this will show you how to make your own torsion ballista out of 2x4s or 3x6s.
Add a Teacher Note to share how you incorporated it into your lesson.
Step 1: Tools
you will need
1 1/4 inch drill bit
1 1/2 inch drill bit
1/2 inch drill bit
1 inch chisel
3 inch wood screws
make sure you use 1 1/4 inch thick dowel
Step 2: Tightening Wrench
you will need one 2x4 that is about two feet long and two that are half a foot long.
there should be a two inch gap between the two pieces, you will need two screws for each piece
Step 3: Make the Frame
you will need two 27 inch long and 12 inch long 2x4s/3x6s and eight screws
Step 4: Attach the Guide Rail
you will need a 42 inch long 3x6 with a groove along it for the bolt to rest in, you can use two pieces of 42 by 6.5 inch pieces of half inch plywood screwed on to each side.
you will need four screws on the bottom, and one on each side of the rail going in diagonally.
you can also use two 42 inch 2x4s and two 42 by 2 1/2 pieces of 1/2 inch thick plywood to make a rail.
Step 5: Reinforce the Rail
attach a seven inch long 2x4/3x6 with two screws on the bottom, and two screws on each side diagonally, make sure that there is enough space between the screws to drill a 1 1/4 inch hole.
Step 6: Make the Stand
attach a 24 inch 3x6 to the center of a 30 by 12 inch piece of plywood, attach an eleven inch long 3x6 to the top of the other one, make sure there is enough room between the screws to drill a 1 1/2 inch hole, attach a 35 inch 2x4/3x6 to the front of the piece of plywood, drill a 1 1/2 inch hole through the center of the top piece of wood, and use a chisel to cut a slight angle into the back of the hole.
Step 7: Make the Arms and the Pegs
you will need two 2x4s that are two feet long, and a dowel longer than twenty inches.
line up your 2x4s and drill through both of them two inches from one end with the 1 1/4 inch drill bit, make sure they are centered, drill a 1/2 inch hole one inch form the other end,make sure it is centered.
cut four five inch long pieces of dowel.
Step 8: Attach the Arms
drill four 1 1/4 inch holes into the frame nine inches from each end, make sure they are centered.
take a piece of rope and make a loop, thread the loop through the bottom hole and place one of the pegs through the loop, thread the rest of the rope through the top hole, make sure one end of the rope goes through the large hole in one of the arms, place another piece of dowel over the hole and tie a naught, so that you have a loop of rope long enough to go through both holes and around both pegs, do this for both sides.
tighten the top peg first, rest part of the arm on the rail, tighten each peg the direction you want the arm to go, make sure the arm stays centered, flip the frame over and tighten the bottom peg.
put a screw on either side of each peg to prevent them from turning, make sure that about one third of the screw is sticking out.
once the arms are attached tie one end of a rope to one of the small holes, and the other end to the other hole, the rope should be just short enough so that it is straight.
you can add more loops of rope to increase the power of the ballista
Step 9: Make the Pivot
drill a 1 1/4 inch hole into the block of wood reinforcing the rail, make sure the hole only goes in three inches and is centered, hammer a piece of dowel into the hole, and cut it so that about four inches of the dowel is sticking out, you should use wood glue if the dowel is loose.
place the dowel into the stand, the ballista should rotate easily.
Step 10: Make the Handle
cut a ten inch long piece if dowel, center it on the back of the rail, attach it to the rail with two screws.