I'm developing an automatic spray-paint shaking machine in order to achieve very well mixed paint for a big project. Since I'm using stone textured paint with lots of fibers and "Stuff" floating around in it, I'd like to go above and beyond in the shaking. Simply put, I want to roughly emulate the human arm shaking a can of spray paint. My only concern is achieving reciprocating motion that doesn't slow down too much near the end and beginning of the strokes. Sorry, as you can tell I'm not formally trained. The usual mechanisms of which I'm aware tend to stroke faster in the middle and slow down toward each direction change, which seems counter-productive to my purpose, although it would certain work. Is there any kind of mechanism that will provide constant velocity? The speed I'm looking for is slightly faster than the average person shaking a can of paint. Of course, the weight of the paint and the carriage will be a factor in terms of inertia. Actually, as I'm typing this I'm thinking of a gear with teeth on one side only, rotating and alternately meshing with two parallel racks, each rack on opposite sides of the gear. That might be my solution, but all other ideas would be appreciated.