If you are running the larger Graupner Schottel drives, Gr2335, then you will
want to run some high torque metal gear servo. Especially with the 900 motors.
If you don't, the motors will sometimes overpower the servo, and spin torque them out of position.
Also, build a small wood gallows for the shaft support ahead of the drive.
The motors will have a tendancy to torque those supports back and forth till they break.