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PVC Version of Clark Cable Tie Launcher

Discussion about Compressors, hose, pipes, fittings, launchers, release mechanisms, and launch tubes.
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aquaquark
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PVC Version of Clark Cable Tie Launcher

Post by aquaquark » Mon Sep 22, 2014 1:57 am

I have modified a piece of 1 inch PVC tube to make a faux Clark Cable tie launcher. I have not seen this modification on the web and since it has worked well for me at pressures of 125 psi I thought I would share it. Attached pictures show how it looks. It is simple to make and has never failed to launch. My apologies to anyone if you have already published such a device.

These are the measurements and methods I used. I am sure improvements could be made.

The launcher is made from an 8 inch long piece of 1 inch PVC tube. A miter saw is used to make 7 approximately evenly spaced strips along the axis of the tube on each end -- the top strips are 4 inches and the bottom ones (to hold the launcher in place) are 2 inches long. Any suitable saw should work. With the miter saw, the PVC strips tend to crack with more than 8 or so strips.

Then the longer top strips are bent outward about 3 inches wide by heating the middle of the strips over a heat gun and then pushing the strips over a 2 liter bottle at the neck end to spread them apart. Hold the strips in place until they cool or cool them faster by spraying or dunking in water. Be sure to keep them centered over the bottle. I keep the bottom 1 inch of the top strips straight. I put the PVC tube about 3 inches above the heat gun at 1250 deg F and keep rotating it until it is pliable enough to bend.

After the strips are cool, they are far enough apart to facilitate making the end tabs that grab the bottle neck. One at a time I heat just the tip of each strip at the same temperature as before. Then I grab a quarter inch of the softened end of the strip with a wrench with a wide flat end and bend it so it is at 90 degrees to the strip and pointing to the middle of the tube. I dunk the tip into water while holding it with the wrench to quickly harden it into position.

Once the tips are made, construction is complete. Nothing is done to the bottom strips. Everything else to launch is standard procedure for a Clark cable tie type launcher. The stiff springiness of the PVC strips has always had enough tension to hold the retainer and never failed to come off the neck of the bottle.

I hope some will give it a try and see if it has any advantages over the standard Clark cable launcher.
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Blenderite
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Re: PVC Version of Clark Cable Tie Launcher

Post by Blenderite » Fri Sep 26, 2014 5:06 pm

That is a really good idea. Have you done any stress tests to see how the strength compares to the cable tie system?


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U.S. Water Rockets1
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Re: PVC Version of Clark Cable Tie Launcher

Post by U.S. Water Rockets1 » Sat Sep 27, 2014 10:16 pm

Wow! That is a very innovative new idea. This looks like a completely new idea. Thanks for sharing the concept!


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aquaquark
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Re: PVC Version of Clark Cable Tie Launcher

Post by aquaquark » Thu Oct 02, 2014 7:00 pm

Thank you for the positive comments. I am new to the water rocket hobby and I have been trying to make things as simple as possible with no electronics. The water rocket population on the web has given me a huge jump start and I hope i can pay back at least a little for their inspiration. it seems nozzle seals, launchers, and parachute deploy systems are the trickiest for me. The first two I think I have solved satisfactorily. The parachute system is still a problem - I am working on the bicycle tire air bladder deploy method which seems very clever and has worked sporadically - the tubes i use keep bursting at weak points.

I have not done any stress tests or compared directly with a cable tie launcher. I'm not sure how I would do such a test. But if the number of strips is kept to 6-8, I think the PVC version will be as strong as the cable tie launcher. If more than 8 strips are cut, they become too thin and thus weaker and also not as stiff. Weakness, as expected for plastics, comes only if you repeatably bend the strips outward far beyond their normal initial bend and thus make weak points that could break or at least decrease their springiness - but that would be far outside the normal use. I have not found any degradation of the launcher response after many uses. For pressures up to 140 psi (about the limit with my pumps), this launcher works most easily for me.



