Antagonistic Actuation Arm (A3): Part I

I'm starting with the design of a 3d-printed arm to test antagonistic actuation.
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.