Basejumper.com - archive

So a while back their was a lot of discussion about curved pin design and attachment methods to bridles. Some of it was in regard to PC in tow incidents in Twin Falls. A lot of it related to how the pin loaded an whether the tip of the pin was being turned upwards or forced down wards into the flap. People were playing with it and had been able to reproduce failure modes on video.

So a month or two ago I got a message asking me about curved pin designs. It got me off my ass and I started looking around and found some one to laser cut me some prototypes. They're rough and need more tumbling to give the edges a better radius but it's some thing to play with. Their are two designs one with the ring tangent to the curve of the pin and one inset a bit more inside. So at this point I'm passing some around looking for opinions. The shaft is a little shorter to keep the pin from becoming too much taller when on edge. It's my hope that they will rotate upwards better then the normal pin with the ring centered on the shaft. The problem with the normal design is that if the bridle loop slides around to the wrong side of the ring it can actually be trying to turn the tip of the pin down wards into the flap rather then rotate the pin upwards. I've actually had pins bend rather then pull out of the loop. I broke two loops made from 1000 lb line on one deployment from this. So they really can jam hard. I'm hoping that by moving the ring inward it will keep the rotation in the right direction. Here are the drawings of the two I'm playing with right now. I have a limited number of prototypes right now. I don't recall who was part of the discussion before but if people are interested in playing with a couple of them and doing a little testing, I'm soliciting opinions on the designs. I only have a hand full but if you're serious get in touch with me.

Lee

I remenber your past post but have forgotten some of the details. I am still interested in the details of how you were able to bend pins. I have replicated what you described but the end result is a few pounds difference and the pin still pulls out. The problem gets worst the tighter the pack but i have never been able to make it so tight that the pin wont come out. Overall i like the idea of the new pin design but am curious to better understand the problem with the current design.

What if instead of a grommet we had a large enough stainless steel plate that precludes pin jamming on container material? (and of course, with proper bridle management that precludes bridle getting punctured by the pin)

Hey Lee, do you have the link to the earlier discussion thread?

I think it's buried in here...
http://www.basejumper.com/..._reply;so=ASC;mh=50;

http://www.basejumper.com/cgi-bin/forum/gforum.cgi?do=post_view_flat;post=2964578;page=11;sb=post_latest_reply;so=ASC;mh=25;

I think it's page 11 post 251 and 252 but their was a lot of discussion in there.

There was also a lot of discussion about this in relation to the floating pin idea in this thread...

http://www.basejumper.com/cgi-bin/forum/gforum.cgi?post=2980780;sb=post_latest_reply;so=ASC;forum_view=forum_view_collapsed;;page=unread#unread

Lee

As to the bent pins. It was about a 2,500 lb payload with an even higher snatch force on the drogue. The pins were attached to a heavy HMA line and it was able to slide around to the wrong side of the pin. the pack was tight. We close it with a car jack as the pull up tool with 2000 lb pull up cords. You can bend and break a lot of things with 5000 lb plus force.

Lee

I'm not sure if a wider stiffener in the flap, plastic or metal is the answer. In fact I think it could exacerbate the problem. I'm thinking the way to deal with this is to make the pin want to turn up into the correct position for extraction from the loop. That's why I'm looking at the geometry.

Lee

What about having bungee cord for closing loop ?

A bungee loop makes it more forgiving. The biggest problems occur when the loop is tight and you can not easily pull up slack in the loop. To some degree a bungee over comes that. But depending on how you pack a pin rig you can get big variations in pin tension. And when you tighten the harness or change body position some pattern sets can go way up in tension. If you stretch that loop out it may be just as tight as any loop. Keep in mind that the loop is short and has a limited stretch. And even if it did have a enough stretch to protect you from that increase in tension now you could have a big geometry change between the flaps and grommets. It could threaten the security of some cover flaps.

I just don't think that a bungee closing loop is the end all solution. I think that it would work best in rigs with a inherently long loop like a rig with a through loop. And on rigs that are fundamentally loose with low flap tension to begin with. But that's not what most people are building right now. But if you're asking my opinion. I think there is a place for a wide soft rig with low flap tension with bungee through loop providing the tension for the security of the pins. Or a longer flex pin. There is a guy that messaged me about a double ended center pull cable design. I think that has it's own issues but might serve well with a no tension flap design secured with bungees. That could avoid hard kinks in the cable at the grommet.

