Champaign-Urbana Community Fab Lab
University of Illinois at Urbana-Champaign
Champaign-Urbana Community Fab Lab

Locamoting Pom Pom Robots Project – David He

Motivation and Initial Design:

Instead of doing something that mimicked walking, as seemed the case for most others, I decided to work with something more mechanical instead. Now, obviously wheels and propellers were out of the question, since the servo could only rotate 180 degrees at most. Instead, I happened upon the idea of a rowboat, and realized I could obtain a loop-like motion by chaining two servos together (https://www.youtube.com/watch?v=bpvC5AVfEVY for inspiration)

I wanted to use the base of a Grecian/Viking warship, with a large number of oars as propulsion. The ‘oars’ would be made using basic wooden dowels, and for lightness’s consideration I wanted to use cardboard/paper for the body. However, the main issue was the ‘slots’ for the oars to be sturdy enough to withstand the oar’s rotating motion, so I decided to stick with cardboard for the first prototype and hopefully laser-cut a housing for the second one.

The basic sketch/conception of the robot.

Build Process and Modification

There were a few things that came up on the prototype. The first was the fact that the servos had tiny extensions on the side to allow them to be screwed or bolted on external surfaces. This becomes problematic when attempting to lay the servo on its side, so I had to use some extra cardboard to elevate the servo so it stayed flat:

Padding at the bottom of the servo to allow it to lay flat

I also used thin-gauge wire to substitute in as a push rod/extension for the servo arms. The thin gauge allowed it to loop and slot into the servo arms nicely, but when placed under pressure and movement it also began to bend easily.

A good view of the arm extensions and oar mechanism. Note the bending in the extensions (green wire)

I attempted to rectify this by reinforcing the center areas with thicker-gauge steel wire, but its effect was limited. This are is probably the weakest part of the design, with the best alternative to use actual push rods found with servos.

The overall result was a bit lackluster (demo video found here: IMG_5476). The primary issues were that the servos were not properly secured to the cardboard, the extensions bent too much and the overall robot was a tad too heavy for the wooden dowels to move without sufficient leverage. I will likely transition to using paper and glue for the next iteration to help secure the servos more, as well as reduce weight. I may also have to acquire more servos and push rods in order to complete this, so until I find push rods the second iteration may have to be held back a bit.

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