Originally Posted by
son_of_clyde
theta = angle of crank to horizontal
r1 = crank length
r2 = pedal height (pedal axis to top of pedal)
R = distance from top of pedal to crank axis
assume pedal only translates relative to ground with r2 remaining vertical (i.e. no rotation relative to ground)
then R = [(r2 + r1*sin(theta))^2 + (r1*cos(theta))^2}^1/2
R varies with theta, no circle
Your calculation is not relevant, because the path of the pedal is not centered on the crank axis. The path of the pedal is circular, centered on a point a distance r2 above the crank axis.