Here is a guide to help you build your own desktop catapult, great for launching your balled up waste paper at the garbage can, giving your wastebasket hookshot arm a rest!
Step 1
Buy the materials needed for the project. See the complete list under Things You'll Need, later in the article. All the components for this project cost less than $15 (US), and there was no problem finding them.
Step 2
Assemble your tools on a convenient workbench or other suitable location. The following were used in this assembly:
- Circular saw
- Battery and electric drills with bits
- Sander
- Hotmelt glue gun
- Measuring tape
- Hammer
- Utility knife
Step 3
Cut out the following required pieces. You will need:
- 1 piece 3/4 plywood, 9X16 inches
- 2- 1/2 inch diameter dowels, 12 inches long
- 2- 1/2 inch diameter dowels, 18 inches long
- 4- 1/4 inch diameter dowels, 18 inches long
- 2- 1/4 inch diameter dowels, 16 inches long
- 2- 3/8 inch diameter dowels, 7 inches long
- 3- 3/8 inch diameter dowels, 18 inches long
- various spacer blocks cut from the dowels listed above
- various lengths of twine to lash dowels together while assembling. These lashings give the catapult its structural soundness.
Step 4
Lay out plywood for holes required for the frame, as shown in photo. Mark the board lenthwise at 1 inch and 9 inches with a framing square or rule, then mark the center line, from which you measure out 3 inches either way for the holes.
Step 5
Drill holes with a 15/32 inch bit to install uprights at the 9 inch mark. These holes are drilled perpendicular to the board.
Step 6
Drill holes with the 15/32 inch bit at the one inch marks at a 50 degree angle to the board.
Step 7
Drill one hole with a 5/16 inch bit in each 18 inch by 1/2 inch dowel at 6 inches and 1 inch from one end. These are the holes for the cross beams to fit into.
Step 8
Drive the 18 inch by 1/2 inch dowels into the holes on the 9 inch marks. Drive the 12 inch by 1/2 inch dowels into the holes at the one inch marks, they should intersect the vertical dowels at their tops. Some carpenter's wood glue applied to the ends of these dowels will help hold them securely in place.
Step 9
Glue the dowels together where they meet at the top, then lash them with twine for support. Hot melt wood glue will save a lot of time on this step, and a dab of glue will help secure the lashing twine when it is knotted.
Step 10
Taper the ends of the 3/8 inch by 7 inch dowels with sandpaper so they fit snugly into the two holes at the top of the upright 1/2 inch dowels, then spread the uprights to fit them in. If these are not snug enough, glue them in place.
Step 11
Lash the 1/4 inch by 18 inch dowels to the upright 1/2 inch dowels with twine, then hotmelt glue the twine to prevent it from slipping.
Step 12
Assemble the two 3/8 inch by 18 inch dowels together, parallel, with space blocks between them cut from the same material. The spaces should be located so that the pivot point is an open space about 1/2 inch wide, which will be the location for it to be placed on the pivot beam. Leave another space about 1 1/2 inches long at the top end of this assembly (the launch arm). This is where the cup, or projectile holder will fit.
Step 13
Spread the uprights sufficiently to install the launch arm, then replace the cross arms, gluing them into position.
Step 14
Carve a suitable cup, or projectile holder from your scrap of 2X4 lumber, rough shaping it with a circular saw, then rotary rasps, and finally a sanding disk or sand paper. This can be carved by hand if you prefer, since it will be a fairly small piece of wood to hold securely while using your power tools for carving.
Step 15
Lash the projectile cup into the notch at the end of the launch arms using the twine. You will want to be certain to lash this tightly and glue the lashings in place to avoid accidentally launching the complete cup when you fire the catapult.
Step 16
Glue or lash guide pieces for the travel of the launch arm between the two cross beams, and from the base diagonally up the path of travel of your arm. These will keep the launch arm assembly in line while it swings during launch. If the arm and pivot bar are tight enough to keep the assembly in alignment, these pieces can be left off.
Step 17
Fasten a spring at the bottom of the launch arm to a point on the opposite side of the base, using twine. Adjust the tension so that the launch arm can be drawn back to a horizontal position for loading and firing. Using a stronger spring will make your catapult more powerful, but this is not always desirable, since it causes a lot of stress on the moving components. Most hardware stores have an assortment of various springs, so you may need to experiment a bit here to find one that works for you.
Step 18
Trim any loose strings, check all glue joints, and you should be ready to fire. Pull back the launch arm and release it from various draws to determine the range and power you are looking for. If none of the parts become loose or lose tension, you can launch similar size and weight projectiles with remarkable consistancy using this device.
Tips
- Be careful drilling the dowels, as an off-center hole will severely weaken the structure.
- Be careful with the hotmelt glue while attaching the winding lashings. The glue secures all lashings so they do not loosen with use.
- Be careful doing the catapult and good luck building it!
Warnings
- Be aware that this assembly can throw a projectile with significant force.
- Use power tools with care.
- Hotmelt glue can stick to skin, causing painful burns.
- Do not aim at people this could cause injury.
Things You'll Need
- 2- 36 inch by 1/2 inch hardwood dowels
- 2- 36 inch by 3/8 inch hardwood dowels
- 4- 36 inch by 1/4 inch hardwood dowels
- 1 scrap piece of 2X4 pine lumber, 6 inches long
- 1 scrap, 3/4 inch plywood, cut to 9 inch by 16 inch
- 25 feet of hemp twine
- 1 coil spring
- hotmelt glue
