6.1 Locomotion principles for wheeled and tracked robots
2 min read•july 25, 2024
Wheel configurations and are crucial for mobile robots. Different setups like , , and offer unique advantages. Understanding forward and helps determine robot position and required wheel velocities for desired motion.
Control systems are vital for robot motion, employing techniques like and . Tracked robots offer unique performance benefits, especially in challenging terrains. Their mechanics involve and , with like and guiding their performance evaluation.
Wheel Configurations and Robot Kinematics
Wheel configurations for mobile robots
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Top images from around the web for Wheel configurations for mobile robots
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- Differential drive employs two independently driven wheels allowing simple design and control but limited stability on uneven terrain
- Ackermann steering utilizes car-like mechanism enabling smooth turning at high speeds with larger turning radius than differential drive
- Omnidirectional wheels facilitate holonomic movement in any direction through complex design and control at higher cost (mecanum wheels)
- used in tracked vehicles and some wheeled robots performs well on rough terrain but less precise turning (bulldozers)
Kinematics of wheeled robots
- determines robot position and orientation from wheel rotations using odometry equations
- Inverse kinematics calculates required wheel velocities for desired robot motion
- relates wheel velocities to robot linear and angular velocities
- accounts for mass, inertia, and forces acting on the robot using Newton-Euler equations or Lagrangian mechanics
- and incorporate Coulomb friction model and Pacejka's Magic Formula for tire-ground interaction
Control Systems and Tracked Robots
Control systems for robot motion
- PID control utilizes Proportional, Integral, and Derivative terms with tuning methods (Ziegler-Nichols)
- Model Predictive Control optimizes control inputs over prediction horizon handling constraints explicitly
- implements path following algorithms and pure pursuit controller
- employs potential field methods and Vector Field Histogram
- incorporates Simultaneous Localization and Mapping and Kalman filtering for sensor fusion
Performance of tracked robots
- Tracked robot mechanics involve track tension, sag, and grouser design for traction
- considers soil mechanics (terramechanics) and Bekker-Wong theory for soil-vehicle interaction
- Mobility metrics include drawbar pull, tractive effort, and
- Turning mechanisms utilize skid steering for tracked vehicles with neutral turn capability
- Comparison with wheeled robots shows lower ground pressure for soft terrains, higher traction in loose soil or snow, but increased complexity and maintenance requirements
Key Terms to Review (24)
Ackermann steering: Ackermann steering is a geometric arrangement of linkages in a wheeled vehicle that allows for optimal turning by ensuring that the wheels turn at angles proportional to their distance from the center of the turn. This design minimizes tire wear and enhances maneuverability by preventing skidding during turns, making it particularly important for vehicles navigating tight corners.
Differential drive: Differential drive is a type of locomotion used in wheeled robots that relies on two independently driven wheels located on either side of the robot. By varying the speed and direction of each wheel, the robot can move forward, backward, or turn in place, making it highly maneuverable. This system allows for precise control over movement and navigation, essential for many robotic applications.
Drawbar Pull: Drawbar pull is the force exerted by a wheeled or tracked vehicle when pulling a load, measured at the drawbar or towing hitch. This concept is crucial for understanding the performance and efficiency of locomotion in wheeled and tracked robots, as it directly relates to their ability to move heavy loads across various terrains and conditions. Factors such as traction, weight distribution, and wheel or track design significantly influence drawbar pull, making it an essential consideration in robotic mobility engineering.
Dynamic model: A dynamic model is a mathematical representation that describes how a system changes over time, considering the effects of forces and motion. It is essential for predicting the behavior of robots, especially wheeled and tracked types, by simulating their movements in response to various inputs and environmental factors. This model helps in understanding how different parameters influence the locomotion, stability, and efficiency of robotic systems.
