Yeah, I'm only looking for something like a 50% improvement or whatever; the 550 in there works fine, it's just a little on the slow side and pretty strained lifting another robot (the lifter has a max lift of 20kg before it stalls). A bit of extra power and speed would just be nice.

I've got all the parts to make a pneumatic lifter setup like the one you described Max, but it'd be too drastic a change; the lifter I've got works very nicely so don't want to change it too much. May have a look at pneumatics in another robot; I'm currently hoping to experiment with LP pneumatic flippers made from 2 stroke engine parts at the moment :P