Excuse me for jumping in late on this thread, not having followed it closely, but this may be worth a mention from the peanut gallery (unless it has already been covered)...
WRT the current squared hypothesis - there should an obvious way to falsify, or to add a level confirmation to this. Unfortunately, if there is more than one thing going on, like the heat hypothesis, then the following may not tell you much. That would be to measure the RPM at DC for your baseline and at various levels of current and the same voltage. Is the rotational response linear or exponential to the current? Even with friction and other losses, it should be exponential, no? ... and alternatively, or in addition to that, compare against the same setup at 50% duty, square wave, but the same voltage and twice the current. In the case of twice the current, over half the time interval, the expected proportionality would be 4/2 or double. Correct? The implication of that is that very low duty, but very high current (cap discharge?) might even make the thing useful... (Unless I am missing something which is likely) i.e. 1% duty with 100x current pulse gives an enticing relative gain .... -----Original Message----- From: Horace Heffner [mailto:[email protected]] One obvious conclusion from the hypothesis that the torque of the ball bearing motor is primarily due to hysteresis in the balls and races, and thus is proportional to i^2, is that the most efficient motor will, all other things being equal, have a shaft with the least possible resistance. This implies the following conclusions regarding the shaft: 1. copper is better than iron or steel 2. silver is even better 3. shorter is better 4. solid bar is better than pipe 5. good electrical contact between the shaft and the inner race is important Best regards, Horace Heffner http://www.mtaonline.net/~hheffner/
