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jt512
Oct 14, 2010, 4:58 PM
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spikeddem wrote: jt512 wrote: jbro_135 wrote: i like to use revolvers to reduce impact force when i'm top-roping on a sketchy single-micronut anchor Too bad, because when you reduce the friction on the anchor, you increase the impact force on it. A belayer getting pulled off the ground doesn't produce lower peak forces?
Whether the belayer is anchored or not, reducing friction at the anchor increases the force on the belayer and decreases the force on the climber. If the climber is anchored (and the belay static), then reducing friction increases the force on the anchor because the increase in the force on the climber is greater than the reduction of force on the belayer. If the belayer is unanchored, then I'm unsure what the net effect on the anchor would be.
Jay
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redlude97
Oct 14, 2010, 6:41 PM
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jt512 wrote: spikeddem wrote: jt512 wrote: jbro_135 wrote: i like to use revolvers to reduce impact force when i'm top-roping on a sketchy single-micronut anchor Too bad, because when you reduce the friction on the anchor, you increase the impact force on it. A belayer getting pulled off the ground doesn't produce lower peak forces? Whether the belayer is anchored or not, reducing friction at the anchor increases the force on the belayer and decreases the force on the climber. If the climber is anchored (and the belay static), then reducing friction increases the force on the anchor because the increase in the force on the climber is greater than the reduction of force on the belayer. If the belayer is unanchored, then I'm unsure what the net effect on the anchor would be. Jay
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kachoong
Oct 14, 2010, 6:45 PM
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Everyone knows pieces of gear are worthless without pics!
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jt512
Oct 14, 2010, 7:54 PM
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redlude97 wrote: jt512 wrote: spikeddem wrote: jt512 wrote: jbro_135 wrote: i like to use revolvers to reduce impact force when i'm top-roping on a sketchy single-micronut anchor Too bad, because when you reduce the friction on the anchor, you increase the impact force on it. A belayer getting pulled off the ground doesn't produce lower peak forces? Whether the belayer is anchored or not, reducing friction at the anchor increases the force on the belayer and decreases the force on the climber. If the climber is anchored (and the belay static), then reducing friction increases the force on the anchor because the increase in the force on the climber is greater than the reduction of force on the belayer. If the belayer is unanchored, then I'm unsure what the net effect on the anchor would be. Jay Just to clarify, you don't mean unanchored but just not leaving the ground correct?
No, I mean anchored and unanchored, and I'm assuming, pursuant to spikeddem's question, that the force is great enough that it would pull the belayer off the ground (if he is unanchored).
Jay
(This post was edited by jt512 on Oct 15, 2010, 2:11 AM)
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chossmonkey
Oct 15, 2010, 1:40 AM
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Gmburns2000 wrote: rangerrob wrote: I've done Flyin' Hawaiin at Rumney, and I don't remember ever owning a stick clip. It's not impossible. I agree with anti stick clip guy on this one. He values his ethic that he needs to be able to confidently climb the entire route without the aid of an artificial long arm. It's sort of arbitrary, because the bolts are more or less arbitrarily placed, so the danger is arbitrary. I would use a stick clip if I felt I needed it, but I would admire someone much more who climbed routes that they were comfortable with on their own terms. The whole concept of a stick clip, and sport climbing in general is kind of absurd. You are manufacturing a route with whatever degree of danger you want to have in it. If it's okay to stick clip the first bolt, why not stick clip the second, or third? Why not leave the rope hanging from all but the chains? What's the difference? Aside from bolting on the lead, why would someone intentionally make a sport route dangerous to lead? That's what i don't get about sport climbing. When you're placing gear you are either good enough to place the gear or you're not. With a sport climb you can easily make the route safer by just adding a lower bolt, and spacing them closer together. It's a joke, a farce...something that is there for pure entertainment. Not something to REALLY push the limits of what you yourself find as acceptable risk, and how close you can push yourself to the edge while still being in control. RR quoted just because it is well said, and to remind people once again that the question was, in fact, posted in the trad forum.
