The Walking Arm Trebuchet

This is the world premier for our new trebuchet design. Not only is this trebuchet simple, it is extremely efficient. It has many of the advantages of a floating arm trebuchet, but with fewer parts, less friction, and a unique projectile launch path. As you can see in my son's video, above, the projectile never swings backward beyond its starting point, reducing the danger to bystanders behind the trebuchet. Using this design last fall, my 8 year old son set the all-time record for best design at the Vermont Pumpkin Chuckin' Festival. His 20 pound, 41 inch tall trebuchet threw a 3 ounce ball 266 feet. My 500 pound, 10 foot version threw a 5 pound cantaloupe over 700 feet, but it went so high and so far that the spotter never saw it pass over him on its way into the woods. You can read about these trebuchets' success here on the VT Pumpkin Chuckin site, and you can see mine in action in the video above. [**update: I just added a better view of the 500 pound treb in action on Saturday, 9/28/19. The 5 pound rice-filled soccer ball flew about 870 feet and rolled to 975'. Unfortunately, at the VT Pumpkin Chuckin' event yesterday, all of the real fruits were crushed during the launch. My son won the grand prize again.]

The instructions provided here show how to make a 20 pound, 41 inch version, like my son's. The dimensions were chosen to adhere to the lightweight division rules at the VT Pumpkin Chuckin' Festival. As you will see, my son did all of the work himself. I did help out by holding some things in place and showing him how to complete the steps.

I have made other versions of this trebuchet with longer arms, mostly for throwing the excess apples that fall in our yard. While they would not be legal at our state competition, they can really whip an apple.

[**Update: In response to one of the replies, I just made a small, 3-D printed version and added a video. I was going for a desktop version, but it seems more at home on carpet. This is a rough version 1.0, but I attached a .stl file if anyone wants to print one and doesn't have CAD capabilities (scroll down, below the supply and tool lists). I used pieces of a large paper clip for the spikes and the finger. For good measure, I sharpened the spikes with sandpaper. I used fishing line for the sling and the tuning string. As you can see in the video, there's no pouch on this version. The sling is just one loop of fishing line, and it is permanently attached to the projectile. They fly off together. The proportions are different than those of the larger versions, which may be why I needed to bend the finger forward on this one to get a good release angle.]

Supplies:

Wood:

1. One 1/2"x3"x36" pine board
2. 1 foot of 2"x4" lumber
3. Three 0.75" x 36" square dowels

4. Several popsicle sticks (at least two, plus extras)

Hardware:

1. 1/2" x 6" lag screw
2. Heavy 1/2" washer
3. Three 3" nails
4. Two 2" drywall screws
5. Eight 3" drywall screws
6. One 1/4" x 2 1/2" hex bolt
7. One 1/4" x 1" hex bolt
8. Four 1/4" washers
9. One 1/4" hex nut
10. One 1/4" wing nut

Miscellaneous:

1. Several Feet of thin cord or twine (at least 10 feet). We used duck decoy anchor cord.
2. 2 cable ties
3. 10" square of fabric (we used ripstop nylon).
4. 17.5 pounds of iron weights (we used one 10lb, one 5lb, and one 2.5lb). Any weights can be used, but they will probably require modifications to the design. My daughter made one of these with concrete from the hardware store. Generally, denser weights are best, so iron is preferable to concrete, sand, or rock.
5. (optional) 3" long piece of 3/4" PVC pipe.

Necessary Tools: Pencil, Saw, Hammer, Power Drill/Driver, Assorted drill bits, 3/4" (19mm) Wrench, Phillips head driver bit, Scissors, Bolt cutters (or something else that will cut the head off of a nail)

Optional Tools: Center punch, Large file, Torch and vise grips (for heating and holding a hot nail), Slow motion video camera (for fine tuning trebuchet performance), Sharpie for drawing on fabric

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