I'm trying to build a humanoid robot that will be capable of replicating a human's running gait. However, even though I have already gotten my hands dirty in motors, encoders and software, one thing remains a mystery to me : gearboxes. I have consulted many research papers that document the construction of humanoid robots, I still can't figure out how their gearing works. Take for example ARMAR-4, a 63 DOFs robot. They say that RoboDrive RD85 are used in the legs, along with CPL25 harmonic drives. They then list the maximum torque as 157Nm, which happens to comply with the maximum specs for the drive they are using (100:1 ratio). No problem so far. They then go on to talk about applying a displacement at the joints which significantly improves the torque.
I'm confused as to what this means, and ARMAR-4 is far for the only one applying a mechanism that increases torque far beyond the rated specifications of the gearboxes.