John Tuttle inquires (on behalf of a customer) [230102 MMD] about
how to measure the speed (assume revolutions per minute) of an air
motor. Although there are numerous ways to do this involving expensive
tachometers of differing capabilities, the customer may want to
consider a "smart phone app".

I'm not sure what may be available for the iPhone crowd, but for
Android users there's one called "Magnetic Counter - RPM Meter" by
UAB Sailracer. I have not tried it personally, so I can't recommend it,
but it looks promising.

Some experimentation is most likely in order, but it works by placing
a magnet (not further specified) on some moving part of the motor.
In the case of an air motor, likely either on the output sprocket or
one of the individual pneumatics, then placing your phone near the
moving magnetic, whereby the magnetic sensor (assuming your phone has
one) will count the magnetic pulses and give a reading of RPM.

Hopefully, the customer will inform us of the reason why this
information is important to him/her or what use is to be made of it.

John Grant