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Who else would like to see more wide cams on the market?
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By DannyUncanny
From Vancouver
Aug 24, 2012

I have a design in my head for a large cam that probably infringes on a number of patents. 3 lobes, an offset loading point on the one lobe, kind of like Max cams but without the 3 axles. A complete 360 degree spiral like the Super cam, and a hook that can flip everything around to hook behind flakes like that flake grabbing thing that guy cobbled together, but only have one set of cams on the outside.

Here's a quick idea of what I mean. Nothing is necessarily to scale. I think it should be able to get about 2:1 range. No idea if the flake pinching part would work out. It would require a lot of rotation and torque on the lobe.


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By brenta
From Boulder, CO
Aug 24, 2012
Cima Margherita and Cima Tosa in the Dolomiti di Brenta.  October 1977.

Too many spirals in my figure, but the bottom line is that it agrees with the one posted above.


Spirals
Spirals


  • The red line has constant 14 degree pitch
  • The green line has constant 15 degree pitch
  • The blue line has linearly increasing pitch starting at 14.1 and going up to 17.85
  • The cyan line has polynomial pitch starting at 14.1 and ending at 17.89 such that the pitch at the 60% expansion point is still below 15 degrees


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By Aric Datesman
Aug 24, 2012

Hey Brenta- been on the fence about publishing the equation I'm using, but if it saves you some trouble I can forward you the equation and/or Mathematica program. Thx for double checking my work, btw. Seriously. Been staring at this stuff way too long, and all too easy to miss something stupid. :-)


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By brenta
From Boulder, CO
Aug 25, 2012
Cima Margherita and Cima Tosa in the Dolomiti di Brenta.  October 1977.

This is my script; it works with both Matlab and Octave. I have a more efficient version, which uses closed-form solutions for the differential equations in three of the four cases, but it's messy and efficiency doesn't matter much for this problem.

-------------------------------------------
clear, clf
% Useful constants.
crackWidth = 100;
minRadius = crackWidth / 2;
numPoints = 1000; % for plotting

% Anonymous function handles for generic spirals. All these spirals are
% described by dr/r = tan(pitch(theta)) dtheta. Pitch is a polynomial in theta.
% If the polynomial is a constant, the curve is a logarithmic spiral.

pitch = @(coeff) @(theta) polyval(coeff,theta);
spiral = @(r0,pitch,theta0) @(theta) r0*exp(arrayfun(@(x) quad(@(t) tan(pitch(t)),theta0,x),theta));

% Define curves to be plotted.
spirals(1).color = 'r'; % red
spirals(1).coeff = [14*pi/180];
spirals(1).plot = true;

spirals(2).color = 'm'; % magenta (used to be green)
spirals(2).coeff = [15*pi/180];
spirals(2).plot = true;

spirals(3).color = 'b'; % blue
spirals(3).coeff = [1/33 14.1*pi/180];
spirals(3).plot = true;

spirals(4).color = 'c'; % cyan
spirals(4).coeff = polyfit([0 pi/6 pi/4 pi/2 2*pi/3], [14.1 14.2 14.3 15 17.2]*pi/180, 4);
spirals(4).plot = true;

