been kicking around on my bench and the floor -- it pulled to about 25 pounds before it let go, after which it didn't pull past 10 pounds.
The others were the straps from the plane. Each one pulled to 45 pounds without letting go, and did so repeatedly. Given that the battery weighs 14 ounces and there's two straps, I'm going to run with this -- and keep inspecting the straps, and possibly pulling them periodically.
I flew two flights back to back at 150 seconds run time, for a total of 5 minutes. The motor was very warm -- warmer than I would have liked -- at the end of the second flight, but I could hold my fingers on it. I'm going to open up a tight spot in the air passage, and call it good.
I used about 2200mAh for my two half-flights, so I'm feeling pretty good about battery power. I'll have to check again after I start doing full flights.
And, finally -- I've gotten gun shy with this plane again. Dangit. I hate being afraid to fly a plane, but dangit, it's one of Paul Walker's old ones! I'm not sure what I can do about that other than just start working on trimming the plane out, and hope that i get over it.
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The motor you picked is too small for the job. That is why it heats up so much. I would not be surprised if you also have a hot ESC and battery too.
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The motor you picked is too small for the job. That is why it heats up so much. I would not be surprised if you also have a hot ESC and battery too.
I'm pretty much with Dorian on this one . The 2826 series always seem to run hot unless they are in profiles. I've even tried then with fans on them with no luck. If you want an unobtainium fan for your motor I think I still have one, but honestly I think your results will be exactly the same. The other problem I see is a limited number of 5 cell 35 series motors available. Most are 4 or 6 cell. For some weight penalty you could use a cobra 3520/12 which matches a 5 cell battery well. You might get away with a cobra 3515/18 which is a 740 kv motor but I and most others that use that motor fly it on 6 cells. Are you using the 11 or 12 inch cox ressinger props. You can pitch them up a little if needed. For what its worth ,or not worth, I've used Velcro and magnets in my plane and never ever threw a battery or hatch in thousands of flights,I COULD BE DUE!!!usually I have a hard time pulling the battery out after the flight and even though I've been very successful or very lucky I know it can be done but recognize the risk and will always tell others that there can be a problem. My current High Voltage Nats plane has a screw down battery holder and a magnetic battery hatch. The hatch has never ever given me a problem and I'm at about 190 flights on the plane.
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I suspect it is in this thread somewhere but just what are we hauling around. In other words how big is Atlantis and how much does she weigh? I had my 2826 in a converted 58oz Nobler that was every bit as cramped as Atlantis. Didn't overheat. A 2820/12 would have been a better choice for me on a 3000 4s.
The 2820 runs cooler. You don't have room for a 3520 so talk of a bigger motor is of no value. Screw around with props and RPM. When they hit their sweet spot they run cooler.
Good Luck - Ken
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I suspect it is in this thread somewhere but just what are we hauling around. In other words how big is Atlantis and how much does she weigh? I had my 2826 in a converted 58oz Nobler that was every bit as cramped as Atlantis. Didn't overheat. A 2820/12 would have been a better choice for me on a 3000 4s.
The 2820 runs cooler. You don't have room for a 3520 so talk of a bigger motor is of no value. Screw around with props and RPM. When they hit their sweet spot they run cooler.
Good Luck - Ken
Much better answer than mine. I used the 3520 as an example of a good 5s motor Yes, I'm sure way too big and should have clarified that. I considered suggesting a few 4s setups but it seems that he was trying to work with what he has. I do think there are many more choices in 4s sizes in both batteries and motors available.
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There might be a solution that is a bit pricy. I was at a contest last year and had to borrow a battery for my 2826. I had been running 4s because of size. What I was handed was a ThunderPower 5s that was about the same size and weight as my Turnegy 4s. Just a thought since the 2826 will take a 5s and they do run cooler at higher voltage.
ken
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I've checked the battery and ESC -- they're running nice and cool.
I'd have to do a lot of cutting to make room for a larger diameter motor, and I may end up cutting through the wood if I try (this would be much easier if I were building from scratch, obviously). I'll take a look and see if I can wedge a larger diameter motor in there, though.
Does the motor fail catastrophically when you run it too hot? Or does it show obvious distress for more than one flight before it dies? Because if it's going to give me enough warning that I can swap it out, I'd just as soon doom it to a short and unhappy life and keep flying.
