# Descriptive transcript: Task-and-Motion Sequencing

Complete narration and original visual descriptions. Untimed non-video learning path.

## 00:00 — It fits. Until it picks.

Visual: Top-down overhead gantry moves empty across opening, then a separate planned loaded path stops at first model collision. Do not depict crashing hardware.

Narration: This robot can reach both sides of the opening. Its empty gripper fits. But pick up the box, and the same route fails. The goal is reachable. The sequence is not.

## 00:11 — What next? How exactly?

Visual: Pick/carry/place nodes pulse in order; geometric failure at carry sends feedback to earlier choice. Label candidate route, not execution.

Narration: Task planning chooses what happens next: pick, carry, then place. Motion planning checks how each action can happen. They must talk to each other. A grasp that works here can make the next movement impossible.

## 00:27 — The robot got wider.

Visual: Loaded box beside the opening; dimension brackets show 60 + 5 + 5 = 70 cm versus 40 cm. The top-down rectangle is the collision geometry.

Narration: In our simplified top-down model, the opening is forty centimeters wide. The box presents sixty centimeters across it. Add five centimeters of clearance on each side: seventy centimeters will not fit. Checking just the gripper misses the problem.

## 00:44 — Turn before crossing.

Visual: The box rotates in the left bay, moves through the opening, then rotates in the right bay. Each stage highlights during motion. The 30 cm demand is compared with the 40 cm opening only after the first turn.

Narration: Try a different sequence. Rotate in the open bay first. The box now presents twenty centimeters across the opening. With the same margins, it needs thirty. Plan the rotation, the loaded crossing, and the final placement together. In this model, that candidate clears the sampled checks.

## 01:04 — Endpoints can fool you.

Visual: At the opening's center, ghost poses at 0 and 180 degrees both fit horizontally. The attempted rotation stops at the first colliding sample. A separate translucent 90-degree pose is labeled blocked.

Narration: Do not postpone the turn until the narrow opening. These two end orientations both fit, but the box sweeps into the wall halfway through. Collision checking has to cover the motion, not just the start and finish. Sampling still leaves gaps between samples.

## 01:23 — Did it actually grasp?

Visual: An event timeline connects close, result plus object evidence, attached geometry, and carry. Missing evidence suppresses carry. A scene-version change prevents dispatch of the old plan. This is the lesson's illustrative model, not the ROS action-state machine.

Narration: Now execution. Sending close is not proof that the box is held. Wait for the action result and evidence of the object. Only then add the carried geometry and permit the transfer. If the scene changes before that transfer, stop dispatch and check the plan again.

## 01:42 — Which plan survives?

Visual: The transfer problem shows 35 + 5 + 5 = ? against a 40 cm opening. A separate accepted-command token is distinguished from object-held evidence. There is a three-second silent pause before the answer.

Narration: Your turn. A wider box needs thirty-five centimeters across the opening, before margins. The opening is still forty. Would our five-centimeter margin on each side pass? And would an accepted grasp command let the robot carry immediately? Pause and explain both decisions.

## 02:07 — A sequence needs evidence.

Visual: The 45 cm demand exceeds the 40 cm opening, so the candidate is rejected. Accepted is not held. A moving marker connects task choices, motion checks and evidence in a feedback loop. The closing invitation points to the course simulation.

Narration: No to both. Thirty-five plus ten is forty-five, so that clearance test fails. Accepted is not completed, and completed is not automatically proof of a secure grasp. Choose compatible actions, check their whole motions, verify the results, and revise when evidence changes. Try the simulation in our AI Robotics course.

A three-second silent retrieval pause precedes the answer. Pause longer as needed. This is a simplified simulation, not hardware guidance.