I suggest using a non-contact laser digital tachometer to measure
the speed of rotating things like pulleys, Mills Violano Virtuoso
bow wheels, air motors, etc.

You put a small piece of reflective tape on the shaft and the
tachometer counts the number of time it goes around in a given time.
The readout is in RPM (revolutions per minute). These tachometers
can be found for about $25 on Amazon.

Wayne Finger