Roko.ca

As with many projects, a mini sumo has been several years in the making, and has undergone several design revisions without actually having time to begin construction. But, finally, I took a bit of a break from the quadruped to start work on a mini sumo robot in the past couple days.

I had some round aluminum stock sitting around, and felt like playing around with the lathe. I got my trusty hack-saw out, cut off a chunk of aluminum, chucked it up on the lathe, and started spinning. Over the course of one evening, I came up with a basic wheel and hub assembly to go with the Maxon 17:1 gear motors I’ve had lying around for almost a year now, waiting for a sumo robot to be built around them. This is the same Maxon motor many people use, and I had to contend with the same issue, that the motor length itself is half the maximum width of a mini sumo robot (About 50mm). This called for making a hollow wheel that would slide over the motor.

I made a two piece assembly, with a hub that is attached to the motor with a set screw, and a wheel that is attached to the hub with several 2-56 screws.

Overall, the boring went well on the lathe, but was definately a learning experience. The process itself was tedious, starting with drilling out a center hole using drill bits of incremental sizes until I had a center hole large enough to fit the boring tool, then slowly boring out a 21mm depth, 0.1-0.2mm at a time, slowing down as I approached the desired tolerance.

The tool itself chatters easily if you’re not careful, but I managed to produce a mostly clean bore. I’ll have to experiment/research a bit more on the best chip rates for turning aluminum stock…

Making the inner hub itself was easy to do, simply turning down the outside of a piece of aluminum, then using a couple drill bits to center drill a hole to about 2.85mm, then using a reamer to finish the center hole at a nice, clean 3mm to fit the shaft. A 4-40 set screw fit nicely, though I did have to file down a fraction of a millimeter that was sticking out from the hub itself, as that part of the hub fit with close tolerance into the wheel itself.

[caption id="" align="alignright" width="150" caption="Prototype Wheel Assembly"][/caption]Using a milling machine to precisely drill the holes that I would then use to tap and mount the actual wheel to the hub helped keep everything nice and accurate. Once finished, the wheel and hub aligned very well, and I had a completed wheel assembly.. Now to finish the other wheel, make a tire mold, mold the tires, mount the motors to a chassis, and make a brain for it all.. Hopefully I can have a basic robot ready in time for this year’s Robot Games.