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Body attitude control of a planar one-legged hopping robot using a novel air drag assisted reaction wheel

Akmandor, Neşet Ünver
In the literature, spring-loaded inverted pendulum (SLIP) model with damping has been used to represent the dynamics of legged locomotion. Based on a planar version of the model, a group of existing work focus on controlling the hip torque (between body and leg) in stance and in flight phases to generate stable planar locomotion (the SLIP-T model). Most of these studies assume an infinite body inertia such that the applied hip torque does not affect the attitude of the robot body. In practice, for any finite robot body inertia, applying time varying hip torque profiles will result in a dynamic change in the body attitude. To cancel this attitude disturbance, a compensating torque is required to be applied directly to the robot body. It is possible to use a reaction wheel to generate this torque. However, if the required torque is biased with a positive or negative direction over each stride (which is the case for hopping locomotion) the resulting wheel velocity becomes unbounded and unrealizable in practice. To solve this problem in the scope of the thesis, we propose a novel air drag assisted reaction wheel that generates a torque proportional to both wheel speed and wheel acceleration to achieve sustainable stabilization of the body attitude. We derive the dynamic model of both (regular and drag based) systems and present them in detail. Using these dynamics, we perform hybrid system simulation (with ground contact) of the planar robot system during locomotion. Under two different locomotion controllers from the literature, we demonstrate the disturbances on the body attitude and propose PD and PID based control of the regular and drag based reaction wheels to stabilize the platform. Having successful results from our simulation experiments, we also test the feasibility of the approach by conducting physical experiments to determine the required and obtainable drag torque.