BWR Coupling

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Post Wed Jun 15, 2011 12:31 pm

BWR Coupling

Over the last few months the BWR crew have been trying to find new ways of constructing new couplings to join bottles to make larger rockets there has been many failed designs but one stood out and was the simplest to construct it involves heat welding two bottle caps back to back it took a few attempts to get it right but i think we have mastered it for more info checkout the team blog
http://www.bwrockets.blogspot.com i am in the process of making a construction tutorial video

Dan B Team BWR
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Post Wed Jun 15, 2011 4:59 pm

Re: BWR Coupling

Ive added a tutorial video on making the coupler on my vimeo page.
here is the link

Dan B
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Post Fri Jun 17, 2011 11:58 am

Re: BWR Coupling

At the end of the video the last frame the bottle is grey ? It´s that a Pepsi bottle ?

I had 2L grey pepsi bottle without parachute so it crashed every time, it would get crushed and would get marks.

I represurized it to 110 psi and it never blasted...I don´t know what the PET from Grey Pepsi bottle had better than others. In fact it´s like a grey/blue color.

Maybe it´s like this one if I remember:

http://www.flickr.com/photos/like_the_grand_canyon/2790578020/
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Post Sat Jun 18, 2011 4:07 am

Re: BWR Coupling

In the uk these silver grey bottles are 1L in capacity and have cheap energy drink inside them i had a 4L rocket it crashed hard on several occasions and these bottles just kept on going i think they must be a thicker PET.

Dan B
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Post Sat Jun 18, 2011 10:00 pm

Re: BWR Coupling

danb wrote:In the uk these silver grey bottles are 1L in capacity and have cheap energy drink inside them i had a 4L rocket it crashed hard on several occasions and these bottles just kept on going i think they must be a thicker PET.

Dan B


Have you had them up to pressure at all? We made cheap couplers using special glue that is designed for this kind of plastic because welding them didn't hold up to much pressure. They make "tornado tubes" this way, and we tried to copy it but it was not a success. Is there a trick to getting the welds to be strong? If so, what did you find out?
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Post Mon Jun 20, 2011 2:36 am

Re: BWR Coupling

I have had them up to 120psi and left them there for 2 mins trying to simulate launch conditions i am yet to test there full bursting pressure. The way i welded them was when i saw a ring of molten plastic form round the outside of cap i knew they were ready to be joined together. Im yet to test the couplers in flight so when the weather behaves itself i will update the results.

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Post Sat Jun 25, 2011 1:00 pm

Re: BWR Coupling

does that really hold??? 1 year ago I glued 2 caps with epoxy and 5 bars was enought...
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Post Sat Jun 25, 2011 9:08 pm

Re: BWR Coupling

danb wrote:I have had them up to 120psi and left them there for 2 mins trying to simulate launch conditions i am yet to test there full bursting pressure. The way i welded them was when i saw a ring of molten plastic form round the outside of cap i knew they were ready to be joined together. Im yet to test the couplers in flight so when the weather behaves itself i will update the results.

Dan B


It's possible that you came across a new way of getting them welded. We could never get them hot enough to form a bead like that without melting the whole cap causing it to sag or get distorted. Do you have a temperature setting you used? Or a duration to hold the cap in the heat? It sounds like you have solved the problems!
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