1. Storm the Castle Building Portfolio Mini Competition 2011
By: Bogdan M.

2. Design Type #1: The Hinged Counterweight Trebuchet (HCW)
Pros:
Easy to construct
Basic trebuchet design
Cons:
Less potential energy than super propped catapults (where the arm is locked to the hanger when cocked with the arm pointing almost straight down, and the hanger almost straight up

3. Design Type #2: The Floating Arm Trebuchet (FAT)
Pros:
Efficient when turned
Forced increase in projectile path by axle displacement allows lower arm ratio and therefore a larger drop than a comparable FCW (Fixed Counterweight: a trebuchet where the counterweight is attached directly to the short arm)
Cons:
Harder to make than an FCW or HCW
Track gap in existence

4. THE FOLLOWING 4 SLIDES ARE DEDICATED TO THE COMPONENTS OF A TREBUCHET AND HOW THEY WORK.

5. Arm
Description: The arm of a trebuchet is the moving part which is attached both to the counterweight and the pouch.
How it Works: As the counterweight falls, the arm (which acts as a lever), is “pulled down”, allowing the side with the pouch attached come up, swing around and launch the projectile.

6. Pivot Point
Description: The pivot point of a trebuchet is basically the fulcrum of the arm (which is a lever). It is usually a fixed rod or an axle. In the FAT, it is attached to the two rollers, while on the HCW, it is attached to the frame.
How it Works: When the counterweigh falls and the arm is turned, it rotates around the pivot point.

7. Launch Sac/Pouch
Description: The launch sac is the part of the device that the projectile rests in before being launched. There are two strings attached to it. One is attached to the arm firmly while the other has a loop at the end that is set around a pin.
How it Works: The pouch holds the projectile before launch. During the launch, the string with a loop on the end comes off of the pin and the launch sac is fully extended, allowing the projectile to come out at be hurled.

8. Triggering Device
Description: The triggering device is basically a pin that is pulled to allow the counterweight to fall and put the arm in motion.
How it Works: The pin blocks the movement of the arm when in the closed position. When it is pulled, the arm is not blocked anymore, allowing the counterweight to fall and the arm to swing around.

9. THE NEXT SIX SLIDES ARE DEDICATED FOR THE MATERIALS FROM WHICH A TREBUCHET CAN BE MADE OF.

10. Lab Equipment Pros: -Easy to build a device
-Speed of Construction: Extreme
-Cost: None
-The arm can be rather good if used with a good frame
Cons:
-Frames usually collapse at competitions
-Adaptability and Structural Integrity: Low
-Compliance With The Rules: Moderate
-Only useful if you are within two hours from the impound time; completely avoid this if you can help it
-No recorded cases of such devices getting anything other than last place

11. Polyvinyl Chloride (PVC)
Pros:
Versatile and easy to assemble
Arms: easy to build, sturdy
Frames: easy to build
Can be used to construct counterweights
Rails (FAT): probably the only valid use of PVC, take advantage of the curved cross-section
-Speed of construction: High
-Structural Integrity: Low to High
Compliance With The Rules: High
Easily bought at hardware stores
Cons:
Arms: VERY heavy
Frames: useless on on all trebuchets but the HCW
Cost: Moderate
Adaptability: Low/Moderate
Structural Integrity: Low to High
-The cost forces design limitations
-They do not tend to do well
-Used by less imaginative teams

12. Wood
Pros:
Material of choice for 90% of teams; national winners from both divisions have used this material with great success
Both arms and frames are easy to build; very sturdy; recommended for building
Adaptability, Structural Integrity, and Compliance with the Rules: High
Cost: Low
Wood is the best material if one has moderate resources.
If the design is failed at first, it is easy to take apart and start again
Cons:
Moderately heavy
Sometimes hard to find straight pieces of wood at stores

13. Metal Pros: Structural Integrity: High Compliance with the Rules: High
Arms made of aluminum are common and recommended among competitive teams; lighter and stronger than wooden arms and last longer
Rails on the FAT are usually made of metal strips because they create smoothness and strength
Metal parts are easy to find at most hardware stores
Both arms and frames made of this are sturdy
Cons:
Difficult to build, hard to use
Frames are VERY heavy, need wheels
Speed of Construction: Very Low
Cost: High
Adaptibility: Moderate
Metal has limited use for trebuchet building; has seldom been used
Waste of money because they usually perform as well as ones made of wood

14. Space Age Materials Pros: Best materials money can buy
Arms: carbon-fiber arms are extremely light and sturdy
Speed of Construction: Varies (could be high)
Cost: Low to High
Structural Integrity and Compliance with Rules: High
Choose space age for victory
Used by high-performance schools
Cons:
Adaptability: Usually low
Materials are almost only found on the internet
Speed of Construction: Varies (could be low)
Cost: Low to High

