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soccer_fan
Aug 13, 2003, 10:42 PM
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I am about to start my senior design class, and, as a mechanical engineer who climbs, I would like to know if anyone has links to or information on the design of cams. I've read Wild Country's 'Cam Book' and would like input as to what would make an ideal cam, but be realistic enough to use as design criteria for a capstone design project. For example, on RC.com I've read the disadvantages of Camalots in the largest sizes is that they walk, the same for Rock Empire Robots and most other cams. BD's patent on the double axled cam expires next year I believe, so there are many possibilities from a design point of view (ie double axle u-stem).
And as a side note if anyone has any hard links to research done on gate flutter; I'd be interested in seeing that as well.
Thanks for any input.
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epic_ed
Aug 13, 2003, 11:05 PM
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Good luck. My personal hope is that someone comes up with a viable challenge to Aliens. The market is ripe for a challenger since they have little interest in meeting the demand for their superior product. This certainly isn't a knock on their stuff -- just their inability to keep thier prospective (and faithful) customers happy.
Ed
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flagstaff_climber
Aug 13, 2003, 11:25 PM
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Think hydraulics :) And hello from a fellow Arkansan....
Rick
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repete
Aug 14, 2003, 1:07 AM
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I do think that BD used to make their camalots with a double axle and a u stem.
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geezergecko
Aug 14, 2003, 2:59 AM
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In reply to: BD's patent on the double axled cam expires next year I believe...
Does that mean that we can expect to see double axled Aliens in a year or two? Or double axled Friends? All these patents eventually expiring could result in some amazing gear. I remember this happening to windsurfing gear. Once the original patents expired, the quality of the gear greatly improved.
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kirot
Aug 14, 2003, 3:07 AM
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wow! hydraulics and stuff in a cam. that's pretty nasty!
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alpnclmbr1
Aug 14, 2003, 4:11 AM
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http://www.mit.edu/~custer/rocking/cams/cams.body.html
http://www.cc.nctu.edu.tw/~mclub/meichu/project/friend/friend.html
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kzemach
Aug 14, 2003, 4:58 AM
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This may not be particularly helpful, but here's my input:
For smaller sizes, I carry both quad and tri cams. I find that unless I'm climbing granite, I end up using the tri's a lot more, due to either cracks that aren't deep enough, or cracks that aren't parallel. (My tri's are Metolius, and I like them). My small quads are Camalots, and I wish I had Alien SLs instead.
In the midrange I have Camalots, and love them. The double axel gives that extra range that makes them more versitile, albeit somewhat heavier. I think in the midrange that's worth it. The largest I have is a #3.5, which is probably the limit of what you'd want a double axel for. Larger than that, you've got significant range with even a single axel, so I don't think the extra weight is worth it (and see other's comments above regarding walking).
One feature that I'd LOVE to have in my cams that they don't have is the double looped slings. Now, most companies that make double looped slings IMO don't make them long enough. A LITTLE bit longer on the slings, make them double looped, and for relatively straight cracks you'd need a lot fewer slings and biners. Think about it: you'd save the weight of one, and sometime two biners PER CAM (depending upon how you rack your slings). If you set 15 cams on a fairly straight climb, and say that saves you using 10 slings, that's a lot of weight, or at least certainly more than the extra weight of a double axel cam! Note: I am not saying that with a double loop sling on the cam you wouldn't need regular slings on many placements: nothing is worth the risk of walking out your placement, but that extra length at virtually no weight in a double sling on a cam makes a lot of sense.
Also, not sure it would offer any advantage, but what about a "double splitter gear" cam. Splitter Gear's cams are interesting (I've only used them for aid climbing) and might pose some advantages with two in parallel, like, perhaps, a narrower offset cam.
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soccer_fan
Aug 14, 2003, 5:32 AM
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Thanks to alpnclmbr1 for the links, both are good reads. Has anyone got any info on the mechanism or an explination for cam walking? And does anyone have any specifics of things that don't work well with cams that are avaliable?
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apollodorus
Aug 14, 2003, 6:23 AM
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The double axle BD design offers a larger range for a give cam size. Basically, the pointed end of the cam hits the opposite wall after moving through a larger rotation angle. The range of the cam is how far it rotates before it hits, well, you get the idea.
