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slacklinejoe
May 7, 2008, 8:34 PM
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I finally received my new digital load scale capable of measuring up to 10,000lbs that has a load cell light weight enough to incorporate into slackline systems without being a major pain. It has the usual peak and minimum load memories along with a lot of other features that I'm still figuring out.
What type of experiments would you guys like to see? I don't want to go straight into breaking stuff just yet, but if you want to know the load for a certain scenario post it up with your proposed experiment.
(This post was edited by slacklinejoe on May 7, 2008, 8:49 PM)
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AlexCV
May 7, 2008, 9:29 PM
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How about setting up a slackline, tensioning it and then take baseline measurements of "normal" loads so there's something to compare against later? I've no idea what's the load on the anchors when walking on the line. 500lbf? 1000?
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slacklinejoe
May 7, 2008, 9:33 PM
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Here are the key measurements that matter for the force when setting up the system:
Line length
Slacker Weight
Amount of sag in middle
That however will only give static loads. Dynamic stuff like surfing, jumps, leash falls etc is the variables we haven't be able to accurately assess yet.
For your proposed "normal" line what length, weight and sag would you want tested.
(This post was edited by slacklinejoe on May 7, 2008, 9:36 PM)
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AlexCV
May 7, 2008, 9:40 PM
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I honestly have no idea. I'd think to standardize on a single slacker weight of about 200lbs and make a table of the other variables with a range of reasonable values (whatever those may be, something like 20, 40 and 80ft for length? I've never even bother noticing sag which would probably be expressed as a ratio of length I would think.)
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slacklinejoe
May 7, 2008, 9:45 PM
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Generically I use the ratio of 6"- 10" of drop per 10 feet between the anchors for a typical line. Obviously you can go much tighter or much looser, but that's about the average.
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AlexCV
May 7, 2008, 9:50 PM
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Have you used polyester (does anyone?) webbing instead of Nylon? Since it has much lower stretch.
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slacklinejoe
May 7, 2008, 10:07 PM
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I've used polyester, polypropylene, nylon, spectra, dyneema and even hemp & cotton stuff for slacklines & slackropes. What I have learned is you can't always group them together as some polyester weaves stretch, others are near static. It's all in the weave and fiber type.
To address it past that I'd leave that up to people line Jim from Sterling as he's got a better grasp of the manufacturing process and what all you can do to condition the fibers for specific types of characteristics.
Material and weave type will make minor changes to the shock absorbing capabilities of the line, thus changing the peak load, but not the static load assuming the sag is the same.
Unless it is a very long line I can't see it making a large difference in the load results.
(This post was edited by slacklinejoe on May 7, 2008, 10:21 PM)
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sully264
May 8, 2008, 7:24 PM
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My vote would be for measuring the tension a ~30 foot line with ~2.5 ft of drop in the middle with a ~175 lb slacker. Some measurements such as tension with (a) nobody on the line, (b) just standing, (c) peak loads during jumping and surfing would be awesome to see.
Obviously they would be only ballpark figures because every line is different and everyone jumps/surfs differently and stuff, but I think the readings would be really useful none the less.
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slacklinejoe
May 8, 2008, 7:39 PM
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In case anyone is interested in replicating these tests on their own I plan on setting up with a couple slackers and using a weighted backpack to simulate other body weights. Teale my production manager will be handling the lightweight testing and I'll be handling the heavier simulations.
Unfortunately I think that A-frames may be requred for certain lengths that I simply cannot find the perfect span for on natural anchors. I expect that they will play havoc with my peak force measurements due to the increased dynamic anchoring involved. Even using a vehicle would reduce peak as it would rock with the movements. Does anyone have a more ideal suggestion for length testing?
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slacklinejoe
May 11, 2008, 1:42 AM
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As promised here is the first test results + a write up. Slackline Load Testing Results - Test 1
Right now I'm overdocumenting things but I figure if I want to evaluate things like the effects of humidity or wind that this information might come in useful later.