% Compute details for each curve.
for i=1:length(spirals)
  if spirals(i).plot
    spirals(i).pitch = pitch(spirals(i).coeff);
    % Compute the rotation required to fit the cam in the crack,
    % whose width is twice the minimum radius.
    tmpfun = spiral(1,spirals(i).pitch,0);
    spirals(i).phi = fsolve(@(theta) tmpfun(theta) - 1/cos(spirals(i).pitch(theta)), 0.1);
    spirals(i).theta0 = spirals(i).pitch(spirals(i).phi) - spirals(i).phi;
    fprintf('theta0 %s = %g degrees\n', spirals(i).color, spirals(i).theta0*180/pi);
    % Get the specific spiral.
    spirals(i).curve = spiral(minRadius,spirals(i).pitch,spirals(i).theta0);
    % Compute the final angle.
    spirals(i).finalAngle = fsolve(@(theta) spirals(i).curve(theta) .* cos(theta) + minRadius, 0.7*pi);
    fprintf('final angle %s = %g degrees\n', spirals(i).color, spirals(i).finalAngle*180/pi);
    spirals(i).maxRadius = spirals(i).curve(spirals(i).finalAngle);
    % Compute range. The factor of 2 accounts for the two opposing lobes.
    spirals(i).range = 2 * (spirals(i).maxRadius * cos(spirals(i).pitch(spirals(i).finalAngle)) - minRadius);
    fprintf('range %s = %g mm\n', spirals(i).color, spirals(i).range);
    % Percentages of range.
    spirals(i).pr = zeros(10,1);
    for j=1:10
      spirals(i).pr(j) = fsolve(@(theta) spirals(i).curve(theta) .* cos(spirals(i).pitch(theta)) ...
        - minRadius - j * spirals(i).range / 20.0, 1);
    end
  end
end

% Plot
hold on
for i=1:length(spirals)
  if spirals(i).plot
    spirals(i).t = linspace(spirals(i).theta0,spirals(i).finalAngle,numPoints);
    spirals(i).handle = polar(spirals(i).t, spirals(i).curve(spirals(i).t));
    set(spirals(i).handle,'color',spirals(i).color,'linewidth',2);
    plot([0 minRadius*cos(spirals(i).theta0)], [0 minRadius*sin(spirals(i).theta0)], ...
      spirals(i).color, 'linewidth', 2);
    plot([0 spirals(i).maxRadius*cos(spirals(i).finalAngle)], ...
      [0 spirals(i).maxRadius*sin(spirals(i).finalAngle)], ...
      spirals(i).color, 'linewidth', 2);
    plot([0 spirals(i).curve(spirals(i).pitch(spirals(i).phi))*cos(spirals(i).pitch(spirals(i).phi))], ...
      [0 spirals(i).curve(spirals(i).pitch(spirals(i).phi))*sin(spirals(i).pitch(spirals(i).phi))], ...
      spirals(i).color, 'linewidth', 1);
    for j=1:10
      plot([0 spirals(i).curve(spirals(i).pr(j))*cos(spirals(i).pr(j))], ...
        [0 spirals(i).curve(spirals(i).pr(j))*sin(spirals(i).pr(j))], ...
        spirals(i).color, 'linewidth', 1);
    end
  end
end

xlim([-52 52]);
ylim([0 82]);
line([50,50], ylim);
line([-50,-50], ylim);
axis('equal')
hold off


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By Aric Datesman
Sep 1, 2012

Crap. Had a long explanation of where this project is, and the combination of exhaustion and drooping thumbs on a laptop with touchpad lead to losing the whole thing.

Sigh.

Short version:

Thanks for posting your program Brenta. Seeing that, I'm embarrassed to post mine... Clearly I've not even stayed in a Holiday Inn Express, given how ugly my program is. But it does what I need it to do, so all is well I guess.

Key bit I was talking about is this... the equation I'm using for the curve is along the lines of: (sorry about the lack or reformatting... its hours past when I should have been in bed)

reg[\[Theta]_] = areg*Exp[Tan[\[Theta]reg]*\[Theta] + b*\[Theta]^c + d*\[Theta]^e]

where:

areg = the minimum size crack the piece can fit, taking into account single or double axle and the axle spacing

[theta]reg = the tangent angle of the curve

b = first modifier

c = first exponential modifier

d = second modifier

e = second exponential modifier

In a nutshell, it's not much different from what I heard was done with the SuperCam (with its second order modifier), but with a slight twist that allows the curve to grow within acceptable tan angles within normal rotation (like what I surmise happens with the SuperCam), and then shoot outwards in the last final bit of rotation. IIRC the formula for the plot I posted earlier was something along the lines of:

reg[\[Theta]_] = areg*Exp[Tan[14Deg]*\[Theta] +0.005*\[Theta]^2 + 0.0005*\[Theta]^6]

