Machsupport Forum
Tangent Corner => Tangent Corner => Topic started by: Overloaded on October 22, 2019, 11:03:06 AM
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:) Hi folks.
I've got a project that requires a cam lobe of specified duration running in a yoke/fork with minimal clearance through complete revolutions.
Say the yoke/fork had a 2" opening. A 2" diameter cam follower offset .1" from its shaft centerline would oscillate the yoke .2 per revolution.
But ......
I want an egg shaped cam lobe that will have a duration of lift as much as possible per revolution but always measure 2" diameter at any point as to keep the yoke/fork free of backlash. I assume it would be shaped sort of like a guitar pick. ::)
Is there a formula, or generator for this sort of thing ?
I can make a crude sketch if necessary.
Thanks.
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In the attached, can I assume that as long as the red and blue are exact mirror images of one another that the OD would be the same anywhere around the periphery ?
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uh .... nope. I see that wont work ...... standing by :)
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Arts Gearotic might help?
http://gearotic.com/
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That did cross my mind. I have it on a different pc, will check it out, thanks.
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Didn't see anything related in the SW, might ask on their forum.
Here is an example of a triangular cam and yoke I found.
The radius's of the cam are ever changing but the ramp up and down at the duration segment are relatively gradual, not a pure motionless dwell but blended closely enough for practical purposes.
This is giving me a worse headache than the Wankel engine :P :o
Cheers :D
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Found a link to exactly what I need, just need to figure how to draw it so I can cut it out with my nc mill.
https://www.youtube.com/watch?v=bSVPOGibdHA
I can get it pretty close with cad but wondering if there is a "dead nuts" way/formula/generator out there.
Thanks,
Russ
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https://www.youtube.com/watch?time_continue=65&v=rKpjAKivfM0
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Thank you Brett, Graham and especially Mr. Reuleaux ;)
All is good now.
:)
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Graham knows all them fancy words! Reuleaux, who would have thunk?
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I started with the image and then using an inscribed circle of 10
Started building the triangles, circles and tangent points then trimming.
seems the lobe circle is a factor of 1.5 and then slid back to a second triangle tip point.
using the intersection point a circle can be created to a tangent point then trimmed.
now to figure out how to work backwards from the needed lobe size.
or you can always scale the item to suit once drawn.
My way of proof of concept and grasping the idea
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now to figure out how to work backwards from the needed lobe size.
I knew someone was watching me ::) THAT was my next question !
I fiddled with it last evening a bit but gave up early.
The other issue is where to place the center of rotation to produce a given "throw".
https://en.wikipedia.org/wiki/Reuleaux_triangle
Thanks :)
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If you know the fork width (2), and the desired corner radius,
wouldn't the base triangle just be the fork width minus 2 x the corner radius ?
::)
Now, make the throw 1.
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After I posted, went back and found I ASSumed some things and I was visually close, but mathematically wrong. :-[
wish id have seen that webpage before i posted
will have to go back and re-address.
thanks for the link
another good brain teaser to fend off dementia :'(
pretty cool functional device, it did remind me of the Wankel engine
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I'm no trig'er, but it looks like everything could be worked out from a few right triangles.
GIVEN:
Fork width = 2
Corner rad = .2
Complete throw of the fork = 1 (.5 x 2)
:)
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:)
Simpler than I initially thought.
Thank Ya folks,
:)
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Arts Gearotic might help?
http://gearotic.com/
Maybe Art could add this to his assortment of "Gearotic Gizmos" :)
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Still did not follow all that last image but it gave me some ideas.
once i understood the tangent points i could create a circle from three points
then the light bulb came on and it all made sense
thanks again
Proves how we can not see the obvious sometimes. yep pretty simple.
will have to pass the info off to Art and see if someday he can fit it in. He does stay busy coding.
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Id forgot to post this image of two different ones
changed only the tip radius
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I knew you could do it 8)
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Still a little confused by the relationship with height and tip radius as I notice the tangent points can bite me if you assume they follow the triangle leg extension logic.
That's why I rely on cad to verify
Trying to get a handle on this to beable to write a function to calculate