|
|
|
|
omenbringer
Oct 6, 2004, 6:29 PM
Post #26 of 87
(11907 views)
Shortcut
Registered: Sep 19, 2003
Posts: 248
|
After reading thru this entire thread I feel there are some fallacies that just need to be addressed;
[*:1dc34b3524]BD's larger expansion range is not due to a different cam angle, it is due to the use of 2 axles
[*:1dc34b3524]BD does not have a lower pullout strength than any other Cam on the market, in fact it is quite the opposite, majority of there cams are rated higher than the competition 16 KN vice 14 KN
[*:1dc34b3524]Yes BD's can be used as passive pro but they are not the only cams on the market that can be placed like that. As was said by mingleefu cams with full strength cam stops can also be placed passively i.e DMM, WC, Metolius. BD is however the only one I have heard of thats passive strength is above 10 KN
[*:1dc34b3524]According to all the sources I have read from, including WC's Cam book, spring tension has nothing to do with pullout strength. It does, however, have a lot to do with the units tendancy to walk in a placement
With this being said, let me say that I am not a big fan of the BD's myself, not to say that they are bad cams just that I dont use them. I think the redesign will address a lot of the reasons I chose not to buy them.
|
|
|
|
|
chico
Oct 6, 2004, 6:30 PM
Post #27 of 87
(11907 views)
Shortcut
Registered: Jan 28, 2004
Posts: 39
|
mingleefu,
I hear what you are saying. All apologies to Ike Newton. Yeah, alot of this info is hard to turn up. Nonetheless, BD does have a weaker...or should I say softer, less rigid spring. That is why it is so easy to operate. Prove it to yourself. Take one of each cam and squeeze'em. One is easier than the other, duh. What the much debated spring does is to try to keep the cam lobes in its fully open umbrella position:that's the function. So... the more rigid the spring, the more the cam wants to stay open, and therefore pushes against the sides of the crack, even when it is unweighted. This is not a ridiculous statement. It's not my job to prove all ot these details. Talk to a Rep, or don't. Buy BD or don't. I'm over it.
Consider this, if a cam that was not weighted had no spring at all, it would likely fall out of the crack because nothing is making it try to open up until it is weighted. However minute the phonomena of cam bounce may be is something for physics grad students to study, however,it is absolutely effected by the rigidity of the spring. And that is the whole point of what I have said. But I'm talking about brand new cams, don't even get me started on how much the spring effects cams that are all goobered up and need to be lubed. I Know, I've got a BD .75 that needs to be lubed, and takes about five seconds to open back up after it is closed, Hmmm weak spring getting worked by goo how safe is that? Enough said.
|
|
|
|
|
caughtinside
Oct 6, 2004, 6:34 PM
Post #28 of 87
(11907 views)
Shortcut
Registered: Jan 8, 2003
Posts: 30603
|
In reply to: After reading thru this entire thread I feel there are some fallacies that just need to be addressed;
[*:b2721189c5]BD's larger expansion range is not due to a different cam angle, it is due to the use of 2 axles
[*:b2721189c5]BD does not have a lower pullout strength than any other Cam on the market, in fact it is quite the opposite, majority of there cams are rated higher than the competition 16 KN vice 14 KN
[*:b2721189c5]Yes BD's can be used as passive pro but they are not the only cams on the market that can be placed like that. As was said by mingleefu cams with full strength cam stops can also be placed passively i.e DMM, WC, Metolius. BD is however the only one I have heard of thats passive strength is above 10 KN
[*:b2721189c5]According to all the sources I have read from, including WC's Cam book, spring tension has nothing to do with pullout strength. It does, however, have a lot to do with the units tendancy to walk in a placement
With this being said, let me say that I am not a big fan of the BD's myself, not to say that they are bad cams just that I dont use them. I think the redesign will address a lot of the reasons I chose not to buy them.
I think you're wrong on a couple points. #2 you talk about pullout strength, but the 16 Kn isn't pullout strength, it's the breaking strength of the unit.
#3--passive placements. It's true that other cams have full strength cam stops to prevent inversion, but that is only in relation to the other cam lobe. They can still flop sideways if you try to place it passively. BD cams won't because the cam stop is the axel, unique as far as I know.
