Thrust Control, Stabilization and Energetics of a Quadruped Running Robot

In order to achieve powered autonomous running robots it is essential to develop efficient actuator systems, especially in the case of the actuatorsfor generating the radial thrust in the legs. In addition, the control of the radial thrust of the legs can be a simple, effective method for stabilizing the body pitch in a running gait. This paper presents the mechanical systems, the models and control strategies employed to generate and control leg thrust in the KOLT quadruped running robot. An analytical model of the electro-pneumatic leg thrusting system is presented and analyzed to evaluate its performance and to facilitate the design of control strategies. Several experiments have been conducted to estimate the energy losses and determine their origins as well as to compute the energetic efficiency of the actuation system. Two thrust control methods are also proposed and tested experimentally. The closed loop method regulates thrust through the control of the hip liftoff speed, a conceptually simple control strategy that has the property of stabilizesing the body pitch in pronk and trot gaits without the need of central feedback, even on irregular terrain. An The open loop control method that can regulates the energy added in each hop based on the model of the actuator system is also presented. The efficacy of these models and techniques is tested in several planar trot and pronk experiments, and the results obtained are presented and analyzed focusing particularly on the body stabilization, the power consumption, and the energetic efficiency of the locomotion. 3 The authors would like to thank Paul Csonka and Surya P. N. Singh for their assistance in this work. The authors also acknowledge the support of the National Science Foundation, Grants Nos. IIS-0208664 and IIS-0535226, and the Secretaria de Estado de Universidades of the Spanish Ministry of Education and Science.