A Headless Walking Robot

People generally take walking for granted. It is something we have done since the earliest days of childhood, and now stride with ease from place to place. Walking is, however, an intricately complex sequence of actions, all designed to prevent our face from meeting the ground. It is an inherently stable method of moving, for if you have ever tripped or slipped up, you know how easily you can continue with your stride. Robots, on the other hand, can barely mimic the way human beings walk, and do so in a jerky, ungraceful way. Michael Coleman in the Mechanical Engineering department here at UVM, studies human walking, and is trying to translate human motion into something a machine can do.

A human body has a large number of finely tuned and responsive control systems to maintain walking, keeping our top-heavy body over our feet. However, all of these might not be necessary for walking at all, as recent research suggests that walking is stable without much intervention, and all it really needs is an energy source to keep going.

That energy source need not be large as well, as anyone who has been on a long walk, or paced around the dorm room, knows it is a very efficient process, requiring very little conscious effort on each step. For humans, the energy source is your muscle, but for a new, fun, and very unique toy, it is a simple ramp.

This toy is a simple mechanical model of a walking stride that is remarkably similar to the fashion humans use when walking. Such machines have been built before, notably by Tad McGeer, originally at Simon Fraser University in Burnaby, British Columbia, and now at the Insitu Group in Underwood, Wash. McGeer’s walkers had either straight legs or joints for knees, and could walk down a short incline with a steady gait. However, between each stride, the walker settled into a stable point, with one leg ahead of the other. This raised the issue that perhaps its stability while walking had to do with the fact that it was in a stable stance at the end of each stride. Michael Coleman’s walker, however, is not stable while standing still, and needs to move to stay standing up.

Originally, he used a simple model, with two legs, round feet, and small balancing rods extending outwards from the feet. When modeled in the computer, it did not produce a walking motion, and so while playing around with some plastic Tinkertoys¨, he built the model in the computer and stuck it on a ramp. It did walk, but not very well. A few modifications made it into something that could walk easily down the ramp, swaying from side to side as one foot moved in front of the other.

Since the Tinkertoy¨ “feet” have small holes in them, they were covered with a strip of brass held on with electrical tape. If the holes are left uncovered, the walker will stumble and fall, and the springy properties of the metal strip could be helping to absorb energy as it steps down and provide a boost as the other foot comes down, much like modern athletic shoes do. On a slope, the walker is capable of taking seven to ten steps, covering a distance from 30 to 40cm. To do this on a level surface, all one would need is a small amount of power to keep the legs moving.

The walker itself is easy to assemble. Each leg is made from a yellow spool, light-green rod, and dark-green hinge glued together. The legs slide onto a red rod, which acts as an axle. Three orange washers separate the green hinges and keep them from sliding off. The side weights are supported by a yellow spool on a red rod that is inserted into the “ankle” of the walker, and each weighs about 50 grams. Fully assembled, the walker weighs about 120 grams, equivalent to four and a quarter ounces. One massive box of 200 Tinkertoy¨ parts costs about $25, and you can probably build at least 3 of these walkers from one set. For further information, go to http://www.cems.uvm.edu/~mcoleman.