Loading ...
Sorry, an error occurred while loading the content.

362Fw: mini robot sumo ring

Expand Messages
  • Howard
    May 1, 2001
    • 0 Attachment
       
      ----- Original Message -----
      Sent: Monday, April 30, 2001 1:24 PM
      Subject: Re: mini robot sumo ring

      Hi 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
      preference).
              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
      lying around.
              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
      reflection).
              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.

              Regards,

                      Bill