Driving average values with limits in blender

Question

1. I have two blue bones that move freely along the x axis.
2. I have mulitple red bones that are ment to only move when they are between the blue bones
3. the red bones when they are inbetween the blue bones have a location limit of 0 to 0.1 and they have an even distribution value from 0 to 0.1 according to the distance value of the 2 blue bones so there is a nice gradual fall off.
4. any red bone outside of the left blue bone remains at 0
5. any red bone outside of the right blue bone remain 0.1
6. The blue bones can slide past any of these red bones and effect them.

Any ideas on how to achieve this. I have tried a few things.
I have a blend file with thie scene setup. no drivers or constraints yet.[](https://blend-exchange.com/b/6wp4e3BL/)

Answer 1

Add a driver to a red bone and set the world x-positions of the blue bones as two variables in the driver editor.

Initially, $L_1 = 0$ and $L_2 = 3$ with your setup.

Then, check Use Self in the driver and enable Auto-Execution for python script in the preferences.

We need the original x-position of the red bone in regards to the space between $L_1$ and $L_2$. But we can't read and write its x-position at the same time. You will either have to use and alternate bone for supplying the initial position (like a parent bone), hard-code the starting value or use the rest position of the armature. I will use the rest position. We shall assume, that the system is not rotated via a parent, and we can rely on only the x-values.

To access the edit bone (which holds the rest position) from the pose bone, use this expression: self.bone.matrix_local.to_4x4().to_translation().x. We need to use the matrix_local in order to get world coordinates.

If the edit bone's global x-position was $1$, the driver would show the following.

Next, normalize the position to the range $(L_1, L_2)$.

(self.bone.matrix_local.to_4x4().to_translation().x - L1) / (L2-L1)

To prevent a division by zero (when L1 and L2 share the same x-position), add a max() expression, to stop L2-l1 from going below 0. Since we have fitted the range of $(0, 1)$ between the blue bones, multiply by your desired range $(0, 0.1)$ at the end.

[...] / max(0.001, L2-L1)) * 0.1

To clamp self.bone.matrix_local.to_4x4().to_translation().x - L1 to the range $(0, 1), use a min(1, [...]) and max(0, [...])` expression.

^{Python does not have a clamp function.}

This is the resulting expression.

min(1, max(0, self.bone.matrix_local.to_4x4().to_translation().x - L1) / max(0.001, L2-L1)) * 0.1

Right click on the driven property and copy-paste it the remaining red bones.

We don't need to alter the expression, because it uses self to target its own rest pose location and L1/L2 are shared by all red bones.