Week 11 - Robotics and Incremental Bayes

What are the main components of a robot agent?

Sensors (to perceive the world) and effectors (to act on it), including manipulators and mobile platforms.

What are degrees of freedom (DOF) in robotics?

The number of independent movements a robot can make. At least 6 DOF are needed to position an end-effector in 3D space (3 for position + 3 for orientation).

What is a non-holonomic robot?

A robot with fewer control inputs than degrees of freedom, such as a car (2 controls but 3 DOF: x, y, orientation).

What are the two major sources of uncertainty in robotics?

1. Perception (sensor errors, limited resolution); 2. Action (slippage, inaccurate actuators, mechanical noise).

Why do perception errors occur?

Sensors have limited resolution, field of view, and may generate false positives or false negatives due to noise or occlusions.

Why do action errors occur?

Actions are subject to slippage, inaccurate joint encoding, surface friction, and mechanical imperfections.

What is the goal of robot localization?

To estimate the robot’s current state (position and orientation) using motion models and sensor observations.

How is a motion model used in localization?

It predicts the next state based on the robot’s velocity and turning angle (e.g., linear and angular velocity).

How is a sensor model used in localization?

It estimates the likelihood of being in a state given current sensor readings (e.g., distance to obstacles).

What is particle filtering?

A method for robot localization where many samples (particles) represent possible locations. Their probabilities are updated based on sensor data.

Why does particle filtering improve over time?

As the robot moves and collects more sensor readings, unlikely positions are eliminated, and particles concentrate around the true location.

What is SLAM?

Simultaneous Localization and Mapping: the robot builds a map of the environment while simultaneously estimating its own location within it.

Why is SLAM difficult in symmetric environments?

Lack of unique landmarks causes ambiguity, making it hard to resolve the robot’s location.

What is configuration space in robotics?

The space of all possible positions and orientations of a robot, where motion planning takes place.

What is cell decomposition in motion planning?

Divides configuration space into simple cells that can be navigated easily.

What is skeletonization in motion planning?

Reduces the space to a graph of key points (e.g., Voronoi diagram or probabilistic roadmap) to simplify pathfinding.

How is Bayes’ Rule used in robotics?

To update beliefs about robot state or environment based on sensor data and prior probabilities.

What is the incremental Bayes update rule?

P(H) ← P(M | H) * P(H) / P(M), used to incorporate new measurements into belief updates.

What is an example of Bayesian inference in robotics?

Estimating the presence of an obstacle using noisy sensor data, factoring in false positive/negative rates.

What was the DARPA Grand Challenge?

A competition where autonomous vehicles had to navigate a desert course. Stanley, from Stanford, was the first to finish using lidar and probabilistic mapping.