So why would you bring up a piece of sport climbing gear?
By your argument it should be limited to dodads and widgets.
Perhaps the most worthless piece of gear is your mother's failed diaphragm?
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climbingaggie03
Oct 15, 2010, 3:15 AM
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chossmonkey wrote: Gmburns2000 wrote: rangerrob wrote: I've done Flyin' Hawaiin at Rumney, and I don't remember ever owning a stick clip. It's not impossible. I agree with anti stick clip guy on this one. He values his ethic that he needs to be able to confidently climb the entire route without the aid of an artificial long arm. It's sort of arbitrary, because the bolts are more or less arbitrarily placed, so the danger is arbitrary. I would use a stick clip if I felt I needed it, but I would admire someone much more who climbed routes that they were comfortable with on their own terms. The whole concept of a stick clip, and sport climbing in general is kind of absurd. You are manufacturing a route with whatever degree of danger you want to have in it. If it's okay to stick clip the first bolt, why not stick clip the second, or third? Why not leave the rope hanging from all but the chains? What's the difference? Aside from bolting on the lead, why would someone intentionally make a sport route dangerous to lead? That's what i don't get about sport climbing. When you're placing gear you are either good enough to place the gear or you're not. With a sport climb you can easily make the route safer by just adding a lower bolt, and spacing them closer together. It's a joke, a farce...something that is there for pure entertainment. Not something to REALLY push the limits of what you yourself find as acceptable risk, and how close you can push yourself to the edge while still being in control. RR quoted just because it is well said, and to remind people once again that the question was, in fact, posted in the trad forum. So why would you bring up a piece of sport climbing gear? By your argument it should be limited to dodads and widgets. Perhaps the most worthless piece of gear is your mother's failed diaphragm?
BURN!!!!!!
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Perihelion
Oct 15, 2010, 5:45 PM
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Interesting. There are some things to think about here. I printed the pdf & will review that, however, there is an abbreviated version available at http://en.wikipedia.org/wiki/Fall_factor. I need to work a few examples using real-world values before I comment further.
I will add one thing, in passing: Although it is mathematically possible to have FF=0, in practice, if that were true you would have no fall. FF is always > 0, even in a TR situation. It would be more accurate to say that the limit of FF approaches zero as the length of fall approaches zero. You'll never quite get to zero, though.
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spikeddem
Oct 15, 2010, 5:49 PM
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Perihelion wrote: Interesting. There are some things to think about here. I printed the pdf & will review that, however, there is an abbreviated version available at http://en.wikipedia.org/wiki/Fall_factor. I need to work a few examples using real-world values before I comment further. I will add one thing, in passing: Although it is mathematically possible to have FF=0, in practice, if that were true you would have no fall. FF is always > 0, even in a TR situation. It would be more accurate to say that the limit of FF approaches zero as the length of fall approaches zero. You'll never quite get to zero, though.
IIRC, stretch is not included in calculating the FF. So, it's definitely possible to have an FF of zero. The "fall distance," as I understand it, is equal to the distance fallen before the rope is weighted.
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Perihelion
Oct 15, 2010, 5:54 PM
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spikeddem wrote: IIRC, stretch is not included in calculating the FF. So, it's definitely possible to have an FF of zero. The "fall distance," as I understand it, is equal to the distance fallen before the rope is weighted.
You are correct. My mistake. If you hang on the rope like wet laundry, you could have a FF=0.
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spikeddem
Oct 15, 2010, 6:00 PM
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Perihelion wrote: spikeddem wrote: IIRC, stretch is not included in calculating the FF. So, it's definitely possible to have an FF of zero. The "fall distance," as I understand it, is equal to the distance fallen before the rope is weighted. You are correct. My mistake. If you hang on the rope like wet laundry, you could have a FF=0.
