3D Printed Robotic Arm, draft 2
I have received the second draft of my robotic arm from Shapeways.com (for those of you just tuning in, you can see the first draft in my robotic arm series here). Shapeways was trying out a new material on the community, so I jumped on the bandwagon, and here are the results (video at the end of the post):
The material is called “Alumide”. Effectively, it is aluminum mixed with their another popular 3D-printing material: PA2200 (White Strong & Flexible). The aluminum gives the printed parts a nice sparkling grey texture. The materials feels more brittle to me, and possibly not as tough. This is partly due to the material properties, but it also may be due to the fact that I shaved off a lot of material and shrunk the gear (and the teeth) down a fair bit from the last print. The gear housing and motor mounts were a little too flimsy (1mm thick walls). They held together alright, but I had to be careful when mounting the motors and working with the gears so as to avoid damaging the housing. The surface roughness of Alumide seems about the same as the PA2200 to me. Although I had significantly more trouble working the gears to get them to run smoothly, I attribute that to the smaller gear size and the slightly misaligned (on purpose) worm gear.
One of the improvements I made was to reduce the number of gears types down to three: two wormgears (same size), two large gears (one merged with the outermost limb), and 8 compound gears. I arranged them so that they could all (not counting the worm-gears) share the same six axles. I was concerned that the surface roughness would cause problems with gears rubbing against each other, but I didn’t have a single issue with that, even with the gears packed in so tightly. I even made the housing sandwich together such that I could give them more room if necessary, but I didn’t end up needing it.
As a bonus addition to this project, I found a wiimote at my local thrift shop. I used cwiid (a wiimote library) to take in the arrow commands from the wiimote. The program then passed simple commands to an Arduino, which then drove the two small motors using two H-Bridges and a cellphone charger wall-wart. It is a rather inelegant and jury-rigged control system, but it works for the purposes of testing.
This draft showed itself to be a decent success. It is fairly responsive and fast. It is a little jerky, but that could have been avoided if I had utilized PWM. Control options with the wiimote were limited due to the program having no knowledge of what the relative segment orientations were. In future revisions I will try to incorporate some sort of feedback loop (so the program knows the orientation of the limb). Another degree of freedom would also be nice. Touch sensors will also eventually be essential to a useful robotic limb. Also a rocket launcher would be cool.
Tags: 3D-Printing, Arduino, Robotics, Wiimote