Using Kevin's PWM outputs for a quieter drive system.

[Al Skierkiewicz]

Phil et al,
I feel a need to go back to the original line of questions. The 120 HZ Victor output repition rate more closely matches the brush timing on the many of the motors we use. Previous versions of the Victors had a higher rep rate. This design then allows a smoother control of the motors due to the averaging of current in each winding in the motor as it contacts the brush assy. This is especially true at low speeds where everyone wants the greatest control. A higher output frequency (2kHz with the 883) gives relatively short pulse width for the brush timing at low speeds. Often the pulse could occur during the transition from one commutator segment to another. This gives a much more erratic response at low speeds. As long as the drive system uses a pulse to drive the motors there will be some noise. Remember that a variable DC current (no pulses) needs to be at a certain voltage level to just get the shaft turning. That level may be too fast for the kind of control you require. The full +12 volt pulse starts the motor turning and still gives you relatively low drive current (speed) with a short duration pulse.
As to lubing the Banebot transmissions, I am sure there are some people who would disagree with the addition of heavy or thick lubricants as the efficieny starts to drop with this type of lubricant. Remember that an intermittant application like ours, does not allow the transmissions to reach full operating temperatures for which those lubricants were developed. I think I would rather have a loud and efficient transmission than a quiet one in this application.