You will need
- A cardboard box - A pair of scissors - An A4 sheet of card - A thick plastic bag - Thick tape - Some ammo - And some help from an adult! We used ping-pong balls as ammo and our box was about double the size of a shoebox. You can experiment with other sizes though!
First you have to unfold your box and lay all the sides flat. To do this, just cut across a corner of the box with your scissors.
Once your box is laid out like a big flat rectangle, you'll need to cut off one end piece of the box, and the 4 flaps from the top and bottom of the box. Cut the final 2 end flaps into triangles, like the image below.
Use your A4 sheet of card to make a tube for the barrel of your cannon. To get the right size for your tube, put your ammo at one end of the paper and wrap the paper around it. Use a pen to mark the paper when it's tight enough to let it through. Do this again on the other end of the paper and then draw a line between your 2 marks. This line is how wide your tube should be and marks where you should seal your tube up using tape.
Make sure that the tube is the right size to fit a ping-pong ball through it. If your tube is too tight then you can't load the cannon. If your tube is too loose, or if you haven't sealed the tube up with tape, then the ball won't go very far.
Trace the end of the tube, marking out a circle on the end panel of your cardboard. Then cut out the circle of cardboard - this is where the barrel for your cannon will be poked through in a couple of steps.
First fold up where the barrel is going to sit and tape across the triangles that you cut out. Then, put tape across the top and bottom of the two cardboard seams. We recommend taping up the folds on the box to make it a bit stronger. You might not have to do that though!
You now need to attach the bag to the barrel, and tape it up so that it's airtight. This means that you need to tape up all the loose parts of the opening to the bag, and attach them to the barrel. Leave the bottom of the bag sitting freely.You may want some help from an adult to make sure all the air goes through the barrel and none of it escapes.
Now it's time to assemble your two different pieces. Slide the round barrel into the hole that you cut earlier until it is halfway through.
Now you need to secure the bag, to make sure that it inflates itself after every shot. You can do this by taping the bottom of the bag to the cardboard base of the cannon and by taping the back of the bag to the back of the cannon.
To fire the cannon, lift the flap at the back to fill the bag with air. Then just pop your ammo in the end of barrel and stamp on the flap to push the air out and launch your ammo across the room! To fire again make sure you re-inflate the bag - then pop the ammo in again. If the ball didn't fire, check that there are no extra holes in your bag, or loose parts of your barrel. Make sure to watch the video for a better look at how we made ours, and to see just what it can do!