Phase Two: First Linkage Design

The Phase Two snake was our first linkage design. It consisted of a 13 "ribs," attached to a Lexan spine in series via clamp collars.

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

Mechanical Design

Overview

Initially, all ribs were assembled using the thermal press; however, after spending 30 minutes per rib for 6 ribs, we decided to use 440 screws in tapped holes to fasten the ribs together. In the end, this cut our assembly time down by a factor of 10. In an effort to conserve raw material, the final revision for this phase used both types of rib. The servo-bearing ribs (driving ribs) were heat-staked and the non-driven ribs (dead ribs) were fabricated using screws. This prevented us from having to fully re-cut the whole of the snake from Delrin, yet still minimized assembly time.

Problems and Solutions

Our first problem was with assembly time. It was prohibitably difficult to make ribs, so we switched to a different design which helped cut the assembly time down immensely. The real problem with this phase was the sandwich design for the ribs. There were two points of contact on the spine for each rib, making turning the ribs in normal actuation very difficult. We ended up switching to a different clamp rib design in later revisions of the snake.

Initially, we used Lego wheels to support the snake. However, because there were two wheels attached to one long axle without a differential, the snake couldn't turn effectively, so we ended up scrapping the wheels entirely and just running the snake on its "belly."

Successes

All things told, the continuous spine idea worked very well. The snake managed to move under its own power on the surface of the table. It produced more of a side to side motion than the kind of forward directional movement one would expect from a snake, but it moved successfully.

Electrical/Computational Design

Overview

Both electrically and computationally, the Phase Two snake is essentially identical to the Phase One snake.

Problems and Solutions

Because of the length of the snake, we had to fabricate servo-cable extensions out of 22 AWG solid core wire (that was all we had on hand at the time). The added weight and stiffness of of the snake made bending the spine a more difficult job for our servos. Additionally, the placement of the wire was far away from the axis of the spine. Depending on which way the snake was curving, the wire would either have to be longer or shorter, further decreasing the flexibility of the spine. To fix this, we switched to stranded wire for future revisions, and put the wires directly beneath the axis of the spine.

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