Author Topic: Electrocuting the Atlantis (Read 14166 times)

Mark Scarborough · « **Reply #100 on:** July 10, 2020, 04:12:31 PM »

Quote from: Ken Culbertson on May 24, 2020, 07:42:11 PM

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

Ken Culbertson · « **Reply #101 on:** July 10, 2020, 04:43:12 PM »

Quote from: Mark Scarborough on July 10, 2020, 04:12:31 PM

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.

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

Tim Wescott · « **Reply #102 on:** July 10, 2020, 08:02:50 PM »

Quote from: Mark Scarborough on July 10, 2020, 04:12:31 PM

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!

Tim Wescott · « **Reply #103 on:** July 10, 2020, 08:06:59 PM »

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.

Mark Scarborough · « **Reply #104 on:** July 10, 2020, 10:09:12 PM »

Quote from: Ken Culbertson on July 10, 2020, 04:43:12 PM

Let me guess - you used magnets for the hatch cover. Don't use magnets for the hatch cover. 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

Ken Culbertson · « **Reply #105 on:** July 11, 2020, 12:12:52 AM »

Quote from: Tim Wescott on July 10, 2020, 08:06:59 PM

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

Tim Wescott · « **Reply #106 on:** July 11, 2020, 10:40:51 AM »

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.

Ken Culbertson · « **Reply #107 on:** July 11, 2020, 01:09:05 PM »

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

Tim Wescott · « **Reply #108 on:** July 11, 2020, 02:29:30 PM »

Quote from: Ken Culbertson on July 11, 2020, 01:09:05 PM

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.

Tim Wescott · « **Reply #109 on:** July 11, 2020, 06:03:23 PM »

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.

Tim Wescott · « **Reply #110 on:** July 13, 2020, 07:46:21 PM »

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.

Tim Wescott · « **Reply #111 on:** July 13, 2020, 07:51:51 PM »

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).

Randy Powell · « **Reply #112 on:** July 14, 2020, 11:45:04 AM »

Good luck. I've learned, like Mark, to stay away from Velcro. Far away.

Tim Wescott · « **Reply #113 on:** July 14, 2020, 12:32:37 PM »

Quote from: Randy Powell on July 14, 2020, 11:45:04 AM

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!

Howard Rush · « **Reply #114 on:** July 14, 2020, 12:46:40 PM »

Quote from: Tim Wescott on July 14, 2020, 12:32:37 PM

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.

Howard Rush · « **Reply #115 on:** July 14, 2020, 12:49:04 PM »

I should note that I haven't used those particular Amazon straps. The ones I use came from REI.

Ken Culbertson · « **Reply #116 on:** July 14, 2020, 12:59:05 PM »

Quote from: Tim Wescott on July 14, 2020, 12:32:37 PM

So far two people have told me not to use it. No one has said what to use.

Help me out, here!

Quote from: Randy Powell on July 14, 2020, 11:45:04 AM

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.

Tim Wescott · « **Reply #117 on:** July 14, 2020, 01:41:09 PM »

Quote from: Ken Culbertson on July 14, 2020, 12:59:05 PM

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.

Ken Culbertson · « **Reply #118 on:** July 14, 2020, 04:28:36 PM »

Quote from: Tim Wescott on July 14, 2020, 01:41:09 PM

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

Tim Wescott · « **Reply #119 on:** July 14, 2020, 04:59:37 PM »

Quote from: Ken Culbertson on July 14, 2020, 04:28:36 PM

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.

Mark Scarborough · « **Reply #120 on:** July 15, 2020, 05:38:37 PM »

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,,

Tim Wescott · « **Reply #121 on:** July 15, 2020, 08:29:22 PM »

Quote from: Mark Scarborough on July 15, 2020, 05:38:37 PM

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.

Tim Wescott · « **Reply #122 on:** July 18, 2020, 03:07:30 PM »

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.

TDM · « **Reply #123 on:** July 19, 2020, 09:27:50 AM »

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.

William DeMauro · « **Reply #124 on:** July 19, 2020, 05:24:56 PM »

Quote from: TDM on July 19, 2020, 09:27:50 AM

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.

