The NEW “Rebel” Launcher

Presenting the new “Rebel” Launcher!

After working with my original design for a launcher for a while  it became obvious that it could sometimes require too much fumbling to get the bottle locked down. Loose parts that needed two hands to get them attached and frequent adjustments between different bottles were aggravating when dealing with the heat, humidity and countless flying insects getting in your face.

My original design relied on pressing the neck of the bottle tightly against a rubber hose washer to achieve the seal. It worked but I wanted to try the more common O-ring sealing method. So I decided to rebuild the retaining mechanism but keep the rest of the launcher.

I wanted something quick to attach a bottle and mostly self-contained. I looked at the quick connects used for water hoses as well as quick connects for compressed air lines. One of the mating parts on both the water and air connections had a flange just like a bottle neck, I just needed to create the other half.

Those other connectors used ball bearings to lock down the flange so that was what I wanted to do. I know that ball bearings had been used before in a bottle launcher made by a machinist and a picture has been posted on the internet. It can be found near the bottom of the page here:

http://dogrocket.home.mindspring.com/WaterRockets/launcher.html

That version rotated a collar to release the grip on the bottle but I wanted to have a pull down collar similar to those on launchers using cable ties to grip the bottle. That would allow even the smaller rockets to have ring fins and still fit the launcher as before without getting in the way of the mechanism.

So good luck, have fun, and by all means be careful! Make sure the spring is strong enough to keep the Locking Collar up until you want to launch!

Here are the details of the new launcher’s components.

Here is a description of the features numbered in the photo. They will also be referred to later in the building instructions, so pay attention!

1.

Locking collar made from half of a 1 1/4″ PVC slip coupling with two small bolts for attaching the launcher’s pull cords. Pull is straight downward from here to the launcher’s base, then changed to horizontal to the launcher’s operator.

2.

Retaining tube made from a 1″ PVC slip coupling half way over a 2 1/4″ length of 1″ PVC pipe. A bottle flange fits closely within the 1″ coupling. A metal spring made from stiff wire wraps around it and presses against part #1 and part #3.

3.

A 1 1/4″ PVC male threaded adapter with a 1 1/4″ x 1″ PVC reducer bushing inside. The other half of the 1″ PVC pipe from above fits in the bushing. The 1″ PVC pipe used must be bored out enough to allow the 3/4″ PVC pipe (see #11) to easily pass through it. Possibly 1″ pipe with thinner walls but the same outside diameter could be found and substituted.

4.

A 1 1/4″ PVC female threaded adapter. It works with the other threaded adapter above to provide vertical adjustment for different bottle thread lengths.

5.

Three small bolts pass through the adapter and the 1 1/4″ PVC pipe inside to hold them together rather than cement. Appropriate size holes are drilled and threads are cut in the PVC with a tap. The bolts also press tightly against the 3/4″ slip coupling around the air supply pipe inside (see #12) to hold it at the right height.

6.

A piece of 1 1/4″ PVC pipe supports the launcher assembly on the base, which in this case is the base from an office chair with the wheels removed. The pipe fits right in where the chair seat lift was mounted. It also contains the air supply pipe inside and may provide a little protection if the air pipe should explode.

7.

Slot cut in the bottom of the pipe to allow the air supply pipe’s elbow (see #13) to pass through when the air pipe is installed.

8.

Launch tube made from 1/2″ PVC. It is forced over a piece of 5/8″ O.D. plastic pipe coming out of the air supply pipe.

9.

O-ring 5/8″ I.D. x 7/8″ O.D., placed around the 5/8″ plastic pipe between the launch tube and a smaller ring of 1/2″ PVC. I believe it is a Danco #94 if you can find it. It was a #62 of another brand at a True Value Hardware where I bought them.

10.

Red rubber garden hose washer around the 5/8″ plastic pipe and on top of the end of the air supply pipe. The lip of the bottle neck rests against this washer to stop it from pushing down any farther.

11.

The air supply pipe made of 3/4″ PVC. A few inches of 1/2″ PVC pipe is reduced in outside diameter to just under 13/16″ and fit inside the end. The piece of 5/8″ plastic pipe is forced into that with a few inches left out to attach the launch tube (#8)

12.

