Create a freewheel mate condition?

martin_kopplow

I'm trying to design and animate a gearbox which involves a freewheel clutch at some point, so a rod rotates a sprocket wheel in one direction, but not in the other. This would require a rotate mating condition or a gear relationship that works only one way, but it looks like I can't model this function. Did I miss something or is there no way to define this kind of relationship?

Best,
Martin

EvanReese

I'm not aware of a way to do it currently

martin_kopplow

Thanks, Evan, for the confirmation. It would in fact be quite useful to have such an option, for all kinds of step forwarding devices, agricultural equipment and so on. I wonder if I am the only one who had such design requests in the past (and my old CAD could not do it either).

steve_shubin

@martin_kopplow

So this doesn’t sound like a modeling issue. Because I think you’re going be able to model whatever you want in Onshape.

But I’m not sure if you’re asking for collision detection, or to simulate collision in an animation.

Either way, I think you should probably look into something like Blender, Cinema 4D, or Maya for the animation portion of your work

S1mon

It is possible - albeit a bit insane - to do complex animation in Onshape.
https://www.youtube.com/watch?v=SMTeEhbCPzo

See full thread about how it was done:
https://forum.onshape.com/discussion/10484/rubiks-cube-mate-animation/p1

martin_kopplow

Well, Blender, C4D or the like may appear well suited for animation, if that alone was the goal, but that would require a second stem of data being prepared and kept up to date, and I am not after that specific kind of animation anyway. I want to demonstrate the workings of the mechanism, that's all, and I believe this is part of the mechnical design process or rather the design intent communication part of it.

While I can model almost everything in Onshape, no doubt about that, visualizing the motion is another thing. I am not asking for collision detection. This thing I ask for is very closely related to the revolute mating connection, ideally just an enhancement of the latter:

 

martin_kopplow

Simon, wow, that's a very great project. Food for thought. I'll need a bit of time so watch all this ...

steve_shubin

@martin_kopplow

So when you say freewheel, though this may be far from your design, are you roughly speaking, trying to reproduce something along these lines?   Where something is engaged part of the time, and then not engaged at other times ?

Keep your eye on the center polygon

matthew_stacy

@steve_shubin, do tell... and share the URL please.  That looks impressive.

steve_shubin

@matthew_stacy

Matt, the animation ABOVE - that's trickery. That's two videos edited together. Everything was modeled and animated in Onshape. But it was two separate videos. One with the pawl in the outward unengaged position. The other with the pawl engaged in the inward position. In that video, the pawl is NOT actually pushing that inner gray piece. I just had all 3 parts locked together, for the second part where the pawl APPEARS TO BE PUSHING the inner part.

I did this simply to show that there may be another way to accomplish this without having to delve more heavily into certain types of animations. I always think it's good to have a back up

Now as to the GIF below, it does have a little bit of trickery, but only that of the pawl flipping outward ——— the little flip at 3 o’clock. And that was accomplished simply by where the GIF loops

BUT, in the GIF below, the pawl actually does engage the inner gray part and pushes it along.

Now the way that happens is, that the pawl comes to the end of its tangent path. When it does, it starts pushing the end of that path. Now that path is part of the gray part itself. So as it’s pushing the end of the path, it’s pushing the gray part. So an actual type of collision, so to speak, is taking place.

But the other problem is, I couldn't use the animation dialog to make the pawl work the same way. I had to move my finger in a circle on my trackpad which is difficult to do if you want things to look smooth. Maybe if I had a mouse on a desktop, that might have worked better.

Here's the file if anybody wants to try and get it to work better.

https://cad.onshape.com/documents/888c437882be057f0def40c5/w/6d6439b7783f2418d8685b57/e/525cbdaae947f41cd5962909

Again, watch the polygon in the center

steve_shubin

It would really be nice if Onshape had just the most basic of animation.

Now of course, it would work within the confines of the mate connectors.

But doing basic key framing is so easy.

I did this GIF in my little $20 video editing program for my iPhone. In LumaFusion. It took hardly any time at all to do

All I do is I tap the key frame button. Make sure my part is in the position I want it to be

Move the playhead to the next point in the timeline. Press the key frame button again. Move my part to a different position. And that’s it

The program will move that part from one position to the other over the period of time you have between key frames.

So doggone easy and it would work great with Onshape.

martin_kopplow

@steve_shubin

That comes at least close, though I get a feeling I might have triggered a bit of a misunderstanding by using the term "Animate". I see a huge difference between an animation and motion inside the design model.

While we could always use some fancy extrenal animation tool and do sopisticated trickery visualising even the most impossible things, I consider defining mechanical motion within the design an actual design tool, driven by engineering conditions, not trickery.

That said, what I am after, is just a way to define the abstract behaviour of a freewheel. It is not necessary to model the movement of a pawl, and there also does not need to be any discrete position for it to engage.

Take a component as follows for an example: https://www.gmn.de/freilaeufe/baureihen/kugellagerfreilaufe/

 

This is a standard part used with all kinds of machinery. It looks like a ball bearing and works as if it had a 'revolute' mate between inner and outer ring, when turning one way, and as if it had a 'fixed' mate when rotated in the opposite direction. It also has no 'ratchet' type pattern of engagement.

Is there a way to activate and deactivate mate conditions depending on direction of rotation?

steve_shubin

I’d be curious to see that part disassembled

Unfortunately, your link is in a language that I just couldn’t figure out how to view in something I could understand — at least not at this time

Here is a video of the disassembling of a rear end of a bike. And it does show that there are pawls, at least in the case of this bike part

https://m.youtube.com/watch?v=T_vRbBRPr3c

Nonetheless, regardless of whatever it is that makes the part you show above work the way it does, if your main concern is about the rotation in one direction only, well, you can animate by choosing the direction you rotate. But if this is something that you want to manually rotate a  bit and then stop and then rotate a  bit more and stop, And you want your mate connector to keep you from accidentally rotating in the wrong direction, then I’m not sure what to tell you

As @S1mon pointed out, there is one person extremely knowledgeable about assemblies.

John McClary

If John‘s not busy. Maybe he can say what’s what on the matter 

matthew_stacy

martin_kopplow said:

... I consider defining mechanical motion within the design an actual design tool, driven by engineering conditions, not trickery.

That said, what I am after, is just a way to define the abstract behaviour of a freewheel. It is not necessary to model the movement of a pawl, and there also does not need to be any discrete position for it to engage.

Take a component as follows for an example: https://www.gmn.de/freilaeufe/baureihen/kugellagerfreilaufe/

 

This is a standard part used with all kinds of machinery. It looks like a ball bearing and works as if it had a 'revolute' mate between inner and outer ring, when turning one way, and as if it had a 'fixed' mate when rotated in the opposite direction. It also has no 'ratchet' type pattern of engagement.

Is there a way to activate and deactivate mate conditions depending on direction of rotation?

____________________
@martin_ko@martin_kopplow, like you, I was very much hoping for a uni-directional-revolute mate.  I'm currently working on a design that utilizes drawn-cup-roller clutches like the hardware that you showed.