# t000__ep040__blocks

- **suite / variant:** `` / ``
- **instruction:** Stack the yellow block on the wooden block
- **success:** False
- **control steps:** 426  (8.4s at 51 Hz)
- **policy inferences:** 74  (replan_steps=6)
- **video:** `blocks/ep040/rollout.mp4`
- **features:** `74` prefix tensors (`prefix`; model=``)

## Semantic timeline

| seconds | control_step | policy_step | phrase |
|---|---|---|---|
| 0.0–3.0 | 0–151 | 0–25 | lowering gripper toward yellow block |
| 3.0–6.0 | 152–303 | 25–50 | closing gripper and lifting empty |
| 6.0–8.4 | 304–425 | 50–70 | moving empty gripper over wooden block |

## Failure

- **yes**
- **onset type:** obvious_mistake
- **onset:** 4.714003944773175 s (00:04.7)
- **frame / control_step:** 239 (policy_step=39, chunk_index=5)
- **coarse onset:** 4.2 s (refined=True)
- **mode:** grasp_failure
- **reason:** The robot attempted to grasp the yellow block, but failed to secure its grip, raising its empty gripper into the air while leaving the block on the table.
  Summary: failed grasp on yellow block; lifting empty gripper
- **recovery:** Move the arm back over the yellow block, lower the gripper around the block, close the fingers securely, and then pick it up.
  Summary: re-align gripper over yellow block; grasp and lift yellow block
- **prevention:** Ensure the gripper is properly aligned and centered around the yellow block before closing the fingers to achieve a firm grasp before lifting.
  Summary: center gripper on yellow block; secure firm grip before lifting
- **justification:** At 00:04 (4.0s), the robot closes its gripper on the yellow block, but fails to grip it securely. By 00:05 (5.0s), the arm lifts up leaving the yellow block behind on the table, continuing to execute the stacking motion with an empty gripper.