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Electric Stunt => Gettin all AMP'ed up! => Topic started by: Crist Rigotti on July 03, 2015, 01:13:35 PM
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I need some help. This is on my Legacy 40 I just completed a few months ago. When I first flew it, at the end of a full flight the motor temp was like 190 degrees F! Yikes. The battery and ESC temps were fine. Since then I added a baffle in the intake are passage to deflect the air upward toward the motor. The temp went down like 10 degrees. I then redid my battery mounting system thinking that the tray and battery straps were blocking a lot of air. The motor temp is now 165 degrees F. Getting better but still way too high.
When I started building this model, I widened the fuselage by about 3/8 from 2 inches to 2 3/8 inside width thinking that the extra width would help with the cooling. Apparently not so!
I'm including a lot of pictures to show what my installation looks like. I'll give some dimensions too.
Intake hole is 2 inches long with the large end has a 1 1/4 inch 1/2 round and the small end has a 3/4 inch half round.
The exit hole on the bottom of the fuselage is 4 inches long by 1 3/8 wide.
The bulkhead behind the motor has an opening of 1 3/4 by 1 3/4. The lower opening is 1 3/4 wide by 7/8 high.
The battery sits on the 2 lower crossbeams and is held in place by the 2 swing arms along the top. It is pretty much wide open all along the battery.
The baffle is about 2 inches wide by 7/8 tall and is about 1 1/4 inches aft of the air intake.
I'm doing a little thinking that the slope of the bottom nose area isn't allowing a lot of air to get into the motor area. By time it get into the nose area it is behind the motor. At least that's what I'm thinking. I know that there are other Legacy 40 electrics flying and I'm assuming that they have no problem with cooling.
Any ideas as to what I need to do to get the temp down to about 125 F?
I know I could cut a scoop into the top and even the sides. I've read that air is supposed to flow through the motor but I can't see how on a lot of electric models. I could fly it without a spinner to see what happens but that won't solve my problem.
The motor is a Cobra 2826/10 760Kv with a 5S battery and a Jeti Spin 44 and Igor's Active timer.
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I had the same issue with a cobra 2826 - 930kv in a Vegas and I added an air deflector and it helped a little but not enough. I switched to a scorpion 3026 - 890kv and it ran much cooler. For some reason the Cobra ran much hotter.
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I could fly it without a spinner to see what happens but that won't solve my problem.
Hey Crist:
Sometimes it is very useful to do a test that you know is doing things "wrong", not because it leads to a solution (you don't want to fly without a spinner), but because you learn what direction you need to go. It's a good thing to do when you're stuck. I'd fly the thing without a spinner and check the motor temperature. If you've blocked off the path of air through the motor I'd open that up.
Looking at the pictures, I see a system that (forgive me for being blunt) does a fine job of piping a lot of air next to the motor without actually running any by, much less through, the motor.
I think that you need to get air moving through the motor. Here are some random suggestions for a solution to the problem that I think you have. They won't do a bit of good if the problem isn't lack of airflow through the motor.
- Make a plenum that goes from your intake scoop to the front of the motor. If your motor is front mounted on the very front of the fuselage it won't work -- whether you can change things at this point, well, you know. This means the air will have to reverse direction, which is pretty lossy. It probably also means that you'll want to divide your scoop to make sure that you're getting fresh air to the electronics, separately from the motor.
- Assuming that the front of the motor isn't sealed off, put a fan on the back of the motor. The ones I've seen are just centrifugal fans, and I've heard good things so apparently they work. The fan will create a vacuum in back, but if it's to suck any air there needs to be an opening in front for air to get pulled in
- Give up and use an undersized spinner, so the front of the fuselage makes a scoop. These seem to be very popular, although I see them too much
- Perforate the spinner
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Hi Crist,
That is a bummer! First I would fly it without the spinner to see if it is then cooled down. I think there are spinners designed to stream air back into the motor area (probably ugly) which might cure the problem.
Secondly I think I would look into ways to force air upward to flow over the motor. You can try blocking off the lower opening in F-2 (Gorilla duct tape??) so that the air must flow upwards around the motor. It is hard to tell from your photos if F-2 is open entirely with a brace (black) in front (below the motor). I also have difficulty visualizing for sure but it looks like the battery is going to be directly behind the motor and the may interfere with air flow too. In other words can the air be simply flowing straight back beneath the battery and pretty much bypassing the motor?
