362Fw: mini robot sumo ring
- May 1, 2001----- Original Message -----From: bill harrisonTo: howvin@...Sent: Monday, April 30, 2001 1:24 PMSubject: Re: mini robot sumo ringHi all,
I've been asked about how to make a Mini Robot Sumo ring so many
times, I thought I'd post to the network just one e-mail I've recently
sent. If any of you have any input, coments, or questions, feel free to
contact me. I'm planning to support a Robot Sumo web page with
information like this. Any input I get can be considered in this.
Thank you so much for your support of Robot Sumo. Feel free to
keep in touch with me, as I'd be most willing to be an e-mail advisor.
I'm working on several kits, aimed at the High School
environment, so stay tuned: http://www.sinerobotics.com But I won't
have much more than remote control stuff ready by July.
For your situation, I'd suggest a practice Mini Sumo Ring. They
are very easy to build and inexpensive. Surprisingly they work almost
as good as the contest grade rings. If you are really interested in a
contest grade ring, let me know and I can give more details, but I feel
the practice ring will do for you for now.
There are several materials that work for a ring, but the best
is that black melinte (I don't know how to spell it, but it's the
particle board with a thin hard coating layer, usually on both sides,
usually white). 1/2 inch think works just fine (I use a few loose
spacer blocks to bring the ring up to the 2 1/2 cm min height call
out). If it's glossy, dull it down with some 400 sand paper, as it's
not supposed to be glossy. The stuff I saw was non-glossy to start
with. Use paint to make the white ring at the edge (I assume you can
get the dimensions, but if not, let me know).
I use polyurethane paint, that is used to make stripes on
floors, as it's not very brittle. Brittle paint scrapes off and chips
very easily (epoxy enamel doesn't work very well for this reason).
I cut out the disk on a band saw. Just mount a pivot in the
center of the back of the ring and rotate it through the saw. To get it
accurate (as the saw blade can move some as it's cutting), I get it
close, but just a smidgen bigger, then cut off (actually more like
filing) just a little at a time to get the right size (77 cm, or about 2
1/2 feet 5/16 inch in diameter. It's close enough if you find a disk
that is already cut to 2 1/2 feet diameter). However, if you don't have
a band saw, it's still easy to cut a disk.
Make a compass out of a stick, a nail and a pencil. I pound a
sharp nail through one end of a stick that is longer than 1 1/4 foot.
Then I drill a hole as exactly as I can, 1 1/4 foot 5/32 inch from
pencil point to nail point. I make the hole just right to press in the
pencil (doesn't have to be too tight, just enough to hold the pencil in
place). I find the center of the ring (making several 1 1/4 foot 5/32
inch marks towards the center of the ring, from several points around
the rim, does the trick). Place the nail point on the center of the
ring, not hard enough to make a hole, just hard enough to hold it in
place (there will be a small dent, which is OK). Mark a circle all the
way around, with the pencil. With a hand saw, cut as close as you can
to the line, being very careful to not even let one tooth of the saw go
over the line. If in doubt, leave a little material. Use a coarse file
and bring the edge down to the line you've marked. Use sandpaper to
smooth it up when the ring is at the right size. Sand the corner just a
little to avoid the nasty sharp edges that melenite (sp?) makes. But
don't round it off too much.
To paint the ring, drill a second hole in your stick compass,
about 1 foot 2 5/32 inch (14.173 inches to be exact :-) ) from pencil
point to nail point. Draw a second ring mark with the pencil, as a
guide for the white edge line. This should lay out a ring about 1 inch
wide (2 1/2 cm) at the edge of the surface. Carefully lay paint masking
tape (it should be the stuff for paint, so the paint won't leak under.
The "Blue" stuff work fine). If you stick it down inch by inch, with
the outside edge just on the pencil line, you will get a pretty round
looking edge to the paint (if you go quick and do larger sections, the
edge of the paint will look "choppy"). Be sure to press the edge of the
tape down hard with your finger after it's all been laid down, to seal
the tape on the rings surface. I use a narrow tape, maybe only 1/2 inch
wide for this. Then I put masking paper and tape to cover the center of
the ring, overlapping this carefully laid out edge tape. The white ring
can be spray painted now.
Glossy white is fine for this edge mark. The white paint layer
should be thin. If its' too thick, the robots have more of a chance to
scrape it off. I very lightly spray on the paint, wait about 5 to ten
minutes, to let it adhere well, then give a light, but opaque second
coat over the still wet thin first coat. This way it sticks well, but
doesn't have to be too thick.
