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What mates should I use for a Reuleaux triangle rotation?
john_hackington
Member Posts: 43 ✭✭
Hi,
What mates should I use to get the Reuleaux triangle to rotate within the square in this assembly?
https://cad.onshape.com/documents/c7076af1b7a1f5c3cad9aa33/w/328860a966179beb4ec367d4/e/723a794413f54436d42a9000
An illustration of how the rotation should look like:
https://commons.wikimedia.org/wiki/File:Reuleaux_triangle_Animation.gif
Thank you!
What mates should I use to get the Reuleaux triangle to rotate within the square in this assembly?
https://cad.onshape.com/documents/c7076af1b7a1f5c3cad9aa33/w/328860a966179beb4ec367d4/e/723a794413f54436d42a9000
An illustration of how the rotation should look like:
https://commons.wikimedia.org/wiki/File:Reuleaux_triangle_Animation.gif
Thank you!
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Best Answers
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This is very similar to a Wankel engine - very easy to do.
You will need;
an eccentric cam
2 revolute mates
1 mate relation
Philip Thomas - Onshape5 -
Hi Philip,
Thanks for the cue! I'm able to successfully get the rotation with what you've suggested
https://cad.onshape.com/documents/c7076af1b7a1f5c3cad9aa33/w/328860a966179beb4ec367d4/e/723a794413f54436d42a9000
Wondering though, do you think it's possible to get the same rotation without adding a physical external cam?
@philip_thomas1 -
@john_hackington
@philip_thomas
I have made an example showing it using two tangent mates:
https://cad.onshape.com/documents/6837f48dc8d88fe44c98ed6c/w/edf8e3d61121b32e22b73ef6/e/94fe1bf6544bf4b399de5df3
Just make sure you rotate the triangle slowly otherwise it goes wonky.6 -
@john_hackington if you don't want to use physical cams, use a sketch! https://cad.onshape.com/documents/825620768ae3a5beefc53dc9/w/e8a5d084cdc07c1cee0e63fc/e/f60a9dbb830285433efcaa50
Senior Director, Technical Services, EMEA2
Answers
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This is very similar to a Wankel engine - very easy to do.
You will need;
an eccentric cam
2 revolute mates
1 mate relation Philip Thomas - Onshape5 -
Hi Philip,
Thanks for the cue! I'm able to successfully get the rotation with what you've suggested
https://cad.onshape.com/documents/c7076af1b7a1f5c3cad9aa33/w/328860a966179beb4ec367d4/e/723a794413f54436d42a9000
Wondering though, do you think it's possible to get the same rotation without adding a physical external cam?
@philip_thomas1 -
@john_hackington
@philip_thomas
I have made an example showing it using two tangent mates:
https://cad.onshape.com/documents/6837f48dc8d88fe44c98ed6c/w/edf8e3d61121b32e22b73ef6/e/94fe1bf6544bf4b399de5df3
Just make sure you rotate the triangle slowly otherwise it goes wonky.6 -
@john_hackington - nicely done!
@mbartlett21 - tangent mates are awesome, but they are also very finicky (in any cad system) - wherever there is more than one solution, or a singularity (eg tool in a corner touching two faces its supposed to be tangent to), then they tend to become unpredictable or 'stuck'.
Johns solution is far more robust and mimics the driving mechanics of the mechanism.
Be like John Philip Thomas - Onshape0 -
@philip_thomas - Thanks for the encouragement! I believe @mbartlett21 was trying to answer my contemplation of whether it could be done without an external cam with his example. It's great that we get to use this opportunity to learn from you the pitfall behind tangent mates and get a better understanding of the cad system
On further thought of eliminating the physical external cam, I realize that the cam being "physical" is all a matter of my own perception. I could easily just hide the external cam and it would just be an invisible implicit rule of how my actual physical part should move.
@mbartlett21 - Thanks for looking into the problem and trying to devise an alternative solution! I did consider using tangent mates too, but besides the wonkiness of the resultant mechanism, the Reuleaux triangle would also no longer be an object of constant width if we fillet the edges.
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@john_hackingtonjohn_hackington said:
On further thought of eliminating the physical external cam, I realize that the cam being "physical" is all a matter of my own perception. I could easily just hide the external cam and it would just be an invisible implicit rule of how my actual physical part should move.
BTW, even if you hide the part in the assembly, it will still show up in any drawing that you do of the assembly.0 -
@mbartlett21BTW, even if you hide the part in the assembly, it will still show up in any drawing that you do of the assembly.
You're right indeed! I did a quick search and it seems to be an improvement item that they're working on. Hopefully there'll be a function in the near future for it.
https://forum.onshape.com/discussion/6956/part-visibility-in-assembly-drawings-for-illustrating-assembly-steps
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Gents - not only is there an enhancement request, there is a technical paper written by our top guy
that describes how to do exactly what you're looking for!
https://learn.onshape.com/learn/article/branching-to-control-part-visibility
Philip Thomas - Onshape0 -
@philip_thomasphilip_thomas said:Gents - not only is there an enhancement request, there is a technical paper written by our top guy that describes how to do exactly what you're looking for!
https://learn.onshape.com/learn/article/branching-to-control-part-visibility
But suppressing the parts will make the mates not work.0 -
It would be just for assembly drawing purposes. Your main assembly would still have the cams unsupressed.0
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Thanks everyone for the inputs! It's a treasure trove of information out there and it's great to learn something new everyday. Kudos to the Onshape team too for the extensive learning materials and the continual improvement on the product 0
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@john_hackington if you don't want to use physical cams, use a sketch! https://cad.onshape.com/documents/825620768ae3a5beefc53dc9/w/e8a5d084cdc07c1cee0e63fc/e/f60a9dbb830285433efcaa50
Senior Director, Technical Services, EMEA2 -
@mbartlett21 - You asked how to control the visibility of parts in a drawing, that's exactly what the technical paper explained how to do
What are you trying to do?Philip Thomas - Onshape0 -
@NeilCooke
Wow! Thanks Neil, this is so elegant, it's very much just what I was looking for! I'm utterly delighted in all the capabilities that I continually uncover from Onshape0 -
I wanted it to be able to rotate properly and not have the parts in a drawing.philip_thomas said:@mbartlett21 - You asked how to control the visibility of parts in a drawing, that's exactly what the technical paper explained how to do
What are you trying to do?
Don't worry, @NeilCooke answered it in his post above (https://forum.onshape.com/discussion/comment/37486/#Comment_37486)
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Just noticed,
The reuleaux triangle intersects the outside at some points.
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