I can't tell if you're trying to be wise with that comment, but it's common to see beginners keeping each other very tight when it comes a TR belay.
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milesenoell
Oct 15, 2010, 6:14 PM
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jt512 wrote: milesenoell wrote: jt512 wrote: milesenoell wrote: lemon_boy wrote: the dmm revolver carabiner, without a doubt. i'm always surprised when people recommend using these for a top rope anchor, or other ill advised setups. In what way are you suggesting that that is an ill advised setup? In the way of not providing any friction to reduce the impact force on the belayer. Jay I suppose, but it seems to me that using them on the rope end of draws while leading (as I believe they are intended to be used) would be to subject your belayer to much higher forces in a fall than anything you would see in a TR scenario. You just made another argument for their uselessness. In reply to: Edited to add: I'm not sure how much extra force we are talking about by reducing the friction (but I suspect you do) but I'm just not all that concerned about the forces in a TR system. (I also don't generally climb with anybody who significantly outweighs me.) If the revolver were frictionless it would increase the force on the belayer by about 50%. Let's say you and your partner each weigh 170 lb. Then, if you used a revolver, it would be like belaying someone who weighed 255 lb. How pleasant an experience would that be? Now, imagine that your partner weighed 200 lb. A 30-lb difference is no big deal, but with a revolver it would theoretically be like belaying someone weighing 300 lb. Is this a reason to be "concerned"? No. Is this a reason to be unhappy? Hell, yes. Jay
This one cracks me up. It's basically just a direct response to a comment I made in which you supply information I was curious about and clarify your stance (indicating that we see this similarly). How did that draw 4 one star ratings?
I can understand that there are some folks out there that strongly disagree with you, but can't they at least do so in a more effective way than these ratings? Wouldn't it be more satisfying to actually point out any differences in opinion, or better yet to maybe point out where they think you are incorrect?
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jt512
Oct 15, 2010, 6:47 PM
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Perihelion wrote: Interesting. There are some things to think about here. I printed the pdf & will review that, however, there is an abbreviated version available at http://en.wikipedia.org/wiki/Fall_factor.
I know. I wrote most of the Wikipedia article.
In reply to: I need to work a few examples using real-world values before I comment further.
If you want an easy way to work with the equation(s), you can use my online impact force calculator. It reports results using two models: the standard model and another model that treats friction at the top anchor in a more accurate fashion [source].
In reply to: I will add one thing, in passing: Although it is mathematically possible to have FF=0, in practice, if that were true you would have no fall. FF is always > 0, even in a TR situation.
No, a toprope "fall" with no slack in the rope does in fact have a fall factor of 0. Fall factor is defined to be the length of the fall divided by the length of the rope out, where fall length is defined to be the height of the climber at the beginning of the fall minus the height of the climber just before the rope begins to stretch. Therefore, for a TR "fall" with no slack in the rope, the fall factor is 0 divided by a positive number; that is, the fall factor is 0.
Zero is a perfectly valid value for fall factor in either the standard or friction-adjusted impact force models. With a fall factor of 0, both models reduce to
T_1 = 2w ,
where T_1 is the tension in the climber's side of the rope and w is the climber's weight. This implies, perhaps surprisingly, that the maximum impact force (on the climber) in such a toprope "fall" will be twice the climber's weight, and perhaps more surprisingly, it will be so for a rope of any elasticity.
