View Full Version : A riggable quadratic curve?

07 July 2010, 03:19 AM
In my scene, I have a simple three joint chain arm that I want to have a quadratic curve is bound to. I want to make it so that no matter what angle I bend the elbow joint, the curve will try to maintain its almost semi-circle, quadratic form.

I thought this would be relatively simple but after 2 hours of trying different settings on CV and EP curves and the three point arc tool, let alone the other options I exhausted, I came up with nothing. (By the way, I tried weighting the control vertices to the joints - didn't work).

I found that a normal curve will work about 20% of the time but as soon as I bend the arm to more acute angles, the curve tends to straighten out at the elbow joint.

Does anyone have a solution to keep a curve quadratic while bound to a three joint chain system?

07 July 2010, 05:03 PM
Try the Arc Tool (3 point). Constrain the 1st position to the shoulder, the 2nd to the elbow and the 3rd to the wrist.

Might be what your looking for.

07 July 2010, 06:32 PM
*facepalm* My goodness, how could I forget I could use clusters on the CVs for constraints. >_<. It works the way I needed it to. BUT!

There's one thing I neglected to mention before that I will now. I need the curve to be quadratic AND it needs to pass along the elbow. I have three pictures to help get across what I mean.

When I have the arm in it's default position, the curve is perfect and maintains its quadratic form but as I bend the elbow the curve has a tendency to fall through elbow joint.

Does anyone have a technique that keeps the curve quadratic AND keeps it snapped to the elbow joint?

07 July 2010, 03:51 AM
I found a solution to this problem, it was surprisingly easier than I had expected.

I made a three point linear curve, snapping each point to each joint and then applied clusters to each of the three CVs. I point constrained each cluster to their respective joint.

Lastly, I switched over to the surfaces menu and went to edit curves > fit B-spline (global) and it created a cubic curve that deforms to fit the linear curve. Now when I move or rotate any of the three joints the linear curve moves and the cubic curve compensates!

Thank you so much for your help! Take care!

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07 July 2010, 03:51 AM
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