desmodromic valves

joe_malle015

Hi - I'm an onshape beginner.  I'm trying to model desmodromic valves from https://en.wikipedia.org/wiki/Desmodromic_valve

I have https://cad.onshape.com/documents/bf37568cc295f8da5ab4f41a/w/84bd7e4d3b3520dbb9c8db8b/e/7931a0488897a8f8fe78d87e so far.

As you can see, the part of the cam that controls when the valve closes is wrong.  I did this part of the cam pseudo-freehand to approximate what I'm trying to create. Ideally this part of the cam would be tangent to the orange lever part (named "desmo").



Is it possible for onshape to deduce the shape that this piece must have so that a tangent mate between the face of the cam and the "desmo" lever would work?

P.S. I have some programming experience, so I don't mind if the answer requires scripting.

eric_pesty

I'm thinking the "Rect to Polar" FS might help (or at least could be a starting point for creating something that would work):

https://cad.onshape.com/documents/075755f3a5af3b131044db83/w/1831ce24396a3690795010a3/e/a91b0a601fac142884f40996

Konst_Sh

with cams you always should start from the law of movement, draw it in XY coordinates and then we can use it to drive the cam profile generation feature

john_lopez363

From what I've surmised it seems like the relationship between all the mating surfaces and pivot points in these desmo valves are interrelated.  IE. change the size the main cam and you have to change ALL of the geometry and sizes of everything else.  Now I will say this is just me observing whats happening.  I'd say the engineering/mathematics of these valve is fairly complex.

ANYWAY... thought I'd play around a bit and came up with this!

steve_shubin

Interesting that the most expensive car ever sold uses this type of valve

joe_malle015

Thank you for your advice.  I tried using rect to polar and drawing the laws of movement.  I was able to create this https://cad.onshape.com/documents/eaaac03eb7ff33f7c40ce3ca/w/ef37dd9bebdc9fce55acac5a/e/f0b58e55156236ee4ba2bbb1

I'm pretty satisfied with this result, although there is still a small overlap between the new "desmo" lever and the cam at some angles.  Any advice on how to rectify that?