Phase One Snake: Direct Drive

 

The Phase One was designed to have an extremely simplistic mechanical design, allowing for very fast manufacture. It consists of 6 overlapping plates, pinned together by the output shafts of the servos. The "head" of the snake is a mounting plate for the SD-21 servo controller.

The point of the simplistic design was to allow the electrical engineers on the team to write code for the servo controller while allowing the mechanical engineers to continue developing new designs for snakes.

For a video of the Phase One snake, click here.

Mechanical Design

Overview

All of the parts were cut from sheets of 1/8" Delrin by a laser cutter. All of the servos were mounted on the each plate so that their output shafts were exposed on the underside of each plate.

Problems and Solutions

The major issue with the Phase One snake was the stairstep approach in the rib design. The design caused the snake to bend in an arch, with the front and rearmost plates lifting the middlemostplates, preventing them from any significant movement. The snake was therefore able to squirm in the air, but unable to substantially move. Also, the fact that this snake was built in the discrete-segment philosophy made it literally only a prototype for testing and development. The solution, of course, was to continue developing our original continuous spine idea for the snake.

Successes

As our first revision, this design was a triumph for being a snake. It moved, and that was enough.

Electrical/Computational Design

 

Overview

During this phase, we managed to connect all of the components together, getting the PIC mediating between the servo controller and the host computer over USB and I2C.

A sinuosoidal position signal was sent to individual servos, with a phase shift between each servo. This signal resulted in a undulating serpentine motion in the snake, but wiring and mechanical problems made it unlikely that it would have actually movied.

Problems and Solutions

The wires became very tangled because there was no organization. This substantially inhibited the usefulness of this revision. Future snakes would have a spine, so the wiring would run parallel to them, with mounting for it on each rib. Additionally, we burned out two laptop computer system boards because the SD-21 did not turn on and off well on the USB power. To fix this, we added an external 5V power supply to power the PICs, and tied its ground to the laptop computer USB's ground.

Successes

Along with the mechanical engineering success, we got all of the electrical and computational hardware, software, and firmware integrated in this phase.

Copyleft 2005: All Wrongs Reserved by Matthew Aasted (2008), Guilherme Cavalcanti (2008), Christopher Dellin (2008), Elizabeth Kneen (2008), and Jonathan Tse (2008).