I'm trying to write an expression for a slider to control the speed of a layers Z rotation so I can control the how fast it spins during an animation - e.g. a bike wheel which slows when it travels up a 'hill' but speeds up when it descends.
Can anyone recommend a method or point me in the direction of achieving this via expressions & sliders?
Controlling rotation speed can be a real pain. Worst case--you have to write an integrating expression that goes back in time, frame-by-frame to calculate what the current total rotation should be. It might be a little simpler, depending on the nature of your speed animation.
However, would it be easier to calculate distance traveled, and convert that to rotation using 360*(distance/(Math.PI*diameter))?