I think SP was designed more for mini games in SU, like a simple car that relies on joints and keyboard controls. Search 3d warehouse for "SketchyPhysics" and sort it by "most likes". You'll come across various great uses of SP. SP, with realtime simulation engine, isn't good with mechanical movements. You could try making gear, but there are low chances that it would be reliable. Collision and joints seem to be flexible. I, once, made a differential gear and it works great, although, if you surround it with a drive-able car, there is a potential for lag and too much resistance on opposite wheels might trigger intersection between gears. I think animation would suit better when dealing with precise and accurate mechanical movements. But it all depends on how complex one wants to get with mechanics. The good thing about SP is that its simple to create simulations that could be exported to separate images and combined into a movie.