And if you placed a stiffener and set of two grommets in the tray you could build a bungee loop with a lot more length and potential stretch to is then some of the short little loops used now.

But right now I'm playing with new pins.

Lee

Pins should be showing up in the mail for people soon. Be advised that they are prototypes that were laser cut. They are not really rounded enough to be usable. They tumbled them for two days but that wasn't nearly long enough to radius the edges. And I don't think they had a aggressive enough of a media. I'll have to buy a tumbler where I can leave them in it for a couple of weeks with a much courser abrasive. But I'm not ready to do that yet till the geometry is settled and I'm sure their is a market for this where I can at least break even.

For the record I don't think their is any money in this.

The numbers are like this. These prototypes cost me $5.20 to get them cut. It's pricey but it allows me to do onesies and twosies playing with designs. In larger numbers we are probable looking at $2.50 per pin. That's just cutting alone. Polishing looks to be the longest process and will probable have to be done in house. It looks like setting up a tumbler wil be a few hundred dollars in it self. And may require a couple of steps. with a deburer and polisher. Let's say $500 to make it work with good ceramic media. I have a ball park bid of $5,000 to set up dies to stamp them which would drop the cost down to $0.15 to $0.20 per pin which become workable. The issue is the size of the market and time for return on investment. Their just are not that many base rigs made. If by some marical you could get the skydiving manufacturers on board. Note that they all have buckets of pins laying around right now and no incentive to change. So let's say that by some marical you could clear $1.00 per pin how long would it take to sell 5,500 pins. We just don't build a lot of rigs. But for now If $3.50 per pin would fly it might pay for the investment in the polishing if we laser cut them. Also, All it takes to make a new pin design is to send them a drawing. So if any of you would like to play with a design or for instance a long straight pin of some type It's just as easy and you can do relatively small batches with out the set up cost of stamping dies.

If you're interested the company I'm dealing with is...

Stealth Industries
Irving, TX

Really nice guys. The stamping bid is from another company called Mercer Metals. Right now I've got $149.94 and a few stamps invested in this. If at any time some one would like to buy me out... take this ball and run with it. I'm just doing it because I think we need to do some thing about this.

Lee

The core of the problem with jamming pins is that once the pin catches on container and bundles up some material, it is impossible to dislodge by any amount of force less than loop breaking force or the force required to rip apart the container material. So, moving the leverage point a fraction of an inch won't solve this problem. Will it reduce the probability of this happening in the first place? Hard to say when we're talking about processes happening in a millisecond. If pin and pull force are positioned just the wrong way, the pin can still catch the container and jam.

Polished steel on steel, on the other hand, has very low coefficient of friction, and there's nothing to bunch up, so there's a ceiling of the force of friction. I can't imagine how stainless steel pin can hang up on stainless steel plate no matter the direction of the pull force.

If the bridle attachment has slipped to the back of the pin then only a very small amount or none of the force of the bridle will be trying to right the pin, and that can be overcome by the tip of the pin pressing against the pack job.

The attached pic shows a pin that would ensure the attachment point applies a stand up force in every configuration of bridle attachment but probably introduces other issues that I cant think of at the moment

I think a big part of the problem is that the curved pin in inherently a 2D static object in a 3D dynamic environment. It can only adapt so much to the myriad of possibilities thrown at it. No matter what the design, you will always be able to engineer a failure mode for it, and while it may be a fairly negligible scenario, statistically speaking, it will eventually come up in the real world environment.

What if you try to increase the pins ability to adapt to these statistical outliers by introducing an additional curve?

Instead of merely adjusting the geometry on the X-Y plane, what if you also add curvature on the Z (Zed for you Canadians...). You need to have a pin (and loop) design that will release in any of the possible directions in a 360 deg. sphere (well, technically, roughly a half sphere as the pin pull force direction will never go directly through the container).

It doesn't have to be huge, and I haven't really played around with the idea, but it seem you could introduce an additional, off axis bend on the "eye" so that even if a pin lock condition was met on one axis, the force being applied would have an "escape route" via another axis, and that the force required to do this would be less that the force needed to result in the lock up situation. Essentially you would create a compound curve of some sort.

This would not necessarily solve the issues with container design and interference, but might add some additional safety to pin extraction in those situations that arise on the small edges of the statistical bell curve.

