Little side project. I want to build a vertical stabilizer arm for my Glidecam camcorder stabilizer. The theory is similar to the Steadicam. Picture a 10"x3" parallelogram pinned with bearings at the corners. Long dimension is horizontal. One 3" side is fixed and the other floats and holds the Glidecam. A spring runs diagonally between the top end of the fixed side to the bottom of the floating side. The moving parts of the arm weigh 2 lbs and when level the COG is 7" from the fixed end. The Camcorder and Glidecam weigh 4.2 lb and the COG is 12.75" from the fixed end.
How do I figure out which spring to use to just maintain the arm slightly above level? If the spring rate is to high the stabilization effect will be diminished and if to low it won't recover fast enough. The spring can't be longer than 6" with no tension and will need about 3.5" of extension to allow the arm to move from 30 degrees above to 30 degrees below level. There will also be an adjustment screw to pretension the spring.