A 3/4″ PVC slip coupling, either cut in half as shown here or with the center dividing ridge filed out so it will pass over the pipe. Here brown plastic tape is used to position it on the pipe so alterations can still be made. Tape can be removed and a couple dabs of cement can be placed at the ends when the final position is determined.

13.

A 3/4″ PVC x 1/2″ female threaded elbow cemented to the end of the air supply pipe. A metal air fitting screws into the PVC elbow and provides smaller female threads that match my compressed air hose’s fitting.

Assembly #8 – #13 slides into assembly #1 – #7 until part #10, the hose washer, is about half way into part #2, the 1″ PVC slip coupling. The bottle must be pushed down the launch tube far enough so that the steel balls in the retaining tube (#2) are above the bottle flange to lock it down but the bottle’s neck can’t go any lower than the hose washer (#10). When it is just right the three small bolts (#5) are tightened to secure the assembly in place. Rotating part #3 by hand provides some finer adjustment, just don’t tighten it too far or it will jam tight and need a wrench to loosen it.

Making the Retaining Tube

Shown above without the Locking Collar and the steel balls positioned outside the Retaining Tube by the elastic.

Shown above with the Locking Collar in place and forcing the steel balls inside the Retaining Tube.

To make the retaining tube:

Measure the circumference of the 1″ slip coupling and divide that into 6 equal parts. Mark the 6 places near one end of the coupling with a fine tip marker.

To make the holes for the steel balls you will need a 1/4″ drill bit. To position the holes accurately you will need a drill press. Accuracy is necessary to make it work smoothly.

Clamp a “V” block, or something else improvised to cradle the coupling, securely to the drill press table aligned under the drill bit. You will need to make a stop at the end of this holder for the end of the coupling to rest against. Leave 1/8″ from the end intact when you drill the holes, that is, 1/8″ + drill bit radius = centers at 1/4″ from the end. This will allow smaller than 2 L. bottles as well as 2 L. bottles to be mounted. If you only care to launch 2 L. bottles, use 3/16″ + drill bit radius from the end for centers. Necks on 2 L. bottles are tapered longer and therefore fit deeper into the retaining tube than small bottles can. If you want you can drill holes at both ends of the coupling at different distances and switch it around while testing.

Pressing the coupling against the end stop, carefully drill a 1/4″ hole at one of the 6 marks. Rotate the coupling and repeat drilling at the other 5 marks. If all went well you will have 6 evenly spaced holes aligned in a perfect circle. With the power turned off, lower the drill bit and rotate the coupling a few times to make a scratch around the coupling between the six holes.

Now take a small file and make a narrow shallow groove between the centers of the drilled holes at the scratch mark. This groove will serve to hold the elastic cord used later. Then take a very small file and make a small notch at each side of each hole, the notches will be made in the groove. They look like this “-O-” in the photos above. These notches are also for the elastic cord so the steel ball can pass easily through the hole.

Centered between just two of the holes, drill one smaller 3/16″ hole not all the way through. This will provide a recess for the knot you must tie in the elastic cord.

Clean off any burrs or rough edges with a knife and sandpaper. Make sure the steel balls pass easily through the holes without binding.

Preparing the steel balls:

You will need 1/4″ steel balls for the mechanism. DO NOT buy ball bearings, they are more expensive and harder, if not impossible, to drill through. What you need are 1/4″ steel shot used as ammo for sling shots. I bought a box of “Daisy” brand, as in Daisy BB guns, from a K-Mart store. I’ve also seen other brands which I believe have 100 of them plastic sealed to cards. Look in sporting goods stores next to BB guns and sling shots if they haven’t already been banned in your area, for your own protection of course.

You will need to drill a small hole through the steel balls so that they can be strung on an elastic cord. The absolute best and fastest way to drill a small hole accurately through steel balls is a small metal working lathe. Fortunately I now have a new one and it was a pleasure to use for this. For most of the people who don’t have a lathe, maybe you can find a machinist willing to make some for you. If you have a drill press with a good vise and some experience, that may work. Either way, make lots of extras while you’re at it because you are bound to lose a few. File off any rough spots left after the drilling.

