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Load cell testing: How much force does a bounce test produce?
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USnavy


Jun 12, 2012, 8:27 PM
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Load cell testing: How much force does a bounce test produce?
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After reading the thread from mp.com about bounce testing, I got a bit curious as to how much force a bounce test in the real world actually produces. Two members in that thread said they bounced around in a sling, or dropped a weight in a sling, and got an impact force of around 4 kN. That seemed excessively high to me, especially considering Metolius quotes a hard bounce test at 2 kN. So I decided to replicate real-world aid bounce tests and see how much force they produce. This testing is non-conclusive; it is simply for fun. It is, more or less, a test of how much force I will inflict on pieces I test, rather than an absolute statement regarding bounce testing forces.

The point of this thread was to be as real world as possible. So I conducted this test in Yosemite, on an aid route, on aid placements (an A0 bolt ladder). I conducted the tests using all the gear I normally use on a wall, and in the exact manner I would test a placement on a wall. In every case, I tested the placement quite aggressively Ė I didnít hold back.

-I used a 5,000 lb load cell with a rated accuracy of .02%, and a computer driven strain gauge analyzer that sampled the load cell at 500Hz.

-I weigh 158 lbs

-On the tests I was wearing a rack, the rack weighed 17.5 lbs

-I was using Yates adjustable daisy chains (nylon)

-I was using Metolius wall step 8-step aiders

(1) I conducted six different tests. The first set shows an aider bounce test versus a daisy bounce test, but without a rack.
(2) The second set is the same as the first, but with a [nearly] full El Cap clean aid rack (which weighs 17.5 lbs).
(3) The last set was an absolute worst possible case scenario where I was hanging only from the load cell and no part of my body was touching the lower piece. The first test in the series showed an aggressive daisy test. The second test shows an excessively aggressive daisy test where I was literally slamming myself down onto my daisy as hard as possible. This test was more aggressive than any bounce test I would use on a wall. I was wearing the rack in both tests in this series.













The absolute highest force incurred on the top piece occurred during the last test (the excessively aggressive test,) and racked in 681 lbf. or 3.03 kN. However, that test was synthetically extreme. The highest force incurred during a realistic aggressive bounce test was 643 lbf. or 2.86 kN. But again, I was hanging solely from the piece which is not realistic in a wall climbing scenario. So the highest force incurred using an aggressive daisy bounce test that is realistic to a wall climbing scenario is 618 lbf. or 2.75 kN.

So my testing seems to imply that a hard bounce test in your aiders will produce 400-550 lbf and a hard bounce test directly on your daisy chains will produce 500-600 lbf. I find it unlikely that I would be able to produce a higher impact force using conventional nylon pocketed daisy chains simply because I was bouncing around hard enough that if I were fified into a pocketed daisy, the aggressive bouncing would likely result in the fifi coming out of the pocket. However, it is possible that using a Dyneema daisy chain would result in a higher impact force; maybe I can test that in the future.


majid_sabet


Jun 12, 2012, 8:51 PM
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Re: [USnavy] Load cell testing: How much force does a bounce test produce? [In reply to]
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brand new gear like never been on anything yet

















not to forget the two dangerous self adjusting daisy on the aiders


moose_droppings


Jun 12, 2012, 10:54 PM
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Re: [USnavy] Load cell testing: How much force does a bounce test produce? [In reply to]
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USnavy wrote:
After reading the thread from mp.com about bounce testing, I got a bit curious as to how much force a bounce test in the real world actually produces. Two members in that thread said they bounced around in a sling, or dropped a weight in a sling, and got an impact force of around 4 kN. That seemed excessively high to me, especially considering Metolius quotes a hard bounce test at 2 kN. So I decided to replicate real-world aid bounce tests and see how much force they produce. This testing is non-conclusive; it is simply for fun. It is, more or less, a test of how much force I will inflict on pieces I test, rather than an absolute statement regarding bounce testing forces.

The point of this thread was to be as real world as possible. So I conducted this test in Yosemite, on an aid route, on aid placements (an A0 bolt ladder). I conducted the tests using all the gear I normally use on a wall, and in the exact manner I would test a placement on a wall. In every case, I tested the placement quite aggressively Ė I didnít hold back.

-I used a 5,000 lb load cell with a rated accuracy of .02%, and a computer driven strain gauge analyzer that sampled the load cell at 500Hz.

-I weigh 158 lbs

-On the tests I was wearing a rack, the rack weighed 17.5 lbs

-I was using Yates adjustable daisy chains (nylon)

-I was using Metolius wall step 8-step aiders

(1) I conducted six different tests. The first set shows an aider bounce test versus a daisy bounce test, but without a rack.
(2) The second set is the same as the first, but with a [nearly] full El Cap clean aid rack (which weighs 17.5 lbs).
(3) The last set was an absolute worst possible case scenario where I was hanging only from the load cell and no part of my body was touching the lower piece. The first test in the series showed an aggressive daisy test. The second test shows an excessively aggressive daisy test where I was literally slamming myself down onto my daisy as hard as possible. This test was more aggressive than any bounce test I would use on a wall. I was wearing the rack in both tests in this series.

