Is that a bench grinder motor that you used? I have seen people rig them up to roto-tillers and lawnmowers before. My one buddy left a grinding wheel on the other end to act as a flywheel, it worked awesome.
Another smallish motor that works well is that from an old electric edger, like this:
B&D Edge Hog (brute force torque monster)
These are common garage sale finds, people buy them and use them once or twice. After a few years, she who must be listened to says it's got to go. Once you take the guard off, there is enough room to rig up a method to drive nearly anything with pulleys or gears.