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Moof
Big Wall climber
Orygun
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Mar 26, 2017 - 01:16pm PT
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Duece,
Early on you implied something other than 6061-t6. I have never been able to find small suppliers for 7075 tubing, did you get better luck, or figure something else out?
I'm looking to make a corner block ledge for personal use with your hybrid pole design for kicks (got to do something with all my corner blocks...).
Thanks!
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deuce4
climber
Hobart, Australia
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Topic Author's Reply - Mar 27, 2017 - 10:22am PT
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No, just using 6061-t6, really the ideal material for portaledges. 7075 would indeed be stronger, but not necessarily more rigid as hopefully explained in this thread. But the 6061-t6 is strong enough, and provides the rigidity with my redesign of the frame for the larger "full-size" ledge platform (reminds me, to have a party soon to load up one of my prototypes with six or seven people, then everyone jump up and down until something breaks--the obligatory "Everyman' test!).
As mentioned, i am playing with carbon fiber, but the frame itself is really only about 1/3 of the total portaledge weight, and though carbon would indeed lighten the ledge a couple pounds, the cost is still way too much. I also really don't think the carbon would be as durable in a big wall setting, but still, would like to make one or two for that key expedition to Jannu!
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Moof
Big Wall climber
Orygun
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Mar 27, 2017 - 03:06pm PT
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Thanks for the clarification John.
I overthought my carbon frame for sure, and threw away a large portion of my weight savings on excessive reinforcement. What is hard to discern until you start shelling out $100's for carbon tubes is that most of the poles are made almost entirely of unidirectional fibers with just a single outer layer of woven fabric mostly for aesthetics. Crush resistance is not great as a result, and I feared a sharp nubbin creating the start of failure. I also feared the corners crushing the ends if things torqued funny under load. I think your new invention is the clear way to go.
Using CF as the internal double butting on the sides probably is where the most bang for the buck of stiffness and weight savings, but would add absolutely zero to the look of your design. CF sadly has poorly controlled OD, and the ID tends to be right at size, so it becomes necessary to either sand the CF, or machine down the aluminum to make joints with acceptable clearance. I am really curious to see what you come up with, your string of recent ideas is innovating where I have dumbly assumed things were pretty well rung out.
One follow up on the now obsolete corner blocks. The A5 design always had the short end poles plug into the corner blocks that were permanently affixed to the the side poles rather than the other way around. I have always been perplexed by this choice. What is the wisdom of that choice? What bad stuff happens if the corner blocks were instead affixed to the end poles?
Thanks again!
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deuce4
climber
Hobart, Australia
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Topic Author's Reply - Mar 27, 2017 - 04:35pm PT
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Good point Moof. Might just be another carryover of the "old" way of doing things which was never really been re-thought (it does amaze me more and more, as I develop this new design, that the "old" way has been the status quo for the past 20 years with the main manufacturers, as everytime I actually use or make a new one, new and better ways pop up naturally!)
Anyhow, probably the reason I made it a right angle corner is that the original ledges were made before we invented the bed tensioner concept. So with a tight bed with no other adjustability in the tension, it was easier to lever the corners onto the end tubes, rather than the other way around. I think I did make a round cross section corner at one point that I think set up the alternate way you describe, but didn't like the way the end tube fit into the perpendicular hole drilled into the side of the round cross section corner piece. Not sure if that is clear, never mind, I can try to find my old sketches perhaps, but in any case, with bed tensioning, perhaps the corners fixed on the end tubes and fitting on the long tubes would be a better way to go.
Cheers
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cadl
Trad climber
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Mar 27, 2017 - 06:41pm PT
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John, any issues for the triangle fabric suspension points if the anchor is off-center? For example if the belay is in a dihedral and the anchor bolts are less than 3 feet from the dihedral corner, the straps will be shorter on one side to compensate for the off-center anchor. Seems like this would create stress points on the triangle fabric attach points.
Thanks for your latest project and continuing contributions to the "state of the art"! Much appreciate by many.