I feel compelled to point out that these two considerations never cross my mind when climbing however... :lol:
|
|
|
|
|
mingleefu
Oct 6, 2004, 7:49 PM
Post #29 of 87
(11907 views)
Shortcut
Registered: May 24, 2003
Posts: 466
|
In reply to: mingleefu, I hear what you are saying. All apologies to Ike Newton. Yeah, alot of this info is hard to turn up. Nonetheless, BD does have a weaker...or should I say softer, less rigid spring. That is why it is so easy to operate. Prove it to yourself. Take one of each cam and squeeze'em. One is easier than the other, duh. What the much debated spring does is to try to keep the cam lobes in its fully open umbrella position:that's the function. So... the more rigid the spring, the more the cam wants to stay open, and therefore pushes against the sides of the crack, even when it is unweighted. This is not a ridiculous statement. It's not my job to prove all ot these details. Talk to a Rep, or don't. Buy BD or don't. I'm over it. Consider this, if a cam that was not weighted had no spring at all, it would likely fall out of the crack because nothing is making it try to open up until it is weighted. However minute the phonomena of cam bounce may be is something for physics grad students to study, however,it is absolutely effected by the rigidity of the spring. And that is the whole point of what I have said...
Sure dude, I hear you. But I've never even heard of the phenomenon of "cam bounce". Without question, a stronger spring would press the lobes harder against the rock (as you said), so the cam would be held securely while not under load.
I'm familiar with the different trigger actions of different cams- smoothness of handle, displacement of the trigger- I'm just unfamiliar with what you're exactly referring to when you say "cam bounce". Are you suggesting that a weaker spring may, in the event off a fall, allow the cam to skid out a small margin before the full force of the fall is loaded on the cam? For instance, suppose the full deceleration time of the fall was 0.5 seconds; Does the theory of "cam bounce" hold that for the beginning part of that deceleration (perhaps t=0.0 to t=0.05sec), at which time the force on the cam is not yet 100% load, a weaker spring may allow the cam to slide outwards, even if minimally?
I think the counter-argument is this. While it might be true that a stronger spring would resist that outward movement more, any cam on the market would likely be thoroughly tested to ensure that the spring strengths they are using would be found to be more than adequate to prevent such an anomaly.
That came off like a bunch of jargon, but I'm trying to understand what exactly "cam bounce" means. Your first suggestion seems to be that when loaded, the lobes of the cam actually bounce inward (effectively mimicking a narrower placement) off the rock. However, that is something I have a hard time believing without statistic- which is why I asked for sources.
Help me understand.
|
|
|
|
|
omenbringer
Oct 6, 2004, 8:44 PM
Post #30 of 87
(11907 views)
Shortcut
Registered: Sep 19, 2003
Posts: 248
|
In reply to: I think you're wrong on a couple points. #2 you talk about pullout strength, but the 16 Kn isn't pullout strength, it's the breaking strength of the unit. #3--passive placements. It's true that other cams have full strength cam stops to prevent inversion, but that is only in relation to the other cam lobe. They can still flop sideways if you try to place it passively. BD cams won't because the cam stop is the axel, unique as far as I know. I feel compelled to point out that these two considerations never cross my mind when climbing however... :lol:
As far as the passive placement of cams, playing around with my DMM's I could place them passively and seem to remember reading on there old site that you could do it but it was only rated to 10KN.
I would never use them this way though!!!
In reply to: One other thing, does anyone really place cams passively like BD says they can? That has to be one of the best BS marketing ploys ever. When was the last time you saw that perfect "umbrella" slot to place that #2 wide open? |
|
|
|
|
chico
Oct 6, 2004, 9:17 PM
Post #31 of 87
(11907 views)
Shortcut
Registered: Jan 28, 2004
Posts: 39
|
Yeah mingleefu,
You pretty much summed up what I was trying to say in much better terms. I also had never heard of this phenomena until about a year ago. But ya'know, just because we haven't heard of something before doesn't mean that it is not ultimately true. O.K., so as it has been explained to me (in total layman terms), when a cam gets shock loaded the lobes flex out against the walls of the crack. In the instant that happens and the force is applied outward against the crack walls, there is also an inward force (factional, not equal sorry!) that is kind of like a rebound of the lobes off the walls. Under equal shock force loads, the stronger the spring will resist the rebound force, or "cam bounce", and therefore will be more likely to hold in the position that it was originally placed. In contrast, cams with weaker springs will rebound more, and in licheney, soft parallel or wet cracks potentially skid out of their originally intended placement, and at worst, pull out of the crack. Whew, that's alot to say!