Third possibility is a motor with its own fan.
Keep us post as to your solution.
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Crist,
Maybe try a little smaller spinner, let the opening ram a little more air into the motor.
James
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You could try putting a fan on the motor but my gut feeling tells me it wont be enough. If you have room, switch to a 3515 which weighs only a few grams more. you can put a fan on that too. I had the 2826 on voltron and it ran too hot. I went to the scorpion 3026 890 and it ran fine but was hard on bearings. I now have a cobra 3520 on it with a fan and a Ressinger 3 blade on it and it runs at air temp with plenty of power at only a few grams more than the scorpion. At your weight you don't need a 3520 series motor, so I'd go for the 3515. For some reason the 35 series seem to run cooler.
William
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Although the ideas people gave you above are better than what I'm about to propose, you might try putting a little downward-deflected flap ahead of the air outlet, maybe making the pressure lower behind the flap.
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Hey Crist:
This is totally untried, etc., but it's what I think one needs to do to get airflow through a motor.
See the picture. I think you need to put a bulkhead in the thing, as shown, that goes all the way across the fuselage. Make the hole in the bulkhead so that the motor housing barely passes (obviously you don't want it to extend far enough back that the motor bell rubs on the bulkhead). Make the bulkhead into a scoop that divides the air entry hole so that the top part is guided through the motor, while the bottom part goes over the electronics.
I'd be vastly interested in your results, but if you're more interested in getting into the air and flying, then a motor change or a fan may get you results quicker.
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Hi Crist,
That is a bummer! First I would fly it without the spinner to see if it is then cooled down. I think there are spinners designed to stream air back into the motor area (probably ugly) which might cure the problem.
Secondly I think I would look into ways to force air upward to flow over the motor. You can try blocking off the lower opening in F-2 (Gorilla duct tape??) so that the air must flow upwards around the motor. It is hard to tell from your photos if F-2 is open entirely with a brace (black) in front (below the motor). I also have difficulty visualizing for sure but it looks like the battery is going to be directly behind the motor and the may interfere with air flow too. In other words can the air be simply flowing straight back beneath the battery and pretty much bypassing the motor?
Third possibility is a motor with its own fan.
Keep us post as to your solution.
John,
The battery is aft of the bulkhead by about 3/4 inch so I don't think its blocking the airflow around the motor. Good thought though.
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I had the same issue with a cobra 2826 - 930kv in a Vegas and I added an air deflector and it helped a little but not enough. I switched to a scorpion 3026 - 890kv and it ran much cooler. For some reason the Cobra ran much hotter.
Yeah, I'm getting feedback that the 26mm motors run hot...sigh.
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Although the ideas people gave you above are better than what I'm about to propose, you might try putting a little downward-deflected flap ahead of the air outlet, maybe making the pressure lower behind the flap.
Hmm....I could tape one on easily enough. Thanks for the idea!
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Hey Crist:
This is totally untried, etc., but it's what I think one needs to do to get airflow through a motor.
See the picture. I think you need to put a bulkhead in the thing, as shown, that goes all the way across the fuselage. Make the hole in the bulkhead so that the motor housing barely passes (obviously you don't want it to extend far enough back that the motor bell rubs on the bulkhead). Make the bulkhead into a scoop that divides the air entry hole so that the top part is guided through the motor, while the bottom part goes over the electronics.
I'd be vastly interested in your results, but if you're more interested in getting into the air and flying, then a motor change or a fan may get you results quicker.
Tim,
Your idea has merit! I kept thinking that I would need to have airflow from the forward side of the mounting bulkhead but your way shows that i don't. It'll be tricky to make one but it is worth consideration. Thanks.
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I like Tim's idea. Might be tough to fabricate at this point.
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Tim,
Your idea has merit! I kept thinking that I would need to have airflow from the forward side of the mounting bulkhead but your way shows that i don't. It'll be tricky to make one but it is worth consideration. Thanks.
I hope it works, because unless someone else disproves it it'll be the first thing I'll try if I go electric! The "ring around the spinner" idea probably can't be beat for efficient cooling, but man I just don't like the looks.
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Crist.
What size is the spinner and are there any holes at the motor mount to allow air to pass?
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I copied this pic off of Crist's build thread. Just thought seeing this view of the nose construction might be of assistance in the troubleshooting process.