It's a bit tricky, but I also take the tape off after the paint
is only half dried (still wet to the touch). I pull it off towards the
outside of the ring to avoid smears. I do this to minimize the lip the
edge of the tape pulls up on the paint. This paint lip would make it
easier for robots to scrape the paint off. By pulling the tape off
while the paint will still flow, the lip goes away. But it it tricky,
so experiment on scraps first, if you are not sure you can do it. The
ring will still work OK if you just wait and pull the tape off when the
paint is hard. And this way, there is no risk of smearing the paint.
The side of the ring isn't important, you can either paint it, leave it
bare wood (by masking it), or just let it be "oversprayed" (my
If you can't get the black melenite (sp?), other colors will
work too. I use the BIN white shellac primer, as it will stick to the
melenite. It takes it a few days to really stick well, so don't use the
ring for a week, to let it set in. You can paint over the shellac in a
couple of hours, and just let the finished ring set for a week. This
isn't as good as the black melenite, as any scraps the robots make will
come out white or something. I use a black laundry marker to fix these
"white marks". White-out, used to correct typing errors works pretty
good for fixing the "black marks" on the white line.
Sand the surface of the melenite with 400 paper to rough it up
before painting. Don't sand a lot, or use coarse paper, as the hard
surface is pretty thin, just break the surface shine. Use a "tac rag",
available were paint supplies are, to wipe the dust off the surface for
painting. Paint the hole ring, then paint the white edge over the
black. If the melenite is white, you can mask off the outer edge and
use the melenite's white color as the rings edge.
If you use other woods, use something to fill in any holes or
porousness. I've used the "bondo" car body shops use, with good
success, but there are several products out there that work. Chip board
almost always needs something to smooth up the surface. Try to use a
surface wood and material that isn't too soft, as the robots are more
likely to damage softer materials. Prime and paint as above.
You can use any thin material, glued to the wood disk too.
Flooring material works well (in fact that official stuff is stage
flooring material). But it can be expensive, unless you have a scrap
The two center start lines are optional for practice rings, but
some contestants might need this for the competition. So if you are
using this ring for a contest, you should paint on the center marks.
I lay them out in light pencil marks and lay down masking tape
and paper. Watch over spray on the rest of the board, non glossy black
really picks up overspray, it's best to mask the whole board. A dark
brick red is the official color, but I've use gray paint with success.
The trick is that it has to defuse back IR light at an intensity half
way between the black and white on the ring. This way the robot can
distinguish between the black ring surface, the white edge and the
"gray" center marks. These lines can not be glossy. I use a simple
test rig to measure the paints "IR brightness". Be careful not to
direct the reflection of the IR light into the sensor, it's the defused
light that is measured. Tilting both the sensor and IR light source a
little, and keeping them parallel to each other works. Any reflections
will throw off your measurements (even glossy black looks white in a
I make my IR brightness test rig with a typical IR reflective
sensor pair. I set up the IR to just glow continuously, and the IR
phototransistor as one leg of a voltage divider by putting a 10 K Ohm
resistor from the Collector to 5 volts and the Emitter to ground
(negative). I attach the negative voltage meter lead to ground and the
positive voltage meter lead to the point between the 10 K Ohm resistor
and the phototransistor. Based on how much IR light (and a little other
colors of light) that hits the phototransistor, you will get a voltage
reading to correspond. More light, means the phototransistor conducts
more, bringing the "center voltage" being measured by the volt meter,
down. Measure what Black and what White measure, in volts. Now
experiment with paints till you find one that produces a voltage about
half way between. Glossy paints can be sanded lightly with 400 sand
pager to make them non glossy.
This setup can be done with an analog to digital converter
instead of the voltage meter.
During rings use, quick repairs can be done with a black laundry
marker to restore black areas, typing correction white-out to restore
white areas, quick drying putty for dent fixes, and 10 second glue for
reattaching any pieces that are cut or gouged off the ring surface. I
also use a knife to fix little things that stick up, from minor damage.
It is normal for a ring to have minor damage that contestants must deal
with, as the contests continues. This is more of a consideration on the
bigger robots, but also true of Mini Robot Sumo. As the ring looks more
and more "repaired", it can be puttied, sanded, primed and repainted.
I'd suggest having more than one ring at any contest, in the event one
ring gets serious damage during the contest. The second (or more) ring
also can be used to test robots offstage, during the contest (and there
are always folks fixing and adjusting them during a contest).
I hope this helps. Let me know if you have any questions. And
let me know how the ring construction goes, as well as your contest.