Building wheels for line followers

The LineORE line followers come with a 36mm wheels made from sintra and an o-ring. Depending on the motor gear ratio used in the particular robot, that gives up to around 80cm/s. That’s pretty peppy for the line following and http://wiki.ottawarobotics.org/index.php?title=Line_Maze_Rules events at the CNRG/Ottawa Robot Games coming up in June, but more speed can likely be used in the line racing event because of the more gentle corners and longer straight stretches.

One way to get more speed is to upgrade the motors to something faster from Pololu. The cheaper way is to use larger wheels. I drew up a new wheel and then sized it for 36mm, 42mm, 48mm and 54mm (with rubber band installed). That will give me some options for testing with. That works out to a speed boost of 16.7% for each increase beyond the stock 36mm, topping out at 50% faster with the 54mm wheels.

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The motors sit on a sintra base mounted on the PCB. In order to keep the robot rear end from lifting up and the robot looking like a drag racer, I sized the wheels so that I can add a 3mm sintra spacer under the motors for each 6mm increase in wheel diameter.

I also switched to rubber bands instead of o-rings. The o-rings look nicer, but they are a pain to build because I have to groove the wheels using a motor/wheel mounted in a vice and then cut a groove with a V milling bit. Its hard to keep the wheel straight without being able to clamp it and I end up wasting wheels when things go wrong. What I really need to do is make a nice 3mm rod with a D flat on one end with threads so I can clamp it into my lathe, but haven’t gotten around to that yet.

In the meantime, I picked up a huge bag of rubber bands from the dollar store and I’m using that instead. The rubber bands seem to stick pretty well on the wheels so I think it will be fine. If not, a dab of crazy glue in the 4 corners of the wheel will do the trick.

In other news, the SumoORE libraries have been rev’d up to revision 1.2. The new code has finer control over the motors, added speed ramping to avoid lifting the front end of the robot off the ground when switching directions as well as added more minisumo and line following demo code. Don’t miss the tutorial that we put together for the robot also, showing how to implement a simple sumo strategy from scratch and learn a bit of C in the process!

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