I have been wondering does MIT cheetah purely only use electrical active compliance on it's robot or did they use a Series elastic actuator since they have this webbing tendon?
It seems that the answer is that it doesn't actually use either of those designs.
According to the paper Proprioceptive Actuator Design in the MIT Cheetah: Impact Mitigation and High-Bandwidth Physical Interaction for Dynamic Legged Robots by Patrick M. Wensing et al, the MIT Cheetah robot actually uses a proprioceptive force-control actuator Design.
The development and design principles that led to that design were described in the earlier paper Design Principles for Energy Efficient Legged Locomotion and Implementation on the MIT Cheetah Robot by Sangok Seok et al.
this webbing tendon.... what are you referring to? .... did you forget to include a picture? $\endgroup$