Wright State University
8th Annual Trebuchet Competition

Trebuchet Design Rules

for the year 2009

Rules or comments that have changed or been added since last year are highlighted like this. Really important things are highlighted like this.

1. The contest 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 mass m1) is two un-opened 12 oz. soda pop cans. 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 the figure) 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. Click here for a clarification.
3. The top pivoting lever must not be longer than 12 feet. The length includes the hook (see the hook rule).
4. The top pivoting lever (length L2+L5 on the example figure) 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 (see avi movie or quicktime movie), 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 them arm as shown (Quicktime format, avi format) with a pencil. The trebuchet fails the balance test if it leaves contact with the pencil when raising it to vertical (Quicktime format, avi format).
   • The top pivoting lever may not be less than 1/4" thick.
5. In order to satisfy the balance rule, the counterweights (pop cans) must be removable from their holder.
6. The height H of the center of the axle must be less than or equal to 1 feet 9 inches 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 the figure) 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).
14. Recoiling trebuchets (with wheels) must be on a platform (board) that contains them.
15. Each trebuchet must be outfitted (i.e. come to the tournament ready) with one plastic 1 gallon milk jug target mounted on the side of the trebuchet in a clearly exposed area. The milk jug is to have the bottom 1" cut off and be inverted. The target opening must be no less than 1.5 feet from the ground, and no more than 2.5 feet from the ground. It must be forward facing, and on the front most pillar or support of the trebuchet. It can be mounted at a decline to the direction of fire of up to 45 degrees (pointing forward and up) if necessary (i.e. so that it is even more exposed). This is what the other teams will shoot at. It must not be placed where the operator might block the target during operation (this is also covered in the operator rules). If you do not understand these rules, the simple explanation is "put it where everyone can easily hit it". Trebuchets with inadequate targets will not be allowed to participate.
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 Squash.net.
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.

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, so don't feel that you need a workshop.