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Who else would like to see more wide cams on the market?
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Oct 3, 2012
Right now it's a combination of linear and exponential terms. If there was no friction, a linear spiral would produce a constant torque. The angle increases as the torque arm decreases. But to overcome constant friction rather than constant torque you would want a constant angle. So I just guessed something in between. This is assuming that the goal is a consistent trigger pull force which might not be true. DannyUncanny
From Vancouver
Joined Aug 27, 2010
78 points
Oct 26, 2012
The route in it's entirety.
Good thread bump Kill. My vote is for a stem in the design, but every designers plan are their own personal baby so I doubt my opinion will go very far. Greg G
From SLC, UT
Joined Oct 3, 2008
580 points
Oct 26, 2012
Hittin' Miguel's with the new Chimps in tow
It seems to be that Danny's design could pretty easily accomodate an optional stem that clamped on the axle, and had a trigger w/ wires that wrap the trigger bar. The conversion wouldn't necessarily be a crag-side mod, but it seems that it wouldn't be that difficult to adapt the design to have both possibilities.

Disclaimer: I'm not an engineer, but I did spend four hours in meetings with them this morning.
Matt Roberts
From Columbus, OH
Joined Mar 24, 2010
97 points
Oct 27, 2012
Matt Roberts wrote:
It seems to be that Danny's design could pretty easily accomodate an optional stem that clamped on the axle, and had a trigger w/ wires that wrap the trigger bar. The conversion wouldn't necessarily be a crag-side mod, but it seems that it wouldn't be that difficult to adapt the design to have both possibilities. Disclaimer: I'm not an engineer, but I did spend four hours in meetings with them this morning.


NorCalNomad
From San Francisco
Joined Oct 6, 2011
116 points
Nov 2, 2012
Nope, not dead. Just no time to work on it lately as I finish buttoning up the outside of the house I'm renovating before winter hits (250 feet of hand dug French drain through heavy clay and bamboo forest, several hundred pounds of stucco, paying someone to replace the roof). And now that's almost done I get hit with the hurricane and will be without power for a week or so....

Sigh... On the upside, camping at home means a flush toilet and proper bed. Thankfully the blower on the fireplace insert can run off a small inverter, so we have heat (unlike many of our neighbors). Not so fun is the live 240 volt line sitting on the sidewalk 20 feet from my front door, or the *possibly live* 35,000 volt line laying next to it. Police tape everywhere, and the power company has someone stationed there 24/7 to keep people away from the wires. Oh, did I mention I live in town? That guy's pretty busy. On the upside, watching the neighbor's tree burst into flames when the 35,000 volt line grounded to the ground line in the 240 volt bundle was quite fun.

Good times. Anyway, off to cleaning up debris at the in-process house. Lost a couple trees there, but otherwise no big deal.
Aric Datesman
Joined Sep 16, 2008
145 points
Nov 2, 2012
The route in it's entirety.
Good to know you're safe and sound Aric. Greg G
From SLC, UT
Joined Oct 3, 2008
580 points
Nov 2, 2012
Thx. All in all, I don't have it so bad. Lots of good discussion and play-by-play on ST in the "OT: Sandy" thread. I've got a bunch of pics there, as do some of the other mid-atlantic folks. Only thing that bothers me is the guy a couple doors down who feels it's ok to be running his giant illuminated Halloween display while the rest of the block is without light or heat. The break happened between the pole in front of my house and the one in front of his, and the electric is fed from his side. What a dick. Aric Datesman
Joined Sep 16, 2008
145 points
Nov 30, 2012
Still no time to work on it, but with the holidays coming hoping to still have a proto ready for testing by the end of the year. Unfortunately day job takes precedence, which is also why I only got out climbing once this year... :-( Aric Datesman
Joined Sep 16, 2008
145 points
Nov 30, 2012
Chillin' at City of Rocks
And so many are talking about ice...... Dont get me wrong, i love ice porn, but this thread makes me realize there is nothing better than OW porn....I think I must do a little more awful this season..... Princess Mia
From Vail
Joined May 22, 2006
422 points
Nov 30, 2012
FWIW, the current problem is I simply can't get my head around the math for the quasi-MaxCam thing. Seems a fairly straight forward problem with the effective lever arm being the cosine of the angle * length, but generalizing it such that it has an effective 14 degree cam angle across the entirety of the rotation is giving me fits. To the point that once I get time to work on it again I'm going to give brute force a try and see how close I can get with manually tweaking the log spiral to account for the change in leverage. But with a 2.5 year old running around and life in general, hobby stuff like this has taken a back seat. Sorry about that, but still hoping to get a proto ready by the end of the year.

-a.
Aric Datesman
Joined Sep 16, 2008
145 points
Dec 3, 2012
Cima Margherita and Cima Tosa in the Dolomiti di B...
Aric Datesman wrote:
FWIW, the current problem is I simply can't get my head around the math for the quasi-MaxCam thing. Seems a fairly straight forward problem with the effective lever arm being the cosine of the angle * length, but generalizing it such that it has an effective 14 degree cam angle across the entirety of the rotation is giving me fits.