|
|
|
|
|
trimix
Oct 6, 2004, 11:04 PM
Post #32 of 87
(11907 views)
Shortcut
Registered: Aug 4, 2004
Posts: 33
|
Has anyone gotten there new stuff yet, or seen it in the stores. BD said there shipping mid Oct
|
|
|
|
|
112
Oct 7, 2004, 12:19 AM
Post #33 of 87
(11907 views)
Shortcut
Registered: May 15, 2004
Posts: 432
|
Okay this “cam bounce” makes me laugh. Yes, theoretically it is possible. Its does not just depend on Newton’s 2d law. “Cam bounce” or any bounce depends on stored elastic energy (resilience) due to deformation. Actually it also depends on the materials ability to return that energy quick enough. Slightly squeeze a marshmallow it will never “bounce” back. However, have you ever shot a rubber band, or a spring? The last two examples are much more elastic than a cam lobe, but the principle is the same.
The cam lobe stores elastic energy as it is deformed (compresses) while being loaded. Now the key is that there needs to be a rapid enough unloading of the lobe so that the cam lobes can expand and “bounce”. If the unloading is not fast enough the lobe will just push back and no “bounce” will occur.
Now, I am in no way afraid that this is going to happen in real life. First aluminum does not store a whole lot of energy elastically (plastic deformation occurs after small strains). Therefore there is not a lot of energy waiting to be released in the cams’ attempt to “bounce”. Second, if you use a rope (which you do right) the rope acts as a huge dampener (kind of why we use it) as compared to the compression of aluminum. Third I believe that if itdid occur it would result in a sort of “chatter” not a true “bounce”.
That said, it is theoretically possible, but highly unlikely and maybe not even possible in “reality” with modern climbing gear. I have in no way run the numbers to check, but believe I understand the principles and so do the manufactures of our climbing equipment.
Ken
|
|
|
|
|
skateman
Oct 7, 2004, 2:06 PM
Post #34 of 87
(11907 views)
Shortcut
Registered: Jun 13, 2003
Posts: 186
|
grin-n-barrett,
Here's my 2 cents. I am thinking that you are new to trad leading. I started leading at
the beginning of the summer. Whoever said that your rack is forever obviously hasn't
climbed with me. I lost 2 #2 robots this summer and almost lost a #3. (I ended up being lowered by second and managed to clean the #3 in under two minutes) The point I'm trying to get across is you may end up losing a lot of gear as a new leader, especially if you are also climbing with a new second. Therefore , you may want to pass on buying the new BD's.
I use robots and metolius for the smaller sizes. (personally they seem to both work equally well, I would even give the robots a slight edge) I use BD's for the larger sizes #2 and up! I do not recommend the #4 & #5 robots because of stabilty issues.
I have never lost a BD, but that may be because I do not place the larger sizes as often. It could also be due to the fact you can see the placement a little better in the larger sizes.
That being said, try useing a variety of cams before making your purchase. Pick the one that best suits your needs.
S
|
|
|
|
|
timstich
Oct 7, 2004, 3:20 PM
Post #35 of 87
(11907 views)
Shortcut
Registered: Feb 3, 2003
Posts: 6267
|
All of this hype because BD now has the same stem design as Trango and others? Big deal.
|
|
|
|
|
johnr9q
Oct 7, 2004, 3:42 PM
Post #36 of 87
(11907 views)
Shortcut
Registered: Oct 5, 2001
Posts: 120
|
Chico: Sounds like people are asking you serious questions regarding your conclusions. I am a mechanical engineer and wouldn't think of coming to the conclusions you did as far as comparing DB vs Wild Country without expensive testing. Unless the black diamond failures were so prevalent that anecdotal stories could substantiate them.
