As far as creative freedom goes, don't forget K'nex. A friend of mine and me in high school built a 3 speed transmission with K'nex using one of the 2 AA battery motors. We then rigged it into a bridge and used it as a fixed position crane. It would life a 16 oz. claw hammer, and a one foot long crow bar at the same time. Granted we had it geared down enough in low to the point where it took a hlf hour to life 2 inches but it did it. This was all done with zero instructions as well. Complete with 2 shift levers.