Spine Path Position Drifts After a Length Change

A prop must meet a character a fixed distance from the entrance to a conveyor. The setup works on the original path. After the endpoint moves, the contact frame still plays on time, but the prop arrives farther down the belt. Start by asking which reference the shot needs: a distance from the entrance or a fraction of the trip.

Use two simple paths as a control

The Spine path constraint guide defines Fixed Position in distance and Percent Position as a fraction of the total length. It describes Spacing separately, for bones after the first one. In a project copy, start with one constrained bone and a straight open path. Keep the start, direction, scale, visible attachment and translation mix constant.

For paths of 100 and 200 units, Fixed Position at 30 keeps the bone 30 units from either start. Percent Position at 30% gives distances of 30 and 60. These are expected values for the controlled example. Use the result from your actual path and rig when reviewing a shot with curves, deformation or inherited transforms.

Choose the reference that the shot needs

A pickup at a marked station can be specified in distance. A progress indicator meant to sit one-third of the way through a route can be specified as a fraction. Identify the keyed frames that matter before switching modes. Preserve screenshots of contact points and note what should happen when the route is shortened as well as lengthened.

If the lead bone stays where expected but the rest of the chain spreads out, run a separate spacing comparison. If the lead bone follows a different curve, inspect the target slot and its currently visible path before editing position keys.

Leave a reproducible handoff

Capture the frame, path length, mode, position value, expected location and actual result. Use the Spine Workbench to review suitable exported assets and see the workbench guide for the entry point. Inspect or edit constraints in the Spine editor used by your project. If a second constraint changes a passing result, follow the constraint order comparison next.