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Over four feet long, the Phase Four "polished" snake is the culmination of the first semester's work on this project. All prior problems associated with past designs have been addressed in this revision to ensure its quality. Like the past two revisions, this snake is actuated by the linkage-servo system mounted to alternating ribs. It has a high degree of precision and control and is substantially more reliable than past designs.
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Mechanical Design
Mechanical features of the latest snake include a length of over 4 feet, a thermoformed head, improved linkages, and a sturdy yet flexible design. Prior to designing this snake, the mechanical team set down to address all past design issues:
Linkage Design
In past designs, the wire linkages would pop out of place during actuation. To address this, we used wire with a smaller diameter, allowing for slippage, and secured both ends of the wire by bending it at ninety degrees to prevent it from easily coming out. Bending the ends an additional 45 degrees allowed for easy insertion. We also attempted to use other linkage designs, made of rounded wire and delrin, but manufacturing time made these designs undesireable.
SD-21 Mounting Solution
The SD-21's mounting rib in prior designs had been cantilevered off the snake. In this revision, we added wheels to its rib. Additionally, to minimize wiring problems, we offset it from the rib allowing us to place wire between.
Spinal Deformation
We noted slight plastic deformation in the Lexan spine in other designs. However, after using the INSTRON tensile test machine in the material science laboratory we determined that it was still the best material for its price range.
Problems and Solutions
There were a few problems with the Phase Four snake. We noticed the clamp collars began breaking and plastically deforming in this design revision. This is something to address in the future. Also, a problem with the snap together approach that we kept for this snake design is that the bearing clips (wheel mounts) sometimes snap. This can be solved by changing their tolerances or the material itself.
We also learned a lesson with this revision which was if you are to build 17 like products (the two different groups of ribs), it is wise to set up a jig for consistincy and ease of manufacturing. This will be implemented in future designs.
Successes
This was our longest, most complicated snake yet. By incorporating all of our solutions to previous design issues, we got a very good results.
Electrical/Computational Design
In order to reduce the amount of wires, we used 14AWG stranded core cable as a power bus, tapping off 26AWG wires as we needed power. This way, we only had to run one 26AWG wire down the length of the snake for each servo, which made wiring much simpler, and less stiff. We also laser-cut features into the ribs for wire management, making the overall job cleaner and easier to work with.
We added Purple LEDs with a 500 Ohm resistor on each powered rib for underlighting and Amber LEDs with a 500 Ohm resistor in the head of the snake as eyes for aesthetics, and we can't say that it was a bad decision.
Successes
The wiring system was a big success for this snake revision, because each rib was independent of the others, and connected to the main bus for power. This way, we could remove and add ribs very easily. Also, the LEDs were a big hit with both the team and our classmates.