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CCSRacer
Jul 28, 2010, 1:31 AM
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Hey, just wanted to bump this thread to see if there are any updates. I'm a ME student with a lot of past fabrication and machine shop experience, and this sounds like a lot of fun.
The OP Link Cams are just gorgeous 
(This post was edited by CCSRacer on Jul 29, 2010, 1:17 AM)
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CCSRacer
Jul 28, 2010, 2:19 AM
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I'm attempting to make a logarithmic curve directly in Solidworks using the 'Equation driven curve' command. I'm definitely having luck getting the rough idea with parametric equations:
x = e ^ (.244t) * cos (t)
y = e ^ (.244t) * sin (t)
It seems like Solidworks is using radians in this dialog box and this value would approximate a 14° camming angle, right? Then I can just add a coefficient to scale it to size.
Any tips?
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adatesman
Jul 28, 2010, 3:04 AM
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CCSRacer
Jul 28, 2010, 3:13 AM
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That's a good point, kind of hit or miss to tweak the equations in SW. The nice part is that you can set up tangent center-lines, apply a dimension, then go back and tweak the curve equation.
What are the guidelines to locate the axle relative to the curve?
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adatesman
Jul 28, 2010, 3:20 AM
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CCSRacer
Jul 28, 2010, 3:34 AM
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Cool.
I had to think about that for a second with how I have my curve generated... I think I've got it right though. My curve starts when t=0, so my radius at that point is just 1 * my scaling factor. I added a tangent center line at the beginning of my curve, another at 90* from that point towards the axle's axis.
How does this look?
(This post was edited by CCSRacer on Jul 30, 2010, 6:50 PM)
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CCSRacer
Jul 28, 2010, 3:48 AM
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Hmmm, in the assembly the pivot looks high relative to the contact surfaces on the lobes...
(This post was edited by CCSRacer on Jul 30, 2010, 6:51 PM)
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kennoyce
Jul 28, 2010, 3:57 AM
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CCSRacer wrote: Hmmm, in the assembly the pivot looks high relative to the contact surfaces on the lobes...
I'd have to agree. I didn't measure or anything but eyeballing it, I think it does look like that is quite a bit greater than 14 degrees. When I'm designing cam lobes, I just use an excel spreadsheet and import the points into solidworks (probably like Aric does just in mathmatica or whatever he uses). Good work though, and enjoy building your first cam!
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CCSRacer
Jul 28, 2010, 4:20 AM
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Sorry to be a pain... Can you clue me in on importing a curve? Never done it. I've got a file with the curve data inside. Does it need a specific file extension? What is the command in SW?
Thanks for the help!
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kennoyce
Jul 28, 2010, 4:31 AM
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Yeah, no problem, I don't have solidworks right here on my computer so i am just trying to go by memory, but it seems like you just save the file as a either a coma or space delimited text file (three columns one for x one for y and one for z). You then go to Insert, curve, from file, and you browse for the file you saved (make sure you use the drop down file selection to include text files and not just solidworks curve files). I know that it does matter weather it is comma or space delimited, and I think that for solidworks 2008 or earlier you need coma, and 2009 or 2010 needs space delimited. I could have this backwards though. Hope this helps and have fun!
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CCSRacer
Jul 28, 2010, 4:51 AM
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Awesome, you guys rock. Okay, so I'm running into the same hang up as with my other curve. How to plot the axle's center... By nature the curve doesn't have a center. Are you using the curve's start point?
(This post was edited by CCSRacer on Jul 28, 2010, 4:52 AM)
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kennoyce
Jul 28, 2010, 4:57 AM
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When I make a cam lobe, I always have the axle at 0,0 and as long as you don't offset the curve somehow, it should be naturally centered around the origin. I'm out for the night, but I hope this is helpful, I can't think of how to describe it any better than that.
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CCSRacer
Jul 28, 2010, 5:13 AM
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Hahaha, that's when you know it's too late to be winging it!
I didn't notice that it had inserted that curve already oriented to the origin. Right before you posted that I had made an elaborate method with tangent centerlines and driven angle dimensions... as I'm dragging the axle circle around it snaps to the origin and the angles equalize, hahaha... Time for bed!
(This post was edited by CCSRacer on Jul 30, 2010, 6:51 PM)
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adatesman
Jul 28, 2010, 1:52 PM
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CCSRacer
Jul 28, 2010, 2:03 PM
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Cool link. Yeah, so it's not a 'center' in the traditional sense, more like an origin.
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adatesman
Jul 28, 2010, 2:11 PM
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CCSRacer
Jul 28, 2010, 8:39 PM
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Here is a render of a rough assembly. I got some cam lobes modeled with a 14° angle and mocked up some rough components to make the assembly. I did a quick simulation on the assembly too by fixing three of the teeth 'flats' and applying 40kN downwards on the stem. Using 6061-T6 for the lobes (6mm thick) and a steel alloy on the axle (8mm D), this assembly is very strong. 40kN barely stressed it. This was really just meant to get the camming action right and give a base to start refining the other components, surprisingly the mass comes out as 155g
(This post was edited by CCSRacer on Jul 30, 2010, 6:53 PM)
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kennoyce
Jul 28, 2010, 8:51 PM
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I think that fixing three teeth like you are doing in the simulation is screwing up the results. By fixing the teeth you are not allowing for the cam lobes to rotate as the axel bends which is what will really be happening. I may just not understand what you are doing correctly, but the materials you listed shouldn't be able to hold 40 kN.
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CCSRacer
Jul 28, 2010, 8:54 PM
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That's a good point. I am getting lobe rotation, but in order to rotate it's having to elongate and compress the teeth. I haven't tried an advanced restraint like trying to simulate the cams biting into a surface yet. A quick work around might be to put a frictionless pin through the lobe near the contact surface and fix the pin.
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kennoyce
Jul 28, 2010, 9:00 PM
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You'll still have the same problem since the frictionless pin will remain fixed, but in a true scenario, the point of contact changes as the axle of the cam bends. I think you need to simulate a crack and put a friction boundery between the cam and the crack (I don't know how easy this will be in solidworks, you may need to export your assembly to ansys or comsol).
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kennoyce
Jul 28, 2010, 9:08 PM
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One other thing I noticed, I can't tell if you left room in your assembly for the springs. If you didn't, make sure you do because moving the lobes farther apart to accomidate the springs will increase the bending stresses in the axle.
I hope I don't sound like I'm being a jerk, I'm just trying to point out some things that you may have missed as someone who has gone through this process in the past.
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kennoyce
Jul 28, 2010, 9:11 PM
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Oh, one more thing, adding a PTFTW!!!!! to the assembly couldn't hurt either.
edited to hang my head in shame since Aric made this into a new thread thereby eliminating my PTFTW.
(This post was edited by kennoyce on Jul 29, 2010, 12:26 AM)
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CCSRacer
Jul 28, 2010, 9:13 PM
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Absolutely not! I really appreciate any and all informed feedback. I'm a noob! 
I hear ya on the shaft width / spacing. In reality, I'll have much less control over the axle, since it will simply be sourced. As long as it isn't poorly implemented, that shouldn't be an issue.
That first render has everything butting up to each other, but in the one I'm running a sim on now, there is a good bit of space in there.
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CCSRacer
Jul 28, 2010, 9:22 PM
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Hahaha, damn it, I even searched and haven't gotten my head around PTFTW! I don't troll around here much, so I'm out of the loop. 
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