So I'm currently setting up some corrective shape keys on a character rig.

I want a shape key to activate when a leg location is moved up (variable input A), OR, if the chest location is moved down (variable input B). But I don't know how to write this syntax for the expression. Ideally, if variables A and B are active at the same time (leg is up and the chest is down), I'd also want the value to be averaged out instead of added together, because otherwise this would overinflate the shape key.

Hopefully this wording makes sense. I don't really know a lot about shape key drivers yet beyond the very basic 'activate when bone approaches position' so any help is appreciated. :)


1 Answer 1


Blender's Drivers use Python expressions, as described in the Drivers Panel Expression section of the manual so the simple syntax would be A or B for your two variables.

But I don't think you want a simple or, because of your comment "averaged together". You need to figure out two variables that are driven by "leg is up" or "chest is down" that each range from 0 to 1. Once you have those two variable, then the expression you want would be something like (A + B) / 2 where A might be "how far up leg is" and B might be "how far down chest is".


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