abandon all hope ye robots who enter


 LEGO RoboChallenge Tug-o-War

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  • Longneck: 1st place in Robo-Challenge tug-o-war 2/23/2002
  • The Infernal Brick of Despair: 2nd place in Robo-Challenge tug-o-war 2/23/2002
  • Competed against 20 grade, jr. high, & high school bots from Santa Barbara county
  • Both bots made it to the semi-finals in a later event
  • Had tons of fun


STORY: Many years ago, I helped UCSB Mechanical Engineering robotics professor Brad Paden start up a robotics educational outreach program to teach kids in grade, jr. high, and high school robotics through the use of LEGO Mindstorms.

Years later, it came full circle & Luke Laurie, head of the RoboChallenge program for Santa Barbara County heard about my work through a common friend, Dr. Megavolt, and asked me to do a seminar to show his students my BattleBots and LEGO creations. Just a couple of months later, we found ourselves putting on an all-day robotics workshop for about 130 kids in 3rd-12th grade.

I went through the robot design process & explained what goes into a BattleBot, demonstrated Dr. Inferno Jr. and Hell on Wheels against some remote control toys & what was left (not much) of Bot Will Eat Itself, and showed how to make wireless remote control LEGO bots with Itchy & Scratchy.

But I was really dying to get in on the Robo-Challenge action, so we decided to hold a tug-o-war contest between the different schools, and I was allowed to enter, too! I built a special bot, Longneck (which I figured would either do very well or very poorly), and an ordinary one, The Infernal Brick of Despair (IBoD), which I had built just as a test opponent for Longneck.

After a disastrous 1st-round loss for Longneck, both bots continued undefeated through the winners' and losers' brackets until they met each other in the finals, with Longneck coming out on top. Wow--I didn't expect to sweep!

The Santa Barabara Newspress ran a short article about the day's events.

SPECS: Because this was a pulling contest, not a race, I needed a big gear reduction for serious torque. I built IBoD's drivetrain with a pair of 5:1 reductions. It still was a little fast--it traveled way more than 1 foot in 1 minute (the distance needed to pull the opponent to win). So I built a 2nd version of the drivetrain with an additional 3:1 reduction, which went about 15 inches in 1 minute--perfect. Because all bots were subject to strict rules to keep their specs similar, the only big edge I could gain was to build a bot with a very tall tow point so the string would be pulling down on my bot, thereby increasing the downward force on my wheels, resulting in greater friction & traction (and robbing my opponent of some of his grip, equal to the amount that I was gaining). To keep Longneck from toppling while tugging, I built a loooong neck with lots of weight concentrated at the end (the RCX & 6 metal hooks) to counterbalance its tipping tendencies. It turned out to be a tricky balancing act that took lots of trial & error to refine, but I pulled it off. In a successful run, Longneck's vertical beams would bend noticeably while the head would lift off the ground and then drop back down, dragging the opponent slightly forward, repeatedly until victory. IBoD was simply a 4-wheel-drive block--I used a battery pack as ballast to bring him up to weight and just piled on bricks until he was at the weight limit.

So, the tricks I used to pull off the victory and that I'd love to see students incorporate into their future tug-o-war designs are:

  • Use all of the weight allowed
  • Gear way down for lots of torque
  • Use a high tow bar to "steal" the other bot's traction
  • Counter tipping tendencies with a counterweight
  • Avoid using bevel gears--the spur gears have a greater contact area & won't bend or slip as easily

TECH DETAILS : Every bot needed to weigh under 850g (Longneck was 849.7, IBoD was 849.9), use 2 of the Mindstorms gearhead 9V motors, 1 RCX, and up to 4 "racing slick" tires were recommended. The bot had 1 minute to pull the other bot 1 foot to win the match.

SPONSORS : Still getting serious mileage out of the parts donated by Switzer Communications and LEGO Mindstorms.

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