5. Drilling the Rod Holes for No.2 Robot’s Pencil Holder

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Drilling rod holes in aluminum to hold the pencils.

Drilling rod holes in aluminum to hold the pencils.

There are two 1/8-inch rod holes in the robot’s front comb / pencil holder. I made the mistake of drilling the holes in the aluminum block after the tines were cut. The tines flexed during drilling, so the holes aren’t straight. Whoops! Next time, the holes should be drilled when the block is solid.

The first rod holds the pencils to the robot. This allows the pencil arms to rotate up and down, but they can’t be pulled out.

A rod holds up the offensive weapons of a mini-sumo robot, so that it won’t be disqualified for touching the ground.

A rod holds up the offensive weapons of a mini-sumo robot, so that it won’t be disqualified for touching the ground.

The second rod prevents the pencils from rotating much more than slightly beyond the surface of the robot sumo ring. In robot sumo, if any part of the robot touches outside of the sumo ring, that robot loses the match.

I made this mistake with the flexible spatula on Have A Nice Day. It did indeed slide the opponent over the edge of the ring, but the weight of the opponent on the thin spatula material (it was actually bare FR-4 circuit board substrate -- or garolite) bent it down so that my robot (bottom side of spatula) touched the ground first. It occurred during competition and the judge called it correctly. Bummer for me!

To avoid that mistake on No.2, the pencils are held up by the second rod. (It is still possible, but highly unlikely, that a pencil could get underneath an opponent as it is pushed off the board.)

The final front end of the robot is made of Delrin plastic with a solid aluminum rod.

The final front end of the robot is made of Delrin plastic with a solid aluminum rod.

After all that work, the aluminum pencil holder comb had to be discarded. During combat, the tips of the aluminum tines tended to dig into the sumo ring. Not only is damage to the ring prohibited by the rules, but it sapped motor power that could be better spent on pushing an opponent.

So, I started all over again with a piece of Delrin plastic. (Delrin is a trade name for acetal. It is available on an eBay auction, and from MSC Direct and McMaster-Carr.) Delrin is strong but slippery. It’s also available in solid black -- which is good for absorbing an opponent’s infrared emissions. That’s exactly the kind of material attributes required for the front end of this robot.

The other change that was made was to replace the lower brass rod with a solid aluminum rod. Brass is too heavy, and a sumo robot needs weight over the wheels, not over the sliding front. I didn’t replace the brass rod that holds the pencils, because I was concerned that aluminum might bend during battle.

Next up, making the pencils...