This video was made based on the design numbered as 1303 in volume 2, Mechanisms in modern technic, I. Artobolevski.
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) / ((OA.OA)-(r.r))
The curve center is at point B, on the right of A.
OB = OA.(R/r)
If (OA – r) is small, R is very large.
If OA = r, the mechanism draws a straight line perpendicular to OA.
If OA is shorter than r, the curve center B is on the left of A.