Firm foam (flooring mats used)
Bubble wrap or soft foam (like that used in sofas)
An old vacuum cleaner
A cardboard box about 30 cm for each dimension or larger
A grill (to keep fingers out of where they shouldn’t be)
Hot glue or Caulking
Thin, firm and flexible plastic (I used plastic file folders)
Step 1: Preparing the Vacuum
2. Open the vacuum cleaner. If you have cheap vacuum cleaner, you shouldn’t really have much in the way of electronics. For anything else, you may find yourself looking at a circuit board. Take stock of where the parts are and take a photo. When you have to put it all back together, it helps to have something to refer to.
Your goal is to make the part that was sucking an intake with little obstruction. The vacuum generally vents that air out of several vents. You need to consolidate all of that air into one output with equally little obstruction. If you have an expensive vacuum, you might just be able to reverse airflow by flipping a switch. This would save you a lot of trouble. For the others, you most likely will need to do a bit of sawing. It might seem like you can just reverse the wires and force the motor to spin in the opposite direction, but not all motors are reversible. Another thing that might seem to make sense is to throw out the vacuum cleaner casing rather than try to modify this. A vacuum cleaner motor can produce a lot of torque and needs to be held in place very well. The vacuum cleaner casing is already doing a good job of this along with enclosing the wiring. If you can mount the motor another way, best of luck to you, but it really is more effort than you need.
The vacuum cleaner casing will have lots of air filters (and dust if it’s not new). Get rid of those. The motor will have a rubber/foam gasket on it to prevent vibrations from carrying into the casing. Keep this as it reduces noise greatly. After you’ve figured out how you want to modify the casing, remove the motor and all electronics. As there is a big range in vacuum cleaner casing constructions, there is not much advice to give save for:
a) Remove obstructions
b) Keep as much of the casing as you need to cover the electronics
c) Keep the casing around the switch so you don’t have to worry about mounting the switch later
d) Most shortcomings with the casing modifications can be overcome in later steps but not the engine mounting. Make sure you have enough plastic to keep the motor in place.
Be very careful when cutting the plastic as the saw blade can slip easily.
Step 2: Mount the Casing
Step 3: Build the Loading Chamber
Although the inside of this chamber can be any shape, the chamber exit should be tapered to slightly larger than cannon barrel. To get a nice round shape to the foam, it needs to be cut to aid in bending. Make slices along the foam, bend it and insert hot glue into the cracks so that the foam will hold that shape. If you are using other materials than foam, the forming of them would be different.
To keep balls, toys and fingers from getting into the vacuum motor, insert a grill. I used a plastic grill that is strong enough to withstand a hammer, but you can also make your own grill by inserting rods through the foam. Since my two-year-old is using this, I added window screen mesh behind the grill just in case some really small toys get fed into it. Always test this grill very strongly before continuing building the cannon. If you feel you could rip it out with anything less than your strongest effort, it is not good enough. Redo it.
As hot glue is not hot enough (at least mine isn’t) to partially melt the plastic used for the vacuum casing (which is required to get a proper bond), the best way to attach the foam is with epoxy or superglue. Hot glue is only used for caulking. Making your joints air-tight is very important for the final strength of the cannon. Also block up any holes in the casing that you don’t want. Since I cut the handle right above the switch, I had a hole there to fill in.
Step 4: Place It in a Box and Add the Barrel
6. Make the barrel. Any firm yet bendable plastic sheet will do. Roll it into a tube slightly larger than your ammo. Use multiple layers if it is not sturdy enough. I recommend clear plastic so you can see what has been loaded/is stuck in the cannon. It is better for the barrel to be too big in diameter than too small because too small won’t fire. PVC pipe the right size would also work, but you would need to support the heavier barrel. Fire a few balls to test the barrel length. Mine was too long and firing too far, so I cut back the barrel. You can place foam protection at the end of the barrel if you’d like.
The barrel does not need to be flush with the sides of the firing chamber when you attach it because the air (and the balls) will find the way out. I recommend using hot glue to caulk around the barrel first to get a perfect fit. If the hot glue did not bond well to the barrel, remove the barrel. Now the hot glue is in the perfect shape of the barrel and is the perfect surface to glue the barrel to using super glue or epoxy.