strategy for bicycle chain

john_denver

Hello, I would be interested in the concrete procedure to produce a bicycle chain, complete with the gears. And then mate the whole thing so that it turns too. So far, I've been able to construct and mate the chain itself, but how do I put it around the gears?

NeilCooke

Sorry, this cannot be currently done as it requires intermittent contact that Onshape does not yet support. Please create an improvement request. 

You could try using Tangent mates but I suspect it would not work as expected. 

john_mcclary

Tangent should work, but you won't be able to change gears without stopping the animation and switching configs

To do that, create a path by making an in-context surface for example. Then mate each chain link to eachother, and at least one tangent mate touching the path. A point tangent to the path should be better than any curve/edge/face of your link.

A lot of calculations will need to be made, so it many only rotate smoothly by running an animation. 

Also be wary of tangent mates wanting to flip inside out, so build it up one link at a time in position

john_mcclary

As a matter of fact, my boss requested that I make a sales animation for one of our chain conveyors. So I will be testing out this theory soon and learning along side you. My path is as wavy as your bike chain (assuming you have a derailer) so the same tactics will be needed

romeograham

@john_mcclary
Would you leave the two free ends of the chain loose (unconnected to each other)? I can imagine no end of challenges for the calculations if the length of the path is not precisely correct as the chain is moved along the path. The first / last links could be slightly overlapping / separated so that it's hard to see with the naked eye.

Or do you think it would work out fine to have them connected?

john_mcclary

Definitely loose, Otherwise it would over-constrain

Also, the fewer mates the better. We don't want to calculate a bunch of redundant mates that could bind.

konstantin_shiriazdanov

john_mcclary said:

Tangent should work, but you won't be able to change gears without stopping the animation and switching configs

I can't see how you can animate moovement along closed path and rotation of some object like gear simultaneously. The strategy which you deleoped for rubics cube would hardly work for closed paths of arbitary shape since any guiding object would give several intersections with the closed path and possibly too big nonlinear distorsions of path velosity relatively to the gear itself.

john_mcclary

My initial plan is to create some driving geometry that will be hidden behind the path.

kind of like a cam on a 2d plane. I would add some "floating" mates that only connect to the masterlink. to relieve any math error between the cam and masterlink.

then imagine a grid, plot out some keyframes where the masterlink would be at any given point of time in x,y coordinates

then you will be driving the x and y path of the masterlink by using a cam and pushing the cam around with a wave on a timeline like the rubiks

This is just my first thought, tottally untested, but in theory I don't see any reason that it can't work. Just may run into a work around or two on the way.

FIST and foremost, mate ONLY a master link, and try and drive it around the entire path by dragging with your mouse.

if you can do that. then we animate the masterlink.

if we can do that. then we connect the other chain links one at a time. (which I know we can do from our energy-chain animations)

john_mcclary

Another way to imagine it is an etch-a-sketch.
We just animate the knobs and tie the master link to the stylus

konstantin_shiriazdanov

@john_mcclary hah, this may work. didn't thought about encoding both 2 dimensions of the path with cams, but just after I wrote it, I understood that have already made something like this. just try to animate revolute1 or revolute2 mates:

https://cad-usw2.onshape.com/documents/861406b7153c3c3f8f14b81e/w/543e1bcb3262381030467b73/e/c02c75a4336ae5cb70172f9f

john_mcclary

I'm 5 today...

konstantin_shiriazdanov

it was originally inspired by this gif

romeograham

I thought it shared some content with John's sketch!

konstantin_shiriazdanov

romeograham said:

I thought it shared some content with John's sketch!

Definitely, they are both conveyor contours

john_mcclary

romeograham said:

I thought it shared some content with John's sketch!

Hah, I didn't catch that at first

philip_thomas

Oh boy!

• In general, modelling chains is just a really bad idea! (for 100 reasons - just model a belt)
• If you are modeling an energy chain - Neil has posted an efficient solution.
• If you are a chain designer, understand (as Neil has previously stated), that there is no support for intermittent contact.
• If you are building a 'finger-giver-machine' like Konstantine, then yes tangent mates are the way to go - but remember that tangent mates have limitations
•      They dont like changing direction (avoid singularities)
•      They dont like multiple solutions
•      They are very 'expensive'

• Many mechanisms (eg scissor lifts) devolve to linear motion - in that case, importing a sketch of a straight line and then slider mating to that sketch solves very fast and reliably.
• If you need a tangent mate, an edge solves faster than a face.
• In general a tangent mate is the mate of last resort

john_mcclary

Yes, I understand that

But in my case it is for a sales animation, where detail is requested by my boss.
I assume in his case he just wants to do the same.

Otherwise yes, when it comes to the technical model, Simple is best