Author Topic: Portaledge Suspension Design  (Read 538 times)

Aideerclimbing

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Portaledge Suspension Design
« on: July 05, 2020, 04:35:32 AM »
I have been thinking a lot about portaledge suspension design and want to discuss some aspects of it.
Asymmetric hang
In his book Higher education Andy K describes a way of hanging a ledge asymmetric, and I've always wondered, is this possible, or is it Big Wall Theory!? In my world a portaledge have to hang symmetric if you hang it from one point and want the bed to be horizontal, you can never get the bed horizontal in a asymmetric setup, unless you support it from more than one point, for example short side against a corner. Can someone explain how that asymmetric hang can work from just one point?

The 6th suspension point
I'm a big fan of 4 point suspension and have been thinking about the use of a middle outside suspension point on a portaledge without spreader bar. The only use for this suspension point I can think of is to hang your stove from.
The meaning with this strap must be to keep the outside tube as horizontal as possible when it flex down by your weight. To achieve this you have to tighten this strap, and then you also force the outside tube inwards, making it to flex more inwards than it will do without this suspension point. It works if you have spreader bar on your portaledge, but without it you also can omit the 6th strap, unless you don't need it to hang your stove from...

Length of suspension
John Middendorf have been very generous with information about how to design a portaledge, but one aspect I have not seen so much about is the sizing of the suspension; how high above the bed should the connection point be?
If it is to low you get to small space inside the fly and you get high force on the suspension. If it is to high you add size and weight of fly and suspension, and perhaps also make it more complicated to set up, or is there more aspects? Is it the design of the fly, or rather width of fabric, that states the size of suspension?

And a question @John Middendorf
I have used sailcloth for the bed on my portaledge and this gives a pretty flat bed. It also gives pretty high forces on the tubes, which made me think of placing warp and weft in an angle to the tubes, which should give a less flat bed, and also less force on the tubes. When you made calculation for the tubes on the D4 portaledge, how did you think about the stretch in the bed fabric? You give very detailed advice about tube size related to bed size, but does this not depend on how flat the bed is, or did you make other assumptions?

/Olle

Failfalling

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Re: Portaledge Suspension Design
« Reply #1 on: July 06, 2020, 04:47:56 PM »
Quote
In my world a portaledge have to hang symmetric if you hang it from one point and want the bed to be horizontal, you can never get the bed horizontal in a asymmetric setup, unless you support it from more than one point, for example short side against a corner. Can someone explain how that asymmetric hang can work from just one point?

For extreme  off center placement of the ledge a little extra work is involved.  Depending upon if one has a portaledge with quick links connecting the straps to the frame (and also the reason why we want to check these things and make sure that they are finger tight and finger loosening before heading out on the wall) then to achieve an asymmetric hang where the ledge is off to the side of the anchor, unscrew the quick links on the far sides of the ledge from the anchor and extend them with a sling or draw. Then adjust using the tensioning buckles as normal.

Deuce

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Re: Portaledge Suspension Design
« Reply #2 on: July 11, 2020, 02:07:23 PM »
Hi Olle

Just noticed your post.  Quick reply...

Asymmetrical hangs put excessive loads on a portaledge frame and are to be avoided.

 The new Delta2p design has a short “wheelbase” (The part that rests against wall), so will be better for places where you would like to hang a ledge in an awkward locale.

Suspension points are key to success of a frame design.  Consider beam loading calculations from basic engineering texts.  To analyse a whole frame, I use FEA (Autodesk Fusion).  I can help check a frame/suspension design.  I have moved away from fabric suspended beds (with fins), and now think fully frame suspended is the best way, but both have advantages/differences in distribution of load.

Length of suspension has to do more with ergonomics (head room) and practical aspects like fabric widths.  Longer is better of course for frame stress.  I try to optimize, I generally design at least 65” from frame to suspension point.

Tension of bed does make a difference, but I assume distributed load.  My new Delta2p system allows much more evenly distributed load, as the side to side tension as well as end to end tension are accomplished with just one buckle thanks to the delta shape.

Happy to help collaborate on ledge design anytime, especially if you want to make a cool Olle/D4 ledge for the European market!