|
|
|
|
|
chico
Oct 7, 2004, 8:45 PM
Post #37 of 87
(11907 views)
Shortcut
Registered: Jan 28, 2004
Posts: 39
|
Johnr9q,
I know man! I'm getting my balls busted here, simply for repeating what was explained to me by a knowledgible climbing Rep. Bounce, chatter, whatever. It makes perfect sense to me that that could happen in a shock load situation. Now, I've taken some decent whippers on BD cams (ya'know 15' or so) and everything was hunky-dory. But sheesh, I feel like I'm talking to the Bush mafia about cam bounce. Like people don't want to accept that it even exists. I didn't make up this concept. Someone with horn-rimmed glasses and a pocket protector actually did the testing and came up with it. Bottom line-for reasons X,Y, and Z BD has fallen out of favor for me. My harness is falling apart, my gloves suck, my headlamp is a piece of crap, my skis are delaming after one season, and they all have a BD logo on them. So they came out with a new cam; whoopdie frikkin doo. It's probably also going to be crap. I'm out-
|
|
|
|
|
grin-n-barrett
Deleted
Oct 7, 2004, 9:12 PM
Post #38 of 87
(11907 views)
Shortcut
Registered:
Posts:
|
Bottom line? is it worth the price to get the new stuff? I love reading everyones banter about the gear....
Should I invest the money for the new gear?
Yes or No ?
|
|
|
|
|
sbaclimber
Oct 7, 2004, 9:25 PM
Post #39 of 87
(11907 views)
Shortcut
Registered: Jan 22, 2004
Posts: 3118
|
NO!!!!
Listen, I am a huge fan of BD gear (which means I save up and spend the extra cash), but that is my personal choice. The next guy to post will probably be totally against BD gear and tell you to never buy their gear.
The reason I said "NO" is because if you cant decide for yourself, asking the rest of the people here (including me) isn't going to help you decide, and if it does, it may be the wrong choice for you. All you are going to get is what you have already accurately called "banter" and people's personal opinions. If you really want to know if it is the right gear for you, you will have to try it out yourself and then decide. I know, "easier said than done", but really all comes down to what kind of gear-head you feel you are :wink:
|
|
|
|
|
rockrat_co
Oct 8, 2004, 1:00 AM
Post #40 of 87
(11907 views)
Shortcut
Registered: Sep 26, 2004
Posts: 194
|
In reply to: Johnr9q, I know man! I'm getting my balls busted here, simply for repeating what was explained to me by a knowledgible climbing Rep. Bounce, chatter, whatever. It makes perfect sense to me that that could happen in a shock load situation. Now, I've taken some decent whippers on BD cams (ya'know 15' or so) and everything was hunky-dory. But sheesh, I feel like I'm talking to the Bush mafia about cam bounce. Like people don't want to accept that it even exists. I didn't make up this concept. Someone with horn-rimmed glasses and a pocket protector actually did the testing and came up with it. Bottom line-for reasons X,Y, and Z BD has fallen out of favor for me. My harness is falling apart, my gloves suck, my headlamp is a piece of crap, my skis are delaming after one season, and they all have a BD logo on them. So they came out with a new cam; whoopdie frikkin doo. It's probably also going to be crap. I'm out-
"Although Im the next guy, i do not perfer other companies. BD is the bomb, most all their gear" :wink:
Hey man,
This force thing. For every force there will be an opposite oposing force. This is indeed true but the oposing force is not a dynamic force. It is there, it does not suddenly magnify when a cam is loaded, the cam itself creates the primary force as far as other forces are concerned, and that is outwards in both directions. The springs inside the camalot, or any cam will have absolutely nothing to do with the holding power because any forces are carried directly through the cam. Once it is placed in a good crack, the spring is rendered near useless until you decide to remove it (pulling the trigger lever).
|
|
|
|
|
buzzard
Oct 8, 2004, 1:04 AM
Post #41 of 87
(11907 views)
Shortcut
Registered: Oct 3, 2003
Posts: 62
|
I will let you know this weekend I am going climbing with a BD rep.
|
|
|
|
|
harihari
Oct 17, 2004, 10:03 PM
Post #42 of 87
(11907 views)
Shortcut
Registered: Jan 7, 2004
Posts: 182
|
As a fan of BD and small Aliens, I want to say
a) Yes, i have placed BDs passively quite often, and this feature alone makes them worth having (if the weight factor on the old ones didn't turn you off).
b) despite the lower srping strength rating, the BDs (in my experience) are the most stable cam to use, because the double axles mean the lobes cannot rotate and twist out in different directions. I have some booty WC and (I think) DMM cams, and both are plagued with this problem.
