Snap swivel styles for LPR/MPR?

The Rocketry Forum

Help Support The Rocketry Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

SolarYellow

Basket of deployables.
TRF Supporter
Joined
Aug 6, 2022
Messages
3,084
Reaction score
2,768
Location
First country to put a man on the moon.
Saw several examples in the "Palomar Knot for Attaching Shock Cord to Snap Swivel" thread.

The simplest ones with the cleanest sides can potentially just fail under load by pulling out. The ones that add hooks outside the sheetmetal clasp plate will be stronger, but are also potentially snaggier, causing issues with deployment. The "coast" style that's just a 180 in the wire hooked around itself is non-snaggy, but can still fail by the wire unbending. A quick link is a good answer, but the 1/8 size is way too big and heavy for my rockets. I'm probably not going to build anything over about 12 ounces with motor and most of my builds will be in the 1-3 ounces range without motor.

I'm probably overthinking it, but as an engineer, I'm kind of a compulsive optimizer. What do y'all prefer for snap swivels for changing out different parachutes, streamers, etc. and keeping things neat and tidy while avoiding failure modes?




I also recommend the locking swivels. I've had good luck with normal swivels for a long time, then I had a couple of failures recently. I searched and bought some like these Ocean Cat brand on ebay. Rather than a package of generic snap swivels from Walmart for less than a dollar, these are more like $0.15 to $0.25 each, but the manufacturer does provide a pull capacity for each size. They're only a bit longer than the generic ones I was using from Walmart, but the wire is nearly twice the diameter. IIRC then ones I bought are rated at just over 50# capacity.
View attachment 538405
 
Pros of using a swivel:
- parachutes twist and bind up when deployed. Using a swivel helps to reduce the twisting of the shroud lines.
- higher quality parachutes like nylon parachutes, can be easily moved between rockets without needing to invest in a new parachute for each rocket

Cons of using a swivel:
- adds another failure point to the recovery harness
- mostly only used in LPR/MPR but not HPR. HPR swivels are available but $$$ for quality and strength

In the LPR range, the deployment forces are low enough that standard fishing swivels should not fail and the added benefit of not getting your shroud lines all twisted is worth it.
 
Saw several examples in the "Palomar Knot for Attaching Shock Cord to Snap Swivel" thread.

The simplest ones with the cleanest sides can potentially just fail under load by pulling out. The ones that add hooks outside the sheetmetal clasp plate will be stronger, but are also potentially snaggier, causing issues with deployment. The "coast" style that's just a 180 in the wire hooked around itself is non-snaggy, but can still fail by the wire unbending. A quick link is a good answer, but the 1/8 size is way too big and heavy for my rockets. I'm probably not going to build anything over about 12 ounces with motor and most of my builds will be in the 1-3 ounces range without motor.

I'm probably overthinking it, but as an engineer, I'm kind of a compulsive optimizer. What do y'all prefer for snap swivels for changing out different parachutes, streamers, etc. and keeping things neat and tidy while avoiding failure modes?
I've used the small generic snap swivels for a long time, but mostly for plastic parachutes. A plastic parachute can't generate much shock on a snap swivel, it will probably tear the parachute before damaging the swivel. But when I started building new rockets and getting old ones ready to fly, I ditched the old rubber shock cords and bought a roll of kevlar. You need quite a bit more kevlar per rocket and I didn't want to buy a lot of it so I decided to make the shock cords interchangeable and I put snap swivels on each end of a 10' piece of kevlar for my small rockets. I found that worst case if I had a more powerful than normal ejection charge the force of the nose cone blowing out 10' could pull open the small generic swivel. I bought the Ocean Cat swivels pictured above and they seem to be a lot stronger. The safety loop I think will work better and the wire is quite a bit heavier. So far on a half dozen launches they are working well.
 
The Dr. Fish coastlock swivels look pretty good.

https://www.amazon.com/gp/product/B01G3HUN4G?th=1&psc=1

The video they have showing the failure mode is pretty good. I suspect the loops would have done even better if the tester hadn't used a hex key with its sharp corners to drag the wire around. That binds up the wire, bending it through a much tighter angle and then unbending it. The nice thing about the failure mode is it absorbs energy before letting go, rather than just loading to a force level and snapping. I reckon on the #4, it's at least 40 or 50 inch-pounds of energy absorbed as it deforms.

I have #0 and #1 in my shopping cart. The #1 still fits nicely in a BT-50 and is ~1/3 stronger. But I'm thinking 26 lb is probably plenty for a bunch of cardboard-tube LPR stuff.

I should run some "out the car window" ejection tests. Would be interesting with a load cell.
 
