Cardboard Catapult

This a simple yet effective cardboard catapult design. It is easy to make and easy to repair. Give it a try and make modifications to improve it and add functionality, maybe even motorize it!

Attached the overall DXF file for the built with this step itself incase you decide to laser cut it. Do follow the rest of the pictures to see where to cut and where to engrave.

Supplies

60cm x 40cm Cardboard (Thicker/Not rolled version works better)

3x 6mm Wooden Dowels 10-15cm long

Rubber Bands

Hot Glue Gun

Hobby Knife

Laser Cutter (Optional)

Printer (Optional)

Step 1: Payload Arm

The payload arm is meant to hold the projectile you wish to throw and impart velocity to it. This design uses a ~28cm long arm and is cut from a single piece of cardboard. The drawing below/dxf contains the dimensions. To make the payload arm -

1. Print the file attached with this instructable or draw them out if you don't have access to a printer.

**If you have access to the laser cutter, print the entire file however, in your software, assign the a higher power setting to the solid lines and lower power to the dashed lines**

2. If you have printed the plans on paper, paste them on cardboard and cut them out with a hobby knife.

3. The solid lines have to be cut all the way and the dashed/construction lines have to cut only through the top layer. A good way of doing this is by restricting the size of your blade as shown in the picture below.

4. Once the payload arm has been cut, it can be folded while having the perforated/semi-cut layer on the outside.

5. With a little hot glue, glue the slots in their respective positions to form a box like structure. Ensure you also glue the slot at the payload end of the arm to ensure the projectile doesn't slide into the arm.

6. Now proceed to glue flap for the payload containment.

Step 2: Platform

This serves as the base for the mechanism and holds the payload arm. It can be mounted to a surface to prevent it from moving around, or can be hand held, however some sort of handle would have to be built and glued to its base.

The file for this part would not print on a single piece of A4 or letter paper hence you will have to print on multiple sheets and cut the borders to ensure the lines meet and then glue the plan on to the paper. Alternatively you can print it on a larger A2 or A1 sheet of paper.

1. Print the file attached with this instructable or draw them out if you don't have access to a printer.
**If you have access to the laser cutter, print the entire file however, in your software, assign the a higher power setting to the solid lines and lower power to the dashed lines**

2. If you have printed the plans on paper, paste them on cardboard and cut them out with a hobby knife.

3. The solid lines have to be cut all the way and the dashed/construction lines have to cut only through the top layer. A good way of doing this is by restricting the size of your blade as shown in the previous step.

4. Make all the folds like in the pictures with the semi cut face on the outside and you will obtain a platform with two box like structures. Use hot glue at the slots to assemble it.

Step 3: Rubber Band Mounts and Arm Lock/Trigger Mount

The rubber band mounts serve as leverage points which when mounted on the payload arm, allow the rubber bands to loop through them and deliver the elastic potential energy to payload arm, converting it to kinetic energy/motion.

The arm lock mount is glued below the payload arm and serves as lock to hold the payload arm in a locked position and trigger the mechanism.

1. Both these parts are small and can be printed on a single sheet of paper. They can also be cut using a laser cutter.

2. Like mentioned before, solid lines are cut through and dashed lines are cut only through the top layer of the cardboard.

3. Glue the rubber band mounts using hot glue inside the slots on the payload arm with the pointed side upwards i.e. facing the open portion of the payload bay.

4. Fold the arm lock/trigger mount like in the pictures below and glue it in the centre. Do not glue it to the payload arm yet.

Step 4: Assembly

1. Find the side with the holes on the top surface of the platform. This side will be where the payload arm is hinged.

2. To hinge the payload arm, align the side holes and payload arm holes like shown in the pictures and push a 6mm wooden dowel through. The arm should mount with the rubber band mounts (pointed end) facing upwards.

3. Apply some hot glue at the ends of the dowel protruding from the platform and then trim out the excess dowel.

4. Now on the top end find the series of 3 holes on the hinge side of the payload arm. Choose a hole (the first one seems to work quite well for me) and push dowels through both the holes and add some hot glue to the top and bottom interfaces. The choice of hole will affect the velocity and angle at which the projectile is launched (closer to the hinger, higher velocity and shallower angle).

5. Push a dowel through the rear holes and arm lock and get an idea for where the arm lock has to be mounted on the payload arm. Make a marking.

6. Proceed to glue the arm lock on the payload arm.

7. Loop a rubber band through each of the rubber band mounts on the payload arm like in the pictures.

8. Use hot glue and glue the rubber bands to the top wooden dowels that are sticking out. The rubber bands may move so hold them till the glue cures.

9. The catapult is ready!

The idea for using hot glue is that it is semi-permanent and can easily be removed and reapplied incase adjustments need to be made. Do not be afraid to trim some cardboard here and there, add extra holes, change the shapes and locations of the holes. Everything will have a compounded effect on the working of the mechanism and it is an interesting activity to learn about mechanisms and troubleshooting.