I suppose a pull that is trying to cause the pin to swing around could cause what you are describing. I don't think that was the problem in what I have seen. And it's not the issue that I was able to reproduce on the ground. I'm hard pressed to think of a really practical way to integrate a metal skid plate into the surface of a flap. There have been a number of rigs with plastic flap ends. Generally they did not hold up well. The movement was towards an encased stiffener in the flap like we use now. We do have better plastics now and we have learned a bit about sewing and setting grommets since then. We might be able to eliminate the fabric on top of the plastic stiffener.

I think their is a fundamental problem with the current pin design. And I actually do think that that fraction of an inch change that could make the pin want to turn on edge rather then turn down has value. I think their are other problems as well but that this one is real.

Lee

I think you need to work on your drawing skills but that's the basic idea. See the drawings at the top of the post. The biggest trade off I see is that it tends to make the pin taller when on edge. Where this might be an issue is under a very tight hard plastic flap like on some skydiving rigs where in theory I might make it difficult for the pin to rotate. On the other hand a flap like that tends to directionalize the force side ways. I think that's part of the reason that you don't see this come up a lot in skydiving. But for very good reasons we have very soft, open, unrestrictive cover flaps and a lot of our deployments are sub terminal. Even with large PC's we are still working with lower snatch forces on some of these jumps.

Lee

I'm trying to think about how a spiraling torked pin might work. I'll have to think on that but the obvious thing that comes to mind is that it would not lay clean and flat. I don't now I'd have to think on it.

Lee

Yea, the pin would not lay completely flat like it can currently. I don't feel this is a big deal on a BASE rig as the containers are -generally- not as tight as current skydive rigs.

However, in practice, there is a potential concern with this as it will introduce some additional friction depending on rig design, but I'm looking at it as an exercise in maximising pin extraction without considering interactions with rig design at this point...

You wouldn't want to go as extreme as a spiral, just a bit of an off axis bend on the ring end, like maybe 30-45°.

I'll see if I can dig up some old pins and demonstrate what I mean.

That's the difference between your CAD and my MSPaint haha ;) But you understood. I agree it would be taller stood up but I also agree that shouldn't be an issue in SD as the flap is not normally closed.

I think that when the bridle attachment slips to the wrong side of the eye (which is where I am assuming the problem manifests) then your design that sits on the circle boundary would produce zero righting force, and your design that has the back edge of the eye outside the boundary could produce a negative righting force (both scenarios maximise when the pin is fully home and not primed).

My awful picture suggests that offsetting the backside of the eye from the boundary and inside the circle would always produce a righting force.

Caveat: All this has been carefully calculated using tools similar to that which I created the picture with, aka alcohol fuelled brain thunking!

Well done Lee! Funny I worked on the same thing not long ago - and inevitably reached the same conclusions.

Picture attached :

- two different ways to prevent the locking configuration with classic pins

- prototypes of the new geometry, and a nice way to stitch it to the bridle (it can still fold nicely sideways, but with a tendency to go back perpendicularly to the bridle)

- final product, first batch

The new pins come forged in marine grade stainless steel, and will be available very soon everywhere!

What if the pin is pulled straight down (towards BOC), parallel to container or even slightly "down", like in overrotated front loop - headdown or even slightly past headdown? (also, in wingsuit deployment after a nice flare PC can pull horizontally or even slighly down) The new design will have the pin arc "rise" (away from grommet) much steeper, thus trying to pull the loop out, instead of sliding out of it, and increase tension, possibly even locking.

Here's a little illustration.



Also, how is the resistance to pulling the eye through the loop?

Just trying to think of various "what if's"... I applaud your efforts, Lee and Lucifer. We need innovators!

In that case the pin will lay flat on its side..

Their is some thing to what you're saying but I don't think your drawing is very accurate. The pin is going to be held flat against the grommet where it passes through the loop. So the force in a case like this will always be sliding the pin horizontally through the loop. Their is a leverage issue. It happens as the loop slides along the pin and the ring rises higher and higher. The pin starts to try to leverage the loop out of the flap increasing the force against the grommet. this is going to be the case with any curved pin.

