Make a Variable Speed Rotation Driver to Influence Another Object

Question

What I want to achieve starts pretty standard: the rotation of object A rotates object B. I use a driver. No prob.

Where I’m stuck is that I want certain portions of A’s rotation to rotate B faster and certain potions of A’s rotation to rotate B slower.

For instance:

• Rotate A 0-90deg = rotate B 2xA rotation speed
• Rotate A 91-180 deg = rotate B 1/2A rotation speed
• Rotate A 181 - 270 deg = rotate B 3/4A rotation speed
• Rotate A 271-360 deg = rotate B = A rotation speed

This has to be possible, right?

Answer 1

Use a scripted expression. For what you have, given input rotation "var", you might use something like,

(2 * min(max(var, 0),pi/2)) + (0.5 * min(max(var-(pi/2), 0),pi)) + (0.75 * min(max(var-pi, 0),0.75*pi)) + max(var - (0.75 * pi), 0)

Rotations in drivers are in radians, not degrees, hence all the "pi"s. Be aware that if you're going to read rotations of >180 degrees, you're only ever going to get them from "single property" type variables, never from "transform channel" type variables. max() is a python function that returns the greatest of its parameters; min() returns the least of its parameters.

An alternative is to edit the driver curve in a driver editor viewport. You can add new points to the curve and adjust the controls and handles just as you would any other f-curve in Blender. Adjusting the driver curve would be preferable if you wanted smooth transitions (but you can use vector handles there to make sharp transitions if you want.)