Jolly Logic Chute Release Pin Retention Failure

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NickelRock

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Hey all,

I've seen a lot of topics on the JLCRs but haven't found much about this specific failure.

I'm part of a USLI team and we've been the Chute releases have been in our design since the beginning. We used them on a smaller rocket in January with no issues, but last weekend we had one fail and release the main at apogee.

Upon inspection we found that one of the rubber bands broke. I though this should be a simple fix and tested the retention using kevlar cord in place of the rubber bands. After, I found that all 4 of our JLCRs will open up with a little downward tug on the pins, which gives me very little confidence. It does this whether the unit is on or off. It seems that the tension from the rubber band helps, but a tug will still pop the pin out prematurely. I also attempted to replace the spring inside with a stiffer spring, and the pins still won't stay in.

We've got tender descenders ordered on back-up, but modifying the current rocket for them would be kind of a pain.

As anyone experienced this issue or have any reasonable mitigation for it? All of ours units experience the problem, so it seems to be either something inherent to the JLCR design or something stupid I'm overlooking. I'll try to get pictures up tonight too.
 
You need to contact John Beans the JLCR designer for several reasons, or standby and he will probably find this thread and respond.
 
Weird- I saw this and had to try it. I couldn't get mine to release no matter how I abused it.

Have your JLCRs been taking a lot of shock or something that would damage the mechanism? I've never heard anything like this before.
 
In terms of shock, we have 4 JLCRs, 2 which were flown and 2 are brand new. The fact that it's happening to all 4 really makes me think I'm doing something wrong now.

I've contacted John Beans and he's given me a few thing to check out in to make sure nothing's broken. I'll check on all that, and give an update / post a video in the morning.
 
I have 6 JLCR and all the pins are tight. I have never had a failure with the system. If the rubber band that broke was new perhaps you had too much tension on it. I have connected 2 rubber bands together when needed to reduce the tension on a single band.
 
So we tried a couple of things suggested by John Beans:

- using a micrometer we found that a few of the pins were slightly smaller than the others by around .0008"
- we rotated all of the pivot cylinders 180°
- charged all of the batteries, 2 of them were dead and 2 were close to dead
- opened all of them and checked the pivot action and servo horn position (all were good)

After this we swapped all of the pins for the largest sizes and tugged on them again. At this point all of them held with no issue. We went on to shake tests which revealed an issue with how we have our redundant JLCRs set up and how we pack our chutes, which I'll cover later. Otherwise all of them held for the first 5 shake tests, then on the 6th another one of the CRs released a pin prematurely again.

Our shake tests consisted of spinning in in a windmill, and also - as a teammate described it- shaking it like a dog shakes a rope. The latter test is when the CR failed.

Here's a video of a one of the chute releases with a smaller pin (.1171"). The pin comes out with almost no force. For reference the Kevlar cord be used in parallel with one of the rubber bands if we use them on the chutes.
[video]https://www.dropbox.com/s/898m2y4x22ul9vu/CR3_OldPin.mp4?dl=0[/video]


Here's with the largest pin (.1179"). It holds what I expect would be a reasonable amount of force for a parachute on a 20lb. rocket, but with a stronger tug it still comes out. Not sure if this is normal.
[video]https://www.dropbox.com/s/wmfmqu5hklcihaw/CR3_NewPin.mp4?dl=0[/video]


In case it was the rigidity of the Kevlar cord causing shock on the pin, we tried the largest pin on a rubber band. This is the CR that failed in the shake test. It stretched out to the size of the chutes, but then a few pulls of the band and the pin popped again.
[video]https://www.dropbox.com/s/qzb3nkhgsamq4n0/CR1_NewPin.mp4?dl=0[/video]


We didn't actually measure the holding force, we'll try with a spring scale on Monday when we can get one. But qualitatively, how strong of a tug should these hold? Looking back at the videos it looks like we were putting a lot of force on them, but when pulling on them it didn't feel unreasonable hard. That said my memory could be wrong and we may be pulling harder than would be seen in flight.

