Siegfried, R.

Effect of leg design on locomotion stability for a quadruped robot


When animals came on the ground, they evolved and acquired legs to enable locomotion. This natural solution presents great possibilities, such as the displacement on rough terrains, the passage on obstacles, etc. The biorobotics laboratory (BIOROB) at EPFL developed a compliant quadruped robot called Cheetah-cub that can run very fast considering its size. It is actually moving using three segment bio-inspired pantographic legs. The goal of this project was to explore the possibility to replace those legs by two segment legs that are simpler and easier to produce and assemble. It was made by designing two new leg design: the first is similar to the pantographic leg but with one segment less and the second is made in one single flexible part. The actuation remains the same in the two cases. The production of the flexible leg should be cancelled due to the amount of available time. It appeared that it is very difficult to design properly a flexible mechanism, because simulations don’t prove the feasibility of the real leg. Thus, it is very difficult to find information such as how the flexible blade used in athletics are made. Different design were proposed and simulated, but the good trade-off on the rigidity seems difficult to obtain. In the field of two segment leg, a new design was produced and tested. It appeared that some enhancement could still be made on the design and that the experiment conditions were rough for the project. It seems difficult to generalize the results to all the two segment legs, but it still gives some ideas. It is slower than the best pantographic configuration, it works with less power supply and it is robust to small perturbations. The main influent parameters are the amplitude and the offset of the hind hip and the rigidity of the springs doesn’t influence the speed of the robot if it is enough to support the robot. The final conclusion is that the bioinspired pantographic leg shows more interesting passive characteristics than the two segment leg. In a more general way, it is the most bio-inspired design the pantographic leg that shows the best performances, indicating that the third segment of the leg is needed to perform a powerful and fast locomotion with a quadruped body. What can be still explored is to differentiate the fore legs and the hind legs, using for example two segment legs before and pantographic legs behind.