Tello Leg: The Study of Design Principles and Metrics for Dynamic Humanoid Robots

To be useful tools in real scenarios, humanoid robots must realize tasks dynamically. This means that they must be capable of applying substantial forces and also mitigating impacts that may occur during the motion. Towards creating capable humanoids, this letter presents the leg of the robot Tello and demonstrates how it embodies two new fundamental design concepts for dynamic legged robots. The limbs follow the principles of: (i) Cooperative Actuation (CA), by combining motors in differential configurations to increase the force capability of the limb. We demonstrate that the CA configuration requires half the motor torque to perform a jump in comparison to conventional serial design configurations. And (ii) proximal actuation, by placing heavy motors near the body to reduce the inertia of the limb. To quantify the effect of motor placement on the robot's dynamics, we introduce a novel metric entitled Centroidal Inertia Isotropy (CII). We show that the design of state-of-the-art dynamic legged robots empirically reduces the range of CII to improve agility and facilitate model-based control. We hope this metric will enable a quantifiable way to design these machines in the future.