(http://stunthanger.com/smf/index.php?action=dlattach;topic=37716.0;attach=161469;image)
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Hi Crist,
The 2826 series are quite small and tend to get hot, but remember that the heat comes from the inner core. Igor is flying his Max Bee that is bigger than your model with the AXI 2826/13, and his motor mount system includes a heat sink that gets rid of a lot of the heat from the core. You can see this from the photos below. This is a great idea, but of course his motor is rear mounted.
Kim Doherty's Shockwave stunter, had a few holes on the top of the nose to get air into the motor that was mounted like yours. I tried this on my old Electron with the MVVS 6,5/910 motor also mounted that way and measured a small difference in temperature. The suggestion of a fan on the rear of the motor could also work. The Cobra is a pretty close copy of the AXI 2826 series so maybe their fan will fit your motor. I even tried a fan made from thin aluminium and epoxied it onto the prop boss in front of the motor just to get the dead air flowing and it also makes a bit of difference. Igor's idea is a much better way, but then your nice neat snout will need some surgery. I hope you get it right!
Keith
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Crist.
What size is the spinner and are there any holes at the motor mount to allow air to pass?
It's a 2 inch spinner and yes, there are holes in the mounting bulkhead.
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OK guys went flying this morning and gathered some hard data. Outside air temp was 79 to 83 F.
1st flight - with spinner and no baffle. Essentially how it was flying from previous sessions. A good starting point. Motor 155 F, battery 110 F
2nd flight - spinner nose cone removed. Motor 125 F, battery 112 F
3rd flight - spinner nose cone removed and exhaust baffle installed. Motor 117 F, battery 110 F
4th flight - spinner nose cone installed and exhaust baffle installed. Motor 160 F, battery 115 F
Conclusions:
Cooling air through the motor worked the best. No surprises here.
The exhaust baffle seemed to add some cooling effect when used without the spinner.
The exhaust baffle seemed to be ineffective by itself. The increase of temp from 155 to 160 was probably the ambient air temp went up 4 degrees during testing.
One thing I did not test today was using a different prop. Mike Scott was out flying today with his Cobra 2826/10 930Kv 4S Edge/Hubin set up in an airplane a little larger than mine but almost the same weight and his motor temps, with a tightly cowled motor and minimum exhaust air outlet was running motor temps about 105 F. He was using an APC 12 x 6 cut down to 11 3/4 at 8900?rpm, while I'm using an APC 13 x 5.5 cut down to 12 running at 9600 rpm. Next time out I'll try using a 12 x 6 cut down like Mike was flying. I could be running a prop that puts too much load on the motor. We'll see.
I appreciate everybody's input and maybe we can all learn something together getting through this.
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What are line lengths, lap times, and amps used/flight time on those two plane/motor/prop combos?
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Fred,
I don't know what Mikes numbers are. Mine:
Line length: 63 foot eye to eye.
Lap time: 5.3 secs
Run time is: 5 min 30 secs
MA used: @1900 to 2000
Prop: APC 13 x 5.5 cut down to 12
RPM: @9600
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Crist,
Bite the bullet and buy a Tru Turn Turbo Cool spinner that spins in the direction you like. The overheat will go away.
Bob
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One thing I did not test today was using a different prop. Mike Scott was out flying today with his Cobra 2826/10 930Kv 4S Edge/Hubin set up in an airplane a little larger than mine but almost the same weight and his motor temps, with a tightly cowled motor and minimum exhaust air outlet was running motor temps about 105 F. He was using an APC 12 x 6 cut down to 11 3/4 at 8900?rpm, while I'm using an APC 13 x 5.5 cut down to 12 running at 9600 rpm. Next time out I'll try using a 12 x 6 cut down like Mike was flying. I could be running a prop that puts too much load on the motor. We'll see.
I appreciate everybody's input and maybe we can all learn something together getting through this.
Crist,
It looks like you have tried the easy cooling suggestions except the turbo spinner, and have moved to the other end of the problem, heat generation. I was hoping to see some of the variables other than just prop for comparison. Mike's variables, particularly amps/watts and the factors contributing might be enlightening or, differences between your current plane and prior where you used the same motor, prop, batteries.
With more weight/wing loading, might you be using more gain rpm or time in gain on the Igor setup vs Hubin and then more watts used.
