Is this what you wanted?
Yes!! Thank you a lot, I was wondering that if I made it in wood it would like grnd my metal plate in front, make that horrible sound.
I used a piece of white melamine for mine, so I only had to paint the black center part. I actually cut the round part using my table saw (yes, it is possible), and it makes a fantastically smooth, perfectly round cut.
If anyone is interested, I’ll post some instructions…
- Jon
Well, I think the way I’m going it’s more going to be plywood since that’s all they sell close to me that’s big enough (and I don’t have a car so I dn’t want to go far)
A lot of hardware stores will deliver for a small fee, especially the mom&pop type places…
- Jon
Try using MDF, that’s what they use for the competition rings.
better know how to cut it properly, MDF is easy to use, but the edges will not be very nice looking unless you know what your doing. Need to cut really smoothly with your cutting tools to minimize going back and trying to fix it since this will make it worse.
Well finily I bought some plywood, I think it’s goign to be good, I saw the white melanine one but I needed I special coat before the primer to get the paint to hold so I let the idea go. 
Easier like this.
Do you own a router?
why would he need a router unless he was going to put an edge on the ring. I think he would need a jigsaw…
That fiber board is cheap so I agree that’s the way to go. But…
I always thought black plastic would be a cool surface. Yes a big thick piece of black plastic would be expensive. And it would have to be the right kind of plastic. Maybe some light random-orbit sanding would make a nice, dark non-reflective surface.
The benefit is a surface that is smooth and durable requiring no black paint. Plastic paint is durable and would work well for the white lines.
disclaimer: I have a mini-sumo but no experience in sumo competition.
The robot room instructions are ok, but I dissagree with using gloss white paint for the circle edge. It should be flat white, just as the flat black as is used. It’s not necessary for IR or visual light sensors, and it has a completely different texture.
Isn’t glossy better for reflecting the IR light from the sensor?
Define better. Are you talking about a 0.5% increase? I haven’t heard a lot of complaints about IR reflective sensors not being effective enough with flat white and they wish the ring edge was shiny too. 
In fact having the ring edge be glossy could cause unwanted IR light to be reflected far inside the ring. I’m sorry, but I just don’t get it. 
What ever. I thought it would be better though.
I think you wanted “whatever” not what ever. 
Yeah, just a typo. 8)
You can use a router with a straight bit and a special jig called a trammel to cut a perfect circle. It is similar to a giant compass. If wowy has one, I’ll explain more. Trust me, it’s way better than a jig saw, and no sanding needed.
well, I finished my two sumo rings. I managed a perfect 77 cm evrywhere around the circle! And the white edge is 2.5 cm evrywhere. I managed to trace the circle with an improvised compass (a meter with 2 C clamps hloding down pencils… it work remarquebly well ). I cut it with a JigSaw with a special blade. Traced another circle (for the little white line). I then put sone masking tape on the white (I had put a coat of primer) and painted the center black. The paint was very good! 1 coat and it’s perfect black. Took the tape off and it gave me a very good looking mini-sumo ring.
I didn’t take any pictures along the way but if someone wants a picture I’ll be glad to post one.
Pics please! 