[Jeffy]

Well, Pincers, grabbers, crushers, ect. don't really use kinectic energy much of an advantage, so hydraylics or a linear actuator could work just as well. From my experiance with combat robots, the weight restriction is very much more difficult than it is in first. With that said, I would go with the simplest mechanism and use a linear actuator.

Head the above posts. One small suggestion: Robots have large varieties in shapes and widths, however, their is a much smaller variation in height and most combat robot tops are flat or close to it. This would give an advantage to an overhead crusher.

I have been out of combat robots too long to remember the name of the robot I am thinking of, but it was the only semi-sucessful crusher that I have ever heard of. It believe it was a Canadian bot, and either a 1 kilo or 3lb robot. (my expertise is in small parts and robots, sorry)