Trebuchet Competition


New 2016 Design Challenge

  • Projectiles must be able to clear a 10 ft. barrier located across the center of the court.
  • Projectiles fired beneath this barrier will not count.

Competition Hints

  • Pick opponent trebuchet targets based on strategic value and opportunity - in other words, if you are unable to hit one target, pick another one that you can hit.
  • Concentrate on targets of immediate concern. For instance, if the opposing team has one long-range trebuchet, it may be prudent to focus on the trebuchet's targets rather than their main target. Also, if an opposing team's trebuchet gets close enough to hit your main target, eliminate it before it succeeds.
  • If your trebuchet can fire a long range, then stay back. Use your long range to stay protected from the opposing team.
  • The offensive size of a team is based on three parameters: 1) accuracy of fire, 2) quickness of fire (how fast you can reload and fire) and, not surprisingly, 3) number of trebuchets.
  • Moving your trebuchet will require you to "re-acquire" your targets. Moving may be inadvisable under those circumstances.
  • If your trebuchet is being acquired, then, if given the opportunity, you should move it.

View a Sample Lesson Plan (PDF).


Design Rules

Rules or comments that have changed or been added since last year are italicized. Really important things are in bold. Dimensions change every year!

  1. The competition is open to all high school students. Any number of students from a school may work on a single team. Participating schools are encouraged to submit multiple teams. Only one trebuchet may be submitted by any one student.
  2. The counterweight (see Fig. 1: "mass m1") is three un-opened 10.75-11.5 oz soup cans (similar in size and weight to Campbell's tomato soup), weighing 305-326 grams each. The cans must be either: a) dangling throughout the entire throwing motion (makes no contact with other parts of the trebuchet lever arm: L2+L5 in Fig. 1) OR b) must be rigidly attached to the arm (can't slide, jiggle...). If the cans are rigidly attached to the arm, it will be included in measurements of the arms length. Rigid is defined as anything other than dangling. View a diagram for a clarification.
  3. The top pivoting lever must not be longer than 1.25 meters. The length includes the hook (see the hook rule).
  4. The top pivoting lever (length L2+L5 in Fig. 1) must be balanced toward the projectile end (see L5) throughout the entire range of motion. It may not be collapsible. The arm cannot be locked in place while testing it for balance (including friction, which should remain negligible - in operational condition). Testing is performed by removing the counterweights, lifting the projectile end all the way to within 1 inch of the vertical, and releasing. It should fall to the ground, back to the cocked position (video), and in contact with the ground. If it fails to fall (without being pushed!) all the way to contacting the ground, it is not in compliance.
    We use the "pencil test". With the arm in the cocked position, with neither the counterweight or projectile loaded, raise the arm as shown here (video) with a pencil. The trebuchet fails the balance test if it leaves contact with the pencil when raising it to vertical (video).
    • The top pivoting lever may not be less than 1/4" thick.
  5. In order to satisfy the balance rule, the counterweights (soup cans) must be removable from their holder.
  6. The height H of the center of the axle must be between 0.75 and 1.25 meters from the ground.
  7. You must be able to remove the cans, and only the cans, from your trebuchet leaving all other connecting hardware in place.
  8. Any fastening devices/holders/brackets to be used during the competition will be included as part of the arm during testing for balance. We really, really mean it. This comes up every year. We will not allow you to augment your counterweights with excessive tape, wire, washers, or wood. If you think you have beaten this rule, you have violated it. We will have scales. Allowance will be given for up to 30" of duct tape and 30" of light string.
  9. The hook (the little thing that your sling goes onto at the projectile end of the arm; this is the point where L5 and L3 meet in Fig. 1) is counted as part of the arm length!
  10. No catapults or catapult/trebuchet hybrids are allowed. No energy can be stored in deformation of components. That means no springs, rubber bands or flexible arms. No pulleys can be used. The counterweight must be attached, not looped over, the end of the arm (or in close proximity).
  11. The trebuchets will be inspected for safety. Any parts that are unnecessarily loose must be tightened. No parts of the trebuchet other than the projectile are allowed to become completely disconnected from the trebuchet (A partial disconnect is necessary in order to release the projectile). Any trebuchet deemed to be unsafe will be disqualified.
  12. Counterweights must not come free during competition. If a counterweight falls off, the trebuchet operator must operate with the remaining counterweights. If the trebuchet becomes inoperable due to a loss of any counterweights, it must be declared lost and removed from the playing field.
  13. Trebuchets must not have protruding parts that may damage the floor (no metal may protrude below a wooden or other softer material). A towel (not provided) must be placed underneath each trebuchet.
  14. Recoiling trebuchets (with wheels) must be on a platform (board) that contains them.
  15. Targets will be provided.
  16. The projectiles will be regulation soft squash balls of a variety of sizes. They can be bought at some local sporting goods stores, however you can also order them online. One place to look is
  17. Firing of the trebuchet will be performed by release of the projectile and/or its sling. No other moving part of the trebuchet may be touched during firing.

