Tim Wescott wrote:
Consider using a DC motor. If you want to use a switch then the brute
force method is to use supply with some overhead and a great big
resistor to limit current to the motor. If you want to get fancy then
use a potentiometer on the dancer along with a PLC or other motion
controller ...

I just got a nice 24v DC gear motor off a "stair climber" at the dump.
You might check the places that repair them.

Or, along the same lines: a 3 ph motor and VFD with feedback control.
Can you salvage the gearboxes from the ones that have failed and just
replace the notors? With DC or 3 ph.

Bob