Sadly, after playing with this for longer that I'd like to admit I don't think there's any benefit from going this route for typical single and dual axle designs, as any gains on the tail end are easily met by simply upping the tangent angle a small amount for a regular log spiral (which leads to the usual Metolius vs BD debate). I've not looked at the implications of what happens with large amounts or rotation, so perhaps this is what lets the SuperCam do its magic. Dunno, and frankly have little interest in pursuing this train of though further unless someone chimes in with a compelling reason to do so.

So, any thoughts?




On a side note, I've been on babysitting duty the past 2 weeks, which means naptime has been spent finally reorganizing the workshop to fit the "new" lathe (1970's vintage Clausing 5900). Which in turn means I'm a big step towards having the milling machine back operational, which means this project is closer to moving forward. Which means anyone with an opinion about what they'd like better start chiming in, otherwise Killis is apparently running the show.


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By DannyUncanny
From Vancouver
Sep 2, 2012

If you are making a large cam with a large hollow axle, then you should ditch the stem completely. Spread the lobes far enough apart that you can fit your fist in the middle. This will increase the torque a bit, but an oversized axle should be able to handle it. The trigger can be a bar and curved slot through the lobes that you simple grab and squeeze. This saves weight and volume, and in my opinion, would make it easier to handle and place.

If you want to get extra range, load off the backside of one of the lobes instead of the axle. It's the same principle as the Max Cams (only one pair is offset) and Totem Cams (all lobes get an offset loading). Or do a complete spiral like the Super Cam. Or do both.


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By Zappatista
Sep 2, 2012
Book me, officer.

I'm running nothing, I'm just up for chipping in so you can push the design envelope. Having something that contrasts with the VGs I'm getting sounds like a worthy investment. I'm in, and suggest bright pink anodization to keep the cam fashionable. I'd no more tell you how/what to build than I'd accept sex advice from the average MP drone-it's a matter of familiarity with the subject at hand.

I've only owned large BDs, never WCs, and I've never even held a VG. Soon, though.

Let your imagination run wild, Aric!


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By Aric Datesman
Sep 7, 2012

All Killer No Filler wrote:
I'm running nothing, I'm just up for chipping in so you can push the design envelope.


True, but you seem to be the only one chiming in, so by default you're in charge... :-)


Been cogitating on Danny's suggestion above re: MaxCam-esque design, and am going to pass on that. I've been sitting on what I think would be a solution to the MaxCam flop issue for a while now (really have to get around to cutting one of my #2's apart to try it...), but my solution won't play well with widely spaced lobes on large sizes due to side loading of the inner lobes.

Anyone have any comments re: the increasing cam angle stuff I posted above? Specifically, which would you prefer: a constant 15 deg cam angle or one that increases from 14 to 15 in the normal usable range (66% expansion) and then jumps up to ~18 deg or so for the last bit? Looks to me that there's no advantage to the increasing angle thing range-wise, but it would give relatively more holding power in the usable range.



-a.


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By DannyUncanny
From Vancouver
Sep 7, 2012

The flop issue is only because the stem and trigger were up at the offset axle. If you stick with a single axle it's fine. If you simply load a long sling off the back of two of the lobes so that they are equalized, you get very little side load (long sling = less side pull). If you still think it is too much, it would be very simple to add a spreader bar to the sling, to keep it from pulling the lobes together.


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By Aric Datesman
Sep 7, 2012

So much for being coy about the solution... But given how long the Totems have been on the market I'm not surprised at how obvious it is now. That project has been sitting on the back burner for years, as I really don't want to cut up a cam that's on my regular rack to prove the idea works...