Jay
(This post was edited by jt512 on Oct 17, 2010, 5:24 AM)
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jt512
Oct 15, 2010, 7:04 PM
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milesenoell wrote: jt512 wrote: milesenoell wrote: jt512 wrote: milesenoell wrote: lemon_boy wrote: the dmm revolver carabiner, without a doubt. i'm always surprised when people recommend using these for a top rope anchor, or other ill advised setups. In what way are you suggesting that that is an ill advised setup? In the way of not providing any friction to reduce the impact force on the belayer. Jay I suppose, but it seems to me that using them on the rope end of draws while leading (as I believe they are intended to be used) would be to subject your belayer to much higher forces in a fall than anything you would see in a TR scenario. You just made another argument for their uselessness. In reply to: Edited to add: I'm not sure how much extra force we are talking about by reducing the friction (but I suspect you do) but I'm just not all that concerned about the forces in a TR system. (I also don't generally climb with anybody who significantly outweighs me.) If the revolver were frictionless it would increase the force on the belayer by about 50%. Let's say you and your partner each weigh 170 lb. Then, if you used a revolver, it would be like belaying someone who weighed 255 lb. How pleasant an experience would that be? Now, imagine that your partner weighed 200 lb. A 30-lb difference is no big deal, but with a revolver it would theoretically be like belaying someone weighing 300 lb. Is this a reason to be "concerned"? No. Is this a reason to be unhappy? Hell, yes. Jay This one cracks me up. It's basically just a direct response to a comment I made in which you supply information I was curious about and clarify your stance (indicating that we see this similarly). How did that draw 4 one star ratings? I can understand that there are some folks out there that strongly disagree with you, but can't they at least do so in a more effective way than these ratings? Wouldn't it be more satisfying to actually point out any differences in opinion, or better yet to maybe point out where they think you are incorrect?
If they were capable of responding coherently, I'm sure they would.
Jay
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lemon_boy
Oct 15, 2010, 9:12 PM
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Perihelion, would you use just one revolver or two in your MP anchor for toproping? if you use 2, the pulleys are running in tangentially opposing directions at the location where they are in contact. kind of ruins the point of using a pulley.
that being said using a pulley in a TR setup is a bad idea. as jay pointed out - why do you think they run the toprope a couple times around the anchor bar at the gym - to get more friction. not less.
side note, that was pretty funny that jay wrote the wiki artcile. didn't know that.
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Perihelion
Oct 15, 2010, 10:49 PM
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jt512 wrote: No, a toprope "fall" with no slack in the rope does in fact have a fall factor of 0. Fall factor is defined to be the length of the fall divided by the length of the rope out, where fall length is defined to be the height of the climber at the beginning of the fall minus the height of the climber just before the rope begins to stretch. Therefore, for a TR "fall" with no slack in the rope, the fall factor is 0 divided by a positive number; that is, the fall factor is 0. Zero is a perfectly valid value for fall factor in either the standard or friction-adjusted impact force models. With a fall factor of 0, both models reduce to T_1 = 2w , where T_1 is the tension in the climber's side of the rope and w is the climber's weight. This implies, perhaps surprisingly, that the maximum impact force (on the climber) in such a toprope "fall" will be twice the climber's weight, and perhaps more surprisingly, it will be so for a rope of any elasticity. Jay
Oh, boy. I just worked your math. It was interesting. I'll post more about this later. Heheh.
BWAHAHAHAAAA!!! 
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notapplicable
Oct 16, 2010, 5:09 AM
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Back to the topic at hand.
Mad Rock Aviator Belay Device
And no, I have not used one. I did just look up "superfluous" in the dictionary though, and guess what I saw a picture of...
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ptlong2
Oct 18, 2010, 12:05 AM
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jt512 wrote: This implies, perhaps surprisingly, that the maximum impact force (on the climber) in such a toprope "fall" will be twice the climber's weight, and perhaps more surprisingly, it will be so for a rope of any elasticity.
Any linear elasticity. If the rope deviates from Hooke's Law over the range in question the force may not be twice the climber's weight.
And it may not be twice if you add in other real-world complications such as a real climber instead of a block of iron, a real belayer instead of a static belay, or friction over the top anchor.
It would be interesting to see what range of forces real toprope falls generate. Most of them are probably not fall factor zero.