Ken Culbertson · « **Reply #125 on:** July 19, 2020, 11:07:04 PM »

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

William DeMauro · « **Reply #126 on:** July 20, 2020, 06:03:14 AM »

Quote from: Ken Culbertson on July 19, 2020, 11:07:04 PM

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.

Ken Culbertson · « **Reply #127 on:** July 20, 2020, 12:27:26 PM »

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

Tim Wescott · « **Reply #128 on:** July 20, 2020, 02:54:13 PM »

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.

Dane Martin · « **Reply #129 on:** July 20, 2020, 03:12:04 PM »

Quote from: Tim Wescott on July 20, 2020, 02:54:13 PM

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

TDM · « **Reply #130 on:** July 20, 2020, 04:16:01 PM »

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

Fred Underwood · « **Reply #131 on:** July 20, 2020, 04:27:10 PM »

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.

Fred Underwood · « **Reply #132 on:** July 20, 2020, 04:31:40 PM »

Quote from: TDM on July 20, 2020, 04:16:01 PM

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.

Tim Wescott · « **Reply #133 on:** July 20, 2020, 04:40:15 PM »

Quote from: TDM on July 20, 2020, 04:16:01 PM

10500 rpm sounds awfully high rpm for electric.

I would have to tell three world class competitors that their ideas about props are wrong.

Quote from: Fred Underwood on July 20, 2020, 04:31:40 PM

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.

Quote from: Fred Underwood on July 20, 2020, 04:27:10 PM

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.

Tim Wescott · « **Reply #134 on:** July 20, 2020, 04:44:45 PM »

Quote from: Dane Martin on July 20, 2020, 03:12:04 PM

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).

Fred Underwood · « **Reply #135 on:** July 20, 2020, 04:52:16 PM »

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.

Ken Culbertson · « **Reply #136 on:** July 21, 2020, 11:23:33 AM »

Quote from: TDM on July 20, 2020, 04:16:01 PM

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

Paul Walker · « **Reply #137 on:** July 22, 2020, 02:34:08 PM »

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!

Tim Wescott · « **Reply #138 on:** July 22, 2020, 03:17:27 PM »

Quote from: Paul Walker on July 22, 2020, 02:34:08 PM

... 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.

Ken Culbertson · « **Reply #139 on:** July 22, 2020, 03:41:25 PM »

Quote from: Tim Wescott on July 22, 2020, 03:17:27 PM

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!

Ken

Tim Wescott · « **Reply #140 on:** July 22, 2020, 05:08:06 PM »

Quote from: Ken Culbertson on July 22, 2020, 03:41:25 PM

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!

Ken

Well, it was more that it was the shortest road to getting into the air with electrons.

Tim Wescott · « **Reply #141 on:** July 23, 2020, 08:23:31 PM »

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.

Ken Culbertson · « **Reply #142 on:** July 23, 2020, 08:51:44 PM »

Quote from: Tim Wescott on July 23, 2020, 08:23:31 PM

First full flight -- less than a year after I started, tada!

Kim Doherty · « **Reply #143 on:** July 28, 2020, 02:14:29 PM »

Quote from: Tim Wescott on July 14, 2020, 12:32:37 PM

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.

Kim Doherty · « **Reply #144 on:** July 28, 2020, 03:18:12 PM »

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.

Wolfgang Nieuwkamp · « **Reply #145 on:** July 30, 2020, 09:19:59 AM »

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

Randy Powell · « **Reply #146 on:** July 30, 2020, 10:45:55 AM »

Tim,

I promise to never tell you what to do again. Besides, you probably know more than me at this point.

Tim Wescott · « **Reply #147 on:** July 30, 2020, 02:23:38 PM »

Quote from: Randy Powell on July 30, 2020, 10:45:55 AM

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.

Tim Wescott · « **Reply #148 on:** October 25, 2020, 04:57:10 PM »

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.

Tim Wescott · « **Reply #149 on:** October 28, 2020, 07:33:30 PM »

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!