Really, with two back to back half-flights, the motor is only hot in human terms -- I doubt that any part of the motor is reaching 100C. I'm not sure what a Cobra can take, or what lets go first, but nothing is smoking, even gently, on landing, nor do my fingers sizzle when I touch the case.
Ken: I'm already running a 5S. The plane weighs 72 ounces, so it's not a lightweight for that motor. In-flight RPM is around 11000, give or take 500 or so.
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Does the motor fail catastrophically when you run it too hot? Or does it show obvious distress for more than one flight before it dies? Because if it's going to give me enough warning that I can swap it out,
I believe, as you know, magnets don't particularly like heat or abrupt impacts. So with the heat situation, if it's grossly overheating a failure is obvious and immediate. With chronic exposure, I believe they slowly lose their pizazz. So there may be no real warning. Just one day you'll swear it had more than enough power, mean while it's slowly dwindled away. Now, you may not even be in that boat, but I've had that on a few of my other electric RC racing flying objects
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10500 rpm sounds awfully high rpm for electric. Try a prop with more pitch, I am thinking at least a 6 in pitch. Also consider the lightest prop you can find and 2 blade props work very efficient. Think electric, electric motors are happy at low rpm IC motors create power at high rpm. I suggest you buy a XOAR 12X6 2B and try it.
https://www.ebay.com/p/1249428526?iid=161899725901&chn=ps&norover=1&mkevt=1&mkrid=711-117182-37290-0&mkcid=2&itemid=161899725901&targetid=917185845248&device=c&mktype=pla&googleloc=9010799&poi=&campaignid=10454706842&mkgroupid=100467643101&rlsatarget=aud-412677883135:pla-917185845248&abcId=2146000&merchantid=112301579&gclid=CjwKCAjwgdX4BRB_EiwAg8O8HcQU6uKQqkT0w2xCxYoPjdfVJR3FGwJRVvbWWYL_Lx9n94MvhcbzzxoCaCwQAvD_BwE
https://www.ebay.com/p/1144831844?iid=161948813868&chn=ps&norover=1&mkevt=1&mkrid=711-117182-37290-0&mkcid=2&itemid=161948813868&targetid=915282956376&device=c&mktype=pla&googleloc=9010799&poi=&campaignid=10459990224&mkgroupid=100467642221&rlsatarget=aud-762207186714:pla-915282956376&abcId=2146000&merchantid=112301579&gclid=CjwKCAjwgdX4BRB_EiwAg8O8HepGbL91iUf-tJe2f9-3ojRXvYtyJC8ljLtNFS--iTar3_f-c1wwYhoC0mMQAvD_BwE
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Here are a couple of previous threads on temperature.
https://stunthanger.com/smf/gettin-all-amp'ed-up!/how-hot/msg557704/#msg557704
https://stunthanger.com/smf/gettin-all-amp'ed-up!/cooling-fan-using-rearthrough-the-bulkhead-rear-mount/msg557513/#new
E-flite noted 220°F max operating temperature in some of their specs. Operating temperature is difficult to obtain, unless they mean temperature after landing, which may be hotter as airflow ceases. If I recall correctly, I once asked Lucien at Innov8tive about Cobras, and he tries to keep them at under 160° and I took that for the Stator temperature.
BA motors claim wiring and magnets tolerate quite a bit hotter than that, so if problems, you might switch to the BA 28 series. Specs here
https://innov8tivedesigns.com/badass-2826-820kv-brushless-motor.html
If you overheat a wire and burn through, it sounds like that could be dramatic without warning. But then, you are the electric guy.
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10500 rpm sounds awfully high rpm for electric. Try a prop with more pitch, I am thinking at least a 6 in pitch. Also consider the lightest prop you can find and 2 blade props work very efficient. Think electric, electric motors are happy at low rpm IC motors create power at high rpm. I suggest you buy a XOAR 12X6 2B and try it.
Igor's props are 5" pitch and 10.7 - 11k is about right. I think that some of the other 3 blade carbon fiber props also have 5 pitch. If the voltage and kv support the rpm, it seems to work fine.
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10500 rpm sounds awfully high rpm for electric.
I would have to tell three world class competitors that their ideas about props are wrong.
Igor's props are 5" pitch and 10.7 - 11k is about right. I think that some of the other 3 blade carbon fiber props also have 5 pitch. If the voltage and kv support the rpm, it seems to work fine.
Howard gave me a pair of Cox-Resinger 3-blade props ("They're great props! I don't want 'em!" -- I'm trying to to apply too much logic to that). I'm starting out using the prop as he pitched it (5.5"). If I did jigger with the pitch, it'd hate for it just to be about keeping the motor cool.
