Throughout history, the Trebuchet has been used as a siege weapon for armies during warfare. However, today we will be using it as a fun way to launch tennis balls over 50 feet. The motion of the trebuchet is one that is fluid and beautiful due to the motion of the counterweight and the string attached to the arm which causes the launch of the object. The one that we will be making will end up being 6 feet tall when fully extended yet still easy to move due to the locking wheels that allow for smooth transportation.

Supplies

For this project, I found all the needed supplies at my local hardware.

2 x 4's (Three 8-foot boards) (Online Link)
3/4 inch plywood (Online Link)
1-inch outside diameter PVC pipe (Online Link)
4 2-inch swivel and locking wheels (Online Link)
5 1-inch 2-hole pipe straps (Online Link)
5/8-inch medal bar with threads (Online Link)
4 5/8-inch Hex nuts (Online Link)
4 5/8-inch washers (Online Link)
2-inch star-bit screws (Online Link)
3-inch star-bit screws (Online Link)
1/2-inch Phillips-head screws (Online Link)
1/8-inch twine/string (Online Link)
20-pound dumbell (Online Link)
duct tape (Online Link)
Cheesecloth or other flexible fabric (Online Link)
1 nail with no head

The tools I used for this project were:

Miter Saw
Drill
Circular Saw

Step 1: Cutting the Wood

The First step in the project is to cut all of the wood to length.

Using the miter saw, make two 3-foot cuts on the 2 x 4's for the stand of the trebuchet.

Using the miter saw, make four 28 1/4-inch cuts using the 2x4 as well. Then cut two 45-degree cuts into the 28 1/4-inch boards so there is a long end measuring 28 1/4-inch and a shorter end parallel to the long end. The final shape of those cuts should be a trapezoid and is going to be used for the support connecting the 3-foot cuts to the plywood.

Then make a 4-foot cut on the 2 x 4 to be used for the arm of the Trebuchet.

Finally, make 2 14-inch cuts using the 2 x 4 to be used as extra weight and support on the arm.

For the 3/4 inch plywood, cut the long end to a length of 43 1/2-inch and the shorter end to a length of 20 inches using the circular saw.

Step 2: Make the Stands

On the 3-feet long pieces of wood, drill a 5/8-inch hole, 1 3/4-inches from the end of the piece of wood.

Then making sure the bottom of the stands will be level, drill the 28 1/4 inch piece of wood into the side of the 3-foot piece, using the 3-inch star bit screws, so it creates a fork shape truss, with the hole that was just drilled at the top. I recommend pre-drilling all of these screws. For added strength, you could also glue the pieces of wood together before you screw them together using wood glue or super glue.

Taking the two stands that you just made, drill both of the trusses to the plywood, using the 3-inch star bit screws, so that the corners of the trusses are all flush with the edges of the plywood. Both trusses should sit 17 inches apart from each other. Make sure to pre-drill the holes so the screw does not split the wood.

Step 3: Securing the Pivot Point to the Stand

First, make a 16-inch long cut in the PVC pipe.

Then thread the medal rod and Hex nut and washers through the hole drilled in the previous step, with the PVC pipe resting in between the two trusses with the medal rod going through it. Make sure the hex nut and washer are tightened to the wooden truss and not the PVC pipe.

Step 4: Making the Arm

Screw the two 14-inch pieces of wood to the 4-foot piece of wood so there is a sandwich between the two pieces. The edges should all line up with each other.

Then with the edge without the two added pieces, draw a line from the edge of the sandwiched pieces of wood to about 1 1/2 inches from the bottom of the wood. Then using the circular saw, cut along this line. This step helps add more weight to the shorter end of the arm and takes away weight from the longer end of the arm making the arm swing faster when released, generating more power.

Step 5: Securing the Arm to the Pivot Point

Make a line 1 foot from the end of the sandwiched part of the arm. This is the point of rotation. Then using two of the 1-inch pipe straps connect the arm to the PVC pipe using the 2-inch star bit screws. I recommend pre-drilling these holes.

Step 6: Securing the Weight to the Arm

Using the last 3 1-inch pipe straps, connect the 20-pound dumbell to the arm. Use the 2-inch star bit screws and make sure to pre-drill these screw holes.

Step 7: Making the Sling and Pouch

Cut the cheesecloth or other fabric into a square measuring 7 1/2 inches by 7 1/2 inches.

Then using the duct tape, fold the tape over each of the edges of the cloth in order to increase the strength while still keeping the flexibility.

Then using a 1/4 inch piolet hole drill bit, drill a hole in the 2 top corners 1/2 an inch from the top and 1 inch from the sides. Then, drill the third hole in the middle of the bottom of the pouch 1/2 of an inch from the bottom.

Then cut three 3-foot pieces of string and tie them to each of the corners, using an overhand knot, leaving as little excess as possible. On the free side of the singular bottom string, tie a loop into the string that is about 3/4-inch in diameter.

Step 8: Connecting the Sling to the Arm

Using the 1/2-inch Phillips head screws, screw a screw 1 inch from the top of the arm halfway in, so the head is still sticking out on both sides of the arm.

On the top of the arm, using the nail with no head, hammer it into the middle of the face leaving 1 inch extruding from the wood. This is the release point on the Trebuchet and will need some adjusting in the angle of the screw depending on if the string releases too early or too late. If the string releases too late, hammer the nail so it is pointing more at the ground when the trebuchet is loaded. If it releases too early, hammer the nail so it is pointing more toward the sky. I had to hammer mine so it was pointing more toward the ground when loaded and ended up being at a 45-degree angle in relation to the end of the arm.

To attach the pouch to the arm, tie the top two strings to the extruding screws using a double overhand knot. Make sure the pouch is level and that each of those two strings are the same length.

For the bottom string, the loop will rest on the nail, and when launched, should fly off allowing the releasement of the object being launched.

Step 9: Attaching the Wheels to the Base

Position the wheels at the edge of the plywood and mark where the holes for the wheels are. Then pre-drill the holes that were marked making sure not to drill all of the way through. Then, using the 1/2-inch Phillips head screws, drill together the wheels and the plywood.

Step 10: Go for Launch

Launching the trebuchet is super easy.

First, hook the looped string to the nail.
Then Pull the arm down and pouch to the end of the plywood.
The arm should be about 6 inches off the ground before launch.
Finally release both the pouch and arm at the same time and let your tennis ball fly!