Cheers

« Last Edit: July 11, 2020, 02:21:28 PM by Deuce »

Deuce

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Re: Portaledge Suspension Design
« Reply #3 on: July 11, 2020, 02:16:51 PM »
By the way, this Kind of  thread perhaps better here In the design section:  http://bigwallsforum.com/index.php/board,4.0.html

Not sure if this bigwalls forum will be used a lot for general info, as the facebook one that MungeClimber and I set up seems to be the main big wall chat spot now (i am not on FB now, however).  But certainly the design info and feedback i will archive and save, like I did with the old big walls forum, which had tons of good info And tips from folks like Mark Hudon.  (And will definitely save good info posts like the treasures from Patrick K)!



« Last Edit: July 11, 2020, 02:28:55 PM by Deuce »

Aideerclimbing

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Re: Portaledge Suspension Design
« Reply #4 on: July 13, 2020, 12:17:45 PM »

Thank you for your answers!

By the way, this Kind of  thread perhaps better here In the design section:  http://bigwallsforum.com/index.php/board,4.0.html


I perceived it as a section for D4 design...


Asymmetrical hangs put excessive loads on a portaledge frame and are to be avoided.


Thats's true, but just if the bed are horisontal; how do you achieve that with just one suspension point?


For extreme  off center placement of the ledge a little extra work is involved.  Depending upon if one has a portaledge with quick links connecting the straps to the frame (and also the reason why we want to check these things and make sure that they are finger tight and finger loosening before heading out on the wall) then to achieve an asymmetric hang where the ledge is off to the side of the anchor, unscrew the quick links on the far sides of the ledge from the anchor and extend them with a sling or draw. Then adjust using the tensioning buckles as normal.

If you do like you describe, with a portaledge hanging off center from one point, it will slope downwards on the side with longest straps, eh? How do you avoid that?

Thanks :)

Failfalling

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Re: Portaledge Suspension Design
« Reply #5 on: July 13, 2020, 02:04:09 PM »
When doing an asymmetric hang, you have to set the straps with weight in mind so strap length when tensioning requires you to be in the ledge, figure out the adjustment, make adjustment, stand in ledge, continue adjust as needed. This also needs to be done with the object that will be supporting the shorter side by the anchors in place as no ledge will accept an asymmetric hang if there's nothing forcing the asymmetry and will instead slide in the direction that will center the anchor over the ledge. This is the reason why asymmetric hangs is only something done when you have to.

Also you don't need to bold "one point" as all portaledge hangs are from one point.

Failfalling

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Re: Portaledge Suspension Design
« Reply #6 on: July 13, 2020, 02:11:33 PM »
Quote
Thats's true, but just if the bed are horisontal; how do you achieve that with just one suspension point?

All asymmetric hangs use something to support the shorter side, that's the reason you're doing an asymmetric hang, because there's some reason why a centered hang will not work. The issue might be the image Andy has in the book  under the first "4 Bolt Anchor" showing a ledge on the left without anything supporting the right side. This image is because it's not an extreme side hang and so the tension of the straps can support the ledge being flat but it still would slide a little bit. If you look at the other photos where the hang is extreme off to the side of the ledge, both of these are using the other ledge to support the off center nature of the hang.

Aideerclimbing

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Re: Portaledge Suspension Design
« Reply #7 on: August 02, 2020, 03:07:42 AM »


Quote
Thats's true, but just if the bed are horisontal; how do you achieve that with just one suspension point?

All asymmetric hangs use something to support the shorter side, that's the reason you're doing an asymmetric hang, because there's some reason why a centered hang will not work. The issue might be the image Andy has in the book  under the first "4 Bolt Anchor" showing a ledge on the left without anything supporting the right side. This image is because it's not an extreme side hang and so the tension of the straps can support the ledge being flat but it still would slide a little bit. If you look at the other photos where the hang is extreme off to the side of the ledge, both of these are using the other ledge to support the off center nature of the hang.


When doing an asymmetric hang, you have to set the straps with weight in mind so strap length when tensioning requires you to be in the ledge, figure out the adjustment, make adjustment, stand in ledge, continue adjust as needed. This also needs to be done with the object that will be supporting the shorter side by the anchors in place as no ledge will accept an asymmetric hang if there's nothing forcing the asymmetry and will instead slide in the direction that will center the anchor over the ledge. This is the reason why asymmetric hangs is only something done when you have to.

Also you don't need to bold "one point" as all portaledge hangs are from one point.


Thank you for your patience, Failfalling! Your answers explain a lot to me.