Circle Fun

This generates perfect circular motion centered around the original position of the layer.

After Effects 7
Useful things
Expressions

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I recommend that you map the radius and cycle inputs to Expression Control sliders, and the
phase input to an Expression Control angle.
Apply this expression to the position of the layer.
by Michael Natkin & Brian Maffitt

radius = 75; // the radius of the circle
cycle = 1; // number of seconds to complete a circle; higher value = slower
if(cycle ==0){cycle = 0.001;} //avoids a "divide by zero" error
phase = 27; // initial angle in degrees from bottom
reverse = 1; // 1 for ccw, -1 for cw
x = Math.sin( reverse * degrees_to_radians(time * 360 / cycle + phase));
y = Math.cos(degrees_to_radians(time * 360 / cycle + phase));
add(mul(radius, [x, y]), position)

(Min. Version: After Effects 7, Category: Useful things, Type: Expressions)