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The Phase Three "weighted" snake was the first to achieve a repeatable serpentine gait. It is composed of radically different "dead" (no servo) ribs and "live" (servo-holding) ribs. It was the first snake explicitly designed with wire conduits in mind.
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Mechanical Design
Beta 3
There are two independent wheels and axles on each live rib, which permits individual ribs to turn. Previous snakes attempted to combine two wheels on one axle, which forced wheels to slip as the snake attempted serpentine motion. The ribs were designed with ease of assembly in mind. Snap-together plastic assembly techniques were investigated and successfully implemented, and as a result each rib assembled in less than 2 minutes. With all of these new developments, we could install and remove servos without disassembling the entire snake, which was previously impossible.
Problems and Solutions
The center of mass of the live ribs was on the border of the wheelbase, and as a result the snake was unstable in short sections. Additionally, the snake itself was too light, compounding the problem. In order to weight down the snake, we taped on large sockets from our toolbox. The addition of weight allowed the snake to successfully display a serpentine gait.
Successes
The updated mechanical design, when meshed with the new algorithm performed astoundingly well. The completed snake undulated its way across the robotics lab floor to the end of its tether.
Electrical/Computational Design
The electrical system on the Phase Three snake worked very well. Abandoning 22 AWG solid core for 26 AWG stranded core eliminated the flexibility problem. Additionally, the wires ran along an axis immediately below the spine, reducing the amount of travel for the wires and increasing the flexibility of the snake.
We successfully managed to implement the brute force calculation of servo-space controls from a world-space sinusoid. We also extended our algorithm to allow to the snake to follow a sinusoid projected on any parametrically defined curve, enabling the snake to do things like slither in a gradual curve, or slither along another, larger world-space sine wave.
Successes
This was the first phase in which we were able to successfully implement our continuous spine serpentine gait algorithm. We also were able to steer the snake very coarsely using the superimposed sinusoids.