The alternative would be to use 1/4″ beads from a craft store. Make sure they are accurately round and sized. Also get them in the hardest material that you can find so that they are the strongest.

When you have 6 drilled steel balls or beads, string them on a thin elastic cord. Don’t use rubber band, use thin round elastic with a woven cover over it that is found in sewing supplies. You need to make a little necklace around the retaining tube. Stretch the elastic around the tube and tie a tight knot so that the loop fits snug but is not stretched out completely. Move the knot around to the recessed spot and the 6 balls or beads into the 6 holes. You should be able to press them into the holes and have them pop right back out again. If not, you need to smooth out your work on the retaining tube and try again. You can also more loosely thread a piece of thin braided fishing line along with the elastic cord to prevent losing the balls should the elastic wear and break while outdoors. It would be a good idea to make up a few spare “necklaces” to take along to your launch site.

Get the half of the 1 1/4″ slip coupling used for the locking collar and try to slide it down over the necklace. It will be a close fit but it should not have to be forced. If it is too tight, the other half of the coupling may be looser. When it slides over the retaining tube, the steel balls should be forced down into the tube. You can try pushing a bottle neck into the tube but it won’t get past the 6 balls. Move the collar down and the bottle neck should now pass through. Move the collar back up and the bottle should now be locked in place. Success!

A close-up of the assembled mechanism.

The Shopping List

The following PVC parts were purchased at Home Depot and were all MADE in the USA.
I have no connection whatsoever to Home Depot, that is just where the specific parts used were available.

PIPE

1 1/4″ Schedule 40 PVC pipe ( approximately 16 inches were used and can vary as you want ) [ part #6 ]

3/4″ Schedule 40 PVC pipe ( approximately 16 inches, depends on the length of the 1 1/4″ pipe ) [ part #11 ]

1″ Schedule 40 PVC pipe ( 2 1/4″ length, can substitute thin wall pipe if the same outside diameter ) [ fits between part #2 and part #3 ]

1/2″ Schedule 40 PVC pipe ( at least 1′, for launch tube [ part #8 ] and fitting inside air pipe [ part #11 ] )

5/8″ outside diameter plastic pipe ( PEX ) for connecting launch tube [ part #8 ] to air pipe [ part #11 ]

COUPLINGS

Note on couplings:
The ones I used were straight sided and cylindrical. They also fit inside of each other, the next larger size fits over the smaller one. They seem to have a slight taper to them. If you fit one end together it will be loose but if you turn it around it will be a snug fit. Remember to check for the desired fit first when putting together the assembly.

3/4″ PVC slip coupling ( to secure air supply tube ) [ part #12 ]

1″ PVC slip coupling ( retaining tube ) [ part #2 ]

1 1/4″ PVC slip coupling ( locking collar ) [ part #1 ]

SPECIAL PVC FITTINGS

436-012HC 1 1/4″ male adapter ( part #3 )

437-168HC 1 1/4″ outside x 1″ inside reducer bushing ( fits inside part #3 )

435-012HC 1 1/4″ female adapter ( part #4 )

407-101HC 3/4″ slip to 1/2″ female threads elbow ( part #13 )
Note: Or substitute any 3/4″ PVC slip connector and air fittings that will mate best with your own air line.

MISC. PARTS

PVC cement, if you don’t have some already

stiff wire to make a coil spring around part #2, about 2′ or less

thin round elastic cord with a woven cover, from a sewing goods store

thin braided fishing line as a back-up for the elastic

5/8″ I.D. x 7/8″ O.D. O-rings typically used in launchers [ part #9 ]

red rubber garden hose washer 5/8″ I.D. x 1″ O.D. [ part #10 ]

1/2″ long size 10 machine screws for attaching part #4 to part #6 [ part #5 ]

1/4″ steel balls ( sling shot ammo from sporting goods ) or 1/4″ round beads ( from craft store )

Evil Personal Note:
Extra sling shot ammo will come in handy when one of your rockets gets stuck in a tree.
No, you don’t shoot it down, that would damage your rocket.
You wait until an athletic young person passes by and you use the sling shot to “persuade” him to climb the tree and retrieve your rocket.

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