Saturday, May 9, 2009

Water Rocket Launcher Construction Tutorial: Part 7

Welcome Water Rocket Enthusiasts!

In this part of our water rocket launcher construction tutorial, we will be showing you how to fabricate the cable tie clamp collar. This is one of the most important pieces of the launcher because the quality of this one piece will determine how easy or hard the rocket is to launch and how well the rocket will seal on the o-ring. Putting the extra effort into making this piece well will pay off handsomely in the long run. Do not cut corners on this part of the launcher and you will be glad you spent the time to get it right later.

The safety of the launcher depends heavily on this single part, so even if you don't care about the ease of use or the reliability of the o-ring seal, please put the effort into this piece to insure that your rocket is safe and secure on the launcher and will not launch by itself unexpectedly.

Step 1:
You will need to decide on the proper diameter for your clamp collar. It is important at this time that you sort out your rocket bottles and decide on a standard bottle to use with this launcher. If you examine your bottles closely, you will discover that some brands of soft-drinks use a different size flange on the neck of their bottles (see image below). The flange is used as the "handle" for the bottle, so it can be gripped by one hand and poured without slipping out of your grasp. Different bottling companies use different size flanges and you will need to decide which size you prefer to use because your launcher will be fitted for one size only.
Step 2:
The critical dimension for your clamp collar is the inside diameter. You will need to find a sturdy plastic tube with the appropriate diameter for your flange diameter. We found that a tube which is 1/8" to 1/10" larger than the flange diameter works extremely well. In our case we use the larger of our two bottle flanges and picked a 1.25" PVC pipe for the tube that will become the clamp collar for our launcher. If you see the image below, you can clearly discern that there is a 1/10" gap between the collar clamp and the flange. This gap will provide clearance for the cable ties to pass through but it is too narrow for the cable tie heads to pass through. This is the proper cable tie launcher setup.
Step 3:
We used a miter box to cut our PVC pipe to form our clamp collar. The length of the collar is not critical, so we arbitrarily chose a length of 1.5 inches purely for aesthetic reasons. The only real requirement to the length of the collar is to provide a bit of extension below the cable ties when the collar is mounted so that there is room to tie a cable to rope to remotely operate the launcher. The collar should be cut as square and straight as possible because it will seat against the rocket perfectly straight this way and that will make the collar slides smoothly when in use. A crooked collar can bind up and jam or move with more difficulty.
Step 4:
We will also take some time to clean up the edges of the collar with sandpaper. This makes it look more professional but really doesn't affect the operation of the launcher. In a later installment we will be showing how to personalize and dress up the launcher so we recommend cleaning up all the exposed edges now so you don't have to dismantle everything later and clean ut up.
In the image below, you can see the nice square edges of the clamp collar after we have finished sanding it. At this point we would like to mention that you may find that standard size pipes will not fit your particular nozzle size or flange size. This is particularly  true if you modify the bottles or add fairings or boat-tails. If you find you cannot use an off-the-shelf piece of PVC pipe, you may wish to check the supplier stock of PVC fittings. Sometimes you can find specialty fittings which have different inside diameter dimensions than the pipe itself. Female couplers are a good example of this, as their inside diameter is the outside diameter of the pipe itself. Some people use a section of FTC tube or a plastic pill bottle or film canister for the collar. Get creative and find out the best piece for your rocket!
Step 5:
You will next be adding some holes to the collar clamp so that a rope or cable can be attached and operated manually. Drill a hole completely through the collar at the exact center line of the tube. If the holes are not centered or uneven then the clamp will try and twist and could bind up during use. Make sure to drill holes sufficiently large enough to pass through the cable you will want to use.
Tip: If you are unsure of your ability to drill the holes straight on the first attempt, don't bother to sand the collar tube cut edges until after you have drilled the cable holes. This way if you screw up the holes, you haven't wasted time and effort sanding. Once you get the holes to your satisfaction you can then sand the collar. We simply sanded first because we have done this many times and have the experience for getting the holes straight on the first attempt.

Step 7:
Slide the collar down the top of the launch tube and over the cable ties. If necessary you can grip the ties with one hand and constrict them to allow the collar to pass over them. Slide of bottle down over the launch tube and push it down until it friction fits over the o-ring and seats against the washer on the base of the launch tube. If you have tightened the hose clamp on the bottom of the launcher you will want to loosen it up now so you can adjust it perfectly.
Step 8:
With the clamp loose you will move the group of cable ties as a unit up and down until they are overlapping the flange, Push the collar up so that it slides over the heads of the cable ties causing them to constrict around the flange. See the images below for reference and note how the heads of the cable ties overlap the flange and grab hold of it when the collar is pushed up. This is the secret how the launcher operates!
Step 9:
Press down on the bottle so that it is pressing firmly into the washer at the base of the launcher. The harder you press the better the secondary seal at the base washer will be. While keeping the pressure on the bottle, pull the cable ties assembly tightly down away from the flange as hard as you can pull and then tighten the hose clamp to secure the cable ties in this position. Be sure to leave enough room between the hose clamp and the bottom of the clamp collar so that it can move down all the way off the nozzle when it operates. The collar usually cannot pass over the clamp so you need to provide some distance for it to operate. You should try to get 0.75" to 1.0" between the top of the clamp collar and the bottom of the flange on the bottle when the clamp collar is fully retracted.
Step 10:
Practice operating the clamp a few times and see how it works. It should push all the way up against the rocket and sit neatly and squarely on the bottom of the bottle. It should slide easily down the cable ties and come to a stop against the hose clamp at the bottom with enough room for the cable ties to expand around the flange and allow the bottle to slide off the o-ring and up the launch tube. Push the rocket back onto the launch tube and allow the cable ties to surround the flange as the o-ring seals inside the neck. Push up firmly on the collar and notice the tension of the cable ties pulling taught against the flange causes the bottle to seat snugly against the washer at the base of the launch tube. That's perfect!
Next week we will begin detailing how to mount our launcher onto a portable base and give some tips and tricks how to create the base easily and inexpensively.

See you next week!

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