Connecting Links

The Rocketry Forum

Help Support The Rocketry Forum:

Bruce

Well-Known Member
Joined
Feb 21, 2019
Messages
231
Reaction score
35
Any suggestions on what to use to connect the parachute and shock cord to the screw eye in the nosecone on low and mid power rockets?

We swap payload sections and parachutes often enough that tying them on is not desirable. Looking for a link that can be opened and closed.

Tried fishing snap clips, but they seem weak and some of the stronger ones have bits that stick out and snag on things...

For larger rockets, screw links work well, but the smallest are 1/8" which are too heavy for C-F powered rockets.

So we currently use split rings, but they are hard to open and not super strong.

IMG_9872.JPG


(The pink covering over the loose ends of the Kevlar is adhesive heat shrink)

Any suggestions?
 

tfish

Well-Known Member
Joined
Dec 8, 2009
Messages
2,688
Reaction score
759
cut a loop off one of your kevlar cords..run it through the screw eye, then through the loop of the other kevlar cord..then join them all with a knot like a bowline and maybe a "stopper knot" at the end.

Tony
 

Bruce

Well-Known Member
Joined
Feb 21, 2019
Messages
231
Reaction score
35
Thanks, that sounds reasonable, but I was hoping to minimize the number of bulky knots while still having both the shock cord and parachute attached to the screw eye independently...
 

Zeus-cat

Well-Known Member
Joined
Mar 14, 2009
Messages
4,619
Reaction score
827
I second quick links. Cheap, fast and easy to use. The only drawbacks are they may be a little heavier than you like and can take up too much space if everything is a tight fit.

1614615985478.png
 

Tractionengines

Well-Known Member
TRF Supporter
Joined
Aug 29, 2020
Messages
139
Reaction score
61
Location
Northeast Ohio
Thought about these the other day. Chain master link. One cord over each pin. Anyone tried them. Small size lighter that quick links. ... "loosing the keeper" is a problem, but the are cheep, and can get very small.
Thoughts?
20210301_231033.jpg
 

Bruce

Well-Known Member
Joined
Feb 21, 2019
Messages
231
Reaction score
35
I wish they made tiny quick links, but I'm afraid that 1/8" is the smallest and those are too heavy and bulky for lightweight C thru F powered rockets.

I think the chain master link is an excellent idea! I'll give it a try.
 

Bruce

Well-Known Member
Joined
Feb 21, 2019
Messages
231
Reaction score
35
I found a chain master link from a single speed bike. It weighs about 3.8 grams,

IMG_9879.JPG


By comparison, the split ring we were using before weighs about seven tenths of a gram,

IMG_9880.JPG


And the smallest screw link weighs about 8-1/4 grams,

IMG_9881.JPG


So I put the chain link on the rocket and it worked fine

IMG_9882.JPG


Not the easiest to open, but that's probably not so bad. I'll bet it's stronger than the split ring by quite a bit...
 

OverTheTop

Well-Known Member
TRF Supporter
Joined
Jul 10, 2007
Messages
5,047
Reaction score
2,311
Location
Melbourne Australia
At least that is a captive springy type clip. Less likely to come off compared to some I have seen. Great idea!
 

Tractionengines

Well-Known Member
TRF Supporter
Joined
Aug 29, 2020
Messages
139
Reaction score
61
Location
Northeast Ohio
I like the look of that !
Not easy to open "IS" a good thing. With the size of your cord and knots, it looks like the sliding plate can't move in too far. Also a good thing, so keeper does not get exposed to snag on something.
If you have smaller cord: Then a smaller link. And vice versa. (IF you go bigger, then get links with cotter-pins. No spring to fight with, and NOT going to open by accedent. At the moment not sure how small you can get this style.)
20210305_132931.jpg
 

Bruce

Well-Known Member
Joined
Feb 21, 2019
Messages
231
Reaction score
35
I wonder if the shock cord or shroud lines could potentially catch on the exposed sharp end of a folded cotter pin?

Here's some more options I found,

Number 35 roller chain master link. This looks a lot like the single speed bicycle chain link:

IMG_9894.JPG




Number 41 roller chain master link:

IMG_9896.JPG




Number 40 roller chain master link. Why is it bigger than the number 41 even though it has a smaller number?

IMG_9893.JPG


And in the boating section of the hardware store I found this tiny D shackle. Stainless even:

IMG_9892.JPG
 

TSMILLER

Well-Known Member
TRF Supporter
Joined
Aug 31, 2014
Messages
720
Reaction score
350
For low power rockets, this should be more than adequate.
It is all I use on all of my high power kites for exchanging lines, kites and they hold every time. Some of my kites have no problem lifting me off the ground at 230 lbs. They will hold.
A simple Kevlar loop with the knot working as the backer, the parachute, tie on with the larks head.
 

Tractionengines

Well-Known Member
TRF Supporter
Joined
Aug 29, 2020
Messages
139
Reaction score
61
Location
Northeast Ohio
That knot works great when always under some tension. Even a minimum amount if tension. BUT If it gets slack, and the "loop" side is a rope with "memory" that tries to untwist; it can open and allow the "knotted" end to slip out.
 
Last edited:

Tractionengines

Well-Known Member
TRF Supporter
Joined
Aug 29, 2020
Messages
139
Reaction score
61
Location
Northeast Ohio
I wonder if the shock cord or shroud lines could potentially catch on the exposed sharp end of a folded cotter pin?
It would need to be fully folded back and/or trimmed so as to not have a sharp end. A little putty or clay to cover it for extra protection.
 

OverTheTop

Well-Known Member
TRF Supporter
Joined
Jul 10, 2007
Messages
5,047
Reaction score
2,311
Location
Melbourne Australia
I wonder if the shock cord or shroud lines could potentially catch on the exposed sharp end of a folded cotter pin?
One thing I would be careful of if using chain links is to make sure the Kevlar stays on the round pins. That is where the strength of the links are, not across the plates. Maybe a little tape or heatshrink might work in that situation.
 

Sooner Boomer

Well-Known Member
Joined
Mar 21, 2011
Messages
3,333
Reaction score
911
Thought about these the other day. Chain master link. One cord over each pin. Anyone tried them. Small size lighter that quick links. ... "loosing the keeper" is a problem, but the are cheep, and can get very small.
Thoughts?
View attachment 453157
Put it all together, wrap with electrical tape. Should not come apart, or lose keeper. Easy to remove tape, and if done carefully, tape can be re-applied.
 

Greg Furtman

Well-Known Member
TRF Supporter
Joined
Nov 10, 2018
Messages
1,590
Reaction score
879
Location
Webster, Wisconsin
I've been using fishing snaps with swivels. There are many different styles & sizes. I get the ones that don't have anything protruding to snag on things. And since they come in different sizes you can select one that fits.

I have been using these for LPRs with great success and no failures. And I like the fact that I can easily unfasten my parachutes and store them not folded. For example, in the below pic , top row, I would use the safety snap, crosslock snap, or coastlock snap but not the others since they all have something sticking out that will snag on something. And I buy them with either rolling swivels or barrel swivels so my parachutes don't wind themselves up.


Snaps-and-Swivels.png
 

rbeckey

Well-Known Member
Joined
Jul 19, 2012
Messages
1,560
Reaction score
25
I also use various fishing swivels for for low power and ball bearing swivels for mid. No problem finding ones that are the right size with no sharps. I never store chutes attached. They hang on a line.
 
Top