Thanks, just trying to learn as you suggested.
Fred
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Christ, I had similar issues with my electric chipmunk, and tried a few things to get a better idea of whats going on.
Have you tried it with the top hatch off? This will give you an idea of whether you need more exhaust area, a radical change in temp will show that, considering yours is built like mine (or should I say I copied yours almost verbatim) I think you'll find very little change.
Adding a cooling disc to the back of the motor can help create a centrifugal pump out of the the back of the motor.
Emax have them as part of the stuff you get with their GT motors, but I suspect a fine modeller like you could make one out of carbon in a few minutes.
(http://i00.i.aliimg.com/wsphoto/v0/699394518/EMAX-GT5345-08-190KV-Brushless-Motor-for-RC-Aircraft.jpg)
Be careful that you don't stall the airflow out of your motor, but have a 'cooling spinner' at one end and a disc at the other, I'm pretty sure that cooling spinners acutally pull air forwards through the motor rather than let it flow through.
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Greg's "cooling disk" is what I had in mind when I suggested a fan. I've seen them advertised as add-ons to various brands of motors (or you could make one, of course).
I really don't think you need a huge amount of flow through the motor -- when it comes to forced-convection cooling, a very little bit will often go a long way (and if you need heroic measures, that probably means that you need a different motor!).
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Very easy on Cobra motors
http://innov8tivedesigns.com/cobra-c-28mm-motor-cooler-fan
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well, would you look at that!
Hacker has been doing this on their A50 series motors for a while.
As a bit of an academic aside, I did a whole bunch of research into motors after I cooked three in succession.
What I found is that most motors (hacker included) all use .025mm or similar windings as this is what the winding machines use. To get enough current through the run multiple strands, to have enough sectional area for the winding.
This is cheaper, but not necessarily efficient. Overlapped windings will build up heat, but not a great deal of torque. More expensive motors are usually built with windings that have a coating that will withstand greater temperatures before they burn, and usually that's at a temperature where the magnets can be permanently damaged from heat buildup.
In an ideal world, use of heavier guage wire, would allow for a better wind, (no overlaps or odd bunching), which in turn should mean a bit more cooling air through the stator. Innov8tive used to sell motor kits, and I've thought about winding my own motors to make more efficient, stronger motors out of smaller lighter motors, that would have otherwise burnt out at high loads.
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Crist, check Your PM.
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Crist, check Your PM.
Answered back. Thanks.
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Crist,
It looks like you have tried the easy cooling suggestions except the turbo spinner, and have moved to the other end of the problem, heat generation. I was hoping to see some of the variables other than just prop for comparison. Mike's variables, particularly amps/watts and the factors contributing might be enlightening or, differences between your current plane and prior where you used the same motor, prop, batteries.
With more weight/wing loading, might you be using more gain rpm or time in gain on the Igor setup vs Hubin and then more watts used.
Thanks, just trying to learn as you suggested.
Fred
Fred,
Mike is using the 2826/12 930Kv motor with a 4S battery turning around 8600 to 8900 rpm. If I recall correctly. He is using a Castle Edge Lite 50 ESC with a Hubin timer. I suspect my Igor set up demands a little more of the motor because of it being an accelerometer too. Though not enough to cause the overheating problem I'm having.
Later on I'm going to try the APC 12 x 6 prop around 8900 rpm (5.3 sec laps) just to compare it to what I'm running now. I could put in my Phoenix 45 and Hubin timer too, if I wanted too. Again just as a comparison. What I eventually will do is probably go to the 3515 series motor. It'll fit in with little problem. The other full fuselage plane that I have also has a Cobra 2826 with the Phoenix 45 Hubin timer and a 5S battery and the motor runs hot in it also. Hence when I wanted to build the L-40 I widened the fuselage 3/8 for increased airflow. Now I understand that the 2826 motors run hot. If I had known that before I started the L-40, then it would have gotten the 3515 form the get-go.
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Christ, I had similar issues with my electric chipmunk, and tried a few things to get a better idea of whats going on.
Have you tried it with the top hatch off? This will give you an idea of whether you need more exhaust area, a radical change in temp will show that, considering yours is built like mine (or should I say I copied yours almost verbatim) I think you'll find very little change.
Adding a cooling disc to the back of the motor can help create a centrifugal pump out of the the back of the motor.
