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adatesman


Mar 3, 2008, 1:30 PM
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dobson


Mar 3, 2008, 2:06 PM
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Re: [adatesman] Extended range cams- expansion range vs. holding power [In reply to]
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When I hear of "greater holding power", I always think, "greater flake-breaking power". In many marginal placements, a higher normal force could lead to failure of the rock.

I think that cam designers should look at the friction coefficient of cam lobes on rock, and design the cam angle based on this figure. With some safety margin, of course.

Reduced range isn't the only drawback to a reduced camming angle.


basilisk


Mar 3, 2008, 8:44 PM
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Re: [dobson] Extended range cams- expansion range vs. holding power [In reply to]
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dobson wrote:
When I hear of "greater holding power", I always think, "greater flake-breaking power". In many marginal placements, a higher normal force could lead to failure of the rock.

Someone please correct me if I'm wrong, but cam angle shouldn't affect the amount of force on the rock. It affects the range and the "grip" so to speak. That is to say a lower cam angle allows for more surface area on the rock (thus more friction, thus more holding power), but it has less range. A higher cam angle will have better range, but then friction, and thus be more prone to slipping out before it's even loaded.
Cam angle doesn't affect the force on the rock though. Just how likely the cam is to hold and not slip out


To the OP: I wouldn't expect most climbers, even advanced ones, to really understand the concept of holding power. Cam angle and range are easy, you can physically see that. Holding power is a lot more abstract. I know what it is and what it means, but I have no way of quantifying that in my head. I'd imagine you need a engineer of some sort to help you with that front


adatesman


Mar 3, 2008, 9:05 PM
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jestering


Mar 3, 2008, 9:20 PM
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Re: [basilisk] Extended range cams- expansion range vs. holding power [In reply to]
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basilisk wrote:

Someone please correct me if I'm wrong, but cam angle shouldn't affect the amount of force on the rock.

I could be way off, but I believe that it does increase the force. For one cm pulled down on a cam, a Camalot's lobes will push out further than, say, a Metolius Cam. I'm too lazy to wrap my mind around it enough to properly express it, but basically the expansion is inversely proportional to the outward force.


basilisk


Mar 3, 2008, 9:21 PM
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Thanks for the links. I'll readily admit I'm no engineer and still need some schooling; I'll certainly look into them.

I'm probably out of my league, but I'll try to elaborate my thinking: holding power is a result of surface area, right? With a lower cam angle, more material is touching the rock (surface area), and this causes the cam to have greater holding power, right? So clearly surface area is pretty important. Changing the cam angle changes the surface area, and thus holding power.
Or are you suggesting that the holding power is a result of something else? Okay, I'll read those links now

I hope I'm not jacking your thread or presenting misinformation. This is just as I understand things right now. At the very least it's generating discussion, which is vital to the learning process


maldaly


Mar 3, 2008, 9:36 PM
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adatesman,
Take a hard look at a Lowe/Camp TriCam. They have a variable cam angle. Ranges from 12 to 17 degrees. They work pretty well.


Partner rgold


Mar 3, 2008, 9:50 PM
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Re: [adatesman] Extended range cams- expansion range vs. holding power [In reply to]
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I posted this in response to the same question as posted on SuperT, but I guess there's no harm in repeating it here:

I'm not sure that actual holding power in the field is as directly related to cam angle as the basic mathematical model suggests.

Decreasing the cam angle increases the cam's force-multiplication effect in converting downward loads to spreading forces on the crack walls. This would result in greater holding power, unless the higher spreading forces pulverize the crack wall surface and create lubricating granules. On soft rock, higher spreading forces could result in increased "grooving," which may or may not lead to greater holding power but would certainly be destructive. Finally, decreased cam angles would result in poorer performance in flared placements.

There is also the question of the effect of these higher forces on cam structure. There would be more deformation of the lobes under load, a consequence that is not part of the simple mathematical model, and this might decrease holding power unless different materials were used. Finally, the reactions on the axles from the higher spreading forces would also be higher, which could require heavier materials to maintain appropriate safety margins.

So maybe it isn't quite as simple as balancing range and holding power desiderata.

But that's the question you asked, so I'll try to give an answer and not think about all the considerations that underlie the changes you're contemplating.

