This is a way to make Sumo rings for Robot Sumo. In this example, I am making Nanosumo rings, but this should apply to the larger classes of sumo. The final ring will have a black area for combat and a white ring for out of bounds. The white ring should be reflective so the down facing reflective sensors of the robot can see it.
Step 1: Finding the Melamine at the Store
This is what I think is the hard part. Where the heck does Home Depot keep the small pieces of Melamine? Melamine is thin (1/4") particle board coated with plastic (which makes it like a white counter top). In the first photo, I show what the section looks like at Home Depot. The second photo is a picture of the board. This one is 2x4 feet and costs $10. The last photo is an "Easter Egg", a 2x2 feet lucky piece for $2. Since you are not going to make very many Sumo Rings (probably), a smaller piece is better.
In the case of the Nano Sumo Ring, I want to cut the board and get a 1x1 foot piece. I went to the Techhsop and used their Plywood Saw. Home Depot could also cut it for you.
Step 2: Masking, Painting, Cutting
This step is really 5 steps. Make a mask for the white area and stick it on, spray paint the whole piece flat black, then remove the mask. Then you cut off the corners with a band saw and the use a belt sander to make it round.
Here I used the Techshop Vinyl Cutter to make the "ring shape" mask. I made the input file to the Vinyl Cutter in Adobe Illustrator. Without really knowing Illustrator very well, I made a circle with diameter 19.25 cm and then made the .625 cm smaller circle for the boundary. I got the dimensions from the Robogames webpage for Sumo. Watch out. I subtracted .625 from 19.25 and got the wrong answer and wasted a lot of time. The inner circle diameter should be 19.25 - .625 - .625 = 18 cm.
Once I cut out the ring of Vinyl, I stuck it on the 1x1 foot piece of Melamine, and then I spray painted it with Flat Black Krylon paint. After it dried overnight, I pulled off the mask. I then went to the Techshop and cut the corners off with a Bandsaw. Then using the Belt Sander, I finished the ring.
The Belt Sander really gobbles up the board so it can be difficult to get a decent round shape. Don't use the scroll saw, it hammers the black surface and scrapes off the paint. Also, I couldn't cut a decent path with it. It was all jagged and bad, bad, bad.