Mechanism for Drawing Circle

when OA is shorter than r. The curve center B is on the left of A.
Angle between two sides of the blue L-shaped bar is 90 deg.
Yellow bar is always perpendicular to green bar.
Orange and green sliders are connected together by a revolution joint.
When pink crank of radius r rotates, center point of orange slider traces a circular curve of large radius R.
This avoids the need for hinges at distant or inaccessible spots.
R = ((OC.OC).r) / ((r.r)-(OA.OA))
OB = OA.(r/R)