I think I'd vote for increased holding power over increased range, if analysis and testing showed that you really could achieve increased holding power in the field without making the gear any heavier or less reliable. But I'm worried about decreased performance and possible breakage in flared placements, outcomes that are consequences of smaller camming angles.

And Malcom, that's an interesting fact about tricams. Do you mean that individual units have a varying cam angle, or that each unit has constant cam angle but different size tricams utilize different cam angles? I remember holding a tricam up to a camalot and thinking the curves looked to be almost identical...


irregularpanda


Mar 4, 2008, 12:40 PM
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adatesman wrote:
For example, which cam would you prefer... One with a range of 30mm-57mm with a 13 degree cam angle or one with a range of 30mm-61mm with a 15 degree cam angle? A #1 C4 gets 30mm-52mm, so would you opt for the greater holding power or range?

What about a cam with 50mm-96mm and a 13 degree cam angle or one with 50mm-105mm and a 15 degree cam angle? For comparison, a #3 C4 gets 51mm-87mm.

I'm curious what other people's thoughts on this are, so if you have an opinion let's hear the how and why of what you think would be best.

Honestly, I want the trango max-cams. They make my hands sweat just thinking about them. People talk shit about them because they walk, but if you don't climb sandstone with perfectly parallel cracks then they don't actually walk when you place them correctly.
If you're designing new cams, look @ totemcams: its pretty crazy shit for Aid-climbing.


adatesman


Mar 4, 2008, 2:25 PM
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irregularpanda


Mar 4, 2008, 2:40 PM
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adatesman wrote:
Panda-

Yeah, I like the MaxCams too and have been quite happy with the ones I picked up a while back. Is it the range that makes you like them so much? I'm rather fond of the offset axle as I find it helps with placement options where I tend to climb (DWG in NE PA, lots of very irregular cracks).

The Totecams are rather interesting and I tried something similar 2 years ago. I couldn't figure out the stem though and moved on to finding a design with more range.

-a.
Yeah the range rocks, but with the cracks i climb (irregular) I find when you place them correctly they are very stable and don't walk at all. Early on I found a link about how to place them. I can't remember it all but basically it had to do with pressing the larger lobes (offset axle) against the crack and then releasing the trigger. I'm not against metolius, i just don't like their extended range cam. I also have more than enough cams, but somehow I find some stupid reason to keep buying more.


(This post was edited by irregularpanda on Mar 4, 2008, 2:40 PM)


basilisk


Mar 4, 2008, 8:23 PM
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basilisk wrote:
[
Someone please correct me if I'm wrong, but cam angle shouldn't affect the amount of force on the rock.

Alright, I've since been proven wrong about this by various sources, so I'd like to apologize to everyone for that.
It also fills in a little hole that I've been wondering about. I'm sure most of us have heard the whole deal about "If a cam takes 100 pounds of force, it exerts X amount of force on the rock." I've heard a lot of variance in what number X is. Everything from 200-400. Of course the reason I've heard this variance must be because those numbers were form different brand cams (due to different cam angles). This brings me to my question: Is there any kind of formula one could apply to a cam to find out how much force it exerts on the rock?


dobson


Mar 4, 2008, 8:54 PM
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Re: [basilisk] Extended range cams- expansion range vs. holding power [In reply to]
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In reply to:
Is there any kind of formula one could apply to a cam to find out how much force it exerts on the rock?

cos(x)

edit: sorry, looks like 1/tan(x)


(This post was edited by dobson on Mar 4, 2008, 9:00 PM)


basilisk


Mar 4, 2008, 9:23 PM
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dobson wrote:
In reply to:
Is there any kind of formula one could apply to a cam to find out how much force it exerts on the rock?

cos(x)

edit: sorry, looks like 1/tan(x)

Ha, this is looking simpler than I expected. Shouldn't there be a place for the angle in the formula though?


patto


Mar 4, 2008, 9:59 PM
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basilisk wrote:
dobson wrote:
In reply to:
Is there any kind of formula one could apply to a cam to find out how much force it exerts on the rock?

cos(x)

edit: sorry, looks like 1/tan(x)

Ha, this is looking simpler than I expected. Shouldn't there be a place for the angle in the formula though?

