Counterweight and gas spring

Locate both mounts relative to the hinge

Use the hinge as the coordinate origin and keep angle and coordinate signs consistent. The panel-side mount rotates with the lid; the fixed mount does not. A mount near a dead-center position can provide very little leverage even when the spring force is large.

Use the angle table before selecting hardware

The tool samples 19 angles and reports required balancing force and mount-distance range. It does not find every continuous maximum or model a real spring's force progression and friction. Check closing force, stroke reserves, fittings, and behavior throughout travel against the proposed supplier's data.

Following the spring's changing leverage

The gravity moment depends on panel mass and the horizontal offset of its center of gravity from the hinge. The spring moment depends on force and the perpendicular distance from the hinge to the spring's line of action. That perpendicular distance changes as the lid moves. Using the panel-side mounting radius alone as the spring lever arm can substantially misstate the required force.

Inspect the angle-by-angle table, including the sign of required force. A mounting arrangement can assist opening in one region but behave differently elsewhere. The largest sampled balancing requirement is not necessarily the exact continuous maximum between samples. Compare minimum and maximum mount distances with a candidate spring's extended and compressed dimensions, allowing the manufacturer's stroke and fitting requirements. Real gas springs have force progression and friction, so one nominal force cannot be assumed to balance the panel at every angle. Check the required hand force, closure behavior, hinge loads, and end attachments before choosing hardware for a lid or hatch.

Formula

Balance gravity moment about the hinge with the actual spring-line moment arm at each angle.