Restrincting to one of two solutions

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Restrincting to one of two solutions

Postby jsveiga » Mon Feb 22, 2016 8:16 pm


I'm trying to simulate a 4-link suspension in CaRMetal, but I'm having trouble with a constrain that has two solutions.

In the attached (CaRMetal 4.0.2) file (also at, the upperArm segment end point can be defined by the intersection of upperArmLengthSphere with axleAnchorsDistanceSphere with the plane P84-P85-P86.

The problem is that there are two points where these elements intersect, so when we move the axleLowerAnchor up and down, the upperArm "jumps" from one solution to the other.

Can someone point me to a way to restrict the intersection to a single solution?


Joao S Veiga
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Re: Restrincting to one of two solutions

Postby jsveiga » Mon Feb 22, 2016 8:32 pm

Never mind... Got it.

I drew an arc through 3 points over one of the intersecting circles, covering only the "allowed" region, and connected the upperArm to the intersection of this arc and the other circle.

I didn't expect the arc through 3 points tool, which is in the "2D" Construction pane, to work for a 3d arc.

EDIT: Actually, no. It blows up if I rotate the view to the opposite side.

So still stuck. Any help is appreciated...

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Re: Restrincting to one of two solutions

Postby patrice64 » Thu Feb 25, 2016 10:52 pm

Hello Joao, and welcome on the forum.

I looked at your file, looks a bit strange to me..
As you can see in the zir file, P128 point is superhidden, it's the 2nd intersection point, and it is not 3D. Actually, I don't know how you got it...
A few ideas, I'm not really convinced... :
- try create the intersection in 3D (with 3D intersection tool between curves). Problem is the intersection between the two 3D circles should work and it doesn't... You say this is an intersection between two spheres and a plane. Maybe you could try create first the intersection circle between the two spheres and then try to create the intersection with another circle made with the plane.
- create first intersection point in the zir file. Then, with an if expression, you could switch from P128 to that new point... so that in appearance it wouldn't switch (!). (that's very ugly option...)

Good luck. I hope you can get to it.

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