Aric, some time ago, maybe a couple of years, I emailed you a .pdf file. Not sure you got it, but if you did, look up equation (4.6) and the discussion surrounding it. The differential equation is simple enough, but evaluating the derivative requires solving a nonlinear equation at each step.
brenta
From Boulder, CO
Joined Feb 2, 2006
72 points
Dec 3, 2012
Aric Datesman wrote:
FWIW, the current problem is I simply can't get my head around the math for the quasi-MaxCam thing. Seems a fairly straight forward problem with the effective lever arm being the cosine of the angle * length, but generalizing it such that it has an effective 14 degree cam angle across the entirety of the rotation is giving me fits. To the point that once I get time to work on it again I'm going to give brute force a try and see how close I can get with manually tweaking the log spiral to account for the change in leverage. But with a 2.5 year old running around and life in general, hobby stuff like this has taken a back seat. Sorry about that, but still hoping to get a proto ready by the end of the year. -a.


I wrote a simple numerical solver to calculate lever arm cam curves. The basic idea is that the origin is the axle location. You input a starting lever arm location in x,y, and a starting contact location c_x. The contact curve is defined by c_x and c_y. For each increment c_y is defined by the horizontal distance from the lever arm to the contact point multiplied by the caming ratio. So a cam ratio of 0.25 is approx 14 deg. Do this for every incremental step in angle, while rotating c_x and you get your final curve.

So the equations I have xi and yi are simply a rotation of x and y by whatever angle theta. xi=x*cos(theta) - y*sin(theta), yi=x*cos(theta)+y*sin(theta). c_xi is simply the previous contact position, c_x(i-1) ad c_y(i-1) rotated by the angular increment, and c_yi is defined above, the cam ratio times the horizontal lever arm. To get an actual series of points along the curve, you have to rotate the c_x and c_y values backwards by whatever angle they are for.

Here is the excel file, maybe that will better explain the calculation. Sorry I didn't keep the same notation.

dl.dropbox.com/u/107337915/cam...
dl.dropbox.com/u/107337915/cam...
dl.dropbox.com/u/107337915/cam...
DannyUncanny
From Vancouver
Joined Aug 27, 2010
78 points
Dec 3, 2012
Thanks Brenta and Danny. Will see if your work speeds thing up when I get time. Sadly that's the thing that's lacking, and the reason this project stalled. To give you an idea, this was my day today:



Buddy came over and we took out ~2.5 cubic yards of clay and building debris (mostly large chunks of shale). Now that we got to the far wall the plan is to hook right and take out another 10 cubic yards, so that I can fix a pair of floor joists along the back wall (house is 150+ years old and needs a lot of this kind of work). Once that's done we turn around and thing about clearing out another 20 cubic yards the other direction so there's access to rewire the place and do away with any future termite concerns. All before he moves to DC in a couple weeks.

And this was after me hand digging 240' of French drain in clay the past couple weeks... :-(

Sorry this has dragged on so long, but with winter/snow coming life's getting in the way... Still want to get a proto done and to one of you guys by year end, so keep on me about it. :-)

-a.
Aric Datesman
Joined Sep 16, 2008
145 points
Dec 3, 2012
Danny, that's BRILLIANT! I was approaching it as modeling a quasi-log spiral with an increasing then decreasing tan angle, and getting nowhere with it. There's a solution there somewhere, but not one I'm going to find anytime soon. Solving it numerically is less elegant, but actually got the job done so tip of the hat to you!

Will look at it when I get a chance and hopefully this gets me to simply doing the machining (which is the part I'm good at...)

-A.
Aric Datesman
Joined Sep 16, 2008
145 points
Dec 3, 2012
Brenta- I'm sure I got your pdf, but frankly don't recall it... Lost track of a lot of things ~when I left RC, so perhaps it fell in with that?

BTW, took me a couple tries to get through DiffEq... Always been more of a make-it rather than design-it type. :-)
Aric Datesman
Joined Sep 16, 2008
145 points
Jan 14, 2013
Quick bump before (whatever Killis is calling himself nowadays) notices I missed my end-of-year deadline... Project's not dead, but still on pause. The house restoration project takes precisence, and I'm still eyeballs deep. Will get back to this when I can, but anyone gearing up for Spring should probably give Tom@VG a call...

-Aric.
Aric Datesman
Joined Sep 16, 2008
145 points
Mar 28, 2013
Thanks for the ping, Killis.

Let's see... Status of this project.... Well, it was on hold while I finish up restoring this old schoolhouse, and plaster repairs inside have resulted in buying (and spending 2 months fixing) a 1957 Case 310 Loader/Backhoe. And by fixing I mean there was 15 pounds of welding rod involved, just to get it functional.

No chance of me poking at this cam project until at least mid-summer, which likely means next winter, and I strongly suspect I'll miss yet another season of climbing.

On the upside, I think I've finally had enough of old houses, and backhoes are cool.
Aric Datesman
Joined Sep 16, 2008
145 points
Mar 28, 2013
Oh, and as absurd as that all sounds, there's pics in several threads on ST regarding both the house renovation and fixing the backhoe. Too hard to post pics here from the phone, so take a look on ST of you're so inclined. Aric Datesman
Joined Sep 16, 2008
145 points


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