[GeeTwo]

If you don't need to stop in mid-stroke, pneumatic cylinders are a good way to go for this sort of thing. One of the nice things about pneumatics is that most of the weight can be placed in the "main chassis" of your device, and the parts on the periphery are reasonably light-weight and simple. The really good thing is that you don't have to worry about "burning up motors" - pneumatic devices deliver a nice, steady force and don't consume any power or suffer any additional stress holding that force at the end of the stroke.

Edit: Also, IIRC, there are a number of non-cylinder actuators based on pneumatics and/or vacuum which are really light-weight and adaptable to plenty of "biomimicry" applications. They aren't legal in FRC, so I didn't look too deeply into them, but they may be worth it for you.