On Sep 7, 3:46*pm, wrote:
I will need
to take some pictures with a fast shutter to see if the marks always
line up.
Eric

A strobe light would probably be more useful to you.

Make the two flywheels like I suggested. They can be thick and thin
squares of steel plate balanced on a lawnmower blade balancer, nothing
complicated or difficult. Press them onto shafts and put the thin one
in the master chuck as a reference and the thick one in the slave to
make it have to work hard to keep up.

Line up the corners, then accelerate the master rapidly and slow it
gradually. At or above some acceleration the slave will start to slip
and the corners will separate.

You could also watch the slave motor current as you twist it out of
line with the master. Possibly the slave will hold lock until the
current reaches a limit. If so, you could add a meter to see if the
current nears that limit in operation.

Then operate it below the maximum acceleration or current limit.