S6 Snake Robot Prototype (2000-2001)
Materials: Polycarbonate plastic, brass rod, and plastic gears
S6 was an experimental prototype that was a second attempt (after S4) to use a single motor to create undulation along the length of the robot. The upper set of gears caused rotatary motion down the snake that turned a crank that connected one segment to the next via a rocker arm.
A second set of gears performed a similar function but controlled an overall bias to the reciprocating motion, allowing steering of the robot. The reciprocating arms were offset in phase along the length of the snake whereas the steering arms were all in phase.
Unfortunately, the torque on the gears increased linearly with the length of the snake, and given the limited reduction ratio in each segment, the stress on the mechanism became very large.
A second emergent property of the design was the way in which backlash along the gear train could concentrate in certain segments, defeating the steering mechanism locally.
To be successful such a system would need a higher reduction ratio in each segment. A second flaw in the design was that the entire structure was not vertically compliant, so
contact between wheels and the ground would require a compliant suspension underneath the gear train, adding to the height of the snake. The robots failed to undulate successfully as it neared completion and the project was abandonned.