Feet Part 1: The Critical Role of Feet

​Have you ever walked in ski boots that limited your ankle's movement?  Or in a lower leg cast?  Without being able to strike heel first and then roll onto our toes we're forced to walk peg-leg style, revealing how large of a role active feet play in walking.

Mechanical walkers can similarly benefit from active, articulated feet. We began exploring adding some sort of active heels and toes after the first walking tests of our SUV-scale TrotBot revealed we had insufficient foot-contact with the ground.  

​The first result of that effort was TrotBot's heel linkage.  As you can see in the diagram below, TrotBot's heel strikes before the main foot, taking the weight while pushing backward to continue driving the robot forward.  The resulting smoother gait reduces both torque and power requirements (for an analogy of why bumpy gaits require more power, think how much harder it is to do lunges than it is to simply walk).  

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Another benefit of TrotBot's heel is it steps higher on the backside of the foot-path, allowing TrotBot's rear legs to step about as high as the front legs to avoid getting stuck astride obstacles, as can be seen in this heel-path simulation:

​​​Without its heel, TrotBot's rear legs probably would have gotten stuck on some of these 2x4s:

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We've also played around with a few ideas for active toes that push down on the ground as the foot begins to lift:   

Mindstorms TrotBot with Active Toes

Using shaped feet to smooth gaits is explored next in Feet Part 2, and the impact of TrotBot's active toes are explored in Feet Part 3.