A better way to think about this is the amount of arch in the pin. I am not set up to draw on this computer, but think of a line from the center point of the ring to what ever point on the pin that it passes through the loop. Loop at the angle between this line and the tangent to the arch of the pin at that point. It determines how much of the force is acting to slide the pin out of the loop and how much is just pulling on the loop. This is the case in any orientation. Whether you are pulling straight down like you describe. Even if the pin stays horizontal. Or if you are pulling straight out with the pin rotated up. Think of the most extreme case. A pin with a 180 degree arch. By the time that you get to the end it's acting like a hook with no force trying to slide the pin out at all.

This is a fundamental question in the geometry of the design. How much arch you want in the pin. It feeds in to the radius of that arch and how long your pin can be.

The other end of the spectrum is when the pin is fully seated. At that point arch is your friend. It lets the pin start to slide out. The more degrees of arch along the pin between the ring and the loop at that point the better. Best at 90 degrees. Again think about the opposite scenario. A pin with virtually no arch. A straight pin with 0 degrees of arch. It doesn't want to move at all.

So like all designs their are trade offs. Their are compromises between how far you want to inset the ring inside the arch between rotation and pin height. Their are compromises between ring location and amount of arch, radius and pin length.

I actually tried to write this up better with drawing in an earlier thread but I have no clue where it is.

This is why I'm trying to open up this discussion and mailing pins to people all over the world. One of the nice things about having the pins cut like this is that we can actually play with all kinds of geometry or designs. Call those guys up, send them a drawing and they will cut you some pins. I got two dozen of two different designs for basically $5.00 a peace. You could send them 50 different drawings and get fifty different pins at still $5.00 a peace. Ultimately if we can all settle on a design, and if their is enough interest, we can have dies made which would drop the cost down into the $0.20 range. But that would probable require a fairly large commitment from every one to make it work out financially.

Lee

Out standing! Does this mean that I can pull the cutaway handle and bail on this?

I think you mean that they are stamped. I'm not sure that forged is quite the right term. What did your tooling cost you? And what are you going to have to charge per pin to recupe it?

If you're tooling is already made then I guess you're locked into your design. It's a little hard to read your drawing but it looks like the first one of mine. Are you pretty hapy with it?

If you are fully invested in your tooling and every one is happy with your design then I'm perfectly happy to declare you the king of pins. Having looked at the numbers I can say that we need to throw all of our effort behind one manufacturer to make this work. And I am perfectly happy for that person to be you. If every one gets behind this I think you can recupe your money but I don't think you will ever get rich off this.

Lee

Even the classic pin design is quite "scorpiontail"-happy when bridle is pulled in past-headdown or high-perf wingsuit manner. The new designs seem to be even more so. It all depends on amount of tension on the loop and firmness of the packjob - in skydiving scenario, where pin tension is high and packjob is like a brick, the pin will have tendency to lie flat during extraction, while in BASE where pin tension is light or even negligible and packjob is easily pushed in, the pin can scorpiontail just like that. In this case, full 90 degree arc can lock the pin. The arc should be less than 90 degrees minus arctangent of the highest possible coefficient of friction between used pin and gritty loop.

Also, it's one thing to experiment by pulling the bridle by hand, it's totally another when bridle yanks the pin at nearly terminal speed (~50m/s) and the whole pin rotation and extraction takes something like half a millisecond. Inertial effects can play significant role as the pin can experience accelerations of hundreds, if not thousands, of g's. To fully understand what's happening we need to film hundreds of real-life extractions with a high speed 10000fps camera.

Who invented the classic curved pin? Are they still alive? It would be interesting to learn their thought process. The more I think about it, the more it seems that the classic pin is a very thoughtful design that foresaw long ago the problems we're talking about now. And it has a huge advantage of hundreds of millions of real life activations, with very few problems, most of which are user errors or container design flaw. Maybe, "if it ain't broken, don't fix it"?

It was some old guy in Florida with a very long beard. I think his name is Bob or something. I have a message from him from a few months ago about his development process and I'll post that as soon as he gives me the okay.

It was Bill Booth. As I recall the story goes that when he invented the throw out PC he first used a straight pin. That led to some PC in tow scenarios so he developed the simple and highly-effective solution of the curved pin.

I wouldn't be surprised if those PC in tows curved the pins for him.

