4 May 2009 Roko   » (Apprentice)

Mini Sumo Beginnings

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.

Aluminum Wheel Stock sized

Start of a wheel

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.

Wheel Bore Action Shot sized

Boring in Action

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.

Wheel Assembly Parts sized

Prototype Wheel Parts

Wheel Assembly Assembled sized

Prototype Wheel Assembly

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.

Syndicated 2009-02-04 06:02:27 from Roko.ca

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