Emax have them as part of the stuff you get with their GT motors, but I suspect a fine modeller like you could make one out of carbon in a few minutes.
(http://i00.i.aliimg.com/wsphoto/v0/699394518/EMAX-GT5345-08-190KV-Brushless-Motor-for-RC-Aircraft.jpg)
Be careful that you don't stall the airflow out of your motor, but have a 'cooling spinner' at one end and a disc at the other, I'm pretty sure that cooling spinners acutally pull air forwards through the motor rather than let it flow through.
Greg,
I have a Cobra cooling fan that will the motor. I could try that but I'm not convinced that it will do much help. I'll bring it along next time out and try it.
I haven't tried flying with the hatch off. something else to try, again just for some comparisons.
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Hi Crist,
The 2826 series are quite small and tend to get hot, but remember that the heat comes from the inner core. Igor is flying his Max Bee that is bigger than your model with the AXI 2826/13, and his motor mount system includes a heat sink that gets rid of a lot of the heat from the core. You can see this from the photos below. This is a great idea, but of course his motor is rear mounted.
Kim Doherty's Shockwave stunter, had a few holes on the top of the nose to get air into the motor that was mounted like yours. I tried this on my old Electron with the MVVS 6,5/910 motor also mounted that way and measured a small difference in temperature. The suggestion of a fan on the rear of the motor could also work. The Cobra is a pretty close copy of the AXI 2826 series so maybe their fan will fit your motor. I even tried a fan made from thin aluminium and epoxied it onto the prop boss in front of the motor just to get the dead air flowing and it also makes a bit of difference. Igor's idea is a much better way, but then your nice neat snout will need some surgery. I hope you get it right!
Keith
Keith,
Thanks for the information. Stay tuned for further experiments of different things to try just for comparison.
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Crist,
Bite the bullet and buy a Tru Turn Turbo Cool spinner that spins in the direction you like. The overheat will go away.
Bob
I know, but at about $50 each..................
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what about this?
(http://www.modelmotors.cz/products/chladic02b.gif)
(http://www.modelmotors.cz/products/chladic02a.gif)
it is standard axi accessory called COOLER FOR AXI 2820 & AXI 2826 order no. COOL1
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The vented spinners from Bondaero are much less expensive. £5.99 + shipping from the UK.
I am not sure if they have different options for the direction of rotation.
http://www.bondaero.co.uk/Vented_spinner/p1085152_10410725.aspx
(http://d13z1xw8270sfc.cloudfront.net/origin/116710/sg202694_1024x680.jpg)
(http://d13z1xw8270sfc.cloudfront.net/origin/116710/sg202678_1024x680.jpg)
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On the turbo spinner shown I am not sure the back plate would let much air through without filing some kind of impeller vane into it. Flat solid things spinning at high RPM tend to block air. It would act just like a motorcycle spoke wheel at speed.
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I can't remember where I read it, but someone did a bit of experimentation on spinners, and found that those style of spinners actually work best when the slot for the prop is large, and turns the whole spinner into a centrifugal pump, in doing so it actually draws air back to front.
If you want to have air go front to back, you really need a turbo spinner, like this:
(http://www.atlantahobby.com/Store/pc/catalog/759_dkt3623_lg.gif)
..and have no or very small prop cutouts, as they will bleed the high pressure in the spinner off, and reduce your cooling efficiency. Cooling air should be high pressure and low velocity to do it's job properly.
The other way to do it, is Dennis Adamasin's style, with an opening around the outer edge of the spinner. Or no spinner.
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The Turbo Tru Turn claims to be tested to work in lowering temperatures. HobbyKing has the plastic ones similar to above in the international market, so easy enough to obtain and test before and after temperatures.
Lucien at Innov8tive responded to my temperature question - "When I do the testing on the motor, I do not like to see the core of the motor exceed 160˚ F. That is the point where I call the “Max Current Point” on the Cobra motors during my prop tests. The “Can Temperature” will typically be about 30˚ F cooler than the core temperature." and "The magnets used in the motors are rated for 150˚ C (302˚ F) but you really never want to get them that hot. Likewise, the insulation on the winding wire is rated for the same temperature, but you can get localized heating on the inside strands of the wire, closest to the stator core, that can be significantly hotter than the core itself." "If a motor is getting that hot, then you either do not have enough cooling, or you are simply pushing the motor too hard for the application."
