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I have a project where I would like to use a bones rotation value to move another bone along a brzier curve.

I have a bezier curve with the bone that is constrained to the curve with a "follow path " constraint.

I have the bone i want to use to drive the "offset" value of the follow path constraint.

I run into a problem where the driver is affecting the bone to fast. It seems the conversion the driver is doing is muddled.

I have a link to my file.

Please help if possible!

https://drive.google.com/file/d/1OGM6t1OQX3MvETzCNrDbSz-EiSbqyI_W/view?usp=sharing

my objective is to rotate a bone and have it drive another bone along the bezier curve. I wish for the main bone that is driving the bone on the path to complete a full 360 degress before the bone on the path finishes.

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1 Answer 1

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  1. Right-click on the Offset value of your constraint. Add driver -> Scripted Expression (don't worry, no script needed)

  2. Open a Driver Window (Shift F6) enter image description here

  3. In the driver select the armature as the object, and the control bone as the bone.

  4. Choose Y location and local space.
  5. The expression should just be var, nothing behind it.
  6. Move the controller in local y direction (in your scene global z)
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  • $\begingroup$ Hi Frederik! Thanks for helping! I have tried your setup but I cannot get it to work in Local space. Also I need the x rotation to drive the value. here is an updated file where i have tried what you have shown me. drive.google.com/file/d/1miPPLz-mB4seQJUuzO6Crc08e9CbQNU2/… $\endgroup$
    – ben
    Jun 7, 2020 at 7:59
  • $\begingroup$ Thanks again for your help $\endgroup$
    – ben
    Jun 7, 2020 at 8:01
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    $\begingroup$ That setup works... You should join the armatures though, In object mode, select the big bone, shift-click on the smaller one, press CTRL J, go into pose mode and select bigger bone, press R -> X and move your mouse. $\endgroup$
    – Frederik Steinmetz
    Jun 7, 2020 at 8:10
  • $\begingroup$ ah cool this is getting good! Just one more thing if you are up for it. In this next updated file everything is looking great thanks to your help! I need the animation to complete in one revolution of the main bone. so far I get to around 60 degrees and then the animation reaches the end. Do you know how to fix that to one full rotation? drive.google.com/file/d/1iFSHUTIPvYBCc4UORXw9KrjIEWQ54bTX/… $\endgroup$
    – ben
    Jun 7, 2020 at 8:36
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    $\begingroup$ Switching to Euler was the right step., but now your bone has a y rotation > 0. In cases like this, you should only rotate the axis you're interested in. Clear its rotation and it works. $\endgroup$
    – Frederik Steinmetz
    Jun 7, 2020 at 9:06

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