With trad gear, the "once in a while" factor is important. When I am near my limit, I want the gear to have a variety of safe uses, and the last thing I am going to think about is "did this cost too much?" or "does this weigh one ounce more than the Trango?"
To the person asking about what to buy-- buy what you think is best after having tried lots of cams and talked to ltos of ppl and seconded lots behind somebody stronger than you. And don't skimp. When you are leading the crux of your project, the price of the cam will be far from your mind.
|
|
|
|
|
slcliffdiver
Oct 18, 2004, 12:17 AM
Post #43 of 87
(11907 views)
Shortcut
Registered: Mar 18, 2002
Posts: 489
|
In reply to: Nonetheless, BD does have a weaker...or should I say softer, less rigid spring. That is why it is so easy to operate. Prove it to yourself. Take one of each cam and squeeze'em. One is easier than the other, duh.
I believe a large reason the trigger is easier to pull is the double axle design. It allows the pulling wire (where it's connected to the cam) to be farther away from the axis of rotation for the cam (mechanical advantage). Weather or not the springs are actually weaker I can't tell but you can't tell just by how easy it is to pull the trigger.
|
|
|
|
|
curt
Oct 18, 2004, 12:59 AM
Post #44 of 87
(11907 views)
Shortcut
Registered: Aug 27, 2002
Posts: 18275
|
In reply to: Johnr9q, I know man! I'm getting my balls busted here, simply for repeating what was explained to me by a knowledgible climbing Rep.
No. You are getting your balls busted here for apparantly believing the drivel that some unknowledgeable climbing rep told you. Big difference. Do you believe everything you hear, even the BS?
Curt
|
|
|
|
|
david.yount
Deleted
Oct 18, 2004, 9:21 AM
Post #45 of 87
(11907 views)
Shortcut
Registered:
Posts:
|
In reply to: After reading thru this entire thread I feel there are some fallacies that just need to be addressed
Pullout Strength is far far lower than Destructive Strength
In reply to: BD does not have a lower pullout strength than any other Cam on the market, in fact it is quite the opposite, majority of there cams are rated higher than the competition 16 KN versus 14 KN
Only one manufacturer acknowledges pullout strength is far lower than destructive strength, by labeling its cams with an estimate of real world pullout strength; that manufacturer is Metolius. That is why Metolius smaller cams’ force values are so much lower than every other manufacturer’s smaller cams’ force values. Every other small cam is labeled with its destructive force, whereas Metolius small cams are labeled with an estimate of real world pullout force.
Compare Metolius small cams force values with CCH Alien small cam force values. The aliens have large destructive force ratings, but these ratings do not in any way correlate to pullout strengths. Hats off to Metolius for being the first manufacturer that tries to provide the climber useful strength ratings on their cams.
I've read a few times recently that cams are likely fallible under 2000lbs or 9kN. This force if far below most cams destructive strength.
Springs need only exert a threshold force
In reply to: According to all the sources I have read from, including WC's Cam book, spring tension has nothing to do with pullout strength. It does, however, have a lot to do with the units tendancy to walk in a placement
I wish I could cite the source, a university professor in the US leads a graduate engineering class where they destructively test climbing protection. After several years and many classes and lotsa gear, this professor wrote a paper about climbing cams. Based on this report the company Metolius redesigned their TCU’s in three ways. All of these redesigned parameters have to do with the cam lobes, they did not change the spring tension. But spring tension and its roll in pullout strength is covered in the paper.
Keeping the science to a minimum (and assuming the surface of the rock is fairly smooth with no features), if there is not sufficient spring tension supplied to the cam lobes such that there is not sufficient force applied from the aluminum cam lobes to the rock then the frictional force between the rock and the aluminum lobes will be insufficient to hold the camming unit when a downward force is applied.
Same idea slightly different, the metal lobes will only cam when there is sufficient frictional force between the rock and the metal. If the frictional force is insufficient then the lobes will slide down the rock, rather than cam open and hold the unit in place.
