swivel strength ratings

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pythonrock

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I have come across some "torpedo" swivels whose size and shape look advantageous for rocketry.
Problem is, I think these are rated at "breaking strength" while the ones we typically use are "load rated" which is I think 20 to 30% of breaking strength.
Does anyone have experience using these? Has there been any testing of various swivels for load or shock strength?
BTW I can't find the site that had testing of strength of high power materials.. Is it still around? link?
Thanks

Untitled.jpg
 
I use them on a few of my rockets, normally I press them through a bulkhead with a hole a tight fit and secure it on the other side of the bulkhead.
Regarding the strength, I treat all swivels as being rated as breaking strain and size at 100 times the rocket they are going on eg. for a 2lb rocket I wouldn't use any recovery gear rated below 200lb.
attachment.php

Here is a 9.5 torpedo swivel (800lb rating) mounted into a perspex bulkhead in my 38mm painkiller micro. The bolt that I have securing the bulkhead into the nose shoulder passes through the eye of the swivel.
The bulkhead in this model is however machined from 20mm perspex and has a gps tracker sled mounted into the nose and LED strobe lights lighting down into the body tube
 
I only use the SST ball bearing swivels with split rings on the ends. Usually in size #10. They are rated over 400 lbs. The ball bearing one I've used in my 10 lb L2 rocket has 29 flights on it and is still working fine.
serveimage


The non-ball bearing with loops on the ends that I've tried in a 5 lb rocket only lasted one flight.
serveimage


You get what you pay for.
 
Check out the pic of 4 swivels mounted on a wood board..
That's my display board,, or a part of it anyway..

https://onebadhawk.com/stainless-steel-swivels.html


The stainless steel ball bearing swivel on the left
is what I permanently fix on a 3rd loop
so that the drogue can spin freely and you don't get back a dreadlocks for a harness..
In this method that swivel has to carry no more load then the drogue itself can apply...
If you are going to carry the load of the rocket I would not use any swivel lighter then the 3 on the right..
The reason I got those is because I've seen the others fail...
All barrel or ball bearing fishing type swivels give a weight rating that is their failure rating...
All heavy swivels like the 3 on the right in the pic give a weight rating that is a WLL or Working Load Limit rating...
There is a big difference between those 2 ratings...

Teddy
 
Rocketmaterials.org is what somebody is looking for. I do believe it is gone though.
 
Thanks all for the replies.
Vance2loud -- that is a very slick setup. What is perspex and where do you get it? That 100x margin sounds like a good safety factor.

Handeman -- Agreed, would never use the loop type swivels. Are the split rings a risk like open eye bolts for shock loads? I've seen the SST ball bearing swivels with welded rings.

Teddy -- I've seen your broken swivels and I get it. I wondered if there was any actual testing or a good way to accurately compare numbers for the different kinds. especially for smaller rockets say 2-10 #, they might be good if I knew how strong they really were.

Mark -- that was the site. Is anyone doing that kind of testing now?

Thanks again
 
Perspex is the common name for acrylic down here, I had some offcuts from a subwoofer box, so I thought it would be good for practising on a lathe again. being clear it definitely shows any mistakes but also makes it perfect for adding lights for a night rocket.
I figure at 100x for breaking strength if it breaks then I was possibly have bigger issues anyway and when you are using Kevlar shock cord anything below 750lb still feels small to me on a fibreglass rocket, even a lightweight like the painkiller micro.
attachment.php

Heres a better view of the bulkhead before I put the swivel in
 
Dan,,
That barrel swivel you're talking about was from my Mad Cow Arcas...
The rocket was stretched and a bit heavy,, say,, 6 or 8 lbs....
That barrel swivel deforming like that was the reason I stopped using fishing type swivels to carry the load of a rocket...
And that's the reason I got the heavier swivels...
I am asked to permanently fix swivels to harnesses all the time....
My harnesses are never the weak link in the chain when everything is stressed to the point that something gives....
I can't have swivels failing....

Teddy
 
Breaking strength means exactly that. This are commercial fishing swivels, and just like fishing lines, they are rated in breaking strength. Consider it as a load factor of 1. For example a 1000 pound rated swivel should not break with a 1000 pound load, but is could well break at 1100 pounds.......