In 2013 when I was looking at motors, I asked about the 2826-12 vs the 3515-18. Lucien's reply - "Of the two motors you asked about, the 2626-12 actually can handle more power than the 3515-18 motor can. If you needed more power than the 2826-12 motor provides, I would suggest the Cobra 3520-14 instead. It is 1-1/2 ounces heavier, but would be able to produce more power than the 2826-12 motor does."
Looks like a "can temperature" of <130F is the goal, so more motor or more cooling, though that isn't surprising information and doesn't solve the current issue, pun intended.
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what about this?
(http://www.modelmotors.cz/products/chladic02b.gif)
(http://www.modelmotors.cz/products/chladic02a.gif)
it is standard axi accessory called COOLER FOR AXI 2820 & AXI 2826 order no. COOL1
Igor,
Looks a lot like the cooling fan from Cobra. I'll try one in August. Thanks for the info.
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The vented spinners from Bondaero are much less expensive. £5.99 + shipping from the UK.
I am not sure if they have different options for the direction of rotation.
http://www.bondaero.co.uk/Vented_spinner/p1085152_10410725.aspx
(http://d13z1xw8270sfc.cloudfront.net/origin/116710/sg202694_1024x680.jpg)
(http://d13z1xw8270sfc.cloudfront.net/origin/116710/sg202678_1024x680.jpg)
Brett,
Interesting spinners! I'll look further into these. Thanks.
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Greg,
Not sure what to make about what you said about spinners and airflow direction. ???
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Fred,
Good info on motors. 130F is a good target temp. I'll probably go with the larger Cobra 3515 motor. I don't want to go 1 1/2 oz heavier till I at least try the 3515 motor.
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Do you have the 2826/10, or the 2826/12? The 10 is 930kv the 12 is 760kv...
Here is the prop data chart, which I'm certain you have looked at, but on 5S for the 12 wind it shows the 11x5.5 being the ideal prop.
http://innov8tivedesigns.com/images/specs/Cobra_2826-12_Specs.htm
The other question that comes to my mind is if the ESC has a different timing setting that might effect the run of the motor?
I'm bummed that you are having these issues. And I hope that you get them worked out.
R,
Chris
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Crist, I would be very interested in the results just by changing to Mike's prop.
Any chance you and Mike could do that?
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Crist, I would be very interested in the results just by changing to Mike's prop.
Any chance you and Mike could do that?
Yup, but it will be next month till we get a chance.
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I ordered a Cobra 3515/18 740Kv motor along with a fan. More testing later on in August. Stay tuned.
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Hi Crist,
I've been using this vented type of spinner on my new model from day one.
I got it from HK: [url=http://www.hobbyking.com/hobbyking/store/__58222__Turnigy_Turbo_Spinner_51mm_Red.html]this type of spinner (http://<a href="http://www.hobbyking.com/hobbyking/store/__58222__Turnigy_Turbo_Spinner_51mm_Red.html">this type of spinner</a>) [/url] But just like the bondaero, the aeronaut, etc. they're all made by Gemfan: http://www.gemfanhobby.com/Product/Main/En/3e414cea-154d-42a6-a640-a4790179e223 (http://www.gemfanhobby.com/Product/Main/En/3e414cea-154d-42a6-a640-a4790179e223)
I'm running a Torcman NT-350Z with built on extractor fan, combined with the air intake through the spinner seems to do the job. Can touch the motor after flight. The cooling exhaust in the sides are mainly for the ESC, that's sitting in the 'attic'.
I'm following the road of a low (7800) revving , larger (13x6.5) prop to establish enough thrust and so far this combination outperforms my earlier (2006) experiments with an AXI 2826 and a 12x6 Using ~2400 mAh for a 5'30" run time.
(http://www.modelbouwforum.nl/media/20150624_130455.219912/full?d=1435159052)
(http://www.modelbouwforum.nl/media/portret-bb4.220398/full?d=1437634777)
(http://www.modelbouwforum.nl/media/zijaanzicht-bb4.220399/full?d=1437634813)
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Bruno,
Thanks for the info. I'll look into getting one of those spinners.
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Crist,
I ran Eflite32's for about 3 years. They ran at 140 degrees F. PERIOD.