Same idea but more science, (reminding you I’m assuming the surface of the rock is smooth), the frictional force is calculated by using the outward force of the lobe (whose force is supplied by the spring tension) multiplied by the coefficient of friction (c.o.f.) between the rock and metal. The c.o.f. is a fixed value. It is dependant only on the two materials in contact. Metal in contact with rock has a fixed c.o.f., which is quite low actually. I’m sure in the future materials science technology will provide new substances (plastics? metals alloyed with plastics?) that are more durable than metals but with far higher c.o.f.
The c.o.f. of rock to metal may be negatively impacted, or lowered. If there exists water between the rock and metal, this will lower the effective c.o.f. If there exists lichen, this will also lower the effective c.o.f. As well, the c.o.f. for metal to rock is also slightly affected by the exact metal used in the lobes and to a higher degree the type of rock.
So the frictional force that holds the metal lobes in place, so that they may rotate or cam during a fall is determined by the spring tension and the c.o.f. along with any attenuating factors.
As long as the spring tension is above some threshold value, the unit will hold the fall. There exists frictional losses within the camming unit such that the spring’s force will be slightly diminished by the time we’re measuring the outward force of the lobe. As well, after many years use these frictional losses will irreversibly increase, even with proper washing and lubing. Designing the cam springs to supply a force greater than the threshold value is good engineering, in the long run, to overcome these mitigating factors.
But using springs even stronger than this, nothing is gained. Obviously Black Diamond Camalots hold falls, or in the parlance of the previous paragraphs their lobes exert sufficient outward force to keep the unit from sliding while the lobes cam outward during a fall. If is it true that Wild Country Friends (Technical and/or Forged) use springs that create significantly greater outward cam force than BD, I do not believe this extra force aids in holding a fall. There is nothing gained if the lobes exert greater than the threshold force against the rock.
So yes, spring tension has nothing to do with pullout strength. Thanks for your patience.
Like was said:
In reply to: While it might be true that a stronger spring would resist that outward movement more [slight sliding of lobes downward before they cammed], any cam on the market would likely be thoroughly tested to ensure that the spring strengths they are using would be found to be more than adequate to prevent such an anomaly.
Cam Bounce
I have never read about, nor heard about, even anecdotally, the concept of ‘cam bounce’ nor anything remotely similar. Much thanks to mingleefu for the several googles. I arrived at the same conclusion, ‘cam bounce’ is mentioned once on the WC website but beyond that once reference nothing is said about it nor is it defined. I would not put much erudite nor empirical respect in the words proffered by a sales representative.
Trigger Bar pull does not indicate Spring Tension
In reply to: BD does have a weaker...or should I say softer, less rigid spring. That is why it is so easy to operate. Prove it to yourself. Take one of each cam and squeeze'em. One is easier than the other, duh.
The force required to retract the trigger bar is significantly affected by the leverage the trigger wires exert on the lobes. Each manufacturer has a unique design for placing the trigger wires in the lobes, and by design I’m referring to placement. Depending on vertical (proximal vs distal) and horizontal (lateral vs medial) location the trigger pull is directly affected.
If you are in a public restroom and upon leaving push near the edge of the bathroom door, the force you experience is low. If instead of pushing near the opening edge of the door you push near the center of the door, the force you experience is much greater. The location of your hand relative to that hinged door affects the amount of force you need to apply to push that door against its spring.
The location of the trigger wire relative to the lobe affects the amount of force you need to apply (on the trigger bar) to move that lobe against its spring. So when you’re flexing different makes of cams, do not think the stiffness of the trigger pull can tell you anything about the force the springs supply to the lobes.
Camming Angles are constant and universal
In reply to: Camalots have a larger camming angle than most other cams (TCU's for example). This means that it will exert less force outwards on the crack for a given downward force, but is also one of the reasons camalots have greater range.
In reply to: The springs in the cams will not determine the holding strength, the surface area, material strength, and hinge strength are the primary factors!
As experienced and studied throughout the years, as well as concluded in the research paper, cam lobe deformation is the most likely failure mode. As Ken said, plastic deformation [of aluminum cam lobes] occurs after small strains. Stronger materials are warranted for cam units less than 1-inch, and stronger or thicker materials are warranted for cams such as Valley Giants.
