Arduino Locomotion

After last class where we worked with arduinos and sensors, we then moved to using servos with the arduino to make things move. The in-class assignment was to use a single servo to animate something. My thought was to use the materials at hand to create a kind of “boogie bot”.

The idea was the servo would actuate a hinge at about waist-level of a stick-figure-ish mock-up and effectively have the character sway their hips back and forth. Draped with enough fabric, and the stick-figure look would be lost. That was the hope at least, in reality, a lack of large pieces of fabric meant I could not get the coverage I wanted, added to the fact that I made a major mistake in the beginning I did not catch until later which was that instead of creating the 3 articulation points I had planned, I instead created 4, I cut 3 sticks, not 2, so I had too much movement, and not in the places I needed it. The idea sort of worked but was overall a spectacular failure which I did not feel right taking any pictures of as I am sure Emily has it seared into her mind. Let’s say nothing more about it other than I was run over by the “struggle bus”…beep….beep…

To try and lick my wounds from the in-class assignment, I decided to try for something challenging and ambitious, and at the same time make it season appropriate. My plan was to make a crawling severed hand. The dressing would be easy to accomplish as I’d use a large work glove where I could hide the electronics. As far as how to actually make the hand crawl, I figured I’d use a sort of walking motion of two fingers to propel the hand. In addition, I figured I would take a page out of Nature’s book and design the fingers in a similar fashion to how a human hand actually works. This would involve first creating proximal and distal phalanges for my hand which I would create out of plywood. The articulation would be accomplished by using miniature bolts with washers and bolts. The washers would act as a spacer and also articulating surface to make the movement easier between two pieces of plywood. From there, the tendons would be substituted for fishing line complete with tendon sheaths (also made from fishing line). I would anchor the line to similar positions as they exist on the human hand, that being at the tip of each phalanx running under the “tendon sheaths” and secured to the arms of the servos which would be lined up with the phalanges to ensure extraneous torque would not be introduced. In order to insure that flexion and extension could be created predictably, I would run both the anterior as well as posterior tendons. Hot glue would keep everything together, and I would need to round out any sharp edges to help the assembly slide into the glove. For the wrist, I would use a short cardboard tube with a platform glued inside to provide a surface for the electronics as well as give the wrist a arm-like shape. As a first pass, I only articulated one finger to see if the process would work. The build was a bit arduous especially when it came to maintaining tension on the lines to allow for proper articulation. However, it did have some life:


It seemed to have some promise, and I figured with having the other finger to provide support as well as the grip of the leather fingers of the glove it would move. The code changes would be a mirror of the same steps I had for the single finger. So I sallied forth and built out the second finger as well as the code for it, and the result was as follows:

A little tweaking of the movements was in order, but otherwise, it was starting to look like it could walk. placed in the glove finally with the “arm” as well as another arduino shield to make the connections much cleaner, and I had this…

Ok, so I won’t be going to work for the imagineers at Disney anytime soon. The biggest drawback I found was that the servos are not very powerful, at least not for the application I used. It kind of shows you the kinds of crazy forces your own hands go through to do something as simple as typing this post on a keyboard. Add a glove to all of that, and I’m pretty sure I can hear the servos crying trying to move inside there. The glove does move, albeit at a glacial pace and the design of the fingers actually makes it seem like there is a skeletal hand inside the glove every time they print against the fabric. That being said it looked creepy enough that my girlfriend threatened to kick it if she sees it coming for her. I wonder if using either a stiff “tendon” instead of fishing line would make the movement stronger as well and allow more transfer of force as well as make it easier to calibrate. Otherwise, perhaps just some stronger servos are in order can can really move the heavy fabric of the glove and allow the fingers to flex more.

Share on facebook
Share on twitter
Share on linkedin
Share on pinterest