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jeff constine
Trad climber
Ao Namao
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Mar 27, 2017 - 06:55pm PT
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Spreader bars have uses!
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deuce4
climber
Hobart, Australia
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Topic Author's Reply - Mar 27, 2017 - 07:08pm PT
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Hi Cael
The way I have designed the four/eight point suspension is that a majority of the load is on the webbing connections (2 per fin) rather than the fabric, and they equalize somewhat when, as you say, there is an off-center loading taking place. Due to the greater stretch of the fabric, the fabric simply creases to adjust in such as case. The benefit of the fabric is that is does actually take part of the load in a more distributed way.
It was indeed mostly theory for me, too, until I actually tried it on actual rock with off center loadings, plus I have played with it in my gym with most extreme off-center loadings, and the equalising concept does seem to redistribute forces as conceived in this type of situation.
If there are any engineers out there, I actually wouldn't mind a second opinion on the statics analysis. Here's a start (as all good things begin on the back of an envelope, or extra white space in a paper in this case...):
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Moof
Big Wall climber
Orygun
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Mar 30, 2017 - 03:48pm PT
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I'll bite on the 4/8 point suspension. Still working on the math a little, but I'll start with a few assumptions necessary to get started.
1) I assuming that A and B are fixed locations so as to distribute the load over the frame/bed kind of evenly.
2) Further I am assuming that ideally the tension on each of the 8 points is desired to be balanced (force on the bed at A and B equal). Having just a loop guarantees this due to the quick link acting as a pulley for this kind of analysis. This basically means you have to solve for the resulting angles rather than choose them, since things auto equalize. Should I NOT assume the real world pulley action and solve per your picture? I'll keep going with the pulley action for now.
3) The free variable is then the length of the strap connecting A and B. If it is very long you get 8 straps with zero force multiplication, but that is dumb. Make the strap short and there is huge force multiplication. So a good engineer needs to set some target to trade off excess stress trying to rip apart the bed and extra weight from having 8 full length straps. I am choosing a 20% force increase to back calculate the strap length and resulting angles, and will play with this when I have the math figured out..
I am further only going to look at the outside straps where the force is the highest, and assuming a 4' wide ledge body and 5' distance from the anchor down to the bed elevation to be able to calculate all this. I am going to put A 1' from the end pole and B 1' from that (3' in between B to B for a 7' ledge). Reasonable? I am probably missing an obvious simplification as to what I should be solving for, but I am an EE and my statics/physics has about 23 years of rust on it.
Green paper to follow...
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deuce4
climber
Hobart, Australia
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Topic Author's Reply - Mar 30, 2017 - 04:42pm PT
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Moof, you are on the right track, but in addition to stability, I designed the fins to support more of the middle as well. I can send you the specs I created, but would be interested to see what angles you determine first.
Yes, you can assume that the load is distributed equally between each of the two straps in each fin--though of course the fabric does take some of the load in a distributed way (for the better), I ignored this in my analysis. But real-world testing showed this to be largely the case--also when the ledge is set up in a corner, the load does shift a bit so the ledge is better optimally supported by the eight main points of connection--you will start to see how once you do some engineering statics, as the angles change.
Cool, looking forward to seeing what you come up with.
Bottom line, I tested them on a real wall, and the idea works!
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Moof
Big Wall climber
Orygun
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Mar 30, 2017 - 04:59pm PT
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Yep, the vertical fibers of the fabric help spread out the load for sure, but that is well beyond first order statics that I can hope to tackle. If you want to get pedantic the fins should be catenaries (asymmetric ones at that) to provide equal tension along the length of the fabric for a point load at the apex. But at that point you are jumping the shark pretty badly.
I'm looking forward to getting an hour or so of tinkering time this evening after kiddo's bedtime to pencil it all out better.