E-flite noted 220°F max operating temperature in some of their specs. Operating temperature is difficult to obtain, unless they mean temperature after landing, which may be hotter as airflow ceases. If I recall correctly, I once asked Lucien at Innov8tive about Cobras, and he tries to keep them at under 160° and I took that for the Stator temperature.
<snip>
If you overheat a wire and burn through, it sounds like that could be dramatic without warning. But then, you are the electric guy.
No way am I hitting 160. That's getting into shiny spots on your fingertips territory; it's way beyond sizzling when you touch.
I think I'll get one of those cheap non-contact IR thermometers. That should be informative.
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I believe, as you know, magnets don't particularly like heat or abrupt impacts. So with the heat situation, if it's grossly overheating a failure is obvious and immediate. With chronic exposure, I believe they slowly lose their pizazz. So there may be no real warning. Just one day you'll swear it had more than enough power, mean while it's slowly dwindled away. Now, you may not even be in that boat, but I've had that on a few of my other electric RC racing flying objects
Hmm. You ought to be able to test for that. As the magnets get weaker, the Kv gets higher (yes, paradox, but it's how motors work). So if you get a baseline motor voltage reading at some set RPM with the motor unloaded, and check it periodically as you put hours on the motor, you'd be able to see the motor voltage trending upward for the same RPM.
There's other things that'll cause that, so you'd have to sort that out somehow. All the confounding effects I can think of would make the motor turn more stiffly when you just gave it a spin, so you could test for that by hand and ear.
Edit: I forgot to mention that the measurement only has a chance to work with the motor unloaded. As the magnets get wimpier, the motor gets inefficient (which is why it seems "suddenly weaker"). At some point you need more voltage to drive a motor with a prop, because you have to push more current through the armature to get the same torque (that's the flip side of high Kv -- more RPM for the voltage also means less torque for the current. In a properly designed motor that's not a big deal, but in a motor that's getting wimpy because its magnets are weakening, it's a big deal).
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I used a non-contact thermometer for a while. The rotor is considerably cooler than the stator, and therefore much easier to touch (also more accessible to touch). I was running a stator in the 150 - 160° range, in a non-profile fuse at the time. I could brush my finger over it, but not keep any contact as to avoid said shiny finger. I never had a problem with the motor.
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10500 rpm sounds awfully high rpm for electric. Try a prop with more pitch, I am thinking at least a 6 in pitch. Also consider the lightest prop you can find and 2 blade props work very efficient. Think electric, electric motors are happy at low rpm IC motors create power at high rpm. I suggest you buy a XOAR 12X6 2B and try it.
What he said except I got better results and the motor was happier with a light three blade 11 x 6 turning at - are you ready for this - 9000 Rpm and that was on a 76 oz plane but I had serious cooling through a recessed spinner. Don't discount going to a smaller spinner if you have to. I don't think you are going to break any Classic rules by doing that.
One thing that I never learned though was "How hot is Hot" I have always used a "can you touch it rule for the motor and a can you hold it for the rest. I have never had a battery I couldn't hold after flight. Certainly there are some figures somewhere that gives a real temperature. I just don't know where that place is. Hot is relative, grab the cylinder of an IC after you land!
Ken
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Tim,
In answer to several of your questions, yes, they fail spectacularly if over heated too much. Like Nascar motor blowing up, smoke all over. Long story, but it just suddenly blew up.
Replacing the motor, I measured the temps with an IR thermometer. I found that the rear bearing on my rear mounted motors was the hot spot. I saw no issues up to about 170 F
I was afraid to go above that.
The first P-47 had serious heating issues. Turns out it was a cooling issue. Solved it by blocking much of the air into the electronics bay. It dropped 40 F that way. You have seen the P-47, but might not realize that there is only a small amount of air actually passing by the motor.
I have no experience with that motor, so I can't comment too much about the cooling. You are discovering one of the reasons why I don't suggest retrofitting gas planes to electric. The front is generally too narrow.
Good luck. Hope to see you flying it next year!
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... You are discovering one of the reasons why I don't suggest retrofitting gas planes to electric. The front is generally too narrow. ...
Yes, this is one of those "I know this is a stupid idea, but I'm doing it anyway" sorts of projects. Even if the motor temperature lives down to my hopes and not up to my fears, the measures I had to take to make it all work were extreme, and every battery change needs a bit of craftsmanship to get the wires tucked in just right (I'm going to hate it if I have to do any back to back flights).