15. Other Possible Materials
Shelf braces: use for frame as 2nd choice; very strong and at exactly 90 degrees
Angle Irons: used for assistance with the frame; make construction easier, pre-made for certain joints
Golf Club Shafts: used for arm as 3rd choice; hard to work with, light, need to mount in wood
Cold rolled Steel Rods: Axle 1st choice
Pipes and Dowels: not ideal, but are easily installed
Roller blade or skateboard wheels: ideal for use on a FAT; must use additional axle with it
Fabric: need to cut and sew into a sling; 1st choice
Duct tape: a bit heavy, but easily made; 2nd choice for sling
String: possible to make, but usually causes a lot of trouble; 3rd choice for sling
Large Nails: firing pins
Eyelets: used for holding the firing pin

16. THE FOLLOWING FOUR SLIDES ARE DEDICATED TO THE TREBUCHET THAT WOULD BEST FIT OUR NEEDS AND REQUIREMENTS. THEY WILL INCLUDE THE MATERIALS NEEDED FOR THE BEST TREBUCHET, THE DESIGN PLAN, AND THE TEST PLAN.

17. Materials Needed to Have the Best Trebuchet
2.5+ meters of 2”x4” pieces of wood (for frame)
4 m of 1”x2” pieces of wood (for arm, supports, and rails)
Slab of wood (2 cm by 50 cm by 55 cm) for base
2 50 cm pieces of a Cold-Rolled Steel Rod (for axle and counterweight holder)
2 skateboard wheels (for axle)
8.5”x2” of fabric and 100 cm string (for sling)
30 1” long screws (more than needed; just in case)
100 cm string (90 cm for pulling, 10 cm for releasing pin)
1 latch, small ring, and 1” hook
2 50 cm pieces of PVC pipe cut in two long-ways
Counterweights:
1 coffee can (for counterweights)
Approximately 1200 pennies (this and the coffee can equals about 3 kg, the maximum needed)
Measured weights
Approximately 8 cm string (for hanging of counterweight)
Projectiles:
Balloons (50 pack)
Dry rice (to fill balloons)

18. Design Plan
Take approximately 130 cm of the 2”x4”. Cut the long piece into two shorter pieces (65 cm each). Screw them together with the slab of wood.
Take approx. 250 cm of the 1”x2” and cut it into 4 equal pieces. Place these 4 pieces vertically about 5 cm and 10 cm (2 on each side and at each distance) from the front of the base.
Cut a 3 cm thick slit from 2 cm from the top to the vertical plank to the top of the base (a distance of about 65 cm).
Make extensions to the frame on which the arm will go. Add 4 pieces of two by fours, each 25 cm long, with two on each side. 2 should be 25 cm from the front and the other two should be 45 cm from the front. Take the 2 pieces of 50 cm long half pipe and attach these inside the trebuchet about 35 cm above the ground, touching the vertical pieces of wood and being parallel with the left and right side of the base.

19. Design Plan (cont.)
Make the arm. Take 80 cm piece of 1”x2” wood. Drill a hole as wide as the rod through the middle of the thicker side, 25 cm from the end. Stick the rod through the hole and add the skateboard wheels to the ends.
Add secondary braces to the vertical guiders. Cut 150 cm of the 1”x2” and cut this piece in quarters. Screw them onto the trebuchet in such a way that there is a 10 cm difference between the vertical 2”x4” and the bottom of the new 1”x2”. Repeat on both sides of the catapult.
Attach the pin. Attach a small ring to the middle of the arm, just above where it intersects with the rails. Take the latch and add 90 cm of string to the part that opens when you pull it. Attach the other 10 cm to a trigger mechanism on the latch that releases the arm when the long string is pulled.
Attach the sling to the longer part of the arm. Secure 2x5 cm lengths of string to the arm and add the rectangle of fabric to it.
Make the counterweight. Take the already cut piece of wood and put it in the slits of the vertical 2”x4”s. Attach the hook to the end of this piece of wood on the side where the counterweight will be attached. Take the coffee can and attach the string so it is stable and won’t fall off. You put the pennies in while testing (see “Test Plan”).
You now have a completed Floating Arm Trebuchet.

20. Design Sketch

21. Test Plan
Gather all of your materials. You should have a completed trebuchet, a coffee can, about 1200 pennies, a pack of 50 balloons, and dry rice.
Start out with a 1 kg counterweight (the lowest they can give you at the competition). Hang the coffee can onto the hook. Make sure the desired amount of pennies are in the coffee can.
Make projectiles, ranging from 20 to 60 grams, by filling balloons with dry rice.
Fire all the projectiles 3 times and record the average.
Repeat with 1.2 kg counterweight, then 1.4, and so on until you get to 3 kg.
Your trebuchet should now be ready for competition!