We had some strong winds (~17 mph) on our last launch, and when we go again on the 17th it isn't looking much better. We had a lot of weather cocking off the rail, which we expected, but I think the high relative winds at apogee put a lot of force on the JLCRs and that is what lead to the rubber band breaking.

When the rubber band failed at the last launch it was ~17°F outside, so we think that was a big contributor to that problem. Our next test is to put a rubber band in the freezer for a while and seeing which breaks first, and if it's the rubber band I think we'll be satisfied. I'll let you all know how that goes after we finish it tomorrow.
 
I'm curious if your testing ended up putting something out of tolerance such as the hole that the pin gets inserted into. In normal operation the force isn't necessarily completely linear like it is when you pull on the pin with your hand. I can see where testing it like you did could simply be enlarging the opening in the pivot cylinder.

I'm not sure of how much force the unit can take, but we've used the CR with some pretty large chutes up to 6' in diameter and there wasn't a lot of tension on the system.

I own eight CRs and have done well over hundred flights on them. Our kids did SLI last year and were the first ones to use the CR in that competition. We've never had any problems like you've experienced.
 
In our email exchanges, it never even occurred to me that you weren't using the rubber bands as designed. One of the less-appreciated engineering aspects of Chute Release, and the key final part of the design to come together, was the use of an elastic element that would limit tension, but guarantee some tension at all times.

What has happened is that you've cranked them down with Kevlar and swaged the corners on the pins, catches, and pivots so that they are no longer reliably locking. No sharp corners, no locking.

Please return them to me pronto and I'll replace all of the metal parts, and the cases if you've damaged them as well. Bundling to prevent pull out at apogee is a skill, and most likely you've tethered them to the shock cord in such a way that they were being yanked that way as well. The sole job of Chute Release is to keep a parachute folded, not to take any (intended or unintended) shock load.

Using Chute Release on larger chutes can get tricky, but many here have done it. I'm working on a chute bag that is controlled by Chute Release for very large chutes. Hopefully that will be done soon. But until then, send me those Chute Releases, and I'll make sure you have plenty of both sizes of bands. And you can use other bands as well, and combine bands. Just be sure to use an elastic element of some sort.
 
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John, I’ve been using a Fruity Chute “Chute Slipper” to confine my 48” Fruity Chute Classic during launch.

The worst that has happened was that my chute deployed a bit early during my L2 cert flight. In hindsight, the 48” chute packs densely and the new large bands included in the JLCR are a bit longer than the previous model. Tension was not as tight...my bad on not checking more closely.
 
So we've figured out the problem, just as John said. By pulling on the first JLCR with Kevlar we put too much shock on the pin/pivot and popped it out. By continuing to pull on them we wore down both the pins and the pivots.

We tried one of our team mentor's JLCRs with the rubber band and it works great.

John's been kind enough to send us replacement pins and pivots and we'll be putting these back on our rocket with rubber bands for in time to launch next weekend!
 
And THAT'S how you create a loyal and forever following.

The product speaks for itself.
The Designers response.. Speaks for itself.

EXTREMELY Well done John..

Tom
 
Durability of the rubber bands can be pretty poor (I end up having to swap them every other flight on average) but a good solution one of my club members uses with good success is to swap them out for lengths of sewing elastic. This is great because the length can be made whatever you want to get perfect tension, and it avoids the issue you've discovered with using inelastic tethers.
 
Durability of the rubber bands can be pretty poor (I end up having to swap them every other flight on average) but a good solution one of my club members uses with good success is to swap them out for lengths of sewing elastic. This is great because the length can be made whatever you want to get perfect tension, and it avoids the issue you've discovered with using inelastic tethers.

That is interesting. I've been using the same rubber band I started with. It's got at least a dozen flight on it now and shows no sign of deteriorating. From the looks of it, it should last at least another dozen flights.
 
That is interesting. I've been using the same rubber band I started with. It's got at least a dozen flight on it now and shows no sign of deteriorating. From the looks of it, it should last at least another dozen flights.

Mine too, I just replaced my first rubber band in over a dozen flights (19 based on the JL3 that rode along on each flight).
 
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