Silent Partner Top-roping (and rappel)
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Aric Datesman wrote:As I mentioned above, it locks based on changes in rotational velocity of the drum.Heck, the point is that I really could not get that part at first. :P So, if I got it right now, it's not about its absolute speed, but rather its acceleration. Right? |
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Bingo. |
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Aric Datesman wrote:Bingo.Ugh. Theoretically that means that if I keep gaining speed very gradually it would keep rolling even after a while and going quite fast, then. I guess I'll have to experiment a massive lot with that, I just have to realize *where*. I have an anchor on my ceiling but I cant get up that much with that. :P |
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Yup. Fortunately it'll only get so far before the clove starts binding on itself, but yeah, that might be longer than you'd like. |
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Aric Datesman wrote:Yup. Fortunately it'll only get so far before the clove starts binding on itself, but yeah, that might be longer than you'd like. Personally, I use an Eddy for lead solo and Minitrax for TR solo.I can easily see why you use the Minitrax for TR (I do as well and I think I'll back it up with a Petzl Microcender rather than alpine butterfly knots). But, why do you prefer the Eddy for lead solo over the SP? I'd really like to know. The SP is boasted everywhere as the best tool for that job - and it's among the few specifically designed for that purpose. Afaik, the Eddy is not, so I'd really love to know the reason of your preference if you'd like to share it. BTW, Rock Exotica states about the SP that " its speed sensitive locking mechanism will catch even head first falls". I guess it's inaccurate then, being actually the lock not speed, but acceleration dependant. |
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Semantics, but when an object is traveling in a circular path around a fixed point at a constant rpm it is in fact accelerating toward that fixed point. We (or a locking pin) experience this acceleration as a perceived force (ie commonly called centrifugal force). I haven't seen a blueprint for the device but I always assumed this is what was meant by 'acceleration dependant' because this is how an engineer would describe 'centrigual force'. |
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jon apprill wrote:Semantics, but (snip)John, I'm afraid it's not semantics. It's angular acceleration. As in radians per second squared, which has nothing to do with centripetal force or how the device locks. The rollers are free to lag or overrun with respect to the drum and locking ramps, and do so as a result of changes in angular velocity (which is the definition of angular acceleration). jon apprill wrote:I haven't seen a blueprint for the device (snip)If you scroll up you'll see a cutaway view of the device, which should make it clear how the device functions. |
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Febs wrote: I can easily see why you use the Minitrax for TR (I do as well and I think I'll back it up with a Petzl Microcender rather than alpine butterfly knots).Microcender works nice too, as does the Ushba Basic (the Kong Duck works, but needs much more weight at the bottom to feed smoothly). I really only settled on the Minitrax because I can lock the cam open to rap rather than have to hold or detach the device. Febs wrote: But, why do you prefer the Eddy for lead solo over the SP?Well, mostly because I really liked Joe Healey's writeup of his Eddy-based system, tried it, made some tweaks and am now quite comfortable with it. Plus I really didn't want to drop $200 on a SP before I knew I enjoyed lead solo. I still kinda want one since I'm a total gear whore, but it would take a lot for me to move off my current system. At the time I got into it, the popular option was a Death-mod GriGri1. One of the "features" of the Eddy is that the cam is held in the unlocked position by a spring loaded ball detent, which is fairly easily overcome (moving the cam into the locked position) when the sharp end of the rope comes taut. Joe Healey (correctly, IMO) observed that this allows the rope to run freer in a lead solo application than a GriGri1, an switched over to it. His system worked quite well for me with a 10.something rope, but I found it to run a bit too free with a dry treated 9.8 so made some tweaks. Namely, I now not only flake the rope into a backpack and run it over my shoulder, but I also have it running through an old-school oval biner rigged with a biner brake bar to add friction when paying out more rope. As I move upwards, a quick hand to my shoulder pays out the needed rope, but friction from the brake bar keeps the system from running away since it's more than enough to pop the cam on the Eddy out of the detent and into the locked position. On a side note, with my 10.2 this was not necessary as the combination of the rope diameter and suppleness was already right on the edge of popping the cam into the locked position the moment the free end came even a little bit tight. It would run a bit with the 9.8, which was a bit unnerving even with the instinctive grab-the-free-end-running-across-my-chest-to-pop-the-cam. So now I use the biner brake bar and only pay out as much rope as is needed every move or three (which has the side advantage of keeping me from getting my feet tangled in it). Febs wrote: BTW, Rock Exotica states about the SP that " its speed sensitive locking mechanism will catch even head first falls". I guess it's inaccurate then, being actually the lock not speed, but acceleration dependant.The wording is tricky, especially when you're marketing to people who may or may not understand the nuance between speed and acceleration when applied to rotating bodies. Perhaps I'm being overly pedantic about it, but "speed sensitive" in this scenario is actually referring to changes in speed, which is acceleration. |
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Aric Datesman wrote: John, I'm afraid it's not semantics. It's angular acceleration. As in radians per second squared, which has nothing to do with centripetal force or how the device locks. The rollers are free to lag or overrun with respect to the drum and locking ramps, and do so as a result of changes in angular velocity (which is the definition of angular acceleration). If you scroll up you'll see a cutaway view of the device, which should make it clear how the device functions.Yes you're right, I see it now. It's all about acceleration. When I go solo rock climbing on Mars I'll be sure and bring a different device :-) |
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Interesting.... It wouldn't work on the moon, would it? Angular acceleration of the drum due to the linear acceleration of the climber wouldn't be enough to cause it to lock! No wonder it took Blanchard and eKat so many years to work out! Quite the balancing act with the springs, and probably why it's so hard to find other examples of bidirectional roller clutches. |
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Academic at this point, Jon, but my reading of the patent has the spring biasing the roller outwards against the drum, and rolling friction is what causes them to move outwards on the locking ramps. |
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Which reminds me of the other thing I wanted to mention, Febs.... You're right; aside from the SP there's practically nothing out there that's approved for lead solo climbing. Reason for this is that it's a very small niche market with an insanely high liability insurance cost associated with it, so manufacturers are loathe to enter the market. |
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You all can't realize how much I'm loving this thread. It really makes me wanting to study some basic physics to understand it in its details. |
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Febs.... If it dries out this weekend, I will take some vids for you of dropping SP loaded with weights. |
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JacksonLandFill wrote:Febs.... If it dries out this weekend, I will take some vids for you of dropping SP loaded with weights.I love you. :) |
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Here you go: |
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For what matters the top rope setup, what REALLY makes me think that the SP could actually be a very effective device for Top Roping is that you commented at the end of the video: |
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I wanted you to know that I finally received it and it's here all new and shiny.
So far, so good. But this one: ""this device will not catch any fall", glom. I guess it's only a kind of a disclaimer. Isn't it? :) |
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Febs wrote:I wanted you to know that I finally received it and it's here all new and shiny. It's not the most fortunate season to test it, and the following weekends weather forecasts pretty much sucks, but I'll fiddle with it indoor as much as I can. Let's the fun begin. *gosh*, on the unit itself, there's the usual disclaimer about proper training, climbing is dangerous, and so on. So far, so good. But this one: ""this device will not catch any fall", glom. I guess it's only a kind of a disclaimer. Isn't it? :)Yep |
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I spent one hour fiddling with the SP and I think I found a nice, very effective way to rappel with it by having full, easy control on the speed while descending. |