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New custom feature: Arbitrary gear path
imants_smidchens
Member Posts: 82 EDU
hey all! another janky feature from the smidchens household - take whatever path you want (elliptical, polygonal, spline…) and generate gear teeth along that path using local curvature to drive involute profile.
snag it here: https://cad.onshape.com/documents/8f033780ed64a1971e38c2a9/
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Comments
Cool stuff, never had to use one of non-cylindrical gear types but always admired the coherence
Very cool! There are times you could make good use of that, E.G. for retractable devices in automotive applications.
I know not yet which project this will be useful for, but my company has dozens of gear walls in the portfolio. This opens up the design space a little more to get weird with it. Surely we will not regret making square gears the primary drive of an exhibit.
Derek Van Allen | Engineering Consultant | MeddlerLots of improvements in latest version! Better performance, better stability, fixed some geometry issues, added more feature capabilites (root fillet, clocking, editing logic, and lots more)
plus published with guide pdf etc.
What wizardry is this?
I kinda get the pitch circle and the other pitch ribbon, but the other wavy one…. can you explain the man behind the curtain here?
Simon Gatrall | Product Development, Engineering, Design, Onshape | Ex- IDEO, PCH, Unagi, Carbon | LinkedIn
Ok it's a bit jank, but the principle is as such:
it's not hard to set up the path for the pinion (tangency between pitch curves, coplanar), the hard part is getting the rotation to match the motion along the path.
My thought process was:
* I am converting from translational motion to rotation, so I will need something like a rack and pinion relationship
* The ratio changes as the pinion moves along the path. This ratio can be expressed by the accumulated rolling distance along the path
* I wrote a quick script to convert between the x position on the pitch path (assuming it is monotonic in x) and the accumulated rolling distance, fitting a spline to this. That's all that second ribbon is: a geometric representation of the function mapping from x coordinate to rolling distance as a y coordinate
* there's some helper geometry to essentially just capture the relevant stuff from there:
* a line pointing from center of circle to the tangent path, with a tracker on that intersection (the contact point between the rack and pinion)
* a thingy that matches the x position of the tracker and travels along the x axis (probably redundant but ehh)
* a thingy that matches the x position of that, tangent to the function curve
* a thingy that matches the y position of that, locked to the y axis with a slider relation
* a rack and pinion relationship between this y axis thingy and the rotation of the pinion
Clever.
How much more amazing it would be if we ever get FeatureScript in Assemblies? One can imagine a Gear Mate Plus feature.
Simon Gatrall | Product Development, Engineering, Design, Onshape | Ex- IDEO, PCH, Unagi, Carbon | LinkedIn
Along these lines: Here's a truly cursed piece of track I made recently. Nothing so clever as your script. There's a video of this in action coming to a YouTube near you soon.
Pretty cool Imants. Haven't worked with elliptical gears since college. Was a lot of work with a drafting board and math book.(1979) Did manage some velocity curve printouts on the school Main Frame using the punch cards for Wat4-Wat5 Fortran. He He 🙄
Sure didn't try to work through anything more free form like this.
that's pretty neat! I'd love to see the video when it's up :)
now part of me wants to get the script to work on 3D paths…
That's extremely cool. Do you by chance have any photos of the original drafting board drawings?
No. They probably went to the same person I loaned the drafting board to. Didn't ask for it back. It was a beast to move around and by the mid eighties I was working with a computer for drawings and an up to date version of Fortran.