[114Klaatu0x72]

Hellos. On our robot, we have a winch powered by a fisher price. Unlike cims, stalling them at all generally destroys them rather quickly. We decided on using a bicycle disk brake, driven by a single pneumatic cylinder, to lock the winch into position. Because getting the arm into position is not your problem, but keeping it there is, some type of locking mechanism would seem to be ideal.

Moving on to some math, lets say that a bike may weigh 15 kg, and an average rider may weigh 65 kg, with wheels of a .4 m radius, disc brakes are designed to take about 32 Nm of torque, or about 65 lbs on a 3 foot lever arm. While this leaves out various tire dynamics, among other things, unless you have some crazy manipulator, one of those should more than suit your need.
As long as you have access to a drill press, or even a corded drill in steady hands, and some extra shaft, it should be pretty easy to make a mount for the rotor (the disc part of the break). As for securing the mount onto the shaft, you should either used keyed shaft with a keyed mount, or drilling through both the shaft and mount along their diameters and attaching them with either a roll or cotter pin, as unless you have access to some decent machining tools, attaching the mount in a secure manner will be quite a pain.

Good luck and I hope this helps.