• Adobe After Effects Expressions

  Car wheel rotation on an angle

  Posted by Ben Tillett on July 23, 2011 at 8:47 am

  Hi, hope someone can help.

  I’ve got a car set up so that the wheels rotate when the car is moved left to right. But I can’t work out how to extend the expression so that the car may move on a diagonal path with the wheels rotating correctly.

  Not sure if I explained that well, but imagine a car in 2D moving up and down the contours of a mountain. So not flat along the x-axis, but diagonally. Is there a way to modify the expression so the wheels rotate correctly?

  I think it has something to do with trig, and working out the hypotenuse dynamically based on the slope/angle of the car and the distance travelled in x and y.

  Thanks!

  Roger Maus replied 12 years ago 3 Members · 3 Replies
• 3 Replies

• 

  Dan Ebberts

  July 24, 2011 at 9:41 pm

  For an irregular path, you’ll probably have to calculate the length of terrain traversed frame by frame. I’d start with something like this:

  
accum = 0;
for (f = timeToFrames(inPoint); f <= timeToFrames(); f++){
t = framesToTime(f);
p0 = position.valueAtTime(t-thisComp.frameDuration);
p1 = position.valueAtTime(t);
accum += length(p1,p0);
}
accum*360/(Math.PI*width)


  Dan
• 

  Ben Tillett

  July 25, 2011 at 9:34 am

  Dan, thank you so much!!

  After a little tweaking for my particular situation, that worked a dream.

  Thank you sir,

  Ben
• 

  Roger Maus

  April 26, 2014 at 9:36 pm

  Sorry fo waking up this old lad…. can I make this work in 3D space too? how?

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