RE: Bearded One

I once heard that Bill Booth keeps a note pad by his bed
and often wakes up with great ideas then jots them down.

https://en.wikipedia.org/wiki/Bill_Booth


RE: Spring to Leg Pouch to BOC

Yes the throw out was designed and tested in Florida.
On the way from a DZ in winter a years back I stopped
to buy firewood, I had already drank some firewater, so
I asked the only other guy there loading wood if he was
interested in 'jumping out of a perfectly good plane'...
come to find out it was the guy who did the first
throw-out test jumps, super cool older dude.

We finished our chat, I was done loading wood, went in
to pay for mine and paid for his. That guy moved to WY
but still calls me every couple years to thank me again
and ask me about how my adventures jumping.


RE: Manufacturing Costs

Rigger Lee is right about "Economies of Scale" which is
the economic concept that as production increases the
price per unit usually goes down sharply, this is from
spreading the fixed costs like tooling over many units.


RE: Buying Pins

I have been getting mine from Paragear but don't
have the need for hundreds of them but would
love to get them for $1.75 instead of $2.20 so
is anyone here interested in a joint order?

http://www.paragear.com/...ESS-STEEL-CURVED-PIN


RE: New Design(s)

I have used curved, straight, vinyl covered cable, etc.
They all have worked as expected and intended hence
I am doubtful of the gains from changing but do like
thinking and discussing these ideas, thanks fellas.

You know, I was told the first throw outs weren't leg strap but chest strap throw outs... this led to too many pc in tows with people routing the strap/pc wrong (only in the testing phase I hope?) so the leg strap pouch was chosen for simplicity...then the boc for more simplicity.

 

That's hilarious...

hangdiver

Bill never got back to me, but I don't think he'll mind me re-posting his message here, given that I was asking him about it for R&D on a new pin.


I think he probably had a lot of foresight and put a fair amount of thought into the design, but he wasn't operating in the environment we are, so I don't think trying to improve on his design is ill-conceived (even if it is cost ineffective).

Hey buddy :) you've seen the yellow cable pins right? The Acrobat comes (came?) with them as an option (russian container). The containers look just like every other 2-pin basically, with yellow cable for pins, and I can't see why that isn't a nice idea except for a couple of really nasty complications involving kinks in the wire or it getting trapped in the grommet. I think there could be some sort of evolution of this idea, but it would take a better material or something... it would need to be replaced often too I imagine. I did hear someone was using reserve elastic loop for his pin loops in table testing (maybe real testing?), but that idea came to a halt because the pin head could get trapped or other terrible complications or something like that.

Back on topic with the curved pin head pins: I once met a guy at the bridge who always made his pins smile "because that was what he was told." The pin tab was on the back of the pin head, so I told him my opinion was to keep the pin tab on the inner side of the curve to stand the pin up, just in friendly discussion. I don't want to go telling anyone else how to jump or what to do, just I like sharing information so everyone gets to make informed decisions of their own. His response was, "I get the idea, but I don't wanna go changing what has worked for me so far." All of his maybe 20 jumps had probably been done with the pin tab having to travel around the pin head as it pulled the pins, and it worked just fine. It's crazy that the system works, even with non-ideal configurations. I'm excited that the new pins will work to combat these kinds of issues, foolproofing the system some and probably reducing the minuscule chance of hangup to an even lower percentage. I also think it's nice that the total diameter of the pin (straight line from head to tail across the pin's greatest length) will be smaller if the head is curved in slightly. I've seen lots of hangups become more probable (in table tests and ground pulls) because of the head getting snagged under flaps or pinching in the tuck flap. Reducing their total length may eliminate some of this error/snag potential. I wonder if it would be worthwhile to reduce the length of the tail (by a 1/8 inch amount or less) in order to combat this even further... I'm sure it would only be a miniscule amount in order to make sure the head can be left sticking out far enough when the pin is seated in order to stand up properly. I don't think you ever want the closing loops seated all the way up to the pin head... it makes the pin have to work harder to stand up... Aaaaanyway, I just got carried away talking about curved pins and I'm having too much fun thinking about it. Feel free to offer commentary and I'll go to sleep now and shut up. Peace.
P.s. come jump soon!

I realize I'm digging up a 3 year old thread haha, but any thoughts on a ball and socket pin construction? Seems like it would address the issue of the bridle pulling the wrong side of the eye and forcing the pin into the flap by allowing the pin to take the path of least resistance, regardless of pull direction.

How would you construct the attachment between the pin and the bridle?

Would the "socket" be part of the bridle?

My initial though was a welded eyelet similar to the one on a typical pin.