Why Mini Quad Motors Getting too Hot?

Are the motors on your mini quad getting very hot after flight and you are wondering what’s causing it? Here are some tips to troubleshoot motor overheating issues.

Why is Hot Motor a Bad Thing?

  • Motor can burn! When the motor gets too hot, the coating on the winding can melt and cause electrical shorts, smoke + permanent damage to the motor
  • Motor performance will decrease faster over time as the magnets lose magnetic strength because of overheat; Some types of magnet might have higher heat resistance than others
  • Energy is wasted as heat, leads to shorter flight time

How Hot is Too Hot?

It’s normal that motors on a mini quad get warm after a flight, because they can spin up to a few hundreds times per second. But you might have a problem if they get too hot.

So how hot is too hot?

An easy way to tell is to pinch the motor by the bell with your fingertips, ideally right after landing. If you can hold your fingers there for more than 10 seconds comfortably, then it’s fine. If it’s too hot to hold, then it’s definitely a sign of overheating motor.

The Causes of Hot Motors

Your motors will get hot after some aggressive flying. To properly diagnose the issue you should fly slowly – 40% to 70% throttle is a good range, and one or two flips and rolls here and there are fine.

Motor Bolts Too Long

With hot motors, the very first thing I’d check would be if your motor screws are touching the windings.

PID Tuning and Filter Settings

PID and Filter tuning in Betaflight can be a rabbit hole. If you are getting hot motors after changing PID and filter settings in Betaflight, you should reset these settings back to default.

Default settings in Betaflight is known to be conservative and generally pretty good to avoid oscillations and hot motors. Once you’ve made sure you don’t get hot motors anymore, you can start tuning it more aggressively, one setting at a time. Common things to pay attention to are:

If you are still getting hot motors with default PID and filter settings, then that’s an indication that the problem might be mechanical.

Something might be wrong with hardware, keep reading for more tips on troubleshooting.

Mechanical Problem?

Maybe something isn’t done properly with the build.

  • Make sure all the screws are tight (frame and motors)
  • Are all the arms stiff and rigid?
  • FC is installed snugly and doesn’t move (nylon screws and standoffs in the stack)

FC Soft-Mounting

If you are not soft-mounting the FC, then you should! As long as you are soft mounting the FC properly, you don’t need to worry about soft mounting the motors.

Adding More Capacitors!

Adding extra capacitors to the ESC power or XT60 pads, will help reduce the amount of noise in your power. Thus reducing the noise in the gyro data too!

Center of Gravity

If two of the motors are hotter than the others, it could be caused by unbalanced weight distribution. If your quad is front heavy, or tail heavy, two of the motors will have to work harder and therefore get hotter. Make sure the COG is right in the center for the best possible performance.

Motor or Propeller Jammed

Make sure the propellers are not hitting anything on your frame (battery strap, zip tie, standoffs etc), and that the motors are not getting jammed by dirt or grass… If this is the case you should usually hear it when the motors are spinning.

Also make sure the props are not bent. It’s quite hard to tell visually sometimes, change them out if in doubt.

Faulty Motor?

It’s possible that you have one or multiple faulty motors. Maybe the bearing is bad, or the motor bell is scraping the stator due to bent shaft, or a unbalanced motor bell…

If you have one motor that is hotter than the rest, and nothing mentioned above helped, try swapping around the problematic motor with a fine motor on the same quad, see if that’s still the issue with that motor.

It’s Too Hot Outside?

Take into account the ambient temperature outside, your motors will have a harder to time to cool down on a hot day. Black motors will be affected even more when you are flying under the sun.

If this is the case, try again under the shade or in the evening.

Conclusion

These are probably the most common reasons for hot motors in a mini quad. If nothing above helped, you can try to get some help from our forum: IntoFPV.com

4 thoughts on “Why Mini Quad Motors Getting too Hot?

  1. Oscar

    Hi Oscar,

    Few days ago I fried a motor after having insisted too much for take-off. One of the prop was stuck in the grass and I applied full power. The coating of the winding burnt, and after un-plugging the battery and pluging it again, the esc fried because of a supposedly short circuit in the motor winding.
    Is it normal that the esc didn’t protect from overcurrent or jammed motor? I thought esc has this kind of protection.
    Thanks for your input,

    Oscar

    Reply
  2. Francois

    I am not a pro. But i think one of the strand (assuming it’ a multistrand winding on each phase not one solid core) had a short and fuse out. So the remaining (let say two strands) are keeping the motor up and running. Maybe you will not see the end of it. Or maybe you will need to learn the beauty of making your own coils.

    Reply
  3. Jae

    Hi Oscar,
    While testing motors without props, one motor got very hot and I saw smoke. I think coating or something burnt. But after then, motor works OK with props (just warm, no smoke any more). I hovered more than 5 minutes, and it looks good.
    Would it be OK to continue using that motor? Is there any possibility that motor fails during flight?
    Thanks.

    Reply
    1. Oscar Post author

      For practice, yea, but I would not trust it’s reliability though. Just don’t do any risky thing with it :) Like flying over water or tall trees :)
      Keep an eye on temperature of that motor too.

      Reply

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