cogoman wrote: > That price seems overkill to me too. I have been thinking about > trying to develop a product for just this kind of situation. The > solution seems simple, and inexpensive. Take an AVR microcontroller and > have it monitor the Q-encoder signals. The program would start out > counting the time between changes of the signals. When the RPMs get > high enough it could switch to counting encoder events for a certain > small amount of time. The RPM that is found would be converted to a DC > voltage by a PWM signal from one of the counters. The PWM would always > be clocked at a few MHz, so the RC filter would have a high corner > frequency, and the DC voltage would be able to change faster than most > (if not all) servo systems. Can you really do this with PWM? Note that many of these drives have insane velocity ranges, easily 10,000:1. I exercised my velocity servo amps over a 10K:1 range. The tachs go from 7 V down into the microvolt range. How many bits of PWM control do you have in the AVR? At 5 MHz, to get a 10,000:1 range, you can only update at 500 Hz, for a 250 Hz bandwidth. This is REALLY not going to make a modern servo amp happy.
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