Electric motor issues - too hot

[ChuckD]

Hi, all.  I want to put an electric motor in my Trumpeter Avenger that I'm building.  Just looking to turn the prop.  I picked up a set of these small drone motors and am running them off a 2x AA (3v) battery pack.  The concept is sound, and I can get it spinning, but under the load of the kit propeller, the motors get insanely hot within about 10 seconds of running; too hot to handle and certainly too hot to put in a polystyrene engine.  It's been 20 years since my last electrical class, so I'm kinda winging it here, but where am I going wrong?  If anything, since I'm running them slightly under their rated voltage of 3.7v, they should run cooler... right?  

 

If I'm not doing anything wrong, and that's just how these motors run, does anyone have any suggestions for different motor in a similar form factor?  The Avenger has a decently large engine bay, so I've got some room to work.  I might be able to get a larger form factor motor to fit, but I'd prefer to stick with this size if I can.

 

Any help is appreciated!

Edited September 1, 2020 by ChuckD

[LSP_Kevin]

I've heard of people using the small motors used to vibrate mobile phones in their models, so perhaps that's worth pursuing?

 

Kev

[chrish]

Hi Chuck

i could be wrong (often am) I’m thinking those motors are brushless permanent magnet RC airplane motors, if so the 1.5 V batteries maybe of  higher or too high ampere output for the motor. Many I’ve seen run on a battery about the size of a Zip drive or smaller.
If there is an RC modeller group or club (or store) near you give them a shout they’ll likely be able to set you up with a (rechargeable) RC airplane (helicopter) battery

just a thought, hope it works out for you!

[D Bellis]

1 hour ago, chrish said:

I’m thinking those motors are brushless permanent magnet RC airplane motors

Nope. Brushless motors are 3 phase AC-DC (3 wire). The ones in Chuck's link are 2 wire DC motors.

 

3 hours ago, ChuckD said:

the motors get insanely hot within about 10 seconds

Because those motors are trying to turn the prop at 52,500RPM, but they don't have enough torque to make it happen. That strain causes heat, and that heat in turn increases resistance and therefore amp load which will eventually fry the motor.

 

Those motors are rated at 17500kv (which means their no-laod RPM is rated at 17,500 RPM per volt). Try a motor with a MUCH lower kv rating. Even low tripple-digit kv rating around 400 - 500kv should be convincing on 3 volts (1200 - 1500 RPM), and should be able to easily operate at its rated RPM. 

 

HTH,

D

[TaffyMan]

No electrician so will bow to these with a lot more knowledge than me - but what about one of the electric motors Airfix make for use in there 1/24 scale planes.

 

Its an off the shelf solution that has been used in kits. Might be worth a look.

 

Cheers - Taff

[ChuckD]

8 hours ago, D Bellis said:

Nope. Brushless motors are 3 phase AC-DC (3 wire). The ones in Chuck's link are 2 wire DC motors.

 

Because those motors are trying to turn the prop at 52,500RPM, but they don't have enough torque to make it happen. That strain causes heat, and that heat in turn increases resistance and therefore amp load which will eventually fry the motor.

 

Those motors are rated at 17500kv (which means their no-laod RPM is rated at 17,500 RPM per volt). Try a motor with a MUCH lower kv rating. Even low tripple-digit kv rating around 400 - 500kv should be convincing on 3 volts (1200 - 1500 RPM), and should be able to easily operate at its rated RPM. 

 

HTH,

D

 

Perfect, that's what I was finding after some research last night.  I've got a couple of lower-rated motors on order, so I'll give it a shot and chalk this up as a learning experience for a newbie.

 

Thank you for clarifying that!!!

Edited September 1, 2020 by ChuckD

[Out2gtcha]

You might want to have a look around THIS place as well. They have a lot of cool stuff that pertains to this kind of thing. 

[ChuckD]

Hi, everyone.  Just a follow up to this - want to say thanks to all of you and a special shout out to D Bellis.  I found some motors that are rated for much lower RPMs that should fit the bill nicely.  They arrived today and tested satisfactory.  They get warm after a few minutes, but definitely not hot enough to do damage to a polystyrene engine.  

 

@Out2gtcha Thanks for the recommendation!  I found that site while kicking around ideas for the kit and contemplated buying their rig for this Avenger kit.  But, ultimately I decided I wanted the challenge of designing and building the electronics myself.  It won't have the neat audio or startup/shutdown sequences, but I'll be happy just flipping a switch and watching the kit come to life.  I've got plans for a diorama to recreate a fairly well-publicized photo of TBF-1 at Henderson field, so hopefully this will all come to fruition.  Time will tell, but I've still got a long way to go.  

[Sgt Shultz II]

Could youpost some pic's of the engines and link to where you bought them from?

[Theo]

Airfix has an electric motor for there 1/24 models, they are tiny enough for 1/32

[ChuckD]

@Sgt Shultz II Sure, I'll do that when I'm home tonight.  I got them from Amazon and they were like $7 for 5 of them.

 

@Theo I looked into those after the suggestion above and it appears they are out of production and hard to find. 

[ChuckD]

@Sgt Shultz II  Here's the link to what I bought.  I found that I had to reverse the polarity to get the motor to spin the correct way, but it seems to do the trick.