We have a ~120lb robot with a 13lb battery and 2 NEOs per gearbox with an 8.71:1 low gear and a 18.81:1 high gear and 6" wheels, for a free speed of 17.06ft/s in high gear and 7.89ft/s in low gear. We had been driving it around a field at near top speed for 5-10 minutes when it started to smell. All of the other motors were warm, as expected.
We were not using closed loop or any smart features in the firmware and we used the
public void set(double speed) method to set the output of the motor controllers. The Sparks were running firmware 1.0.65.
When looking at the current consumption of the this motor and the other motor in its gearbox as recorded by the PDP, they were both drawing similar average amounts of current, but there was a unusually large difference in the current draw between the motors at some times.
One thing that concerns me now is how easily that blue wire broke off of the hall sensor board. Looking back at the picture, the blue, black, and green wires, and possibly others, were just soldered to the top of the board instead of inserted through, so I’m wondering if this solder joint had already failed before I opened it. I didn’t put much stress on the wires when removing the board (I pried up the side across from the wires with a screwdriver) and none of the other solder joints broke.
To clarify my comment about the case coating, there appears to be a transparent lining or a thick layer of clearcoat inside of the outer case.
Another thing I noticed, it’s only really visible in the left side of this photo:
but one or two pieces of wire seemed to have separated from the top side of the stator on the burnt phase. They did not appear damaged and it was not clear if they came off in the process of removing the rotor or if they were like that beforehand.