Design Principles for Energy-Efficient Legged Locomotion and Implementation on the MIT Cheetah Robot

TLDR

The paper proposes design principles for energy‑efficient legged robots, implements them in the MIT Cheetah, and evaluates high‑speed trotting performance. The authors derive four energy‑loss‑minimizing principles—high torque‑density motors, regenerative electronics, low‑loss transmission, and low leg inertia—and apply them to the MIT Cheetah using large‑gap motors, regenerative drivers, single‑stage low‑gear transmission, coaxial motors with composite legs, and a differential‑actuated spine. In experiments, the 33‑kg MIT Cheetah trotted at 6 m/s (22 km/h) while drawing 973 W, achieving a cost of transport of 0.5 comparable to running animals, with 76 % of energy lost as motor heat and 24 % as mechanical work.

Abstract

This paper presents the design principles for highly efficient legged robots, the implementation of the principles in the design of the MIT Cheetah, and the analysis of the high-speed trotting experimental results. The design principles were derived by analyzing three major energy-loss mechanisms in locomotion: heat losses from the actuators, friction losses in transmission, and the interaction losses caused by the interface between the system and the environment. Four design principles that minimize these losses are discussed: employment of high torque-density motors, energy regenerative electronic system, low loss transmission, and a low leg inertia. These principles were implemented in the design of the MIT Cheetah; the major design features are large gap diameter motors, regenerative electric motor drivers, single-stage low gear transmission, dual coaxial motors with composite legs, and the differential actuated spine. The experimental results of fast trotting are presented; the 33-kg robot runs at 22 km/h (6 m/s). The total power consumption from the battery pack was 973 W and resulted in a total cost of transport of 0.5, which rivals running animals' at the same scale. 76% of the total energy consumption is attributed to heat loss from the motor, and the remaining 24% is used in mechanical work, which is dissipated as interaction loss as well as friction losses at the joint and transmission.