This is a more detailed version of a water balloon launcher than the one that is posted already. I have built several of them using this design which I developed a few years ago and the set up is really quite simple. You will need a sewing machine, but the actual sewing is easy so don't worry.
These launchers are a lot of fun, but they do send a balloon hurtling through the air at a pretty good clip. I would recommend that you NOT fire them at people because it is very easy for someone to get hurt. That said, enjoy!
Step 1: Materials
You will need the following materials to build this launcher:
1) 10ft Surgical or Exercise tubing (I get it from a local medical supply store for a little over $1 per foot and it comes in several different diameters and thicknesses. Here are the measurements for the tubing I used for this launcher 1/4 x 7/16 x 3/32).
2) A piece of canvas fabric 14inx8in. (I use black, but any color will work. Canvas, I have found< works best because of its durability. Other types of fabric tend to rip at the handle and just didn't hold up at well.)
3) Clear vinyl tubing 3/4x5/8 diameter (used for handles so cut length to fit your hands. Not necessary, but it does help make it easier to hold I have found.)
4) 7in length of nylon strap. (used for handle on canvas)
5) Sewing Machine and upholstery thread (this launcher goes through some pretty serious wear the tougher the thread used to put it together the longer it will hold up, trust me on this one.)
Total, one you have all the materials gathered, you should only spend around 30 minutes putting this together if you are at all experienced in sewing. It may take a little longer if you have never used a sewing machine before.
Step 2: Step 1: Constructing the Bag
I want to start with the most difficult part first because this is really the only piece that takes any real attention to details. The rest is really just cut, thread, tie, and enjoy! That said, here we go!
To begin you will want to cut your canvas to size (Fig.1). I typically build several of this all at the same time, so I'll start with about a yard of fabric and cut several smaller pieces out. You should cut each piece at roughly 14x 8 in.
After you have cut the fabric you will want to fold the top and bottom edges in about an inch and run hem them with the sewing machine (Fig.2). This gives the bag a nice clean edge that wont fray over time.
Next, fold the fabric in half, so the edges are inside out (Fig.3), and then hem the outside edge like you did the top and bottom. I recommend using a stronger stitch on the outside edge because you will put a lot of tension on this piece when pulling back on the launcher. You really don't want the seam to pull apart mid pull.
Once finished the fabric should look like a sleeve (Fig 4.). Flip fabric right side out (Fig. 5). You should have a rectangle roughly 7x6 in
Step 3: Constructing the Bag (Part 2): Strengthening
Ok, now that you have the basic bag assembled we will attach the handle, give it a little support, and create some space for the surgical tubing.
Lay the bag out flat and slide a piece of tubing inside either edge (Fig 1). Mark how much space the tube needs (Fig 2) and hem down that line allowing for a little room so you can easily thread tubing once bag is complete. Repeat process on other side as well. I will usually double back once at the top and the bottom of the bag to make the hem a little stronger (Fig 3).
Once you have both sides hemmed and ready make an X from the top inside corners to the bottom inside corners of both sides (Fig 4). It sounds confusing as I type it, but it's really not. Look at the image and it will make sense. This X simply ads some additional structure to the bag and pulls the two sides together.
Run an additional hem across the top and bottom of the bag to help close off the open portions of the X and make everything feel more solid (Fig 5)
Now you are ready to attach the handle.
Step 4: Constructing the Bag (Part 3): the Handle
Now that you have the bag built, it is time to put the handle on.
Take your nylon strap and line the edges up with center inside edges of the bag (Fig 1).
Sew an X, similar to the larger X you sewed on the bag, roughly 1in wide to attach strap to either side (Fig 2). I will usually go over each piece of this smaller X several times to make sure that it is secure on the bag. Like the sides of the bag, this piece gets more tension and wear than any other part. it is imperative that you make sure it is attached very well.
Once you have the bag completed the rest is just plug and play. You have completed the hardest and most time consuming part now for the rest.
Step 5: Step 2: Putting It Together
Now that you have all the parts and pieces, let put them together.
First, take your surgical tubing (roughly 10ft) and cut it in half. If you are making more than one
launcher at the same time, simply make sure that all your rubber tubing is cut to the same length (Fig 1).
Next, thread your tubing through the sleeves sewn into either side of your bag (Fig 2).
Third, cut the handles from the vinyl tubing (measure them to comfortably fit your hands) (Fig 3) and thread it onto the loose tube ends (Fig 4) on either side of the bag.
Finally, tie loose ends on either side together in a square knot (Fig 5) and you are ready to enjoy your launcher.
This launcher can be used by two people if you want, but with three it is much easier and you can get a much better launch.