I came up with a number of goals for this rocket season, and one of them was a new launcher. Don't ask me why. I think I just like making launchers even more than I like making rockets. This one is actually very close to a design I was working on when I was around 15, but never quite got the kinks worked out of. This is another internal grip launcher, and it will have similar performance characteristics to my first working internal grip launcher- http://www.wra2.org/forum/viewtopic.php?f=10&t=894. That one was triggered by depressurizing the air line, this one has a conventional pull string to launch the rocket. That one also had a complicated internal section which ate up a (very small) amount of your energy storage volume, and made it difficult to fill rockets with water while on the launcher (flow rate of water through the internal components was quite low). This one uses standard type M 1/2" copper pipe, and it's internal diameter is unobstructed. This launcher creates a nice ridge all the way around the inside of the bottle neck, so I don't think it will do any damage at all. I might try to launch rockets with this launcher this summer at as high as 300 psi.
So far I've only done one test fire- a 600mL bottle at 20 psi into the garbage can in the shop. Works well so far.
Here is a basic video explanation of the launcher:
[youtube][/youtube]
Here it is in released and locked positions with a bottle in place:
DSCF2655.JPG (807.16 KiB) Viewed 213 times
DSCF2656.JPG (812.61 KiB) Viewed 213 times
And here is a close up of the removable launch tube:
DSCF2653.JPG (397.98 KiB) Viewed 213 times
DSCF2654.JPG (343.59 KiB) Viewed 213 times
The o-ring is a #208- 1/8" cross section by 5/8" ID, nominal. It seals the bottle neck directly to the copper tube. It's a thick o-ring, so the bottle slides on easily, and still makes a good seal (reliability yet to be tested, but I've calculated a compression of about 24% for one of my bottle necks, which is about ideal). Also, as mentioned in the video, 90 degree copper elbows just fit nicely inside 1/2" SDR 13.5 PVC pipe. So with some copper pipe, elbows, a #208 o-ring, and some SDR 13.5, anyone could easily make a nice robust copper cable tie launcher, with built in o-ring and removable full bore nozzles. The only possible downfall is that the PVC pipe doesn't have tight tolerances on the inside diameter, so the fit of the PVC over the copper elbow ends (or what ever other bushing you might produce) could be a little inconsistent. I bought two 10' lengths of the SDR PVC, and every end fits nicely on the bushing I made. Some small bits of pipe I had lying around from a long time ago, however, were a little loose.
Anyways, I'll report back after I get some actual launches with this.
Yup, lathes are awesome tools for a rocket shop. You don't need anything crazy, either. You can do a lot just turning plastic and aluminum. I do all my lathe work on one of the original style Unimat jeweler's lathes. It's a real tiny thing from about 1970. There are many times I wish I could turn some bigger parts, or cut threads, but there are still many things I accomplish with it that I couldn't otherwise do.
SaskAlex wrote:I came up with a number of goals for this rocket season, and one of them was a new launcher. Don't ask me why. I think I just like making launchers even more than I like making rockets. This one is actually very close to a design I was working on when I was around 15, but never quite got the kinks worked out of. This is another internal grip launcher, and it will have similar performance characteristics to my first working internal grip launcher- http://www.wra2.org/forum/viewtopic.php?f=10&t=894. That one was triggered by depressurizing the air line, this one has a conventional pull string to launch the rocket. That one also had a complicated internal section which ate up a (very small) amount of your energy storage volume, and made it difficult to fill rockets with water while on the launcher (flow rate of water through the internal components was quite low). This one uses standard type M 1/2" copper pipe, and it's internal diameter is unobstructed. This launcher creates a nice ridge all the way around the inside of the bottle neck, so I don't think it will do any damage at all. I might try to launch rockets with this launcher this summer at as high as 300 psi.
So far I've only done one test fire- a 600mL bottle at 20 psi into the garbage can in the shop. Works well so far.
Here is a basic video explanation of the launcher:
[youtube][/youtube]
Here it is in released and locked positions with a bottle in place:
DSCF2655.JPG
DSCF2656.JPG
And here is a close up of the removable launch tube:
DSCF2653.JPG
DSCF2654.JPG
The o-ring is a #208- 1/8" cross section by 5/8" ID, nominal. It seals the bottle neck directly to the copper tube. It's a thick o-ring, so the bottle slides on easily, and still makes a good seal (reliability yet to be tested, but I've calculated a compression of about 24% for one of my bottle necks, which is about ideal). Also, as mentioned in the video, 90 degree copper elbows just fit nicely inside 1/2" SDR 13.5 PVC pipe. So with some copper pipe, elbows, a #208 o-ring, and some SDR 13.5, anyone could easily make a nice robust copper cable tie launcher, with built in o-ring and removable full bore nozzles. The only possible downfall is that the PVC pipe doesn't have tight tolerances on the inside diameter, so the fit of the PVC over the copper elbow ends (or what ever other bushing you might produce) could be a little inconsistent. I bought two 10' lengths of the SDR PVC, and every end fits nicely on the bushing I made. Some small bits of pipe I had lying around from a long time ago, however, were a little loose.
Anyways, I'll report back after I get some actual launches with this.
Alex
This is a very fascinating design. The use of the PVC taper and grips seems like a great new idea. There was another internal grip design many tears ago from E.Stoffie in the Netherlands that used a rubber hose that expanded to grip the rocket nozzle internal walls, but that was a friction lock which is different than this system, which obviously cannot slip off. Neat idea.
When I do a second gen of my 5x launcher, I am pretty sure it will involve your design here. That is a really nice design! I'll be curious to know if the PVC "sticks" in the pet any or if launch is instantaneous when you release the lever?
bugwubber wrote:When I do a second gen of my 5x launcher, I am pretty sure it will involve your design here. That is a really nice design! I'll be curious to know if the PVC "sticks" in the pet any or if launch is instantaneous when you release the lever?
