Antagonistic actuation is a technique by which you control some degree of freedom (e.g. a joint rotation) with two opposite actuators at the same time. The actuators are connected by an elastic piece of material, like a spring, that can store energy. When the two actuators move accordingly, nothing special happens, and the result is just like if you had a single traditional actuator. But if the two move in opposite directions, the elastic element will stiffen, and your articulation will get stronger. Varying stiffness actually introduces a new degree of freedom, so you get two per joint.
With a good design, you can probably reuse stiffness control between various joints and get the best of both worlds: Shock absorbing and stiffness regulation from antagonistic actuation and low actuator count.
Now to try this technology, I will be designing an arm (starting with a sole finger as a proof of concept). The arm will be antropomorphic in its design (just because I think it's cooler this way).
You can see a few pictures of my first printing attempts here:
By the way, I'm uploading all designs and files for printing at a public repository in github, so you can actually print one yourself and try it. This is the link https://github.com/technik/a3.
I will be posting more about the actuation system and related matters soon, so keep checking!
Also notice there is a cool video about an antagonistic actuation hand from DLR here https://www.youtube.com/watch?v=YqmRKqFqiok