LandShark
Mini-Sumo
Mini-sumo is a competition where two autonomous robots try to push each other out of a ring. The ring is about 3′ in diameter with a dark middle and a white line around the outer edge. Robots are able to detect the outer white edge and stay inside the ring. The maximum width and length for a mini-sumo robot is 10cm and there is no height limit. They must sit still for 5 seconds at the start of a bout before attacking the other, and the first one to push the other out of the ring 2 out of 3 times is the winner. The Portland Area Robotics Society (PARTS) has the official rules, and the Robot Room has a nice description.
LandShark
LandShark was my second fully autonomous mini-sumo robot. Most mini-sumo robots dawdle around the ring and eventually end up in a head-to-head pushing contest where the stickiest tires and sharpest scoop tend to determine the winner. My thought was that if my robot could follow the white line around the edge of the ring until it sensed the other robot in the middle, then turn 90 degrees and shoot across to broadside the other robot, that would avoid the head-to-head standoff.
I used some very large powerful Swiss-made planetary gear motors that I picked up from a surplus shop for $20 each. They were rated for 6 volts, but at 18 volts they rotated at 600 RPM, which gave me about 40 inches-per-second (IPS) of speed. Since a mini-sumo ring is only 3′ in diameter, 40 IPS worked great!
I designed the PCB to act as the frame for the robot and hold the motor mounts in place. The microcontroller I picked was an AVR Mega128, and all of the firmware was written in C for the GNU AVR compiler. I added lots of LEDs to give me feedback and also to make it look cool. I even put blue LEDs under the motor mounts, which were made of slightly frosted quarter-inch thick plastic that I had laser cut.
The wheels I designed were laser cut from acrylic. The rubber tires were custom-molded from a 3-part chemical solution from Tap Plastics. The formula was a Portland Area Robotics Society (PARTS) mix that we all used to get perfect traction without violating the anti-sticky tire rules. I machined the mold out of Delrin, which made it fairly easy to remove the rubber once it had cured.
Here’s the second version of the PCB, which was a much better design. I learned a lot from the first version.
LandShark was very fast and powerful, just as I had hoped. It was fairly successful in competitions, mostly placing in the top three. I implemented a PID motor control algorithm which served me well. The motors were so strong that I destroyed a few motor controller chips because of current spikes. I had to double up the drivers so they could withstand the current.