🤖Robotics Unit 6 – Mobile Robots: Wheeled, Legged, and Aerial

Introduction to Mobile Robots

• Mobile robots are autonomous or semi-autonomous machines capable of moving and performing tasks in various environments
• Possess the ability to perceive their surroundings using sensors (cameras, lidars, ultrasonic sensors) and make decisions based on the collected data
• Can navigate through unstructured environments (outdoor terrains, disaster zones) and adapt to changing conditions
• Utilize various locomotion methods depending on the application and environment (wheels, legs, propellers)
• Play a crucial role in industries such as manufacturing, agriculture, and logistics, as well as in research and exploration
• Offer advantages over stationary robots, including increased flexibility, adaptability, and the ability to cover larger areas
• Present unique challenges in terms of power management, navigation, and control due to their mobile nature

Types of Mobile Robots

• Wheeled robots are the most common type, using wheels for locomotion (differential drive, omnidirectional)
• Legged robots mimic animal or human locomotion, using legs for walking, running, or climbing (bipedal, quadrupedal)
  • Offer better adaptability to uneven terrain and obstacles compared to wheeled robots
• Tracked robots use continuous tracks for locomotion, providing better traction and stability on rough terrain (military, construction)
• Aerial robots, or drones, use propellers or wings for flight (quadcopters, fixed-wing)
  • Enable access to hard-to-reach areas and provide a bird's eye view for surveillance and mapping
• Underwater robots, or autonomous underwater vehicles (AUVs), are designed for aquatic environments (ocean exploration, pipeline inspection)
• Hybrid robots combine multiple locomotion methods (wheels and legs) to adapt to various terrains and tasks

Wheeled Robots: Design and Mechanics

• Wheeled robots rely on wheels for locomotion, which provides efficient and fast movement on flat surfaces
• Differential drive is a common configuration, using two independently controlled wheels for steering and a caster wheel for balance
• Omnidirectional drive uses special wheels (Mecanum, Swedish) that allow movement in any direction without changing orientation
• Ackermann steering, used in cars, employs a steering mechanism that turns the front wheels at different angles for smooth cornering
• Wheel placement and geometry affect stability, maneuverability, and the robot's ability to navigate obstacles
• Suspension systems help maintain wheel contact with the ground on uneven surfaces, improving traction and stability
• Motor selection (DC, stepper, servo) depends on the required torque, speed, and precision
• Encoders are used to measure wheel rotation for odometry and localization

Legged Robots: Locomotion and Balance

• Legged robots use articulated limbs for locomotion, inspired by animals and humans
• Bipedal robots have two legs and mimic human walking, offering adaptability to stairs and uneven terrain (humanoid robots)
• Quadrupedal robots have four legs, providing better stability and load-bearing capacity (Boston Dynamics' Spot)
• Hexapod and octopod robots have six and eight legs, respectively, inspired by insects and arachnids
• Gait refers to the sequence and timing of leg movements during locomotion (walking, trotting, galloping)
• Maintaining balance is crucial for legged robots, requiring accurate sensing and control of the center of mass
• Compliance in the legs, using springs or elastic elements, helps absorb shocks and adapt to uneven surfaces
• Legged robots can traverse challenging terrains (stairs, rubble) but are more complex and energy-intensive than wheeled robots

Aerial Robots: Flight Dynamics and Control

• Aerial robots, or drones, use propellers or wings for flight, enabling access to hard-to-reach areas and aerial surveys
• Multirotor drones (quadcopters, hexacopters) use multiple propellers for vertical takeoff, landing, and hovering
• Fixed-wing drones have wings for lift and are more efficient for long-range flights but require runways or catapults for takeoff and landing
• Flight dynamics involve the forces acting on the drone (thrust, lift, drag, weight) and their effect on motion
• Attitude control maintains the drone's orientation (roll, pitch, yaw) using sensors (IMU, gyroscope) and actuators (motors, control surfaces)
• Position control uses GPS, vision, or other sensors to maintain the drone's location and altitude
• Path planning generates feasible trajectories for the drone to follow, considering obstacles and environmental factors
• Drones are subject to regulations and safety concerns, such as collision avoidance and restricted airspace

Sensors and Perception in Mobile Robotics

• Sensors enable mobile robots to perceive and interpret their environment for navigation, obstacle avoidance, and task execution
• Cameras provide visual information, enabling object recognition, tracking, and visual odometry (estimating motion from images)
• Lidar (Light Detection and Ranging) uses laser pulses to create 3D point clouds of the environment, useful for mapping and localization
• Ultrasonic sensors measure distance using sound waves, helpful for close-range obstacle detection
• Infrared sensors detect heat signatures, useful for tracking people or animals
• Inertial Measurement Units (IMUs) combine accelerometers and gyroscopes to measure the robot's acceleration and orientation
• Encoders measure the rotation of wheels or joints, providing odometry information for localization
• Sensor fusion combines data from multiple sensors to improve the accuracy and reliability of perception
• Machine learning techniques (deep learning, computer vision) are used to process and interpret sensor data

Navigation and Path Planning

• Navigation involves determining the robot's position, planning a path to a goal, and executing the planned motion
• Localization estimates the robot's position and orientation within a known map using sensor data (odometry, GPS, landmarks)
• Mapping builds a representation of the environment using sensor data (occupancy grid, topological map, 3D point cloud)
• Simultaneous Localization and Mapping (SLAM) constructs a map of an unknown environment while simultaneously tracking the robot's location within it
• Path planning generates a feasible and efficient route from the robot's current position to a goal location
• Graph-based methods (A*, Dijkstra's) find optimal paths in discrete environments represented as graphs or grids
• Sampling-based methods (RRT, PRM) explore continuous state spaces by randomly sampling points and connecting them to form a path
• Reactive navigation uses real-time sensor data to avoid obstacles and adapt to dynamic environments (potential fields, vector field histograms)
• Motion control executes the planned path by sending commands to the robot's actuators (PID, MPC)

Real-World Applications and Challenges

• Mobile robots are used in various industries and applications, each presenting unique challenges and requirements
• In manufacturing and logistics, mobile robots transport goods, assist in assembly tasks, and perform inspections (AGVs, collaborative robots)
• Agricultural robots help with planting, harvesting, and monitoring crops, improving efficiency and precision (autonomous tractors, drones)
• Search and rescue robots assist in locating and extracting victims in disaster scenarios (collapsed buildings, avalanches)
• Exploration robots gather data and samples in remote or hazardous environments (Mars rovers, underwater robots)
• Challenges include robustness to environmental conditions (weather, lighting), safety and interaction with humans, and power management
• Ethical considerations arise when deploying mobile robots, such as job displacement, privacy concerns, and autonomous decision-making
• Standardization and interoperability are essential for the widespread adoption and integration of mobile robots in various applications
• Ongoing research focuses on improving perception, decision-making, and adaptability to enable more autonomous and intelligent mobile robots