Anyway, I'm not sure a spreader bar on a soft good would work as you intend. I played with using roller chain to help constrain things, but didn't like that result very much either. Which brought me back to the belief that extended range cams are a dead end evolutionarily, as they're too wide on the small end and too narrow on the big end. YMMV though, and I'm more than willing to discuss this further.

-a.


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By Zappatista
Sep 7, 2012
Book me, officer.

Being honest, I'm really more in the "I'll go break it for ya" category than anything. The engineering talk goes right over my head, no interest for the time being in additional distractions, I have enough of those happening already.

If the cams are functional and offer any differences/advantages from/over the VGs, I'll call it good. Maybe you should track down Jay Anderson and Pam Pack and a few of those who've logged miles on the wide gear more than most alive and get some dialogue happening with them. I'm a hapless consumer, it's really more of a "I don't want to have to solo that horrorshow" concern for me, personally.

My order of both VGs goes in next week, let's get a plan going before I get too broke to chip in or turn into a sport weenie and sell all the behemoths to pay for a Japanese sex pillow/spotting pad.


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By TBD
Sep 8, 2012

My input would be 15 degree constant angle and as light as possible without sacraficing too much durability.

A mechanism to hold the cam retracted would be great but possibly also a liability...


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By Locker
From Yucca Valley, CA
Sep 10, 2012
...

There are some SMART folks on this thread...


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By Princess Mia
From Vail
Sep 10, 2012
Chillin' at City of Rocks

Well the real question is:

Who wishes there were more wide cracks out there????

:-)


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By Greg G
From SLC, UT
Sep 10, 2012
The route in it's entirety.

haha and the thread comes full circle.


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By Zappatista
Sep 12, 2012
Book me, officer.

I see more wide cracks every time I pick up girls at the all-you-can-eat buffets.

WH-OOOOOOOOAAAAAAAA!

Just for fun.

What's the status, Oh Great One? How close are we to banging out a final design?

Anyone else want to take a chance and order one with me?


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By NorCalNomad
From San Francisco
Sep 13, 2012

DannyUncanny wrote:
If you are making a large cam with a large hollow axle, then you should ditch the stem completely. Spread the lobes far enough apart that you can fit your fist in the middle. This will increase the torque a bit, but an oversized axle should be able to handle it. The trigger can be a bar and curved slot through the lobes that you simple grab and squeeze. This saves weight and volume, and in my opinion, would make it easier to handle and place.


Certainly a cool idea for the interface BUT

Problem with that is the length of the pull needed to retract huge lobes VS the "length" that your hand can open / squeeze. That's why the stems on larger cams are larger. Sure you could come up with mechanisms for solving that problem but that'd just add complexity and weight to the design.

Wish I could commit to buying one of whatever gets produced, but school saps all my time and $


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By Unassigned User
Sep 13, 2012

After the 15th of this month I will be able to afford one. I'll chip in Killer boy. 175 I believe was his price.


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By DannyUncanny
From Vancouver
Sep 13, 2012

Ranar wrote:
Certainly a cool idea for the interface BUT Problem with that is the length of the pull needed to retract huge lobes VS the "length" that your hand can open / squeeze. That's why the stems on larger cams are larger. Sure you could come up with mechanisms for solving that problem but that'd just add complexity and weight to the design. Wish I could commit to buying one of whatever gets produced, but school saps all my time and $


I dunno about you, but I can squeeze a hell of a lot harder with a fist than I can pull on a trigger with 2 fingers and an awkward bend in my wrist. That means a shorter pull with a higher force. I would bet even a weak person could fully retract a cam with only an inch or so of pull if they could use their full fist to squeeze the trigger.


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By NorCalNomad
From San Francisco
Sep 13, 2012

DannyUncanny wrote:
I dunno about you, but I can squeeze a hell of a lot harder with a fist than I can pull on a trigger with 2 fingers and an awkward bend in my wrist. That means a shorter pull with a higher force. I would bet even a weak person could fully retract a cam with only an inch or so of pull if they could use their full fist to squeeze the trigger.


