What about hydraulics? Hydraulics and pneumatics have a lot in common, but instead of using gas to push around pistons, in hydraulics a liquid is used instead. In practice this means two things. For one, the cushioning effect which is due to the compressible nature of gases is gone. Hydraulic actuators will be rigid in comparison. Second, the fluid used as a medium for transporting the force will need to be recycled, so when in pneumatics could just release the "used" air out, in hydraulics you have to guide that stream of liquid back to a tank. So what is the main advantage? The amount of power you can put into one tiny actuator is enormous. It really is the pump that decides the amount of force you can swing around with, the cylinders stay pretty much the same.
|Hydraulic pump with tank
|Double acting hydraulic cylinder
However there still are some drawbacks. The return hosing I mentioned means alot more hoses everywhere, the rigid nature of hydraulics may not suit your application, and you still have the whole inertia/delay/sluggishenss of the system due to the fact that you are relying on fluid running around in tubes. So hydraulics in my robot? We will have to see...
This concludes my series on actuators, however I will post more on actuators when I get to test some of them. I need to figure out what I really want to use in my robot.