[billbo911]

This thread got me thinking, ( I know, sometimes that can be dangerous) " How could I simply implement something like this with the hardware and software we already have?" Here is what I came up with.

In a nutshell, the EMF system is taking feedback directly from the motor during a period of "coasting" without any drive signal.

Why not add a small motor or generator, like an Micro RC car motor, to the driven axis and get feedback from it? The drive motor will turn the driven motor causing the driven motor to create a voltage/current source proportional to the speed of the drive motor. With gearing, and a little programming, this could be used in a closed loop feedback system similar to the EMF systems. This would negate the need to interrupt the PWM signal, sample the EMF value and then re-apply the PWM in our systems. We could do the sample and drive signal modifications in real time.

BTW, I know there are already motors available with tachometer circuitry built in. Many of these use optical encoders and put pulse trains out and some are strictly analog. Either design should be fairly "easy" to implement.

Thoughts???