The plane, BTW seems to like things just fine.
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Yes, this is one of those "I know this is a stupid idea, but I'm doing it anyway" sorts of projects. Even if the motor temperature lives down to my hopes and not up to my fears, the measures I had to take to make it all work were extreme, and every battery change needs a bit of craftsmanship to get the wires tucked in just right (I'm going to hate it if I have to do any back to back flights).
The plane, BTW seems to like things just fine.
You can't learn not to do it again if you don't do it at least once! We have the luxury here of flying on asphalt in 100+ temperatures. It is easily 120 on the circle by noon most days. Flying may actually cool it down! LL~
Ken
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You can't learn not to do it again if you don't do it at least once! We have the luxury here of flying on asphalt in 100+ temperatures. It is easily 120 on the circle by noon most days. Flying may actually cool it down! LL~
Ken
Well, it was more that it was the shortest road to getting into the air with electrons.
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First full flight -- less than a year after I started, tada! (Granted, it's barely less than a year -- my first post in this thread was 364 days ago, but still).
2400mAh went back into the pack -- so I can try it out with my 3000mAh pack and see how it likes a further-back CG.
I'm rusty as all get out, and I'm sure the plane is out of trim but I need to fly more to tell exactly how. And I need to fly with both batteries to decide which one I like, and buy a few more of the winner. Then I can settle down to trim & fly, and maybe actually show up at the Regionals with a plane.
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First full flight -- less than a year after I started, tada!
#^ #^ #^
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So far two people have told me not to use it. No one has said what to use.
Help me out, here!
Yes you can use Velcro. ONLY use Industrial Velcro. (available at Home Depot). Put a strip of the Velcro on the contact edge of your battery and the mounting floor then use the straps you are using to hold it in place. Used with much bigger batteries than you will ever use in a control line model.
Kim.
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Tim,
As for heat, 160 F is as far as you would want to go for the motor.
While flying in front of an old man you know in a land far away with an ambient temp of 106F, my batteries never went above ~104F. (over boiling hot asphalt and merciless sunshine)
To ventilate, don't worry about how much air is coming in. Pay attention to how much is exiting. So more exit area is good. You are not trying to "COOL" the motor or the battery. They will produce whatever temperature that they were going to produce regardless of what you do. You are trying to get rid of the heated air around the motor and battery.
Kim.
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Just a general point: Te air that cools the motor should not go to the battery and ESC. It is better to create a second, fresh cool air inlet (and outlet) for battery + ESC.
Regards,
Wolfgang
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Tim,
I promise to never tell you what to do again. Besides, you probably know more than me at this point.
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Tim,
I promise to never tell you what to do again. Besides, you probably know more than me at this point.
I doubt that -- at least that you know more than me. And I welcome suggestions.
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I love my job at a startup. Really, I do. But this is the third day I've had off in nine weeks -- and one of those was evacuating our house because of the fires.
So I flew the Atlantis. It crapped out right after the triangles (just about 200 seconds of flight, instead of the 300 it was supposed to do). I'm so lucky it didn't wait until I'd gone vertical for the horizontal 8's -- which it may have, because that would have been a higher current draw and I think it happened because of low battery voltage.
The motor wires were scrubbing the motor, because there's not much room in that cowl, and I plain forgot that I need to route the wires each and every time I put that thing together. That extra friction (I assume) caused the thing to draw extra current from the battery, and then the speed controller to shut it down.
I think I'm going to see if I can find room for a shroud around the motor, to hold the wires off. If not (and maybe anyway) I'll see if I can make it part of the preflight to make sure the prop turns freely. Oh, this would be easier if the thing had been purpose-built as an electrical appliance!
The pictures don't show the wire scuffing well, because it was the black wire -- but you can see the marks on the motor. They spell "d'oh" in code.
The battery's charging now -- I expect to find it's been almost fully discharged. I wanted to get it charging ASAP, because my understanding of LiPo and undervoltage is that things start to corrode in there at low voltages.
And someone's going to ask -- no, I didn't check the battery voltage after the flight. Mostly because it didn't occur to me until right now. Seeing how much charge has been put back in should be a better indication of how discharged it was, anyway.
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Well, that was more painful than I would have liked.
