Figure P12.50D shows a wheelchair brake in its retracted position, with a tension spring exerting a force of 4 N, which holds the handle against the pin stop. When the handle is moved clockwise, pivot A drops below the axis of the spring (thereby going "overcenter"), and the spring acts to hold the brake shoe against the tire. Available space limits the outside diameter of the spring to 10 mm. Estimate the dimensions needed by scaling the drawing. Determine a satisfactory combination of D, d, N, wire material, and free length of coiled section.