At one time I thought that was too high, and set about to cool it. I put in baffles, ran a vented spinner, ran with no spinner, no cowl, etc. The motors were all rear mounted (because there were different planes), and all ran at around 140 degrees no matter what I did. I gave up and just lived with it. The result, I ran a single motor for over 2 years with no issues until the bearings finally went. It had maybe 600 to 700 flights on it. I don't think that was too bad.
I now use the Cobra 3520 and it runs cooler. But is that going to make it last longer???
If you are in the 130 to 140 range, I would not worry about it.
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Thanks Paul! I'll install the new cobra motor and if it's 130-140 degrees I'll be a happy camper and move on to doing some serious trimming.
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I'm back home and on to curing the motor overheating problem. I bought a Cobra 3515/18 740Kv motor and will be installing this along with a few other small changes. Stay tuned!
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OK, here's what I did to go from a Cobra 2826/12 760Kv to a 3515/18 740Kv motor. The 3515 motor od about 3/8 diameter larger than the 2826 motor. I used my carbide ball grinder that I extended using a piece of 5/32 od brass tubing and a couple inches of 1/8 music wire all soldered together and chucked up in my Dremel tool. I ground out the top blocks and the side tri pieces. I sealed them using some SIG-Ment. I then fashioned some 1/8 spacers out of 1/8 thick PC circuit board having a diameter of 3/8 with 1/8 hole for the motor mounting screws. These were epoxied in place using some 4-40 screws and nuts. The screws were greased near the top so they wouldn't get glued in!
After that I redid my disconnect plug and shortened the motor wires about 3/4 inch. I then covered them with heat shrink and installed everything. All ready to go out and see what happens! Perhaps Saturday morning!
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Good luck with the re-maiden. Super curious how this will work compared to the other setup.
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Ok, I flew it this morning. The results were very encouraging! Air temp was 76 degrees.
Without spinner Motor temp = 112 Battery temp = 112
With spinner Motor temp = 128.4 Battery temp = 109
The set up wasn't changed except for the motor. The same prop, ESC settings, same timer settings, etc.
It also looks like just about the same MAH draw on the batteries with the larger motor. I'll know more when I charge them up the next time out.
I think I'll add a small baffle to direct the air more towards the motor. The L-40 has a long slope to the nose area and the majority of the inlet opening is behind the motor.
Then I'll explore a vented spinner.....maybe.
Thanks to everyone and their input. Will, you were right on.
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So, is it the motor, or the fan, or the combination? At least I believe that you have the fan on the 35 series as shown. Did you try it with the fan off for curiosity?
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Crist,
I'm becoming more and more convinced that the 35 series Cobra's work way better for most of our needs and that they should be used in place of any equivalent 28 series motors whenever possible if they will fit. Joe Daly jr has a similar problem with Rounder last week and is also switching to the 3515. I have not run my motor with the fan off it so I don't know what the effect will be. All I know is that its working so well I don't want to change anything. I do have an baffle on my inlet I'm sure that helps. BUT keep in mind I also ELIMINATED the vented spinner so I did take a cooling source away too. I flew today in 90+ temp and while I never took an actual temperature my motor was not even warm to the touch. It was coming down as though it was never run. I cant ask for better than that. To me this means all my battery energy is going to the prop and not into making heat. This makes for a very efficient system.
William
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So, is it the motor, or the fan, or the combination? At least I believe that you have the fan on the 35 series as shown. Did you try it with the fan off for curiosity?
Fred,
I really don't know. Though I suspect the motor was the big fix. In reality, I think the fan doesn't do that much cooling. I'm with Will in that the fan is on so I'll leave it on. Maybe when I get more adventurous, I'll do some testing with it off.
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Really glad it worked out for you, Christ.
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Crist,
Great that the overheating is solved. Just my curiosity, and a little help for others, about with and without the fan. Good for you to be able to concentrate on flying again.
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Thanks Fred. I'll let everyone know when I do more testing and the results.
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Crist,
One thing that has worked well for me is to make sure the air outlets is at least 125% of the inlet. As the air flows over the motor/battery and picks up heat it expands and you need more outlet area to care that heated air out. I have a Stuka with the same cowl as used on the IC version with a baffle to kick the air up toward the motor and an additional outlet at the back of the tank portion of the cowl. For my ships I like a clean spinner and spinner fit to the fuse. Big outlets keep the air flowing nicely.
