Watch James Bruton Experiment with Tripedal Robot Locomotion
Inspired the robots imagined by H. G. Wells, James Bruton built an experimental tripedal robot to develop a reliable gait.
If you take a look at inexpensive walking robot kits, you will notice that most of the options have six legs. That's because it is very easy to give a hexapedal robot a stable gait: three legs can remain in contact with the ground at all times. Quadrupedal and bipedal robots are also fairly popular. But you almost never see tripedal robots, because it is difficult for them to walk in a stable manner. Inspired the robots imagined by H. G. Wells, James Bruton built an experimental tripedal robot to develop a reliable gait.
The difficulty here all comes down to the robot's center of gravity. A quadrupedal robot can balance on two legs at a time, keeping the center of gravity between the two. A bipedal robot can shift its weight slightly so its center of gravity moves over the foot on the ground. But if a tripedal robot lifts one leg, it is a challenge to move the center of gravity between the other two legs — the robot will just topple.
Bruton's idea was to make the legs pivot. In their normal positions, the legs touch the ground at points 120 degrees apart from each other. That is a stable tripod arrangement. Then, when the robot needs to take a step, two of the legs pivot so that they're closer to 180 degrees apart from each other. The robot can then, in theory, balance on those two legs while it lifts and moves the third leg. Repeat that process with each leg and it should walk.
To test this idea, Bruton designed a simple robot. He 3D-printed its body and legs. Those legs have three joints each: one pivoting hip joint, one lifting hip joint, and one knee joint. Beefy servo motors actuate all of those joints and an Arduino Mega 2560 development board controls them.
Unfortunately, the robot didn't work very well. It has to drag its legs to move into position for its balancing act and that negates most of the motion in the desired direction. But Bruton believes that he can improve the gait with the addition of an IMU (Inertial Measurement Unit) for a sense of balance and an actuated weight to facilitate that balance. That would let the robot shift its weight onto specific legs (or pairs of legs) so it can move the other legs more easily.
We'll have to wait and see if Bruton is successful in that endeavor.
