Final Machine

The competition ready slot-bot created by Sei Jin’s Army turned out to be pretty impressive.

It started at the rear of the arena with the arm held up by a small hook formed by the welding rod. At the start of the battle, the bot would drive forward allowing the arm to drop through the center and into the arena. The rubber-band belt on the arm rotated upward pushing the balls out of the arm’s way and preventing them from jamming against the central divider.

Some of the key improvements made in the last week can be seen in the image below. There is the added ¼” aluminum plate off of the rear that helped to act as a counterweight to balance our cart and the delrin slider slightly below and in front of the bot that helped ensure it only traveled straight forward and back.

The total cost our team put into the machine was about $10 but we estimate that the total cost of materials (including those provided) was about $160.

Picture of machine


The competition proved to be an honorable day for the troops of Sei Jin’s Army.

Coming into competition day we were seeded 8th but all of us firmly believed that we had a chance to win. With the use of our intimidating scorpion attack (when we would drive to the other half of the arena and nearly tip our cart over while the arm balanced on the central divider) we upset the number one seed and made it to the final four.

Critical to this success were the Velcro wheels and the geared down planetary gearbox. The Velcro covered wheels gave us a lot of traction that helped to keep the cart on the arena surface during our scorpion attack and prevented teams from pushing us back. The geared down planetary gearbox (500:1 ratio) allowed us to power all the balls over to the other side of the arena and, in some cases, push the opponent’s bot back as well on the way there.

Before the semi-finals match, our arm’s gearbox within the arena broke leaving our belt powerless. After losing to Murphy’s Law we decided to cut the rubber-band belt off to decrease the friction from the balls. This tactic paid off in the consolation match as we successfully won 3rd place.

We were all very pleased with our performance, but at the same time were interested to see what the semi-final match would have been like with a healthy Sei Jin’s Army. Altogether, we had a great time this semester, and our hard work really paid off in the competition.