How to constrain the sum of the length of two lines?

[mechamania]

Hi,

Can I create a constraint to set the sum of the length of two lines? I have a cable in my model that is fixed at both ends.  A wheel will pull the cable until the cable is tight. But the position of the wheel can vary. How can I model this?

[johnsonshiue]

Hi! Are the lines two straight lines or splines?

Many thanks!

[mechamania]

Currently they are straight lines. But if splines is better, I can use splines. One spline is also possible.

[johnsonshiue]

Hi! Are you on Inventor 2019? If yes, you can add a length dimension to a 3D spline with both ends fixed.

Many thanks!

[mechamania]

Hi,

Yes I'm on 2019. I tried to set a dimension on a spline. But I do not see how. I tried this on a sketch. Is that not the way to go?

And how can I attach one or more control points to an object (the wheel that pulls the cable)?

[johnsonshiue]

Hi! You need to create a 3D Sketch -> Spline. Then add a dimension to the spline. It is available in 3D not in 2D Sketch.

Many thanks!

[Anonymous]

Pro-E, 15 years ago or so. 2D-Sketch. Select elements (line, arc). Right click : convert to perimeter. Now the length of the set will obey the given length while keeping the other constraints alive.

Used it all the time to simulate bending material in electronics connectors.

It's all mathematics and we're working on number crunching machines...

[JDMather]

If you are using lines and arcs - this is simple in Inventor.

If you are using Splines - must have 2019.

If you can't figure out a particular solution, then attach your example here.

[mechamania]

I can not find that feature in 2D sketch mode

[mechamania]

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@Anonymous wrote:

2D-Sketch. Select elements (line, arc). Right click : convert to perimeter.

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When I select some line elements in a 2D sketch and right click on this, I do not get an option to convert this to

perimeter. What am I doinig wrong?

[Anonymous]

You don't get that command in Inventor because I was talking about Pro-Engineer. That were the first words of the sentence. Merely to emphasize that IV has a long way to go. A very long way.

I have worked with what I have on the desk, all of my live. When it was Autocad, when it was EMS (Intergraph), Microstation, Catia, Pro-E...  If your job is industrial design you do it with the tools that are made available to you. Nevertheless you compare, that's only human I guess. Meanwhile I kinda know what the common ground of CAD is, and where some programs excel and others fail.

Of course this knowledge is outdated by default. But I can't help a nostalgic thought now and then ...

[Anonymous]

Ok - it seems that nobody answered here.

Let me try (IIUC):

Go to Parameters window - click on "Add Numeric" in order to add a new User Parameter. Call it "TotalLength" (or in any way you want to call it). This will be your constraint.

Add the two lines. The one dimension it to "VarLength" and enter any desired value there (smaller than TotalLength).

The other line give it the dimension as formula = TotalLength - VarLength.

This is it. If you want to factor the cable used on the wheel then, if the lines are parallel, the cable used on the wheel is always PI * WheelRadius (half of its diameter - again: this is true only if the lines are parallel).

[mechamania]

Thanks John,

But this is not exactly what I need. This will define both lengths (bij the sum and one of the lenghts). I would like to specify only the sum and then still being able to move the end points of the lines with the mouse (while the sum of the lengths is kept to some specified value).

[Anonymous · Accepted solution]

By having "VarLength" as named parameter which describes the length of one part of the cable you can change it in order to see how the both parts of the cable behave. IMHO we all understand this.

Perhaps you don't know (or remember) that you have two ways to change this parameter:

1. Using keyboard: Enter in "Parameters" window and type various values in Value box of above-mentioned parameters. The model should update to reflect your changes.
2. Using mouse: You need to make a form and put a slider linked to the parameter you want to modify. On the slider you must change the Step property if you want an increment different of 1 ul. Then you will have a visual feedback of your cable how it behaves if the wheel changes its position. See the attached video for a demo.

Note that if the wheel's radius is significant then you must calculate the cable spent there and then the things gets complicated. Also note that not all values work - it depends not only of TotalLength but also on the distance between the anchors. As I said, watch the attached video.

Can I ask you a question also? 🙂

It is a school assignment or something IRL? 8)