When the patent expires, anybody can make cams with two axles. There is no way to extend the life of a U.S. patent, except by Congressional decree (not going to happen on that patent).
If you want a better cam, get rid of the weight. The steel is heavy. Get rid of the steel cable and axle. Use kevlar for the sling and carbon/glass for the axle.
Here's the BD patent:
www.uspto.gov
Patent Number: 04643377
February 17, 1987
expires 18 years from the date of issue: 2-18-05
That's your design project right there. Pay attention to impact strength. The kevlar cord is already used for climbing.
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alpnclmbr1
Aug 14, 2003, 6:41 AM
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In reply to: Has anyone got any info on the mechanism or an explination for cam walking?
As I understand it the two major factors related to cams walking are:
1: the width of the cam, i.e. narrower cams walk easier
2: the amount of tension provided by the return springs i.e. more tension less likely to walk
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mesomorf
Aug 14, 2003, 1:07 PM
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1. Cheaper cams.
2. Lighter cams.
3. A cam that's impossible to get stuck. Maybe a little switch that you can flip to give the cams extra room. Or that collapses the working parts altogether (Scary thought.)
4. One size fits all.
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traddad
Aug 14, 2003, 2:15 PM
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I just wish someone would cobble all the good ideas everyone else has had into one cam:
Opposing cams like the 4cam: allows you to use two lobes in a pinch
Double axles; nuff said.
Large, swaged clip in loops with mobius loop, extendable slings: clip in close, clip in far away.
"Shrinky dink" all the metal parts. Kind of like what has happened to racing motorcycles lately. If it can be small and light, MAKE IT SMALL AND LIGHT!!!
Now my ideas:
Round edged cam lobes to increase cam contact area: the sharp edges of cams scare me. If you are placing a cam in an irregular crack, 10:1 you will have at least one cam with just it's edge in contact with the rock. Think: Metolius Curved Nuts.
Metal/composite lobes on bigger cams: Hey, they make F-16s out of composite materials and glue them together. You could make a stiffer cam lobe with a soft aluminum face to bite into the rock. Can you say "expensive"?
Triggers and trigger wires that can be replaced cheaply and easily. Why, oh why don't they do this?
I'm still thinking....
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traddad
Aug 14, 2003, 2:47 PM
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Here’s an idea for big crack protection: Rather than HUGE cams, why not a cross between a Big Bro and a cam.
Picture an expandable Big Bro tube with a set of spring loaded cams on each end. Presto, huge size range, easier placement in irregular cracks, lower weight (?) and it would take up less space on your rack.
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traddad
Aug 14, 2003, 3:02 PM
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The idea hamster is at work...
How ‘bout getting rid of the stem all together. Replace it with a spectra sling attached directly to the head, covered by a light, cheap, replaceable, stiff plastic tube to allow actuation of the trigger. Basically everything below the cams would be replaceable.
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keinangst
Aug 14, 2003, 3:04 PM
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Since I'm never going to pursue this, here ya go:
Rather than hydraulics, think pneumatics for weight savings. The release spring should set the cam into place, then it should be "power set" via some sort of finger/thumb air pump (think rudimentary reebok pump).
This air would fill a chamber between the lobes, forcing them apart with greater force than any spring could resonable exert. Voila, no walking :D
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soccer_fan
Aug 14, 2003, 3:16 PM
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So far I'm thinking about either doing a design study of why Aleins seem to do so well, and how they might be improved. Or a way to lock a cam into place: once its set, lock the lobes such that they cannot retract until the cam is unlocked to prevent walking. Perhaps a mechanism as simple as the small tab that is used to hold open screen doors. Someone mentioned hydraulics, and that would provide a very strong hold on the rock, however it would most likely increase the weight of unit. Or something like traddad's suggestion of creating a better way to change trigger wires or, a better way of actuating the cam sans wires.
Aside from the cam lobes, titanium could be introduced for some of the other components.
Is there a reason that the Forged Friends have some of the longest stems of most all the cams avaliable? Why do most of the other manufacturers go with a shorter stem?
Besides cam walking, bad trigger wires, and weight of cams; what are some other design gripes out there?