You're missing this part.

Sure you could come up with mechanisms for solving that problem but that'd just add complexity and weight to the design.


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By DannyUncanny
From Vancouver
Sep 14, 2012

Having a different amount of trigger pull doesn't take any additional mechanism. With regular cams it is only a function of the location where the trigger wires attach to the lobes. With the squeeze thing I'm talking about it is a function of the curve you cut your slot at. These are all basic features that you need regardless of whether you want long trigger pull or short.


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By Greg G
From SLC, UT
Sep 15, 2012
The route in it's entirety.

Danny let's see a drawing of your design! I can sort of picture it, but am still having trouble grasping the full package.


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By Aric Datesman
Sep 17, 2012

All Killer No Filler wrote:
What's the status, Oh Great One? How close are we to banging out a final design?



I thought it was mentioned a couple posts up that the thread has come full circle, like Finnegan's Wake?

Kidding aside, I don't know I've seen opinions one way or the other on the expanding cam angle thing, so that's still up in the air as far as I'm concerned (in spite of my vote against it).

Also, with the wide-mostly-used-for-TR-as-you-go I'm coming around to the MaxCam-esque design. I've got quite a few MaxCams and thinking on it more most of my issues with them are easily avoided with the push-the-gear-as-you-go-TR-the-wide approach. I mentioned there being an issue with off-axis loading earlier, but that's easily solved by me simply getting thicker material... And frankly, I'm much more excited about doing a quasi-MaxCam (with the aforementioned change to single-axle, loaded on a lever thing) than a larger BD knockoff, so I guess that's where my vote is. Simply the more I think about it, the less concern I have about larger sizes getting over-square (to steal the car engine term) and getting tippy, since they're generally not left as pro and instead pushed ahead on TR.


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By Aric Datesman
Sep 17, 2012

DannyUncanny wrote:
Having a different amount of trigger pull doesn't take any additional mechanism. With regular cams it is only a function of the location where the trigger wires attach to the lobes. With the squeeze thing I'm talking about it is a function of the curve you cut your slot at. These are all basic features that you need regardless of whether you want long trigger pull or short.



I completely get where you're going with this, Danny, and strangely spent the past couple weeks pondering this very thing. Personally I think it's a dead end since I think you run into issues with getting it to handle unequal expansion and have to resort to the MaxCam 3 axle solution, the quasi-MaxCam solution mentioned upthread or a fun-but-not-practical double-axle-cam-with-only-one-axle solution I may or may not have mentioned upthread. On the off-chance I didn't mention it, the short version is that it's possible to mimic the relative lobe movement of a double axle cam in a single axle design. And not only that, once it's simplified to a single axle you can turn what had been the spacing between the axles into additional expansion range, but in the end the springs are a nightmare since it involves both rotational and linear movement. For a while I though magnets were the solution, which lead to a really-fun-but-going-nowhere-because-of-the-Splitter-Cam-patents springless design, but even that didn't get around the fact that the slot needed to make the single axle behave as a double axle compromised the strength of the lobes in flaring placements.

Anyway.... I'm voting for a single axle, loaded by a sling on the center lobes design. I had written that off for the smaller stuff I've been working on, but I've come around to the idea that big stuff is used differently.


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By DannyUncanny
From Vancouver
Sep 18, 2012

Greg G wrote:
Danny let's see a drawing of your design! I can sort of picture it, but am still having trouble grasping the full package.


Here is a quick mockup of how a squeeze trigger would work. Obviously the top bar wouldn't be floating free like that. The back face is just another spiral with a very steep curve. So you don't have any stem, you just fit your hand between the lobes and squeeze the bars together. When you let go, the bar should spring back out so it doesn't interfere with anything.

I've got some ideas about how this could work for smaller cams too.


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