IMO any potential single point failure in a hobby rocket recovery system should be rated for 100 G if no shock mitigation devices are implemented. So a 1000 pound breaking strength swivel should not be used if the rocket weighs more than 1000 pounds /100 = 10 pounds. This is the level of shock generated in a +/- 5 second off apogee main chute deployment. If you use dual deployment, a typical delta-V could be 96 fps - 16 fps = 80 fps. That is equivalent to 2.5 seconds off apogee or 50 G, so a 1000 pound breaking strength rated swivel could be use for rockets weighing 1000 pounds /50 = 20 pounds. If you use a chute opening retarding system to increase the chute opening time and reduce the G shock, you can in increase the allowable rocket weight by the reduction in the peak opening G-shock.

Bob
 
bobkrech said:
Breaking strength means exactly that. This are commercial fishing swivels, and just like fishing lines, they are rated in breaking strength. Consider it as a load factor of 1. For example a 1000 pound rated swivel should not break with a 1000 pound load, but is could well break at 1100 pounds.......

IMO any potential single point failure in a hobby rocket recovery system should be rated for 100 G if no shock mitigation devices are implemented. So a 1000 pound breaking strength swivel should not be used if the rocket weighs more than 1000 pounds /100 = 10 pounds. This is the level of shock generated in a +/- 5 second off apogee main chute deployment. If you use dual deployment, a typical delta-V could be 96 fps - 16 fps = 80 fps. That is equivalent to 2.5 seconds off apogee or 50 G, so a 1000 pound breaking strength rated swivel could be use for rockets weighing 1000 pounds /50 = 20 pounds. If you use a chute opening retarding system to increase the chute opening time and reduce the G shock, you can in increase the allowable rocket weight by the reduction in the peak opening G-shock.

Bob
Click to expand...

Bob ,,
I have never disagreed with you before...
Right now I could not disagree more...
A 1000 lb rated fishing type swivel I would not use on a 5 lb rocket... No less a 20 lb rocket...
I do not know why,, I always trust greatly in your math,,,
but you're way off this time...
Dave M took the pic of a deformed fishing type swivel that came out of my Arcas...
And that swivel was attached to a 9/16" Tubular Nylon harness,,
so that has a bit of give to it,, maybe not much,, but certainly more then if it were Kevlar...
As I said before ,, this example is why I got heavier swivels...

Teddy
 
Bob,
Good explanation.
Thinking of it by associating the G forces with seconds off apogee makes it easier to visualize.
Thanks
 
onebadhawk said:
Bob ,,
I have never disagreed with you before...
Right now I could not disagree more...
A 1000 lb rated fishing type swivel I would not use on a 5 lb rocket... No less a 20 lb rocket...
I do not know why,, I always trust greatly in your math,,,
but you're way off this time...
Dave M took the pic of a deformed fishing type swivel that came out of my Arcas...
And that swivel was attached to a 9/16" Tubular Nylon harness,,
so that has a bit of give to it,, maybe not much,, but certainly more then if it were Kevlar...
As I said before ,, this example is why I got heavier swivels...

Teddy
Click to expand...
Teddy

Could you send me an e-mail with all the gory details of the flight, especially the recovery details. Commercial swivels are used by commercial fishermen who rely on them for a living so if they are made from a reputable manufacturer and/or supplied by a reputable supplier, I believe they will meet specs. They are also easy to test with dead weights.

My recommendations are for designing for a 100 G shock. The effect you are describing should only occur if the shock load was higher than 100G.

Bob
 
Bob,,
My Arcas,,
The booster would spin on the way down from apogee..
So I put a barrel swivel on the eye that was in the top centering ring..
My harness attached to this swivel..
This is down in the booster,, so not normally visible..
On the top the loop of this harness was looped through an eye that was not welded / full circle in the av bay bulkhead..
I am not one to oversize e charges..
The rocket flew with this set up a dozen flights or so..
Always gentle graceful separation,, I'do not remember seeing the 2 halves slamming to the end of the harness,, ever..
as opposed to separation sounding like 30-06 going off...
After all of these flights the nylon harness was getting crunchy so I decided to change it..
When I took everything apart the barrel swivel was deformed and the eye
though you couldn't see it with the nylon material looped through it was deformed and was opening...
Mad Cow Arcas,, stretched a bit,, bout 8 lbs....