Best, DennisT
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Crist,
One thing that has worked well for me is to make sure the air outlets is at least 125% of the inlet. As the air flows over the motor/battery and picks up heat it expands and you need more outlet area to care that heated air out. I have a Stuka with the same cowl as used on the IC version with a baffle to kick the air up toward the motor and an additional outlet at the back of the tank portion of the cowl. For my ships I like a clean spinner and spinner fit to the fuse. Big outlets keep the air flowing nicely.
Best, DennisT
Thanks Dennis on that info. My outlet is about 2.5 times the air inlet. I think the slope of the nose cowl is my biggest problem right now. It angles back so far putting in an effective baffle to direct the air more upward toward the motor will be a bit of a challenge.
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Stating the obvious, a front mounted motor has most of the air inlet behind the motor mount and motor, and most are fairly sloped back. Perhaps the baffle acts as a bit of a dam to help air up toward the front and perhaps the fan is then more effective with a cool air supply. I did the fan, and then the baffle, each helped an increment. I cut a thin saw line to each side of the opening, guessed the angle and inserted a piece of 1/32 ply and a little Ca. It could have been removed, and repositioned, but worked well enough to stay. Perhaps there is a more scientific approach to position and angle but it did not seem so earlier in the thread.
Good news is that you already have an adequate solution, though it may still be a bit hot in 90 degrees and up.
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The hole is too far back, you're getting natural draught cooling. Maybe make a baffle but, it's not going to be ram air just a high pressure area that's hopefully higher pressure than the vent in back of the motor.
You made changes for electric system in the fuel tank area but, you're compromised with the cooling hole of a glow engine. We need a design that's dedicated to electric.
Why don't you re-construct the bottom of the cowl to have a big ram air scoop right under the spinner that would funnel the air up in front of the fire wall and through the motor. It doesn't have to be as big as a navy A7.
MM
P.S. That spinner thing looks like a whiffle ball.
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The hole is too far back, you're getting natural draught cooling. Maybe make a baffle but, it's not going to be ram air just a high pressure area that's hopefully higher pressure than the vent in back of the motor.
You made changes for electric system in the fuel tank area but, you're compromised with the cooling hole of a glow engine. We need a design that's dedicated to electric.
Why don't you re-construct the bottom of the cowl to have a big ram air scoop right under the spinner that would funnel the air up in front of the fire wall and through the motor. It doesn't have to be as big as a navy A7.
MM
P.S. That spinner thing looks like a whiffle ball.
I tried to build a faithful rendition of Alan's Legacy 40 which included the slope of the nose. If I did it all over, then yes, I would redesign the slope/nose area.
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Crist, You did Alan's Legacy 40 proud and l'm sure he would be pleased!
I think you have a handle on the cooling and l'm eager to hear how the model trims out!
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Thanks John.
I fabricated and installed a baffle tonight. I made it from 1/32 ply and epoxied it in. I'll show the front view later today when the glue cures.
Here is what the baffle looks like.
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Here is what the baffle looks like when installed. I kept the end closest to the motor ahead of the fan. I didn't what all the ram air to blow on the fan, thus reducing its effectiveness drawing air through the motor.
Now I'll do some test flights this week and report back.
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I'll be watching to see what change, if any the baffle has to your temps.
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I took it out this morning. Flew 3 flights. Outside air temp was about 80 to 85 degrees.
Flight 1 - Motor 109 degrees Battery 106 degrees. The motor was warm to the touch, no problem holding your finger on the motor.
Flight 2 - Motor 115 degrees Battery 112 degrees. The motor was warmer to the touch, no problem holding your finger on the motor.
Flight 3 - Motor 112 degrees Battery 112 degrees.
Success! On flights 2 and 3 I even worked on trimming the plane!
I'm a happy camper.
Thanks to all for their help.
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Sweet, Christ. Glad to hear it worked out for you.
Sounds like the 35 series makes a big difference, and that fat motors might be better to use where they will fit.
I'll be keeping that in mind for future projects.
R,
Chris
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Flew 4 flights today. Motor temps were about 105 degrees. 80 degree outside air temps.
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Wonderful, glad you got it sorted out. And just in time to get it good and trimmed for the El Dorado meet up here in Arkansas in November! :)
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Wonderful, glad you got it sorted out. And just in time to get it good and trimmed for the El Dorado meet up here in Arkansas in November! :)
Yup, working on trimming the airplane now.