Nothing, that's what. Except that this has to be absolutely safe because it is going to be part of a free-to-the-public Halloween shindig for kids. And, ideally, it should have something to do with candy.
Part 2 of this instructable, when posted, will show how to construct the cannon (hint: it has a lot in common with the more-powerful cannon by Part Time Chef.com). This instructable will outline the creation of a glorified pop-gun mechanism.
Step 1: Gather Tools & Materials
- Power drill with 1/4" drill bit
- Channel lock-style pliers (to open PVC Cement)
You'll need to gather or acquire these materials:
- Bike Pump (get this first, the next items will need to be adjusted to work with your specific pump)
- 1" (interior diameter) PVC Pipe
- PVC Cement (Please work in a well-ventilated area)
- PVC 'end cap' (internal measurement should be the same as the external measurement on the PVC pipe)
- Hose Barb Adapter - Threaded (like a screw) on one side, ridges on the other side to grip the inside of hoses
- Rubber stopper (internal measurement should be the same as the external measurement on the PVC pipe)
- Barb Hose Splicer (just like the adapter, but barbed on both sides)
- 3' of fuel hose the same internal measurement as the bike pump's hose
All together, these materials totaled less than $20 for me, your mileage may vary. With the exception of the bike pump, all these items should be available in the plumbing section of your local home improvement store.
I bought the "cheap" bike pump & got great results - it seemed made to be taken apart (which is good, because your going to have to take it into the other store to make sure the Hose Barb Adapter will fit your pump's hose).
Step 2: Examine Your Pump
In my case, the connector screwed right off & the hose itself screwed off near the base of the pump. Awesome! Now I don't have to carry a bike pump into Lowe's.
Visually compare the hose with the assortment of hose barbs in the plumbing section. You want it to be nice & snug. A hose barb has a series of peaks & valleys on the skinny end to grab onto the inside of a hose; the other side (on the one I bought) is threaded, which helps it stay in your PVC pipe.
Step 3: Cut & Drill Your Pipe
In a well-ventilated (preferably outdoors) area, use the PVC cement to glue the end cap onto one end of the pipe section. The lids are on real tight, I had to use the channel-lock to open it up.
Next use your power drill to make a hole that is slightly smaller than the threaded portion of the Hose Barb, that's important so you don't need glue or pipe thread tape or o-rings or anything else to make an air-tight fit for the hose barb.
I had to use the channel-lock to screw the threaded end of the hose barb into the PVC Pipe. That should be the most challenging part of this instructable.
In the pictures I have inserted the hose barb into the pipe's side. You may want to consider positioning it in the center of the end cap when you see how it will have to be positioned inside of the cannon in part 2 of this instructable
Step 4: Now We're Getting Somewhere
If your pump can't blow up the balloon, you probably have an air leak somewhere.
Mine worked on the first try, but I can see that if you aren't careful, some things can go wrong.
Gluing the end cap on is nearly fool-proof, but not darn-fool proof. Try blowing into the open end to make sure no air comes out there.
The part that can go wrong easiest is the where the hose barb meets the pipe. I left my hole noticeably smaller than the threaded portion, & struggled with the pliers to get it screwed in, but it was worth it.
To trouble-shoot this, have a friend (or robot) continuously pump the (er...) pump. Move your hands over the entire construction to feel for air escaping from some dastardly spot.
Note: It's natural for many bike pumps to have air escaping from some place on it.
Step 5: Plug It Up, Fire Away.
Occasionally when viewing the video linked to below, you will be able hear the pleasing "POP" that only a larger-than-normal pop-gun can give you. Feel free to imagine it in case you cannot hear it at the end.
Step 6: Extend the Hose
But based on the Styrofoam cannon I made last year, this hose is way to short to position the operator behind the cannon (as opposed to beside the cannon).
Another trip to the store fetched me 3 more feet of hose similar enough to the bike pump's hose & a Barb Splicer. You can tell the difference in hose length in this photo.
Step 7: What's Next?