How do I add a driven dimension to an assembly?

[Anonymous]

Thanks for reading!

BACKGROUND:
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I have an assembly I've put together in Inventor 2011. I tried to make an adaptive spring to use with a shock that goes in a car. I'd like the spring to change size as the shock extends and contracts. 

I went through the process of creating an adaptive spring, and it worked, but I could only change the length of the spring by using the "Drive Constraint" feature, which only allows me to adjust the spring when I'm using the "Drive Constraint" menu. It plays like a movie. 

What I want is a part that just moves like you would expect when you push/pull the ends of the shock. I don't want to have to drive it like a movie. 

So then I thought that I could just simulate a spring by making a series of rings (toroids). I could constrain the bottom ring and top ring to the shock geometry and then have the other rings position themselves according to the distance between the top and bottom rings.

SO, I have 5 rings. The bottom ring is grounded the top ring has a Limit Constraint that sets the top ring anywhere between 3 and 7 inches above the bottom ring.

HERE'S THE QUESTION:
===================

How do I create a driven dimension on an assembly that will automatically update the distance between the top and bottom ring? 

I would like to call that dimension "HEIGHT", and then I could use parameters to set the middle ring a distance (HEIGHT/2) above the bottom ring, I could set the ring below the middle to (HEIGHT/4), and I could set the ring above the middle to (HEIGHT*3/4). 

I should then be able to move the upper ring up and down and the other rings reposition themselves automatically to keep even spacing between the rings on either side.


I tried making a sketch in the assembly and using the "Project Geometry" function to add the location of the upper and lower rings to the sketch. I then used the "Dimension" function to create a driven dimension between the upper and lower rings. When I finished the sketch the other rings all updated exactly as anticipated, but when I moved the top ring the projected outline did NOT move, so the other rings did not continue to update. 

I'm completely lost and I can't understand why this is so difficult. Please do NOT link me to adaptive coil video tutorials or explain how driven dimensions work when making parts. I am not looking for that, I am looking for how to create driven dimensions between two placed components in an ASSEMBLY. 


Thanks again!

[nannerdw]

One way would be to use polar component patterns.  You have to pattern each ring 180 degrees about the horizontal axis of the one next to it, and their movement will remain flexible.  When you create multiple patterns like this, some of the rings will overlap existing rings, but you can just suppress them.

I had uploaded an example file, but it's in Inventor 2012 format.  I'll re-upload it in 2011 once I get back to my other computer.

Another option might be to create a skeleton part consisting of 5 angled axes.  Then you could constrain the origin point of each ring to one of the axes, and then make all of the rings concentric.  It might be a little glitchy to try to drag the parts by mouse, though, since Inventor sometimes has trouble recognizing the proper degrees of freedom with a set-up like this.

[PaulMunford]

That sounds pretty cool 🙂

Unfortunatly Inventor doesn't give you dynamic views of parts as they change. It waits for the inputs to change, and then updates the features when you hit 'update'.

You can get some fancy stuff like this going in the part envoironment using iLogic and sliders, check out this video here:

http://cadsetterout.com/personal-posts/happy-halloween/

The value feilds can be replaced with sliders instead.

To get this into your assembly you would derive the spring out. 

Other than that, maybe you should look at the simulation envoirinment:

http://www.youtube.com/watch?v=R4Ui27FU2qM

I hope that this helps,

-Paul-

[JDMather]

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@Anonymous wrote:

What I want is a part that just moves like you would expect when you push/pull the ends of the shock. I don't want to have to drive it like a movie. 

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This is so easy to represent in the Dynamic Simulation environment that it is a shame Autodesk hasn't made it as easy in the Assembly environment. 

[Anonymous]

So what it seems like I'm getting is that there is not actually any way to get a driven dimension from an assembly. 

I can set a limit constraint that lets me push/pull the end of the shock, and I can set the offset as the resting position, so it even pushes back out when released like the shock should. But right now all I have is the damper and shaft of the shock; the actual spring that would be the part to push the end back out is missing.

Another thing I was thinking about is the fact that I'm modeling the front end of this car so I can redesign the steering system. What I thought I would be able to do is to take measurements off the vehicle in real-time as I drag the tires left and right to see where the best spot would be to put the sensors for steering position. 

But, that goes back to my question in my original post - how do I get real-time measurements off an assembly? I can bring up the Inspect -> Distance tool, but I don't think it's possible to leave it up while I'm manipulating the assembly. It's driving me crazy because I don't understand why it's not a feature. Why can't I just create a parameter and have it be the distance from part 1 to part 2??

[nannerdw]

That would be a nice feature, to have real-time updating parameters.  I think the closest you're going to get is the slider method that PaulMunford mentioned

Here's a video with a good example of iLogic sliders:

http://www.youtube.com/watch?v=Mtj2hG3auCI

[JDMather]

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@Anonymous wrote:

But, that goes back to my question in my original post - how do I get real-time measurements off an assembly? .... It's driving me crazy because I don't understand why it's not a feature.

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Sounds to me like you should be using Dynamic Simulation functionality.
Do you have Inventor Professional?

I think it is a feature ...you have to pay more for it.

[Anonymous]

I am a student, so I have the educational version of Inventor 2011 professional. 

[JDMather]

You can do what you want in Dynamic Simulation environment of Inventor Professional, but the learning curve is rather steep.

Where are you located?
Does your school cover Dynamic Simulation?

Can you attach your assembly here?

[PaulMunford]

If you can't use the simulation suite, there are top down design techniques you coud use.

Here is a good video on a 2D to 3D kinematic workflow:

http://www.youtube.com/watch?v=xXDeDB2noP0&feature=endscreen

Here is a post in multibody part modelling:

http://blogs.rand.com/manufacturing/2009/11/inventor-multi-body-modeling.html

Good luck!