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deuce4
climber
Hobart, Australia
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Topic Author's Reply - Mar 30, 2017 - 05:45pm PT
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Interesting you bring up catenaries--my first prototype I did indeed design it with a catenary, but it turns out the longitudinal stiffness of the webbing on the edges prevents the edge from taking the load like a catenary--hence the straight lines on the support fins. The interior shark fins, however, still are designed with catenaries.
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Todd Eastman
climber
Bellingham, WA
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Mar 30, 2017 - 08:44pm PT
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Wind's shifting, getting smoke in my eyes...
... great campfire!
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Moof
Big Wall climber
Orygun
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Mar 30, 2017 - 09:17pm PT
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So I get to the angles pretty easy.
Since you can assume equal force on the two straps at A and B, the angle relative to the main strap is also equal. The force multiplier is 1/cos(180-alpha), which works out to 33.6 degrees for a 1.2:1 force multiplier, or 67 degrees maximum total angle of the fin. I am guess you rounded to 60 degrees?
The angle of the main strap works out to about 21 degrees, so the would for out to an angle of 9 degrees off vertical at B, 51 degrees from vertical (39 degrees from the bed) at A if using 60 degrees for the fin angle.
Sound about right?
Still need to figure out the height of the fin, but my eyes are trying to close on me.
Unless you wrapped the webbing around the fin edge taco style before stitching, I don't know how to get around the stiffness to get a catenary, but again, that is just overkill to begin with.
Edit:
Looking at the pics it looks like you chose 45 degrees, which would put the B point within rounding error of 0 degrees, making much more sense than 60 degrees. Force increase would be just 1/cos(22.5)=1.08, or less than 10%. Ideally the fabric would be cut on a 22.5 degree angle, but that is pretty wasteful for a marginal increase in load spreading. My in-process Ghetto4 ledge will shamelessly copy this approach, though I am aiming to only put bed tensioners on one end to simplify/lighten.
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D-Rail
Trad climber
Calaveras
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Mar 30, 2017 - 09:17pm PT
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Looks amazing Deuce!
I have an Alpine Double that is well traveled. It is probably from about the same vintage as your Jumars. Months of detailed work to update the portaledge and you still roll with the old trusties?
Keep it coming. This is great stuff!
Daryl
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deuce4
climber
Hobart, Australia
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Topic Author's Reply - Mar 31, 2017 - 06:42pm PT
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Last day to order your Expedition D4 Portaledge on Kickstarter!
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deuce4
climber
Hobart, Australia
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Topic Author's Reply - Apr 1, 2017 - 07:58pm PT
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The new D4 Zippered Door Design has gone from concept (imagined while climbing Ozymandias) to first functional prototype in a couple weeks! This new door and vent design will be sent out to Twid Turner this week for full conditions testing on a big wall in Alaska.
There's only 12 hours left to order a D4. I have been open with the design process so all can see how the innovation has progressed, and if history is any guide, these new concepts will be widely copied, but the original is always the best! Thanks for your interest! Cheers, John Middendorf.
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deuce4
climber
Hobart, Australia
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Topic Author's Reply - Apr 2, 2017 - 02:12pm PT
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The Kickstarter has successfully ended at 150% of goal! Many thanks to everyone who supported this reinvention of the modern expedition Portaledge. We will continue our product testing and begin production in the coming months.
We have already gotten new requests for orders for the D4 portaledge. Of course we will fulfil our Kickstarter orders first, and will set up a waiting list for future orders. All Kickstarter orders are expected to ship this year. Thanks again to all!
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Moof
Big Wall climber
Orygun
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Got inspired for my own hobby ledge. Ordered up the crap and I am now assembling.
First step was to cut most of the tubing (one piece is still in transit). Never used a tubing cutter on aluminum, so much easier, cleaner, and nicer than hack saw and files. Who knew?! Next step was to start glueing things up (less eorror prone than rivets for me).
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BLUEBLOCR
Social climber
joshua tree
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NICE Moof!
On those glued up ends, looks like you got female receptors waiting for male tube insertions?!
I was jus wondering how might a male stub(maybe an inch long) would be comparably in strength, and set-up?
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