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traddad
Aug 14, 2003, 4:15 PM
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Innovation shminovation.....
Here’s a good thesis project, get BD or someone to spot you 10 or 50 cams and do an analysis of stress etc. in likely use scenarios and then model where metal could be removed given reasonable manufacturing costs. Concentrate on the steel first: Tubular axles, trim down the head where the stem meets the axle, smaller, lighter swages, replace steel with aluminum where possible, replace aluminum with plastic where possible....
Make them light first, then add the bells and whistles.
Bottom line, we have a LOT of one innovation designs out there banking on that one innovation to sell product. Make it light then crib everyone else’s ideas to make your cam the whole package. I’d pay premium price for a cam that was light, well designed and made, and packed in a lot of useable features.
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soccer_fan
Aug 14, 2003, 4:40 PM
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tradad that would make for a very interesting project indeed, though I think the trick would be getting a large company like BD feel the need to help out a student.
I was also thinking doing a project to provide "Published measurements of force to shear yield and frictional holding ability would provide information that allows climbers to make intelligent decisions concerning SLCDs." {http://www.mit.edu/~custer/rocking/cams/cams.body.html}
Does anyone have any contacts within BD, WC, Metolius, etc that would be interested in helping out a student, or has anyone had any experience dealing with these manufacturers for something like this?
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buckyllama
Aug 14, 2003, 5:10 PM
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Here's a thought:
First analyze the ways in which cams fail: I can think of 4
1) tracking out of soft stone
2) lobes "folding" from sideways pull
3) axles bending
4) walking
not much you can do for 1
but 2 and 3 are fixable:
For example consider putting a thrust bearing between the outer lobes of the cams (or between all lobes of a dual-stem) This would dramatically improve the lateral stiffness of the lobes by making the lobes work in tandem. And you'd make the bearing as large as possible, basicaly as large as the smallest dimension of the axle-cam edge.
Another option which may be viable and perhaps a bit simpler is to use a larger diameter axle. Basically make the axle as large as possible for each size cam you wish to make. And, of course, make it hollow to lighten it. You might be able to get away with something like Ti for the axle but frankly I'd stick with steel. Someone else mentioned carbon/glass. I don' tneed ot tell you this as an engineer, but that's a horrible idea. Carbon/glass on the lobes might work though you'd have a hard time making it cost effective.
As a general idea, you could face the edges of the lobes with a higher friction material than just the plain aluminum. I have little experience with any of these materials but anyting with a reasonable shear resistance might work well. Think in terms of kevlar, and maybe automotive brake pads. This would allow you to use a larger cam angle and reduce the force on the rock, which could potentially reduce the tendancy to track. (or maybe not). Or you could keep the cam angle the same and just make them less prone to walking.
I don't know what you could do to absolutly prevent walking that wouldn't adversely affect some other aspect of the cam, but maybe you can think of something.
hope this gives you some ideas.
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deafclimber
Aug 14, 2003, 5:21 PM
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maybe the cams need better teeth so they wont walk or hold better...
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buckyllama
Aug 15, 2003, 1:12 PM
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In reply to: maybe the cams need better teeth so they wont walk or hold better...
Teeth have nothing at all to do with the cam's holding power. If anything they decrease it. The holding power is determined only by the cam angle and the coefficient of friction between the lobes and the rock. They can have some effect on the cam's desire to walk however. Though wether they make them walk more or less is dependant on the situation.
I have my own personal theory as to why cams have teeth. And I have no proof at all for this and so it's probably wrong, however....
Since Jardine probably didn't have access to a CNC milling machine (since they didn't exist in 1973), The easiest way to prototype a shape like a spiral would be to just scribe out points along the spiral and connect the dots. So you mark out the points, drill small holes, and bandsaw between them. The leaves a smooth surface with half-circular dents where the holes were. aka teeth. It's pretty fast and requires only rudimentary machine tools. By the time he was getting to the later versions he no doubt got more sophisticated but also probably decided he liked the teeth, so he kept them.
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mewalrus
Aug 18, 2003, 6:42 AM
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How about opposeing cams like splitters with a secondary pivot point on each cam lobe. In flareing placements this would allow you to get much more metal in contact with the rock. This sounds scary :shock:, but it might work well for aid especially.
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