Mini-sumo wrestling is a popular robot-sport & after-school activity involving two robots trying to push each other out of a ring. Mini-sumo robots are an excellent way to show kids that science, math, and engineering can be fun and exciting.
But in order to hold a competition you need to have a ring (or Dohyo). This instructable will show you multiple options for making your own SimpleSumo approved mini-sumo ring.
Summary of options presented:
1. Buy a sumo ring poster. As part of my new line of educational line of SimpleSumo toys, I offer a 36"x36" poster to folks uninterested in building their own ring. Since this project is Open Source I have attached the file used to print the poster for those able. I used MS Powerpoint and a large format high quality plotter on thick glossy paper.
2. Build a wood ring. This is the highest quality option for a battle ring. The raised edges of the ring create something to fall off of which makes the winners clear and the game more dramatic.
3. Build a whiteboard ring. This is a fun middle-ground option for making a cheap get-er-done type of hard ring with the added benefit of being able to have the robots draw with dry erase markers. I build a large whiteboard ring to use as a robot catcher underneath my nice wood ring.
Note that all of my rings are intended as accessories for SimpleSumo Robotics toys and are optimized for that purpose. As such, there are a couple minor deviations from official mini-sumo regulations.
Typical mini-sumo regulation rings are a clean, smooth, flat, & hard surface, that is usually black with a white perimeter. For this project I chose to invert the colors because it takes less ink to print posters, and robots don't have a preference anyway. The added benefit of the invert colored ring is that robots programmed to respond to white edges also respond the same way to the edges of tables and will try to avoid falling over the edge if placed onto a table without a change to the program.
Typical mini-sumo regulation rings also have two brown starting lines to assist the placement of robots. I prefer a slight rule change. I mark the center of the ring with a tiny cross, and use that to temporarily position a large visual barrier and then allow the players to choose their own starting positions while blinded to the other players position. This creates an additional element of strategy and fun reminiscent of the game battleship.
My choice of overall dimensions and perimeter width are unchanged from the official rules. See attached picture for guidance.
Step 1: Build a Wood Ring: Gather Tools & Order Materials
I've seen people online cutting out their wooden ring from large sheets of MDF and gluing everything together. I'm too lazy for that, and I'm sure there are others out there also lacking the gumption (or tools) needed to do such a thing. The big trick to this instructable is the knowing that you can buy really nice wooden discs online. These discs are sold as diy table tops are are already sanded smooth!
(1x) Gloss white spray paint, available on Amazon.com or any hardware store.
(1x) Flat Black spray paint, available on Amazon.com or any hardware store.
(1x) Protective clearcoat, available on Amazon.com or any hardware store.
(~) Painters tape, a weight, and newspaper
Drill with 3/16" bit. Pencil & yardstick.
Step 2: Build a Wood Ring: Create a Paper Paint Cover
The purpose of this step is to create a paper ring to mask off the wood to help make better lines. In this instructable I used the paper in lieu of painters tape to make sure the edges stayed round. (Using strips of painters tape will make the edge more crisp, but less round.).
I wanted to make a 30 inch dohyo with a 1" perimeter all the way around so I needd a 28" diameter paper paint cover. I drilled holes in my ruler to help guide the pencil to help me trace a perfect circle0.
Step 3: Build a Wood Ring: Paint It
The first thing to do is paint the entirety of one face of the dohyo white. Unless you have other project plans you might as well used 100% of the white can to make the background as clean as possible.
Let that completely dry then lay your paper cover over the ring and use something to firmly hold the edges down while you spray the black all around the perimeter. I used a wood block but a little paint still seeped under the edges and I had to scrape & cover it up later. Painters tape would make much more crisp lines here but doing so takes more time and you have to be careful to keep the edges round.
Step 4: Alternate Dohyo/Robot Catcher Platform -Measure & Cut
As an alternative to using the wood disc, you can purchase a sheet of whiteboard and a can of black spray paint from just about any hardware store.
Using whiteboard is nice because you only have to spray the edges on and as a bonus if your sumobot is capable of holding a dry erase marker you can have fun tracking its movements!
You can painstakingly cut it into a circle with power tools like I did here OR...just don't. Seriously, the point of mini sumo is to have fun and teach kids STEM concepts. If you are ill equipped for safely chopping up wood then don't worry about it.
My initial experiment was with a square sheet of white board and I did a 5 minute job to see how well everything worked. I found painting to be necessary as my attempts to use electrical tape to make a border caused robots to get stuck due to its thickness. Also, if the tape gets removed it can mess up the whiteboard surface and make it hard to erase.
In any case once the nice wood ring was done I realized that the robots would be pushing each other off of it all day and I didn't want them to fall on the floor. So i went to home depot and got a large sheet of 1/4" thick whiteboard sheet. I used the same techniques laid out in the first steps to raw the ring. I made this ring larger that the official sumo ring dimensions by the width of a sumobot so they couldnt make it over the edge.
Step 5: Alternate Dohyo/Robot Catcher Platform -Paint & Assemble
This time I used newspaper & tape to divide off the edges and it worked better. Somehow the paint still bled under/through the paper though so I had to come back over it with simplegreen to clean it up.
After the paint dried I laid the two halves down on the floor and squared them up and used gorilla tape to stick them together.
Then I needed some sort of physical edge around this ring to keep the robots from falling out. I found some soft weatherstripping at home depot and I hot glued it on. Im really glad I picked a soft edge because it was friendly on kids arms.
I took the whole setup to Makerfaire PDX 2017 and set it up on a stool. I ended up taping the ring to the stool to keep it from getting pushed off. Everything survived a weekends worth of excited kids shoving each other to play with the robots.
Step 6: Further Reading
I hope this instructable will help some people in thinking about their options for creating a mini-sumo sized dohyo.
If you want to build a full size wooden sumo ring (the 60" diameter version) then there are great instructions in the book Robot Sumo: The Official Guide Paperback by Pete Miles- (Written by the guy that invented the mini-sumo class of sumo robots.) If you are interested in learning more about robot sumo, then I highly recommend it. Its a great in-depth read and there just aren't that many books out there on the subject of robot sumo.