After thinking about where I had room, and how things were laid out, instead of putting a shroud around the motor I put a guide in the cowl. It keeps the wires away from the motor nicely, although it took two tries to get the wires in such that I could put the cowl on.
On the rather dubious plus side, when the plane is upside down and I'm installing the battery, the cowl now sort of hinges up and stays there. This means that the cowl screws won't fall out of there holes.
But -- I can fly!
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Tim,
I've retrofitted 2 gas powered planes to electric. As noted by many, the trick is to be sure you route enough air over the electrical bits. And also, set things up so that doing things like changing batteries isn't too onerous.
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Well crap! I fried the motor. I went out to fly today and the thing just buzzed and tried to move, but didn't. The ESC did manage to turn an eFlight Power 15 just fine, so it's not that.
I should have noticed that the motor feels like it's got a shorted turn -- the bearings feel fine, it turns OK if you turn it slowly, but it doesn't want to spin fast.
It probably overheated, either because it was marginal in there (which I knew) and the extra load of a wire rubbing on the thing pushed it over the edge, or it's because the motor was just too dang small.
I can't know unless I go and do the same thing again.
I think I'm going to buy a 35mm motor & see if I can shoe-horn it in, and another 2826/12, and see if it'll last (and hope it doesn't cut out at the top of a loop). I may tear down the one I have, just to see how bad it looks inside.
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Or maybe a Badass 2826 -- it looks like that may be a viable choice, and they're certainly rated for higher power. Of course, if I'm just cooking the motor that may not make a difference.
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The ESC did manage to turn an eFlight Power 15 just fine, so it's not that.
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A power 15 is a bunch too small for that plane Tim. I was using an E-Flite 32 for that size airplane.
If you can't spin the motor freely, you burned up the windings.
It's toast!
OK, just went back and re-read your previous posts. It was not an E-flite 15 flying the plane. Never mind about that point!
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My Power 15 would bolt right in there, and fly the plane just fine.
Briefly.
At least I think it wouldn't fry until I was in the air.
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Well, it's getting a Badass 2826. Last time I installed the motor as close as I could to the front, cut off the end of the shaft, and sacrificed some cooling. This time out I'm installing the motor so that the "stock" shaft length puts the spinner where I want fore&aft -- that moves the motor back about 3/16 of an inch. I'll work on the cowl to get some air in there.
Also, last time out I routed the air so that it just sort of blew on the bottom front of the motor -- there was a baffle in there so that any air coming in had to go through the motor, but clearly it wasn't effective enough. This time there's, like, holes. I'll probably do some flights with the spinner off, then compare-contrast the motor temperature with spinner on and off.
I won't be getting appearance points for it, so aside from some inevitable comments from Paul if I make it too ugly, it's not like I'll lose anything if I bias the the cooling vs. looks fight in the direction of lower temperatures.
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My usual go-to clamp when nothing else works is tape. Someone, however, has apparently waxed this airplane a bazzilion times, not to mention letting a motor slobber castor oil all over it. So things are wedged in place with balsa, matchsticks and (yes) Q-tips.
It'll hold until the glue sets. Unless a moth lands on it. A mouse running over it would definitely upset the thing. For a mount that was put in place by fittin' and filin' the thing fits pretty good. I'm just lining up the spinner to the front of the fuselage -- it's offset about .02" to inboard, but I think I'll accept that (no appearance points!)
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I added an outlet just for motor air, and I managed to fly yesterday and today.
With just the outlet, the motor was cooler than the Cobra, but still hot enough to be worrisome. Based on advise from Paul Walker I added some NACA-ish inlets to the side of the cowl, blowing on the motor. While I was adding the inlets, I noticed that I had failed to modify the baffling from the existing front scoop to match the new motor position -- so I fixed that, too.
This brought the motor temperature down to somewhere in the neighborhood of 50C. This is according to a phenomenally cheap Harbor Freight thermometer -- so I'm not sure I believe it. But the measurement is backed up by calibrated fingertips -- I can touch the motor and hold my finger on it, which is about 50C. Moreover, it starts cooling immediately after the flight, where the Cobra would continue to heat up on the outside of the motor, indicating that it was _really_ hot inside.
I decided that my attempts at NACA inlets were ugly, so I made metal covers for them. Hopefully these will generate even more airflow over the motor -- and they'll definitely cover my woodworking sins. More testing as I get a chance. I'm hopeful that I can start actually practicing flying with this thing, rather than just piddling with the power system.
