Hey!
When my model is bending the knee it doesn’t look good so I wanted to add shape keys to that.
I tried to add a driver that is triggered when x rotating, but for some reasons when I move the foot back, the shape key stays there and messes up the mesh. Looks like Blender does not know where or what the basis is that it can go back to. How can I fix it?
Thanks!
Well. It looks like value of your driver is more than 1.
At rest position of bone, it should be 0.
Rotation of bone on X axis when knee is bend should correspond to a value of 1.
It is supposed to be 0 when leg is straight.
So, you should have a direct relation. Why do you add 1.4 to this variable ?
Hey!
Well I was experimenting around with numbers and landed on 1.4.
When I put the leg in rest position and make the value 0, it applies to when the leg is bent too…
Same like in the screen shot, when I bend the knee and put the value on 1, the value stays the same when the leg is back at it’s resting position again.
When I try to change the value, an error says “can’t edit driven number value…”
Maybe I am missing some sort of steps?
OK. After a quick try, that seems logical.
Quaternion are made of 4 values.
W value is also changed when you pose bone.
Instead of Quaternion mode, choose Swing and X twist for driver.
Then set expression as is : var/(pi/2)
It should work.
When I type var/(pi/2), the value goes to 0 and I can’t change it with the same error “can’t edit driven number value…”.
Also with var/(pi/2) the shape key completely vanishes even on bent knee 