Additional Design-related Information

  • Qualification at check-in does not represent permanent qualification. Trebuchets are subject to random checks at any time. This is done to prevent a) illegal modifications to trebuchets, b) overcome deficiencies in the volunteer qualifiers' judgment. It is your responsibility to make sure that you understand the rules, and that your trebuchets meet the requirements. Failure of us to "catch" illegal trebuchets before the tournament does not take away our right and responsibility to correct such mistakes later.
  • If you have serious concerns about an opponent's trebuchet being legal, please notify the judge, and ask them to have the director perform an inspection. This can be done before, during, or after the match. Please do not be frivolous. A failed challenge will result in a warning. A challenge can be saved by waiting until after a match has concluded. If the trebuchet to be challenged is a member of the losing team, then the challenge is irrelevant. A second failed challenge will result in a penalty. Calling the director's or another's attention to a trebuchet is not the same as a challenge, as the directory will render a quick judgement. A challenge requires a full inspection.

    If a single trebuchet, or group of trebuchets, fails a challenge, the judges and referees may re-decide the outcome of the match based on performance of the remaining trebuchets.

    If an entire team is disqualified, the opponent is declared the winner

    If no challenge is issued before the next round of battles, then the results of the match cannot be changed.
  • Projectiles will not be provided. Each team must provide 10 soft squash balls. As a result, projectiles will not all be the same. You must be able to make adjustments to your trebuchet to compensate for this variability.
  • Expected throws are in the range of 40-60 feet. If your trebuchet can't consistently throw projectiles that distance, you will be hard pressed to do well in the competition. Trebuchets that cannot consistently throw a squash ball 30 feet are unfit for participating in a match. Judges will eliminate unfit trebuchets from a match. Any trebuchet seen throwing under 25 feet 3 times in a row will be deemed unfit for a match.
  • The decision of the qualification judges may be appealed to the director or an appointee thereof.

NOTE: Each trebuchet must be accompanied by a check sheet. The sheet must be filled out in advance of the competition and brought to the judges for qualification. If the check sheet is not filled out in advance (i.e. you are not "pre-qualified") you will be assesed penalty shots; that is, your first opponent will be given free shots at your team on the playing field before you are allowed to return fire. See Matches for details

A well performing trebuchet can be made from household materials. Very effective trebuchets can be built from cardboard, some Elmers glue, and an Exacto knife. Don't feel that you need a workshop.

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Prequalification Check Sheet

The purpose of the Prequalification Check Sheet is to ensure that each and every trebuchet properly meets all of the trebuchet design rules. The Check Sheet is to be completed by both the team advisor and a trebuchet qualification judge.

Prior to the day of the Competition, the team advisor is required to conduct a preliminary qualification check of the trebuchet, checking off all requirements that have been met in the Advisor Check column of the Check Sheet. Note to team advisors: there are hyperlinks throughout the electronic version of the Check Sheet that link to figures available online. If there are any questions regarding the Check Sheet, figures, or design rules, please contact us.

Once the advisor check has been completed, the Prequalification Check Sheet must accompany the trebuchet to the Competition.

At the Competition, trebuchet qualification judges will evaluate all trebuchets for compliance with the design rules and complete the Judge Check column of the Check Sheet. A trebuchet will be considered "qualified" only after the Check Sheet has been completed and signed by a qualification judge.

Teams with incomplete qualification sheets will be subject to a 30-second firing delay per missing, or incomplete, qualification sheet in the first round of the tournament.

For specific details, please see the trebuchet design rules. These are abbreviated. Know the rules, then use this to keep track of compliance.

If you have comments or suggestions, contact