Debug a motion plan

When a motion plan fails with a collision error or produces a path that does not look right, the 3D scene tab lets you inspect the static view of the world the planner sees at the moment you look: configured frame positions, collision geometries, and the arm’s current pose. Most motion planning failures come down to one of a few problems that are immediately visible in 3D.

The 3D scene tab does not replay motion plans and has no timeline, scrubber, or plan-playback control. It is an inspector of the configured frame system and live component poses. If you need to watch a plan execute over time, poll GetPlan from code (see Monitor a running plan) or step the arm to intermediate joint positions manually and reinspect.

Prerequisites

• A machine with an arm or gantry configured and at least one frame defined.
• A motion plan that is failing or producing unexpected results.

Diagnose the problem

1. Open the 3D scene tab

Navigate to your machine in the Viam app and click the 3D SCENE tab. The scene loads your current frame system configuration.

If your machine is online, the scene connects for live pose data. If your machine is offline, the scene still renders the configured frame positions.

2. Check frame positions

In the World panel in the upper-left, expand the tree and click each component in turn. The Details panel on the right shows the selected entity’s world position and world orientation, plus editable local position and local orientation relative to the parent frame. Compare these values to your physical measurements.

Three common mismatches to look for:

• Wrong location: translation values in the frame configuration do not match the physical setup. Compare local position (mm) to your physical measurements.
• Wrong orientation: the arm base is rotated 90 degrees, or a camera points the wrong direction. Check local orientation in the Details panel.
• Wrong parent: the component is attached to the wrong parent, which places it in an unexpected part of the scene. Check the parent frame field in the Details panel.

3. Check obstacle geometry

Obstacles appear as translucent shapes in the scene and as child rows under their parent frame in the World panel. Select each obstacle from the tree to see its geometry type and dimensions in the Details panel.

Verify that:

• Every physical obstacle in your workspace has a corresponding geometry in the scene.
• Each geometry covers the actual physical object. If a box geometry is too small, the planner will find paths that clip the real obstacle.
• Geometries are positioned correctly. A table surface defined at z: 0 when the arm base is at z: 500 will not protect against table collisions.

If obstacles are missing or misplaced, see Set up obstacle avoidance.

4. Look for impossible targets

If the motion plan target is outside the arm’s reach or inside an obstacle, the planner cannot find a path.

In the World panel, expand the arm and select its tip link or the gripper frame (whichever is configured as the motion target). Read the world position and compare it to the target pose your code commanded. Then mentally place the target: is it inside an obstacle geometry? Is it further than the arm can reach from its base?

If the target is inside an obstacle geometry, either move the target or adjust the obstacle definition.

5. Check for self-collision geometry

Some arm models include collision geometry for each link. If a motion plan fails with a self-collision error, inspect the arm’s link geometries for overlap in the current configuration.

If the arm renders without collision geometry, the feature may be disabled: open Settings → Scene → Arm Models and verify that the rendering mode includes colliders.

Self-collisions can happen when wrist joints are commanded to positions that bring adjacent links too close together. If the overlap is a modeling artifact rather than a real collision, allow the frame pair with CollisionSpecification.

Common causes of motion plan failures