Teddy
 
Hi Teddy,
I too am interested to know more about the swivel which failed on you. I also have always tried to design for 100G shocks but maybe in the case of swivels that isn't enough.
I wonder if the type of swivel makes a large difference? I also try to size my swivels to have a higher breaking strength than my harness.
And regardless of what type of recovery equipment you use this goes to highlight the need to inspect your recovery equipment regularly.
Do you know of any heavier duty swivels that have bearings to allow for them to spin freely under load?
The only heavy duty ball bearing swivels I have found are designed for rock climbing and are getting a bit heavy/large for a lot of our models, they are however rated for 30,000N or more of force so may be the way to go.
 
Heavy duty ball bearing swivels are also made for boats..
If you go to Boat US you can find them..
They are very large very heavy and very expensive. ...

Teddy
 
Sorry I should have put 'The only heavy duty ball bearing swivels I have found that might be suitable for our use'. I have seen some for boats but in the load ratings we want they tend to weigh nearly as much as the rocket (and sometimes cost more)
 
I'm a fan of crocheting the recovery line to ease deployment shock. Instead of parachute inflation causing massive deceleration the crocheted line eases the shock over .25-.5 seconds, making considerable differences. It would also help avoid zippering I imagine (unless severe lateral speeds at apogee)

Sometimes I'll still have a foot or so of crocheted line that wasn't pulled out due to the ease of deployment.
 
Jeffmhopkins said:
I'm a fan of crocheting the recovery line to ease deployment shock. Instead of parachute inflation causing massive deceleration the crocheted line eases the shock over .25-.5 seconds, making considerable differences. It would also help avoid zippering I imagine (unless severe lateral speeds at apogee)

Sometimes I'll still have a foot or so of crocheted line that wasn't pulled out due to the ease of deployment.
Click to expand...

I've used crocheting, too. Some Kevlar line is flatter than others, and sometimes it'll cause issues, but mostly it works amazingly well. Really takes up the extra slack on the line and makes it easier to pack in the smaller (38mm and smaller)min or near minimum diameter airframes, as well.
 
Jeffmhopkins said:
I'm a fan of crocheting the recovery line to ease deployment shock. Instead of parachute inflation causing massive deceleration the crocheted line eases the shock over .25-.5 seconds, making considerable differences. It would also help avoid zippering I imagine (unless severe lateral speeds at apogee)

Sometimes I'll still have a foot or so of crocheted line that wasn't pulled out due to the ease of deployment.
Click to expand...

I would love to see a how-to...
 
Once you form the first loop, you can do it by hand (without a tool) easily for the larger cording. I think that the key is to leave it a little loose so that it doesn't risk pulling too tight and it comes apart very easily, but still with enough resistance that it absorbs some energy.
 
onebadhawk said:
Bob ,,
I have never disagreed with you before...
Right now I could not disagree more...
A 1000 lb rated fishing type swivel I would not use on a 5 lb rocket... No less a 20 lb rocket...
I do not know why,, I always trust greatly in your math,,,
but you're way off this time...
Dave M took the pic of a deformed fishing type swivel that came out of my Arcas...
And that swivel was attached to a 9/16" Tubular Nylon harness,,
so that has a bit of give to it,, maybe not much,, but certainly more then if it were Kevlar...
As I said before ,, this example is why I got heavier swivels...

Teddy
Click to expand...
Teddy

You sell various swivels. https://onebadhawk.com/stainless-steel-swivels.html

You list them as 3/16" rated 300 pounds, 1/4" rated at 600 pounds and 5/16" listed at 1100 pounds. So what is the rocket weight limit you rate these for? And how did you determine it?

Bob
 
Common sense tells me not to put a swivel in a rocket that out weights the rocket..

Teddy
 
I've never tried crocheting my shock cord. I usually "Z" fold mine with 1.5 wraps of light masking tape. Slows the shock cord expansion slightly (as I usually put two "Z"s in), makes stuffing the BT easier, and prevents tangles.
 

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