I was overall pleased with my results. There were a few instances where I had deviation from what my Slackline Force Calculator would have suggested but for most of the results it was within 3%. The highest difference I noted was 22% on the highest load tested. This could have been from the suprising rate of line relaxation. We could rig it and just watch the numbers drop as the line elongated. Most of the elongation was impercivable to the feet but the scale caught it in action.
Even waiting 5 minutes and re-tensioning it didn't do much to slow the pre-load decay. Even after a half hour of the same pre-load it still kept dropping after each dynamic load. Normally I'd say that the line was in question but this is normally what I call my "static" line that has been very abused and even used while being exposed to salt water. It suggests such a torn up old line has more elasticity than I'd have expected. I'll be sure to test other materials such as dyneema and see how the elasticity effects the numbers.
Expect more to come. Also additional suggestions to our testing setup are welcome. Right now I'm kind of winging it as I go.
(This post was edited by slacklinejoe on May 11, 2008, 1:46 AM)
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NJSlacker
May 11, 2008, 4:01 AM
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I'd like to see some tests on highline whippers, worst case scenario: falling almost straight down not catching the line. I'm not suggesting you do that yourself, it sounds painful, but maybe with a sandbag or something.
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slacklinejoe
May 11, 2008, 4:15 AM
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NJSlacker wrote: I'd like to see some tests on highline whippers, worst case scenario: falling almost straight down not catching the line. I'm not suggesting you do that yourself, it sounds painful, but maybe with a sandbag or something.
It's a bit worse than a lead fall but I figured I'd do that one for real. I'd rather a 6 foot leash fall than another 30 foot whipper. At least the webbing works as a bungie so it's not a FF1or FF2.
The hard part is going to be evaluating the different types of leashes people use. Some people use stuff like 2 strands of static rope. That will probably produce a higher peak load than the 9.8mm dynamic I use. I like the soft catch stuff even if I have to replace it more often, then again, it's not like I'm out there pushing the envelope on highlines.
If I do end up taking the falls you can bet I'll have major backups and I don't think I'll be up to the same rigorous testings at every possible point on lots of different lenghts. I'll probably do a couple on the most typical spots - bailing at the anchors, bailing in the middle. Probably one 50 footer and one 120 footer.
I guess in theory though it would be important to know the loads on the slacker as well for leashed falls, not just the anchors. That I do think I'll have to build a dummy for. My scale may be lighter than most but I don't wanna get nailed with a 8 lb chunk of metal during freefall.
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majid_sabet
May 19, 2008, 11:15 PM
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Joe
Have you ever broke a webbing during slacklining ?
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slacklinejoe
May 20, 2008, 12:25 AM
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Under these tests or in recent designs - no. In the field, yes.
Keep in mind my testing process used to be use and abuse a line as badly as I could for about six months to see what the weak points were. I took a lot more personal risk during the testing phases back then.
I've overloaded several lines to the point of breaking but they were lighter duty webbing. Failures like that were suprisingly uneventful as there was no hardware in the system.
I've had 2 full strength lines fail due to abrasion on traditional style setup slings and a couple due to friction melting.
I'm a big proponent of padding and ensuring there is no nylon-on-nylon abrasion as a result as one of the failures of the traditional designs left me on cruches for weeks.
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Go-Devil
May 27, 2008, 5:59 PM
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any idea of how much force comes on my line when i jump on it, like aerials 'n stuff.
my line is 20m (thts about 60foot i guess) and i weigh 70kg
(dunno how much lbs that is..., its a rather normal weight for a person )
and it sags a small foot in the middle when i stand on it.
i guess the forces are huge, but so far my setup holds it up so i'm just curious.... 
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slacklinejoe
May 27, 2008, 7:35 PM
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It depends on where you are on the line when you are jumping. Near the ends it will not be as large of a shock to the system (as my tests show) compared to just standing in the middle.
That being that case the load probably isn't as huge as you would think, but unless you actually measure your sag I can't recreate the experiment. From my testing I doubt your line only sags 1 foot in the middle at 20M, you would need somewhere around 1,000 lbs of preload on the system to do that.
I used to think the same thing about the sag on my setups until I actually started measuring it out for these tests.
If you can measure it for me (meters or CM is fine) then I can recreate your setup for the load testing.
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