Last edited by a moderator:
The Dr. Fish coastlock swivels look pretty good.

https://www.amazon.com/gp/product/B01G3HUN4G?th=1&psc=1

The video they have showing the failure mode is pretty good. I suspect the loops would have done even better if the tester hadn't used a hex key with its sharp corners to drag the wire around. That binds up the wire, bending it through a much tighter angle and then unbending it. The nice thing about the failure mode is it absorbs energy before letting go, rather than just loading to a force level and snapping. I reckon on the #4, it's at least 40 or 50 inch-pounds of energy absorbed as it deforms.

I have #0 and #1 in my shopping cart. The #1 still fits nicely in a BT-50 and is ~1/3 stronger. But I'm thinking 26 lb is probably plenty for a bunch of cardboard-tube LPR stuff.

I should run some "out the car window" ejection tests. Would be interesting with a load cell.
I usually put swivels on my parachutes and clip it to the plastic nose cones open center hoop. I would think you would have to use the bigger sizes to do that.
 
Last edited by a moderator:
I've used the small generic snap swivels for a long time, but mostly for plastic parachutes. A plastic parachute can't generate much shock on a snap swivel, it will probably tear the parachute before damaging the swivel. But when I started building new rockets and getting old ones ready to fly, I ditched the old rubber shock cords and bought a roll of kevlar. You need quite a bit more kevlar per rocket and I didn't want to buy a lot of it so I decided to make the shock cords interchangeable and I put snap swivels on each end of a 10' piece of kevlar for my small rockets. I found that worst case if I had a more powerful than normal ejection charge the force of the nose cone blowing out 10' could pull open the small generic swivel. I bought the Ocean Cat swivels pictured above and they seem to be a lot stronger. The safety loop I think will work better and the wire is quite a bit heavier. So far on a half dozen launches they are working well.
Even elastic is better than the rubber shock cords. The rubber shock cords get old and brittle and break. I just toss ‘em.
 
Even elastic is better than the rubber shock cords. The rubber shock cords get old and brittle and break. I just toss ‘em.
I disagree. Use kevlar from the MMT up past the top of the tube and then finish the rest with the stock rubber attached to thst kevlar. This puts it out of the tube so it can be easily replaced so no worry about it aging. Kevlar has no give to it but that rubber sure does. You want lots of give in your recovery line to absorb the shock of parachute deployment. Using both kevlar and rubber gives you the best of both with none of thr drawbacks of either.
 
I disagree. Use kevlar from the MMT up past the top of the tube and then finish the rest with the stock rubber attached to thst kevlar. This puts it out of the tube so it can be easily replaced so no worry about it aging. Kevlar has no give to it but that rubber sure does. You want lots of give in your recovery line to absorb the shock of parachute deployment. Using both kevlar and rubber gives you the best of both with none of thr drawbacks of either.
I will try it. :)
 
I disagree. Use kevlar from the MMT up past the top of the tube and then finish the rest with the stock rubber attached to thst kevlar. This puts it out of the tube so it can be easily replaced so no worry about it aging. Kevlar has no give to it but that rubber sure does. You want lots of give in your recovery line to absorb the shock of parachute deployment. Using both kevlar and rubber gives you the best of both with none of thr drawbacks of either.
This is what I do. It also saves money in that I have so much extra rubber shock cords from Estes kits and using those means I can use less Kevlar (which is far more expensive).
 
I disagree. Use kevlar from the MMT up past the top of the tube and then finish the rest with the stock rubber attached to thst kevlar. This puts it out of the tube so it can be easily replaced so no worry about it aging. Kevlar has no give to it but that rubber sure does. You want lots of give in your recovery line to absorb the shock of parachute deployment. Using both kevlar and rubber gives you the best of both with none of thr drawbacks of either.
I haven't used rubber since Estes stopped using balsa nose cones. I have some balsa nose cones in my stiff with circular cuts on them where they were pulled back into the body tube. I haven't had an issue with shock on the shock cord when the parachute deploys but I've had ejection charges shoot nose cones out pretty fast and rubber shock cords pull them back. I've been using kevlar recently, real long kevlar, for kits up to Estes HiFlierXL size. I've got quite a few pieces of Estes rubber from kits I've built so I might put 2 or 3 pieces together and try it. The problem with that would be the space it takes up in the body tube, and how to keep it from tangling. I crochet my long kevlar, or wrap it around the spool that I built. I don't think either one would work with a long rubber cord.
 
I was in my local Walmart today and looked around in the fishing area. I found some snap swivels that looked like this. I doubt if they are they highest quality but I thought they would work for LPR parachutes and they are cheap so I bought a package.
1664153414867.png
 
I was in my local Walmart today and looked around in the fishing area. I found some snap swivels that looked like this. I doubt if they are they highest quality but I thought they would work for LPR parachutes and they are cheap so I bought a package.
View attachment 539123
What worries me about those are the little snaggy-bits sticking out the side. I don't know the likelihood that they'll get caught up on anything during recovery, but it does give me pause.

