*For the sake of the discussion below, let’s agree that the mini-CIM meets the stated design goal for FRC competition use, but pursue the heating question just a bit more.
Given these two motors, how would one gear them if the goal were instead to share the load in such a way as to balance the motor temperatures as much as possible?
There is no single answer. It depends on the location of the temperature you are trying to balance, and it depends on the duty cycle.
Using the CIM motor curves, at 27A at 12V (Richard’s test), the CIM would be spinning at 4320 RPM and generating 119 watts of waste heat. Only 66 of those watts, or 55%, is due torque-producing current (I2R heating). The other 45% (54 watts) is due to eddy currents, hysteresis, internal friction and windage, etc, which also cause motor heating.
If the mini-CIM is constrained to the same speed as the CIM (1:1), then at 12V and 4320 RPM it would be generating 133 watts of waste heat.
Under these conditions, the mini would be producing just slightly less torque than the CIM.
So it appears at first blush that the mini-CIM would run hotter than the CIM under these conditions.
However, these numbers obviously change as the motor heats up due to changing coil resistance and magnetic properties. And the temperature has a distribution within the motor due to internal structure and the different sources of heat.
It’s possible (but quite a bit of work) to model all these parameters accurately. With the right equipment and setup, a test would yield the answer.
For sake of discussion it would be interesting to include non-competition duty cycles. Are there any teams out there who have a CIM+mini 1:1 on a practice/demo bot? Is either motor hotter than the other after a good hard workout?