Is it possible to setup a gear mates and relation for a counter mechansim?

max_tran483

I would like to setup a gear relation for a counter mechanism. The simplest one is shown in this video:
https://youtu.be/rjWfIiaOFR4?t=40. I tried but so far have not figured it out. Those who would like to try this problem can search for a two disks counter mechanism, a design that used two of these gear arrangements. Such mechanisms are also used in the Curta mechanical computer. But those are far too complicated to analyze. Thanks for any help you can give me.

george_machin

@max_tran483 If you're still working on this I managed to get it to work using a bit of trickery inspired by the Geneva mechanism @EvanReese mentioned.

Assembly | Counter Mechanism (onshape.com)

trevor_tollefsbol

Hi @max_tran483, I just setup a really quick example, but the key to gear mates is setting up the right "Cylindrical" mates first.  I realize this example is extremely simplistic, but the concepts can be used to expand into the counter mech shown in your video. 

In my example below, I use 3 cylindrical mates that are referenced in the gear mates.  1 Cylindrical mate for each counter wheel, and then 1 cylindrical mate for the driving gears.  The driving gears are fixed to each other so they rotate together.



Then, when you setup the gear mates, you set the appropriate gear ratio based on driving:counter tooth count.  In this example, I didn't actually worry about specific tooth counts, just setup a 1:10 and 1:20 ratios.  You have to select the driving cylindrical mate + counter 1 cylindrical mate, for one ratio.  Then select the driving cylindrical mate + counter 2 cylindrical mate for the second ratio.

I made the document public so you can use it here: Counter Mechanism

I'll play around a little more to make the counter wheel not continuously rotate.

trevor_tollefsbol

@max_tran483 my curiosity is piqued now.  I'm going to spend more time on this when I can find it.  The video example looks like a fun one to simulate!  My guess is that you probably already know what I posted above.

max_tran483

Thanks Trevor!  @trevor_tollefsbol I will look at your example once I have time. I did find that Solidworks could do it with its motion study feature. Sadly that is feature is not available in onshape as yet.

EvanReese

Check out this thread about animating a geneva gear. I think it's the same basic problem you have. https://forum.onshape.com/discussion/18614/mates-geneva-mechanism

trevor_tollefsbol

@Evan_Reese That's perfect!  Exactly what @max_tran483 is looking for, I think...

max_tran483

Thanks Evan! @Evan_Reese It looks very close to what I am looking for.

Ste_Wilson

Did you make any progress on this? 
I find it interesting, modeling a mechanical computer in a computer.  Could we 3d print a babbage machine? 

michael3424

An Onshape user created a working model of the Curta calculatoir a few years ago - does that count?

max_tran483

No progress. We can indeed 3d print a mechanical computer.

george_machin

@max_tran483 If you're still working on this I managed to get it to work using a bit of trickery inspired by the Geneva mechanism @EvanReese mentioned.

Assembly | Counter Mechanism (onshape.com)

max_tran483

Thanks George! @goerge_machin exactly what I was looking for a while back. I have forgotten about this project, since I moved on to designing a tri-axial tourbillon.