I have always heard the coast-lock type recommended for parachute attachment; that's what I buy. They're not the quickest to unhook (if you want to move your parachutes from rocket to rocket in the field) but they're pretty darn secure, and no snaggy bits.
1664154450517.png
 
I disagree. Use kevlar from the MMT up past the top of the tube and then finish the rest with the stock rubber attached to thst kevlar. This puts it out of the tube so it can be easily replaced so no worry about it aging. Kevlar has no give to it but that rubber sure does. You want lots of give in your recovery line to absorb the shock of parachute deployment. Using both kevlar and rubber gives you the best of both with none of thr drawbacks of either.
I use 350# Kevlar from the motor mount to a few feet past the end of the tube with a foam ear plug over it where it exits the tube for zipper protection. Then the Estes rubber. On heavier rockets, a bit more Kevlar, otherwise I hook the parachute to the end of the rubber with a snap swivel. Then another 4 feet or so of 150# Kevlar to the nose cone. to the nose cone.

Can't see the argument about Kevlar being expensive. It's just pennies a foot for the Emma's kites Kevlar on Amazon. I use it for everything in place of regular string.

Hans.
 
What worries me about those are the little snaggy-bits sticking out the side. I don't know the likelihood that they'll get caught up on anything during recovery, but it does give me pause.

I have always heard the coast-lock type recommended for parachute attachment; that's what I buy. They're not the quickest to unhook (if you want to move your parachutes from rocket to rocket in the field) but they're pretty darn secure, and no snaggy bits.
View attachment 539124
For the type shown in your photo- I had not used them before but the ones I bought are easy to use. I find them easier to use than the generic type. I put them on my long shock cord so I can switch it from rocket to rocket and they are fairly easy to connect to the loops on Estes BT60 nose cones.

I haven't tried the ones with the snaggy bits either but I will soon enough.
 
Can't see the argument about Kevlar being expensive. It's just pennies a foot for the Emma's kites Kevlar on Amazon. I use it for everything in place of regular string.
Remember, you're not necessarily comparing Kevlar to a more expensive option. In my case, as well as with many others, you're comparing it to something that's free. Also, reducing how much I use means going longer before I have to make another order for modelmaking supplies.

Maybe you don't mind wasting building materials, you do you. But for me, I like to know I've found a method of construction that not only saves me money (even if it's just 5 cents per rocket), but even improves my rocket's performance.
 
Remember, you're not necessarily comparing Kevlar to a more expensive option. In my case, as well as with many others, you're comparing it to something that's free. Also, reducing how much I use means going longer before I have to make another order for modelmaking supplies.

Maybe you don't mind wasting building materials, you do you. But for me, I like to know I've found a method of construction that not only saves me money (even if it's just 5 cents per rocket), but even improves my rocket's performance.
A 10 foot Kevlar shock cord is $0.40. I don't think that's worth wasting money on snap swivels to make them transportable.

Hans.
 
A 10 foot Kevlar shock cord is $0.40. I don't think that's worth wasting money on snap swivels to make them transportable.

Hans.
I don't use snap swivels to connect my Kevlar "base" shock cord to the elastic/rubber shock cord that attaches to my payload bay or nose cone. Instead, I tie them directly together. I've actually never seen anyone use a snap swivel to connect their Kevlar portion of the shock cord to the elastic/rubber portion.
 
I don't use snap swivels to connect my Kevlar "base" shock cord to the elastic/rubber shock cord that attaches to my payload bay or nose cone. Instead, I tie them directly together. I've actually never seen anyone use a snap swivel to connect their Kevlar portion of the shock cord to the elastic/rubber portion.
Well, I was kind of replying to someone up ^^^ there a ways trying to make a shock cord that is transferable from rocket to rocket. I don't get that, as the swivels are more expensive than the Kevlar.

Hans.
 
I was in my local Walmart today and looked around in the fishing area. I found some snap swivels that looked like this. I doubt if they are they highest quality but I thought they would work for LPR parachutes and they are cheap so I bought a package.
View attachment 539123
Yep. I use the same ones for LPR (which is all I do right now). Work fine for LPR. Come in different sizes. Cheap. Conveniently available at Wally World. The “Laker” brand.
 
I was in my local Walmart today and looked around in the fishing area. I found some snap swivels that looked like this. I doubt if they are they highest quality but I thought they would work for LPR parachutes and they are cheap so I bought a package.
View attachment 539123
+1. Eagle Claw brand. They just work for LPR and are available everywhere. Been using them for years.
 
Back
Top