Rotation constraint issue.

[ThinAirDesigns]

Hi Y'all.  JB the noob here again.  

I have watched numerous tutorial videos and searched the forum, but I guess part files speak a thousand words so here goes.

Attached is a demonstration project designed to highlight my question/issue.  I am trying to understand how the Motion/Rotation constraint is applied.

Notice how the small green disk rotates as it is moused around the large grey disk - just as I would expect according to the applied constraints.  Notice how the yellow slides around it's tangent constraint, but doesn't rotate.  It has essentially the same constraint applied.

I have tried a dozen different ways (clicking on different faces/lines/etc. and in different order) but all with the same nada results.  

What am I doing wrong?  How can I get the yellow wheel, constrained to it's mating groove to rotate the same way as the green disk on the flat surface?

Thanks
JB

[CCarreiras]

Hi!

Usually the Rotation constraint is applied in different cases, even though, it works also in these cases.

The issue is, you have to constrain plan faces instead the cilindric that you have.

See the video and Try it.

https://screencast.autodesk.com/Main/Details/f572a83b-d7b3-48e6-bce4-80d817c9d4a7#

Tip: if you want to use a cilyndric shape, build a very very small plain face, just to have conditions for the constrain may work.

Note: In other cases, with different conditions, that kind of geometry also work, but not in these case (you have one element of the rotation grounded)

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[ThinAirDesigns]

Hi Carlos, thanks for your response.  I liked the clever 'work-around' in your video (including a small flat face in the curve), but that still didn't clear up for me the scenarios that allow this sort of constraint and those that don't.

After some more experimenting, I have attached a slightly more fleshed out example of my confusion.  

There are now 4 different examples of the rotation constraint included.

A;  The original green cylinder remains unchanged and works fine.  

B;  The blue wheel is rotationally constrained through the mating curved faces and works fine.  The interesting thing here is that there was no need to add a small flat spot in the curve (as you did in your video) to make it work.

C:  The red wheel is rotationally constrained through nothing more than a sketched circle on the side of the wheel and a sketched line on the side of the rail.  As shown, the line need not even be tangent or in plane with the circle for it to work fine.  

😧  Back to the stubborn yellow wheel -- it is currently rotationally constrained through method "C" (two sketch lines) and as you can see, that doesn't work in it's current iteration.  As we know from my previous posting, it also doesn't respond to methods "A" or "B".

Also, per your 'grounding' comment, you will notice that all three of the base shapes in this experiment are grounded.

So, I'm still unsure when this constraint works as it seems it should (examples A,B, and C) and when it seems to fall apart (example D).  Still wondering if this varied behavior is a "bug", "feature" or merely a noob applying the constraint incorrectly.

Thanks
JB

[CCarreiras]

HI!

Before we can discuss all these scenarios, check this video.
The video shows one example how the motion constrain is applied.

Both wheels are unconstrained and the objective is to put both rotating as if they are connected by a belt.
As the bigger wheel have the double diameter regarding the small wheel, the racio will be 2. Therefore, when the big wheel give a turn, the small wheel have to do two. But inventor doesn't care about this racio value, you have to input based in your calculations. As you can observe in the final of the video, i revert the racio, and that will give a odd behavior When the small wheel does a turn, the big wheel does two!!! Like i said, inventor doesn't care about that... it's your responsibility.

https://screencast.autodesk.com/Main/Details/8159c0b4-f924-4f3f-a1b8-30bbed2cd5ec

In conclusion, it's normal the strange behavior that you observe in your experiences, because you are using a constrain to do something near the function, and sometimes it can work, sometimes... not.

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[ThinAirDesigns]

Thank you Carlos for your time and input, but it's not a "ratio" issue.   I understand that Inventor doesn't calculate or care about the ratio entered and that it's up to us to enter the correct ratio. Even when the correct ratio is entered, the correct behavior does not follow in the case of the yellow wheel.

Thanks again.
JB

[CCarreiras]

Hi!

I don't mean your issue become from a bad racio (after all, if you change racio, the system stay equal), what im trying to say is, what you are trying to do is a non traditional use for that constrain, so it's normal that you encounter some odd behaviors.

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