Second failure mode was superficial rock shattering. If lobe faces are made wider then the force is exerted over a larger area which decreases the pressure on the rock. Wider cams do not decrease the force on the rock, but they do decrease the pressure which helps to prevent rock shattering, which would catastrophically jeopardize the placement.
david yount.
|
|
|
|
|
drrock
Oct 18, 2004, 12:12 PM
Post #46 of 87
(11907 views)
Shortcut
Registered: Oct 18, 2003
Posts: 610
|
edit
|
|
|
|
|
timmah
Oct 18, 2004, 12:40 PM
Post #47 of 87
(11907 views)
Shortcut
Registered: Mar 19, 2003
Posts: 93
|
In reply to: Maybe you have a physics in PhD |
|
|
|
|
sarcat
Oct 18, 2004, 2:18 PM
Post #48 of 87
(11907 views)
Shortcut
Registered: Jan 22, 2004
Posts: 1560
|
david.y
Thanks for the information and the time it took you to write it up. Nice post.
|
|
|
|
|
slcliffdiver
Oct 18, 2004, 8:16 PM
Post #49 of 87
(11907 views)
Shortcut
Registered: Mar 18, 2002
Posts: 489
|
In reply to: Same idea but more science, (reminding you I’m assuming the surface of the rock is smooth), the frictional force is calculated by using the outward force of the lobe (whose force is supplied by the spring tension) multiplied by the coefficient of friction (c.o.f.) between the rock and metal. snip So the frictional force that holds the metal lobes in place, so that they may rotate or cam during a fall is determined by the spring tension and the c.o.f. along with any attenuating factors.
I believe this is kind of missleading the spring tension does not provide most of the friction during the fall rather the cam angle does by turning a downward force on the piece to outward pressure against the wall. One way to look at how a cam works is by turning a downward force into enough friction to counteract the pull by using leverage to magnify the outward force.
Springs minimize walking and provide an intial "set" so the cam is held in place to allow the above to work.
To see that the above is true; the force of friction has to equal the force of the pull in order for the piece to stay in place. You couldn't pull the trigger on a cam with a spring tight enough to provide enough friction to hold the force of a fall.
In reply to: The location of the trigger wire relative to the lobe affects the amount of force you need to apply (on the trigger bar) to move that lobe against its spring. So when you’re flexing different makes of cams, do not think the stiffness of the trigger pull can tell you anything about the force the springs supply to the lobes.
Agreed to a point though with single axil stems the optimal placement is somewhat pre determined too far out and you can't retract the cams fully or it gets harder near the end to close and the'd be too hard to pull. The reason I'm bring this up is I'm guessing this is one of the main secrets of BD success; since the axil is on the other side of the midline it allows for placing the the trigger wire in a position (out a good bit from the axis of rotation of the cam) that allows for an easy pull throughout most of it's range without sacraficing too much spring strength. Mind you this is mostly an educated guess by looking at cams and trying to guess at leverage and how the direction of pull lines up with the arc of rotation that the wire passes through as it's pulled (also effects mechanical advantage). I figure I'm either wrong or it's an interesting thing "not" to advertise add an advantage to the design.
I just remebered I've heard of bounce also in regards to spring strength. What I heard had more to do eith the elacisticity of the rope and the moment of lowest force on the cam do to the bouce at the end of the drop vs stored energy in the cam. I'm not saying I believe it and I'd be more inclined to worry if I climbed on short bungie cord or got some real data showing this was a real problem but I can undererstand how these things can make impressions on people.
My point is I think it's healthy to bring up concerns you have here as long as you don't misrepresent yourself or the facts. Generally there are enough people to sort through things here and it's not neccesarily a bad thing if the poster learns they are mistaken rather than teach other people something. I leave it to others to critisize/praise for how people "phrase things".
|
|
|
|
|
chico
Oct 25, 2004, 5:57 PM
Post #50 of 87
(11972 views)
Shortcut
Registered: Jan 28, 2004
Posts: 39
|
Wow, David and slcliffdiver,
Thanks for your highly informative insight on cams and cam design. I'm not too proud to admit when I'm wrong, and I was wrong, wrong, wrong! Wrong for believing a rep. Wrong for referring to something that Wild Country touts then doesn't back up, and wrong for posting it as fact. I still have my reasons for being only lukewarm on B.D. and I reserve the right to keep them. However, I think now the big question goes to Wild Country. What the heck is cam bounce? If it is not what their reps say it is then what is it and why are they presenting it as such? :?
|
|
|
|
|
|
