nav-backtrack_skill

Overview

This skill attempts to return the robot to a recently known safe navigation cell by replaying bounded local motions. It inspects the stored navigation history, selects safe past poses, and tries atomic primitives to reach one of them. The goal is a fast, local recovery without full replanning.

How this skill works

The skill reads world_state("nav") history and picks up to max_targets safe entries. For each candidate it issues a nav-turn followed by a single motion primitive: nav-move, nav-climb, or nav-descend. After executing a primitive it verifies the robot reached the expected cell using mc-status and reports the recovered pose and method.

When to use it

• After a minor localization drift or small collision where a recent safe pose exists
• When global replanning is too slow but a local undo may restore safety
• If sensors report being off the expected map cell but a prior safe cell is known
• When the robot is blocked on a small obstacle and a reverse step or descent may help
• During runtime recovery before escalating to manipulation or large replan actions

Best practices

• Maintain frequent nav history so safe targets are recent and reachable
• Set max_targets to a small number (1–3) to keep recovery bounded and fast
• Run mc-status after recovery to confirm exact cell match and yaw
• If nav-backtrack fails, follow with place-until-supported or a global replan
• Prefer this skill for short, local corrections rather than long-distance returns

Example use cases

• Robot slightly nudged off course in a corridor: backtrack to last safe cell and continue
• Failed grasp knocked the base; attempt a single-step recover to the previous cell
• Descending a stair caused misalignment: try a controlled descend/recover step
• Localization jump to a nearby cell: revert to the prior verified cell to stabilize
• Blocked by low obstacle: attempt a climb or step back to a previously known safe pose