At this point I'm going to do a few more test flights to check temperature, then start actually flying. I have a spinner that Howard Rush made for me to fit my backplate, but I haven't yet assembled it. I'm a bit concerned that it will block some of my cooling air, so when I do get that done I'll be testing it, and then I may end up making some holes in it for airflow.
I did expect that I'd have a learning curve switching to electric. I did not expect that it would be this steep and this high at the beginning!
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I did expect that I'd have a learning curve switching to electric. I did not expect that it would be this steep and this high at the beginning!
Welcome to the wonderful world of electric power! LL~
Dennis
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Welcome to the wonderful world of electric power! LL~
Dennis
;D
I was telling someone that those scoops look they're on the "C" model of some WW2 fighter. The "A" model had overheating problems so they stuck the scoops on so they could stay in the fight. Then by the time they get to the "E" model they've revamped something else, and either fixed the underlying problem or built those scoops into the "real" cooling system.
The battery and ESC is as cool as I could ever want -- and if you look at the original scoop, you'll see that horizontal divider -- the top goes to the motor, the bottom to the ESC & batteries. So you can see that maybe a revamped cowl would have a different dividing line, and maybe more area.
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I did expect that I'd have a learning curve switching to electric. I did not expect that it would be this steep and this high at the beginning!
True but the view from the top is stunning.
Ken
PS:
This is a response I got from Igor a few years ago when I was having similar problems. Read the thread it makes an important point that we are cooling the wrong part of the motor.
https://stunthanger.com/smf/gettin-all-amp'ed-up!/cooling-fan-using-rearthrough-the-bulkhead-rear-mount/msg557355/#msg557355
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With the scoops, and more careful measurement, I'm seeing about 60 degrees C immediately after a flight.
But where the Cobra motor was hot-hot and got hotter with time after a flight, indicating that I wasn't measuring the hottest part of the motor, the Badass motor is at 60C and falling right after a flight.
Moreover, the setting I started out with was giving me lap times a bit less than five seconds. With lap times between 5.2 and 5.5 seconds (I'm just measuring with my wristwatch, so it's not accurate) I'm seeing about 5 degrees less motor temperature, and it looks like I'm using about 2100-2200mAh.
So, I'm happy. I just ordered a bunch more of the 3000mAh batteries; when they show up I can actually do flying sessions, and maybe start trimming this thing.
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Quite a Saga Tim.
That poor atlantis, Paul tortured it now your doing the same. :)
Cooling is essential.
As soon as I land ,im.at 47C. I personally dont refly until its cooled to a min of 35C which takes about 7 minutes.
Cooling around the can itself is important, then have plenty of exit cooling.
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I'm thinking of adding more scoops, or scooping out the insides of the scoops that I installed.
I think putting the metal scoops on actually reduced airflow to the motor :o -- that's aerodynamics for you.
I think I'll be flying this with rests between flights, unless I absolutely have to do back-to-back for a contest.
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Revised power wiring to the timer. I'd been having some strange behavior where the motor would run rough in inverted flight. The last flight, the airplane cut out early. I landed, and when I was almost to the plane it started up again (!).
I'm 90% sure that this was due to a power wire to the regulator breaking off inside the insulation -- that would provide a condition where the power was cutting in and out, especially in a manner dependent on the airplane attitude. The motor rough running could easily be the wires repeatedly making and breaking contact.
So I've re-done all the pertinent connections, with extra wire length so that the wires won't be pulled, and better strain relief.
So -- fingers crossed, I'm going to go back to practicing on this thing.
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Revised power wiring to the timer. I'd been having some strange behavior where the motor would run rough in inverted flight. The last flight, the airplane cut out early. I landed, and when I was almost to the plane it started up again (!).
I'm 90% sure that this was due to a power wire to the regulator breaking off inside the insulation -- that would provide a condition where the power was cutting in and out, especially in a manner dependent on the airplane attitude. The motor rough running could easily be the wires repeatedly making and breaking contact.
So I've re-done all the pertinent connections, with extra wire length so that the wires won't be pulled, and better strain relief.
So -- fingers crossed, I'm going to go back to practicing on this thing.rye
Must have worked. I saw you flew at the FallFollies recently. Did it perform as expected?
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Must have worked. I saw you flew at the FallFollies recently. Did it perform as expected?
Well, no -- it was better. I'm still delighted every time I fly it at how much I don't have to worry about the engine run.
You should have put an electric motor in it in '88 -- what were you thinking?