Quantifying Frictional Losses for a 2-Degree-of-Freedom Energy-Efficient Walking Robot

A modern goal of walking robots is to achieve motion while maintaining relatively low energy costs. Traditional robots are capable of level ground walking, but they are generally not energy efficient. The Extended Body Rimless (EBR) wheel is a robotic walking device which employs torsional springs and a rotating pendulum to prevent energy from being lost due to foot collisions. In simulations without friction, the EBR wheel has a periodic motion, across level ground, which can completely eliminate energy loss. However, when non-conservative forces are introduced in the system, the periodic motion of the EBR wheel is broken and an external energy source is required. To minimize the cost of transport of the system, the source and magnitude of the friction loss must be understood. Experimental trials coupled with models for the sources of drag have indicated that air drag from the rotating pendulum is a primary source of friction, accounting for about 30% of the energy loss when moving. Air drag is not often considered in robotic walkers, but for fast moving devices, drastic improvements in energy efficiency can be obtained if aerodynamic issues are addressed.