I really like internal grip because it allows nice aerodynamic skirts. It would be cool to test different skirts (straight, full boat-tail, etc.) with this mechanism in a setup like your 5x launcher.
As for sticking, I'm not sure exactly what you are talking about. I certainly don't think the PVC will stick in the bottle neck. The most likely problem will be the cone getting stuck in the spreader piece. I played around a bit with the angle of the taper on the cone. My first attempt was too little taper, and the as the bottle squeezed the spreader piece, the cone got stuck in the spreader. I increased the angle a little bit, and it seems to operate very smoothly now (it's nice to keep the taper as gradual as possible, because this reduces the downward force on the cone, and ultimately means the lever will be easier to pull). Regardless of the cone angle, I suspect that launches will either be virtually instantaneous, or the cone will get stuck and it won't launch at all. I still haven't done any full pressure launches. It's about -20 Celsius here right now, but I hope to try a few in about two weeks.
-1 f with -18 windchill this morning here. Gives me time to think about ice fishing I guess. I was just tossing your design around in my head and thought, as the pressure increases I wonder how much the petals will cause the pet to yield making little divots if you will. So let me ask the question another way- did you ever try flipping the petals around? In over words, spreader on top and the petals push up and out?
I don't think the bottle neck yielding should be a problem. My first internal grip launcher used 4 1/4" ball bearings that pushed outwards and locked the bottle down. That would have concentrated the force far worse than this design, and I took it above 200 psi and never saw any deformation of the bottle neck. My first efforts with this design were as you say, "petals" pushing up and out and cone on top. I had a lot of problems with the petals jamming on the cone in that orientation- the bottle neck pushes the petals up into the cone, and it just doesn't want to release.
SaskAlex wrote:I don't think the bottle neck yielding should be a problem. My first internal grip launcher used 4 1/4" ball bearings that pushed outwards and locked the bottle down. That would have concentrated the force far worse than this design, and I took it above 200 psi and never saw any deformation of the bottle neck. My first efforts with this design were as you say, "petals" pushing up and out and cone on top. I had a lot of problems with the petals jamming on the cone in that orientation- the bottle neck pushes the petals up into the cone, and it just doesn't want to release.
Ah ok that makes sense. Also, perhaps I am not giving PET enough credit for being the wonder material it is! Looking forward to seing this one in action!
SaskAlex wrote:I don't think the bottle neck yielding should be a problem. My first internal grip launcher used 4 1/4" ball bearings that pushed outwards and locked the bottle down. That would have concentrated the force far worse than this design, and I took it above 200 psi and never saw any deformation of the bottle neck. My first efforts with this design were as you say, "petals" pushing up and out and cone on top. I had a lot of problems with the petals jamming on the cone in that orientation- the bottle neck pushes the petals up into the cone, and it just doesn't want to release.
Ah ok that makes sense. Also, perhaps I am not giving PET enough credit for being the wonder material it is! Looking forward to seing this one in action!
Thanks,
Bugwubber
The pet plastic near the threads of the bottle is always very thick and should not bend or yield from the PVC grippers. The PET is probably stronger than the PVC at that point.
It got to around -3 C today, so I thought I'd try some air-only launches with this launcher. I was hoping to get it up to 200 psi with a basic lawn dart rocket I recently made. On the first launch I only went up to 100 psi- I wanted to see how much force it took to pull the lever before I went up to 200 psi. The launcher held the rocket down and released it perfectly, without too much force on the release string. I thought all was well until I went to the launcher for the next launch. The spreader piece had moved down the copper tube and all of the "petals" had broken off.
At first I was quite disheartened, but I then I think I discovered the cause of the failure. I didn't glue the spreader piece to the copper tube, so it was free to move down the tube. I think that as the rocket passed the spreader piece, the pressure forced the spreader piece down into the cone (much further than it's meant to), and this is what broke all the petals off. So I've already made another spreader piece and this time I'm securing it to the copper tube with JB weld. It's curing as I type. Hopefully I'll report back on the results within a week or so.
^^^The weather here just hasn't been cooperating. We've had an unusually cold and snowy spring. I haven't had any opportunities to do any testing, and now that the snow is finally starting to melt I'll probably have to wait until the fields are dry. Could be a while, but I will report back when I can.
SaskAlex wrote:^^^The weather here just hasn't been cooperating. We've had an unusually cold and snowy spring. I haven't had any opportunities to do any testing, and now that the snow is finally starting to melt I'll probably have to wait until the fields are dry. Could be a while, but I will report back when I can.
Winter won't let go here either. We were launching this time a year ago, and this year the lake is still frozen. It might warm up this coming week!
I'm back. By the time the snow was gone and the fields were dry I had a lot of other things on the go. I finally managed to get back out a couple times in the last few days and I've whet my appetite once again.
With the spreader piece secured to the launcher, the launcher seems to be working flawlessly. I got one launch in a couple days ago with a lawn dart at 170 psi. Launcher worked flawlessly, but I lost the rocket. So that was the end of that day's testing. Yesterday I got out again, and got three successful launches in. Two of them were at about 240-250 psi, my highest pressure launches to date (and I finally used my homemade hand pump to achieve those pressures). There was also a fourth launch which triggered prematurely at about 60 psi (and caused damage to my rocket). At first I was concerned, but after inspecting ground video and photos, I realized that I had forgot to push the lever down and lock the rocket on, so it was simply operator error. Most of my previous launchers have not had a locking device that had to be manually activated, and I guess I'm just not used to that. I don't think I'll be forgetting again!