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jt512
Oct 18, 2010, 12:39 AM
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ptlong2 wrote: jt512 wrote: This implies, perhaps surprisingly, that the maximum impact force (on the climber) in such a toprope "fall" will be twice the climber's weight, and perhaps more surprisingly, it will be so for a rope of any elasticity. Any linear elasticity. If the rope deviates from Hooke's Law over the range in question the force may not be twice the climber's weight.
Yes. I stated in an earlier post, the model assumes that the rope behaves according to Hooke's Law.
Jay
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fresh
Oct 18, 2010, 2:02 PM
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jt512 wrote: ptlong2 wrote: jt512 wrote: This implies, perhaps surprisingly, that the maximum impact force (on the climber) in such a toprope "fall" will be twice the climber's weight, and perhaps more surprisingly, it will be so for a rope of any elasticity. Any linear elasticity. If the rope deviates from Hooke's Law over the range in question the force may not be twice the climber's weight. Yes. I stated in an earlier post, the model assumes that the rope behaves according to Hooke's Law. Jay
do you know how accurate Hooke's Law is in predicting the rope's behavior?
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jt512
Oct 18, 2010, 4:40 PM
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fresh wrote: jt512 wrote: ptlong2 wrote: jt512 wrote: This implies, perhaps surprisingly, that the maximum impact force (on the climber) in such a toprope "fall" will be twice the climber's weight, and perhaps more surprisingly, it will be so for a rope of any elasticity. Any linear elasticity. If the rope deviates from Hooke's Law over the range in question the force may not be twice the climber's weight. Yes. I stated in an earlier post, the model assumes that the rope behaves according to Hooke's Law. Jay I swear, the stars have got to go. do you know how accurate Hooke's Law is in predicting the rope's behavior?
As I understand it (which isn't that well), the main difference between a Hooke's Law spring and an actual dynamic rope is that a dynamic rope acts as a dampened spring, resulting in lower impact forces than predicted by Hooke's Law. The standard model also ignores friction between the rope and the anchors or climbing surfaces, assumes the belay is static, and that the falling body is rigid. Were it not for friction, we could probably say that Hooke's Law overstates the impact force on the climber, the belayer, and the anchor. Modeling the effects of friction throughout the system is more complex.
Jay
(This post was edited by jt512 on Oct 18, 2010, 7:39 PM)
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petsfed
Oct 18, 2010, 7:16 PM
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jt512 wrote: As I understand it (which isn't that well), the main difference between a Hooke's Law spring and an actual dynamic rope is that a dynamic rope acts as a dampened spring, resulting in lower impact forces than predicted by Hooke's Law.
That's pretty accurate to say. For the most part, the damping comes from internal friction, Hooke's law terms directed perpendicular to the force load, and non-elastic deformation of the rope.
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ptlong2
Oct 18, 2010, 7:46 PM
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jt512 wrote: Yes. I stated in an earlier post, the model assumes...
I understand that. I was just wondering what range of forces a real no-slack toprope fall would produce since the model can't be relied upon to tell us.
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ptlong2
Oct 18, 2010, 7:53 PM
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petsfed wrote: jt512 wrote: As I understand it (which isn't that well), the main difference between a Hooke's Law spring and an actual dynamic rope is that a dynamic rope acts as a dampened spring, resulting in lower impact forces than predicted by Hooke's Law. That's pretty accurate to say. For the most part, the damping comes from internal friction, Hooke's law terms directed perpendicular to the force load, and non-elastic deformation of the rope.
There is some non-linearity in climbing ropes without considering damping. Look on the ITRS website for a 2001 paper by Weber. It's mainly concerned with static ropes but there are limited data from a slow pull test on a dynamic rope. The non-linearity over the working range is obvious. Less obvious is that for smaller elongations the effect is enough to change the prediction of 2x the climber's weight for a zero FF fall by about 10-15%. It's interesting to see the effect that knots have as well.
edit: typos
(This post was edited by ptlong2 on Oct 19, 2010, 4:07 PM)
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rainman0915
Oct 20, 2010, 6:26 AM
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talk about unnecessarily over complicating a design
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