combined free speed of 3 motors

[DuaneB]

Originally Posted by Ether

But what about free speed? If anyone has published the math for this, I didn't find it with a quick search.

I'm not sure I understand the question. Are the motors tied together in a gearbox or other connected load? If so, there isn't really a free speed. Free speed means there's no load on the motor. Ganging them together in a gearbox means that any motor that isn't trying to spin as fast as the others (based on voltage and its free speed) will present some load on them. The maximum speed of the system, barring additional loads, will be somewhat less than the lowest free speed of the three. How much less will be determined by friction in the system. Whenever you're ganging motors together, you want their free speeds to be as closely matched as possible, taking into account any difference in gearing.

If the motors are not tied together, each will have a free speed specified by its motor performance data.