More and more state-of-the-art robots have employed hydraulic actuating systems. It has a high power-to-weight ratio. Robots with these actuators can bear more payloads and achieve highly dynamic performance. However, the energy consumption is also very high and the system is very complicated comparing to the electronic motor actuated robot. A lot of research has been done to save the energy. Among which the application of springs is one of the most commonly used methods. This paper presents another use of the spring to save the energy by reducing the hydraulic system pressure of a newly built robot called the “Baby Elephant.” The configuration of the spring is designed according to the leg mechanism. The spring gives an assist force in the stance phase of the leg and exerts a passive payload in the swing phase. The maximum cylinder force is then reduced so as to bring down the pump pressure. The energy to be saved depends on how much the hydraulic pressure can be reduced. In this paper, the Baby Elephant is briefly introduced, the design of the springs on saving the energy are described. Simulations and experiments are carried out to confirm the effect.

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