Office of Steam Forum for Model & Toy Steam Gas & Hot Air Engines

For the amount of torque being produced and the low speed, just having gears that are engaged and disengaged should be fine. I had an industrial sewing machine motor once that had a clutch, and it was just 2 conical faces with leather on one that jammed together to lock, I think that again depends on the load being used and the torques involved, but that would be quite easy to miniaturize.