[img]http://img845.imageshack.us/img845/5060/bouncetest1.png[/img]

[img]http://img713.imageshack.us/img713/4073/bouncetest2.jpg[/img]

[img]http://img51.imageshack.us/img51/1306/bouncetest3.jpg[/img]

[img]http://img207.imageshack.us/img207/6531/1001471f.jpg[/img]

[img]http://img405.imageshack.us/img405/2579/1001475dj.jpg[/img]

[img]http://img69.imageshack.us/img69/7007/1001478q.jpg[/img]

The absolute highest force incurred on the top piece occurred during the last test (the excessively aggressive test,) and racked in 681 lbf. or 3.03 kN. However, that test was synthetically extreme. The highest force incurred during a realistic aggressive bounce test was 643 lbf. or 2.86 kN. But again, I was hanging solely from the piece which is not realistic in a wall climbing scenario. So the highest force incurred using an aggressive daisy bounce test that is realistic to a wall climbing scenario is 618 lbf. or 2.75 kN.

So my testing seems to imply that a hard bounce test in your aiders will produce 400-550 lbf and a hard bounce test directly on your daisy chains will produce 500-600 lbf. I find it unlikely that I would be able to produce a higher impact force using conventional nylon pocketed daisy chains simply because I was bouncing around hard enough that if I were fified into a pocketed daisy, the aggressive bouncing would likely result in the fifi coming out of the pocket. However, it is possible that using a Dyneema daisy chain would result in a higher impact force; maybe I can test that in the future.

Thanks for doing this.
I've heard all kinds of guesses as to how much someone can put on a piece bounce testing.


USnavy


Jun 12, 2012, 11:42 PM
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Re: [majid_sabet] Load cell testing: How much force does a bounce test produce? [In reply to]
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majid_sabet wrote:
brand new gear like never been on anything yet



not to forget the two dangerous self adjusting daisy on the aiders
Ugh not quite. That gear has seen many hundreds of pitches of climbing. However, if you would like to swap your brand new rack out with mine, I am down for that. As far as self-adjusting daisys go, no one makes self-adjusting anything, you have to adjust it yourself. And they are not dangerous, I have climbed hundreds of pitches of aid on them. They just have a short lifespan.


(This post was edited by USnavy on Jun 13, 2012, 12:54 AM)


Partner cracklover


Jun 14, 2012, 8:45 AM
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Re: [USnavy] Load cell testing: How much force does a bounce test produce? [In reply to]
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Nice! I tried, but could not get over 2KN bounce testing.* That's why I abandoned that method and switched to using a fuse.

GO

*Admittedly, I only weigh a little under 140.


amarius


Jun 14, 2012, 9:22 AM
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Re: [USnavy] Load cell testing: How much force does a bounce test produce? [In reply to]
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So, imagine a bit heavier person with heavier rack, maybe a water bottle or two, does exactly the same thing you did, and gets a reading of 3.52kN. Maybe load cell was off calibration, maybe it was a locally high gravity day, who knows.
That is one awkward number to say - three point five two.
Having been taught rounding rules somewhere along, they round it, and get 4kN
Voila, mystery solved ;)

Commentary a bit more to the point -
Comparing (No Rack/Daisy) roughly 600 with (Rack/Daisy) roughly 620
If your weight is 158lb, and the rack weighs in at 17.5, there should be roughly 10% difference in measured values when you put your full weight on the aid.


USnavy


Jun 14, 2012, 11:23 PM
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Re: [amarius] Load cell testing: How much force does a bounce test produce? [In reply to]
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amarius wrote:
So, imagine a bit heavier person with heavier rack, maybe a water bottle or two, does exactly the same thing you did, and gets a reading of 3.52kN. Maybe load cell was off calibration, maybe it was a locally high gravity day, who knows.
That is one awkward number to say - three point five two.
Having been taught rounding rules somewhere along, they round it, and get 4kN
Voila, mystery solved ;)

Commentary a bit more to the point -
Comparing (No Rack/Daisy) roughly 600 with (Rack/Daisy) roughly 620
If your weight is 158lb, and the rack weighs in at 17.5, there should be roughly 10% difference in measured values when you put your full weight on the aid.
I am confused, are you asking a question?

Anyway, there are a couple of reasons that could explain why adding extra weight did not produce a linear increase. First off, this was not a precision drop test, it was just me bouncing around, so although I tried to keep the tests as linear as possible, it is of course impossible for me to bounce equally as hard for every test. Second, I believe that although the rack may weigh 17 lbs, it does not actually increase my weight while bouncing around that much simply because while I am bouncing, the cams and nuts are flying all over the place. For the rack to truly increase my weight by 17 lbs, every cam and nut would have to drop down to its dead center resting position every time I am at the apex of my bounce. But I dont think that happens. When I reach the apex of my bounce, I think some of the cams are still flying through the air, not weighting my gear sling.


amarius


Jun 18, 2012, 9:17 AM
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Re: [USnavy] Load cell testing: How much force does a bounce test produce? [In reply to]
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Got it - your maxima are on the down bounce, not push-off.


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