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Since 2000, RoboChallenge has served hundreds of students on the California Central Coast. Competitions have included Tug O' War, Drag Race, Sumo, Catapult, Line Following, and others.See the Rules and Challenges page for more information.Go to Mr. Laurie's Page |
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Video: Getting Started with Tug O' War RobotsQuicktime Version: Youtube Version: IntroductionTug O’ War was the first RoboChallenge event. The original Tug O’ War rules were developed in 2001, in order to have a competition that would allow students of all ages to participate, and still leave room for plenty of creative engineering. Since 2001, hundreds of students have participated in RoboChallenge Tug O’ War events. To this day, it continues to be one of our most popular competitions. At RoboChallenge events, we have seen great Tug O’ War robots built by students of all ages. We’ve had robots built by kindergartners, elementary school students, Junior High and High School Students, College Students, and even Post-Graduates. We’ve seen designs that were very large and incredibly complex, and others that were very small and simple. Tug O’ War is a great way to introduce and apply many basic ideas of mathematics and science, in a fun, competitive, open-ended challenge.
Note for Teachers: Tug O'War is appropriate for students of all ages. You will need to have access to robotics materials such as LEGO Mindstorms, Mindstorms NXT, or another robotics format, such as VEX. The information on this web page and the video offer tips and recommendations assuming that LEGO materials are being used, but Tug O'War need not be limited only to LEGO materials. The time required to build and program Tug O'War bots could be as short as a few hours for older, experienced students, or a few weeks for younger kids, depending also on how often students are able to work on their projects. Materials and Resources Required:
Instructional Information
This tutorial, and the accompanying video, cover the following main topics (click on a topic to go to that section)
Tug O' War RulesThe concept behind the Tug O’ War is simple. Two robots pull on opposite ends of a string, attempting to move the other robot to the middle. The robot that reaches the middle first, loses. The winner is often the strongest robot, but many factors determine which robot wins. There is no guaranteed ‘best’ design for Tug O’ War. Basic Rules
Running Matches and TournamentsIt's easy to set up a match between two Tug O' War robots. Running a competition with several robots can require a little more preparation, but is also not terribly difficult. 90% of the time, the winner in a Tug O' War match is very easy to determine; one robot will easily pull the other across the line. Only rarely do you need to use the rules governing ties or awkward situations. In each match, a robot must win 2 out of 3 rounds. Ties can occur, and if necessary, tiebreaker rounds can be held. See the Rules page for more information. Space Tug O' War can be run in a variety of situations. Nearly any room can be used, as long as there is a smooth surface or some level tables. Tug O' War competitions can also be run outdoors. To make Tug O'War a nice spectator event, it is useful to have seating and bleachers or an elevated stage. College lecture halls work nicely. Basic Supplies At a minimum, the following supplies are necessary: a string, two paperclips, and a flat surface. You may also need a ruler and a stopwatch. The string should be measured so that the two paperclips are securely tied about 2 feet or 60 cm apart. It is helpful to have a mark at the midpoint of the string, and a taped line on the table or flat surface. The ruler can be used in a tie-breaking situation, where one must measure the distance of each robot to the midpoint. The stopwatch is used to time the trials, which should be limited to one minute. By limiting the duration of the rounds, you prevent matches from taking all day. To check to see that the robot meets the mass and size requirements, it is useful to have a ruler and a balance, especially an electronic balance that is capable of measuring more than 1 kg. Surface The flat surface can be a clean floor, such as you might have in a gymnasium. It can also be a long table, or two tables, such as 3' by 6' tables placed end to end. Where the tables meet can be considered to be the midpoint between the two robots. It is important that between each round in a match, the robots switch sides to make up for any minor differences that may be present in the surface. Elimination Chart A Tug O' War tournament can be a simple match between two friendly robots, or a massive event with dozens of robots from several schools. Categories by age can be established for larger groups if necessary, though in our experience with RoboChallenge, we have seen the robots of very young elementary students compete very well against those built by high school and college students. Tournaments can be run single elimination style for large groups, or for 7 or fewer robots, a round-robin style approach can be used. It is important to place robots randomly in a single elimination tournament. A whiteboard is useful for making sure everyone can see how the tournament is progressing, to avoid mistakes in match-ups, and to add to the level of excitement as the tournament proceeds.
