[Ether]

Originally Posted by kamocat

Is torque loss proportional to speed of the motor?

It depends on what you mean by "proportional". To me, "proportional" means means a y=k*x relationship. So the answer is no, because at zero speed there is a non-zero static friction torque loss.

Is torque loss linear with speed? Not really, but for simplicity it is usually modeled that way. For example, see this spreadsheet.

Here are some interesting links about internal torque loss vs speed for Globe and FP motors.

Will 5A at 4v produce the same internal torque as 5A at 10v?

To a very good approximation, yes, as long as we're talking about the same waveform of 5A in each case.

Is the internal torque of a GEARBOX proportional to its speed?

Well, it can vary with speed. A gearbox has static friction. It also has a speed-dependent loss. Both types of loss can vary substantially from one gearbox to the next, even for identical models. Even for one given gearbox the losses can vary as a function of temperature, lubrication, contamination, etc.