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U.S. Water Rockets1
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Re: PVC Version of Clark Cable Tie Launcher

Post by U.S. Water Rockets1 » Sat Oct 04, 2014 11:10 pm

aquaquark wrote:Thank you for the positive comments. I am new to the water rocket hobby and I have been trying to make things as simple as possible with no electronics. The water rocket population on the web has given me a huge jump start and I hope i can pay back at least a little for their inspiration. it seems nozzle seals, launchers, and parachute deploy systems are the trickiest for me. The first two I think I have solved satisfactorily. The parachute system is still a problem - I am working on the bicycle tire air bladder deploy method which seems very clever and has worked sporadically - the tubes i use keep bursting at weak points.

I have not done any stress tests or compared directly with a cable tie launcher. I'm not sure how I would do such a test. But if the number of strips is kept to 6-8, I think the PVC version will be as strong as the cable tie launcher. If more than 8 strips are cut, they become too thin and thus weaker and also not as stiff. Weakness, as expected for plastics, comes only if you repeatably bend the strips outward far beyond their normal initial bend and thus make weak points that could break or at least decrease their springiness - but that would be far outside the normal use. I have not found any degradation of the launcher response after many uses. For pressures up to 140 psi (about the limit with my pumps), this launcher works most easily for me.

You should look at our "Radial Deploy" system. It is by far the simplest design out there. You could figure out ways to adapt it to your own timer system or some air bladder. So far it has only been modified to work with Tomy Timers and Servos. It's very simple to build, and very reliable.


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mahboob
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Re: PVC Version of Clark Cable Tie Launcher

Post by mahboob » Sat Nov 29, 2014 11:46 am

it is easy. but cable tie is more easy to making and good results and Quick change



aquaquark
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Re: PVC Version of Clark Cable Tie Launcher

Post by aquaquark » Sat Mar 14, 2015 1:00 pm

I have made a few modifications to the construction of the PVC launcher. I think 6-7 tabs is probably optimum for strength and release capability. A major change is that I no longer use a heat gun for deforming the tabs. It was easy to overheat the PVC and probably weaken it. The deformation temperature of PVC is ~100 deg C. I now take the cut tube and immerse the long tabs in a pot of boiling water for a minute or so and then shape them over a 2 liter bottle as before. It takes a little more effort since the plastic is not as malleable. To bend the tabs I also put the tips of each tab into boiling water, hold the end 1/8" with flat pliers, bend, and cool in running water. Once the tabs are formed, they can be adjusted by reheating and bending so that all the tabs contact the lip of the bottle.

In terms of strength, I don't have the means to directly measure it but this is what I found. My analysis is simple and naive but may give at least some comparison for strengths of the two methods. I would welcome anyone with more knowledge of this area to correct my analysis!

Most cable ties are made of Nylon 6/6 which has a tensile strength of about 12,400 psi (http://www.plastic-products.com/spec1.htm). It can vary from 1/10 to 2x or more of this value depending on the particular cable tie and type of nylon (esp reinforced ones). Rigid PVC has a tensile strength of about 5,000-9,000 psi (http://www.pvc.org/en/p/pvc-strength). Of course actual values will be different for real products. I only go to about 120 psi in my rockets - just some packing or Gorilla(c) tape for strength. The lip where the ties and PVC tabs restrain the bottle has an area of about 1 sq in. Assuming that the tie tabs cover 80% of that area gives the pressure on the tabs of 150 psi. With 10 ties, that's about 15 psi/tie or with 6 PVC tabs about 25 psi/tab. These values are well within the strength limits of each material. I think the main factor is quality of construction - do all tabs sit on the lip, type of cable tie or PVC, etc.



aquaquark
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Re: PVC Version of Clark Cable Tie Launcher

Post by aquaquark » Sat Mar 14, 2015 1:14 pm

["mahboob"] wrote "it is easy. but cable tie is more easy to making and good results and Quick change"

I think anyone should use what works best for them. I have no idea which rocket modifications to launch system, deployment, rocket construction, etc. is "best". All have pros and cons. I use what works for me and is in my skill set. I love the creativity, ingenuity, skill, and knowledge of water rocket enthusiasts. I have learned much about physics and aerodynamics from them as well as their clever solutions to many problems. This is just my meager contribution. It works for me. In a year, maybe something else will come along.



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