Handling Difficult Situations The following are some of the things that can come up in a Tug O'War event that may require the judges to intervene. These situations are dealt with for the most part in the rules, but is important to know that these situations can arise from time to time. Ties- Sometimes, neither robot can pull the other to the midpoint in the one minute round. The way this is handled, is to hold a a tie-breaking round. In this round, the winner is determined by measuring the distance of each robot from the centerline at the end of the time limit. The robot closest to the line loses. String Breaks- fix or replace the string and try again. Robot doesn't start- Stop the round and call it a false start. Let them check the robot and try again. Sometimes they just didn't hit the button right, or hit it twice. It's no fun to watch a robot pull another that's not going. Robot Can't Pull- It's important to end the match and not allow a robot to compete that can't pull. Even if it can defeat other robots that pull themselves to the line, such a robot is not allowed- it's not a robot if it can't move. Sometimes a student will make a gear train that doesn't generate enough torque, which can cause the motors to stall and use up the battery. Such a match can also slow down the tournament quite a bit. No Show- Sometimes a competitor is not around because of other events or activities. If you can, skip that matchup and come back to it, in the spirit of enabling maximum participation. But don't allow a missing competitor to delay a match. Declare a forfeit, and move on. No program or incorrect program- Sometimes programs get changed or lost on the day of a tournament. If you can, allow them to reprogram the bot before the event begins. If not, sometimes a student can make the robot move, but without the 5 second wait time. At the judges discretion, they could start their robot 5 seconds later This can be awkward, and can lead to disagreements, but it may be necessary to make exceptions from time to time. Interference- It's important to keep people and competitors from touching or bumping the table, or touching the robots during the rounds. A competitor who interferes with the round loses the round. If a spectator interferes, the round should be done over. Robot falls off table- If the competition is being done on tables, competitors and judges should attempt to catch a robot that tumbles off the side to avoid excessive damage. However, a robot that falls off loses the round. Robot cannot be repaired quickly- The judges should make an effort to allow a few minutes for repairs to take place between rounds if necessary, but should use judgement to prevent delays. If a robot is beyond repair, a competitor should concede the match. Adult Intervention- Generally, our events are kid-centered, though it's entirely possible that such an event could have adult competitors as well. Consequently, it should be students, not adults, designing, programming, operating, and repairing the robots. Younger kids may require more adult assistance, but Junior High and High School students should be doing almost all of the work themselves. If judges need to, they may ask adults not to repair students' robots or otherwise interfere with the tournament. Building Easy Tug BotsAny robot that can move or pull a string can be a Tug O'War robot. The most basic robots are wheeled robots, usually with four wheels, powered by two motors. Here are some ideas for building some very basic Tug Bots. RCX Tug BotTo get started, try building a slow, strong, wheeled robot that can pull the string. To do this easily, you can use the instructions included with the Mindstorms Robotics Invention System 2.0 to build the basic driving base with 4 wheels. To improve the traction, you can try adding weight to the robot.
If you do not have these instructions, or have a different version, the instruction booklet can be downloaded from LEGO. Got to LEGO's building instructions download page, and do a search for the brand "Mindstorms" or enter 3804 into the quick finder. Link to LEGO's Building Instructions Page: http://us.service.lego.com/en-US/BuildingInstructions/default.aspx After you've started with a robot such as this, you can experiment with gears, wheels, and mass to build other basic "box" like designs. Think also about how your design distributes weight so that it doesn't tip or fall over, and so that the wheels have maximum traction. Here are a few more examples of Tug Bots built with RCX LEGO's. To see more see the links at the bottom of this page.
To program your RCX bot, you can use Robolab. We have bought Robolab for many schools in the Santa Barbara County region to use for building robots for RoboChallenge. The following is an image of a basic Tug O'War Robot program. The program causes the robot to make a sound when triggered, wait 5 seconds, and then pull with both motors turning at full power for 1 minute. With little modification, a program such as this could be used with many possible Tug O'War robot designs.
You can download a file with this program here: Download Robolab Tug O'War Program .vi NXT Tug BotAny basic bot with wheels can be used as a Tug O'War Robot, but the standard rover-type bots that can be built with the NXT instructions are more well suited for applications that require greater mobility. A good Tug O'War robot should be able to pull in a straight line, with as much force as possible. One great site that features several interesting NXT projects is NXTprograms.com. On this site there are instructions for building a Trailer Pull Robot that would make a good Tug O' War, but the trailer isn't needed. Link: Trailer Pull Robot Instructions Once you have a basic wheeled NXT robot, you'll need to program it. This is pretty easy using the Mindstorms NXT-G software. Such a program might look like this:
Download this NXT Program here .rbt This program begins with a sound, then waits 5 seconds, then causes 3 motors to turn at high power in the same direction for one minute. Note: if your motors are turned different directions, your program will need to account for that. Use the tutorials included with the NXT software to get more ideas for your Tug O'War programs. Example NXT Bots
Advanced DesignsHere are a few ideas for some more advanced designs for Tug O'War robots. Taller, longer Tug Bots A tall robot can be effective if it can lift its opponent and reduce the opponent's ability to get traction. These robots can be longer too, because they will need to be able to resist being pulled over. Two examples below combined strong gearing with long, tall structures. Beware- sometimes these robots can be toppled!
Compound Gearing You can decrease the speed of your robot and increase the amount of force it can produce by using gears. There is a video on Compound Gears in the gallery. Link- Video on Compound Gears.
Fishing Pole, "Reel" Design Your robot can be designed to turn a reel with an attached string to pull the other robot in. Remember, you might also pull your robot towards your opponent.
Levers: You can your robot to get mechanical advantage by using simple machines such as levers. Perhaps you can design a mechanism that will pull on one part of the lever, while the tow-string is attached to another, increasing the force. Or you can use a counterweight, forcing your opponent to lift the weight to pull your robot forward.
Additional ResourcesTeaching Robotics
Where to Buy LEGO Robotics materialsPhotos of Tug O'War Robots
Videos from RoboChallenge Competitions that include TugO'War Tournaments
Programming and Building Instructions Resources
The Engineering Design ProcessStudents can learn and apply the design process for solving technical problems and developing solutions for robotics challenges. This process can be used for solving many kinds of problems, and is used heavily in science and engineering. The process includes the following steps, in a cycle: Identify the need or problemResearch the need or problem
Develop possible solutions
Select the best solution
Construct a prototype
Test and evaluate the solution(s)
Redesign
Communicate the solution(s)
The Robotics Project RubricInstructors can use this rubric for evaluating students and their work on robotics projects. |
