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kimgraves
Mar 7, 2005, 5:28 PM
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Hi Gang,
My partner just bought an Ushba Hogwaller off of Ebay. Does anyone have any beta on this hauling device? Tricks? Good or bad experiences?
Many thanks,
Kim
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niftydog
Mar 8, 2005, 5:15 AM
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Imagine trying to drive a bus using a steering wheel the size of a CD and you'll get the right idea. I'm no physics expert, but I guess it's something to do with friction in the bearings and (for want of a better word) the "levering" action apon the bearings of different sized sheaves.
I have a hogwauler; I was convinced by the cam design which had certain advantages over the minitraxion I was using at the time. It was considerably cheaper than the Protraxion, so I went with it. I have posted a brief review in the gear section of this site.
Both the Protraxion and the Hogwauler are pretty big which is a downside compared to the minitraxion.
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imnotclever
Mar 8, 2005, 1:34 PM
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In reply to: In reply to: Its pulley wheel is too small... I've forgotten my physics.... Why is a small wheel a mechanical disadvantage? Thanks, Kim
Torque is a function of the radius. Think of your wrench. When you need a lot of torque you get out the breaker bar and increase the radius.
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ricardol
Mar 8, 2005, 7:19 PM
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I thought i read a trip report on Tuan's site about someone who had a bad experience with an USHBA wall hauler ..
he was soloing ..
and every time that he'd rap the haul line (which was already through the wall hauler) the rope would slip some short distance when he was like 60' down the line ..
he called it "The horror"
I'd piss my shorts if my line slipped some short distance when i was 60' into a rappel on thin air.
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kimgraves
Mar 10, 2005, 1:02 AM
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In reply to: In reply to: Its pulley wheel is too small... I've forgotten my physics.... Why is a small wheel a mechanical disadvantage? Thanks, Kim
Hi Gang,
My physics intuition is 25+ years old – I was actually a major – but the “wheel too small” claim just didn’t seem right to me. So I wrote to my physics professor who confirmed what my intuition was. He said that this is not a torque problem – you’re not turning a screw so the greater leverage afforded by a longer handled wrench example, given above, doesn’t apply. This is a kinetic/potential energy problem. You’re raising a mass a given distance. Assuming a frictionless pulley (more on this later) the energy stays constant. It takes the same amount of kinetic energy to raise the mass a given distance. The diameter of the pulley is irrelevant to the equation.
This is not to say that there aren’t other potential problems with the Ushba Hogwaller: the pulley might not spin as freely as other pulleys therefore it has more friction, etc. But pulley diameter is not an issue. I can even imagine a system where the bigger pulley would be a disadvantage. Bigger pulleys are more massive and therefore take more energy to get them spinning then less massive ones. But it would have to be really massive to make a difference: the difference between a 1” wheel and 2” is something that can be ignored.
What really worries me is the report that the clamp doesn’t. This means that the angle of the cam pivot wasn’t designed incorrectly. It seems to me that the cam mechanism found in the Ushba is inherently better than the toothed one of the Petzl designs. It can’t shred your ropes; it won’t ice up; it won’t ware out. Too bad someone can’t figure out how to use a GriGri for this purpose.
Regards,
Kim
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ricardol
Mar 10, 2005, 1:39 AM
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here is a link to that TR where the ushba kept on slipping
http://www.terragalleria.com/mountain/info/yosemite/tangerine.html
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kubi
Mar 10, 2005, 2:13 AM
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In reply to: My physics intuition is 25+ years old – I was actually a major – but the “wheel too small” claim just didn’t seem right to me. So I wrote to my physics professor who confirmed what my intuition was. He said that this is not a torque problem – you’re not turning a screw so the greater leverage afforded by a longer handled wrench example, given above, doesn’t apply. This is a kinetic/potential energy problem. You’re raising a mass a given distance. Assuming a frictionless pulley (more on this later) the energy stays constant. It takes the same amount of kinetic energy to raise the mass a given distance. The diameter of the pulley is irrelevant to the equation.
I was thinking the same thing. My theory about why a bigger wheel would be better: Lets assume that the friction in the pulley imparts a torque that is proportional to the velocity of the pulley (this makes sense, right?). The larger the wheel, the greater the torque you are imparting to the axle and the less signifigant the friction torque is. Of course, for a constant velocity the pulling torque and the load torque will cancel.
does this make sense?
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niftydog
Mar 10, 2005, 3:38 AM
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Just been looking at some experiements using "Atwoods Machine" and invloving our friend (or enemy, depending on how you feel about it) Sir Isaac Newton. I don't fully understand the equations, especially the ones that include the kinematic friction and frictional torque and such... but it does show a clear link between sheave radius and friction.
anyone got a laymans explanation of an atwood machine that includes friction and sheave diameter? This is quite interesting!
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kimgraves
Mar 10, 2005, 4:13 AM
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In reply to: I was thinking the same thing. My theory about why a bigger wheel would be better: Lets assume that the friction in the pulley imparts a torque that is proportional to the velocity of the pulley (this makes sense, right?). The larger the wheel, the greater the torque you are imparting to the axle and the less signifigant the friction torque is. Of course, for a constant velocity the pulling torque and the load torque will cancel. does this make sense?
Hi Kubi,
As I said, my physics intuition is +25 years old. However, my feeling is that it doesn't make sense. Friction doesn't "impart" a torgue. But even if you're right, my guess is that you'd also also be right that the pulling and load torgue would cancel. So in whatever case the pulley size still doesn't matter.
I do want to add that the pulley in the Hogwaller I have doesn't spin freely. Maybe friction is the issue. But I was also thinking that maybe it's designed that way so that the drag closes the cam: in effect acting as an additional spring. I'm just going to have to try it out for myself.
I read the Tuan piece. I'd like to know what kind and size hauling line he was using. The device is CE rated from 8-11mm. It's hard to believe they'd miss that sort of slippage. Still the story is pretty scary.
Best, Kim
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kubi
Mar 10, 2005, 4:33 PM
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In reply to: As I said, my physics intuition is +25 years old. However, my feeling is that it doesn't make sense. Friction doesn't "impart" a torgue. But even if you're right, my guess is that you'd also also be right that the pulling and load torgue would cancel. So in whatever case the pulley size still doesn't matter.
Imagine turning the pulley wheel at a constant velocity. Due to friction in the system you would be required to apply a moment to the wheel in order to maintain this velocity, this is what I meant by friction imparting a torque. The larger the wheel the easier it would be to overcome friction, assuming that the friction is constant.
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megableem
Mar 10, 2005, 7:58 PM
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tomtom
Mar 10, 2005, 10:30 PM
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You guys are forgetting about the friction internal to the rope as it bends around the pulley. You can reduce friction with a bigger pulley or a smaller diameter rope.
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megableem
Mar 11, 2005, 3:05 AM
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kimgraves
Mar 15, 2005, 4:34 PM
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Hi Gang,
I just want to publically thank pmyche who did me a real solid. His Hogwaller (I keep wanting to call it a wallhogger) had been stolen and mine was missing a part. So he sent me the part (which hadn't been stolen) along with the direction sheet. It was really generous. Thanks a lot, Mike.
Best, Kim
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