1/tan(x) is the force multiplication factor where x is the angle

Of course this answer has to be divided by 4 if you want to work out the load per cam.


adatesman


Mar 5, 2008, 6:23 AM
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basilisk


Mar 5, 2008, 8:07 AM
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So where would one plug in the angle and starting force (on the stem)? Thanks for being patient with me; I haven't had to do any real math like this since Trig, which was four years ago


ptlong


Mar 5, 2008, 8:29 AM
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Fx=T/(2*ArcTan[theta])

T is the applied force, theta is the cam angle.


Your earlier question about surface area is interesting because common sense might lead one to believe that wider cam lobes would improve holding power. It turns out that this isn't the case as has been pointed out. The larger surface area would result in more friction if the pressure was the same but the since the pressure on the rock is reduced when a wider lobe is employed it ends up exactly cancelling out.

If you read the Metolius marketing fluff about their Fat Cams you might think it does improve holding power:

Metolius wrote:
The optimized cam angle, coupled with 35% more surface area than Power Cams, yields massive holding power and minimizes the chance of your placement "tracking out" in soft rock.

In fact what the wider lobes do is to lessen the pressure on the rock for a given load thus reducing the chance that the rock will pulverize. This can be very important in softer rock which is where Fat Cams make the most sense.


adatesman


Mar 5, 2008, 9:32 AM
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maldaly


Mar 5, 2008, 10:05 AM
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rgold,
Each tricam has a varying angle and it rotates through its range. Greg designed them this way for the soft sandstone flakes in Zion. The theory goes that as the cam rotates, the angle steepens, reducing the outward force so destructive to the soft sandstone flakes and, at the same time, increasing the rate of expansion. It's this increasing angle that makes tricams feel so secure in the small end of the range and tippy at large end.

If there's a lesson for cam designers to learn here, it's that you don't need to have a constant cam angle through the range. Currently, you make compromises in holding power but imagine a future where you could vary the cam-lobe material from being hard (7075) at the small end of the range where the angle is only 12 to soft (6061) at the tips where the cam angle could be 17 - 20. Cool, eh?

Keep dreaming guys!
Mal


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Mar 5, 2008, 10:54 AM
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So, Mal...

When are we going to see this from you? Wink


maldaly


Mar 5, 2008, 11:09 AM
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So many designs, so little time...


evanwish


Mar 7, 2008, 5:30 PM
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adatesman wrote:
I realize that most people here don't know how cams work,

we learned the use of the Logrical spyral today in math..
some kid asked when the hell we'd use that?!?!

i replied by telling them that's how we make the camming units for climbng...

[whatever else it's used for i don't know and really don't care... as long as i know how my gear works]


vanilla_gorilla


Mar 7, 2008, 8:20 PM
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maldaly wrote:
rgold,
Each tricam has a varying angle and it rotates through its range. Greg designed them this way for the soft sandstone flakes in Zion. The theory goes that as the cam rotates, the angle steepens, reducing the outward force so destructive to the soft sandstone flakes and, at the same time, increasing the rate of expansion. It's this increasing angle that makes tricams feel so secure in the small end of the range and tippy at large end.

If there's a lesson for cam designers to learn here, it's that you don't need to have a constant cam angle through the range. Currently, you make compromises in holding power but imagine a future where you could vary the cam-lobe material from being hard (7075) at the small end of the range where the angle is only 12 to soft (6061) at the tips where the cam angle could be 17 - 20. Cool, eh?

Keep dreaming guys!
Mal

Mal,

I can understand (somewhat) about the varying cam angle on a tricam. However on a SLCD when a load is applied i dont "see" the lobes as rotating, i do understand that in almost all placements (especially in softer stone) that the cam does actually rotate due to shear stresses and failures of small grains/texture of the rock and deformation of the lobes, but i always pictured this rotation as being so small that the effect of varying the cam angle would be negligible. Restated: when a cam is loaded the lobes do rotate but i believe it is such a small amount that the increasing cam angle would have no real effect.

These are just some of my humble thoughts with no real evidence to back them up and i appreciate any response in discussing this topic.

Thanks


adatesman


Mar 8, 2008, 11:57 AM
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