[Al Skierkiewicz]

Marshall,
In looking at the schematic, the data for Vout would appear to be a calculation based on the supply voltage to the output stages (Vsense) and the percent of the output PWM commanded for output. In most cases, this should give you good data in the normal operating range for FRC motors. It cannot compensate for voltage drops due to wiring and motor lead length nor can it compensate for LR distortions at low values of pulse width as discussed earlier. At true free speeds, is likely to be inaccurate as well.

As an edit, I just thought of something. Are these brand new motors that you are testing? There may be some discontinuity while the brush assembly is wearing into the commutator shape. Also, I wonder what the reaction time to a command is once the motor starts to speed up. It surely will take a finite time to get the mass moving at a new speed. I wonder if 200msec is long enough. (thinking out loud here)