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I hear this question asked all the time. Are my motors getting too hot? How hot is too hot for motors to get? Anyone have a great way to answer this question, possibly with some temperatures?

I generally go by feel. If I can pinch the motors with my fingers for at least a few seconds without feeling like they will burn me, I know the motors are not too hot. I know a lot of people would like a more scientific answer than that.

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Temperature is a killer of motors over time. If motors are exposed to prolonged heat, the magnets in the rotor lose their magnetic field strength over time and consequently reduce the lifespan of the motor.

Generally, a well-tuned drone should not have extremely hot motors after flying (with a few exceptions). It depends on the motor, but you should avoid raising the motor’s temperature past 170°F; any hotter, and you run the risk of damaging the rotor’s magnets and decreasing performance and longevity.

https://dronenodes.com/drone-motors-brushless-guide/

https://www.rcgroups.com/forums/showthread.php?1329288-Normal-brushless-motor-temperature-range

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    $\begingroup$ Do you have a source you could cite for the temperature figure? $\endgroup$
    – ifconfig ♦
    Commented Apr 19, 2020 at 0:05
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Too hot to touch is generally too hot, but it's far from the temp at which you'll kill them.

As mentioned there are issues with the magnets losing efficacy over certain temps (which vary depending on the type of magnets) but the other consideration, and the reason you burn out a motor, is that if the current is too high, the windings get too hot and burn their protective enamel off. Without this the windings short and you have no more motor (and, often, no ESC as they don't much like being shorted).

A well tuned quad shouldn't come down too hot, but of course there are exceptions with hard flying, and extreme loading etc.

Those are different to the most common problem resulting in heat; tuning overload issues. These come from PIDs being too high resulting in the flight controller sending many rapid and extreme commands to the motors to change their speed. They can't respond that fast and so you get a lot of excess heat from the extreme currents and risk burnout as a result.

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