Dynamics: Dynamics is the branch of mechanics that studies the forces and torques that cause motion in systems, specifically focusing on how these forces affect the behavior of objects in motion. This concept is crucial for understanding how robots interact with their environment, as it involves analyzing movement patterns and energy transfer, which are fundamental to both legged and wheeled locomotion systems.
Forward Kinematics: Forward kinematics is the process of calculating the position and orientation of a robot's end effector based on the joint parameters, such as angles and displacements. This process is crucial for understanding how movements in a robotic system relate to its physical configuration, enabling precise control and manipulation in various applications.
Friction models: Friction models are mathematical representations that describe the interactions between surfaces in contact, focusing on the forces that resist motion. These models help in understanding how robots can effectively navigate various terrains by predicting the frictional forces at play, which is crucial for designing control systems for wheeled and tracked robots.
Grouser Design: Grouser design refers to the specific shape and pattern of traction elements on the surface of tracked vehicles or certain wheeled robots, aimed at enhancing grip and mobility on various terrains. These protrusions increase the contact area between the ground and the vehicle, which significantly improves traction, particularly on soft, muddy, or slippery surfaces. Effective grouser design is essential for optimizing the performance and stability of robots that rely on continuous tracks or specialized wheels.
Inverse Kinematics: Inverse kinematics is the process of calculating the joint parameters needed to place the end-effector of a robotic arm or manipulator at a desired position and orientation in space. This technique is essential for controlling robotic systems, as it allows for precise movement and positioning based on the goals set by a user or program.
Kinematics: Kinematics is the branch of mechanics that studies the motion of objects without considering the forces that cause this motion. It focuses on describing how objects move in terms of position, velocity, acceleration, and time, which is crucial for understanding the movement patterns in various robotic systems. By analyzing these parameters, one can optimize the design and control strategies of different robotic platforms, enabling them to navigate their environments effectively.
Localization and Mapping: Localization and mapping is the process by which a robot determines its position within an environment while simultaneously creating a map of that environment. This dual task is critical for autonomous navigation, allowing robots to understand where they are and how to navigate effectively using the information from their surroundings. Efficient localization and mapping rely heavily on various data sources and methods for accurately interpreting sensor data, ensuring precise movement in both static and dynamic environments.
Mobility metrics: Mobility metrics are quantitative measures used to evaluate the movement capabilities and performance of robotic systems, especially those employing wheeled and tracked locomotion. These metrics help in assessing how effectively a robot can navigate different terrains, maintain stability, and adapt to dynamic environments. Understanding mobility metrics is crucial for optimizing robot design, ensuring efficiency in operations, and enhancing overall functionality in various applications.
Model Predictive Control: Model Predictive Control (MPC) is an advanced control strategy that utilizes a model of the system to predict future behavior and optimize control actions accordingly. It allows for real-time optimization of control inputs by considering system dynamics and constraints over a finite prediction horizon. This approach is particularly useful in complex systems where dynamic interactions and constraints must be managed effectively.
Motion resistance: Motion resistance refers to the opposing forces that a robot encounters while moving, which can affect its speed, efficiency, and ability to navigate various terrains. This concept is critical when designing wheeled and tracked robots, as it encompasses factors like friction, incline angles, and surface materials. Understanding motion resistance helps in optimizing locomotion mechanisms to ensure reliable performance under different conditions.
Obstacle Avoidance: Obstacle avoidance refers to the ability of a robot to detect and avoid obstacles in its environment while navigating towards a target or following a desired path. This capability is crucial for ensuring safe and efficient operation, particularly in dynamic environments where unforeseen objects may be present. Effective obstacle avoidance relies on various sensors, algorithms, and decision-making processes that allow robots to interpret their surroundings and make real-time adjustments to their movement.
Omnidirectional wheels: Omnidirectional wheels are specialized wheels designed to allow vehicles to move in any direction without changing their orientation. They are composed of several smaller rollers positioned at an angle around the wheel's circumference, enabling lateral movement and rotation while maintaining stability. This unique design provides significant advantages in maneuverability and flexibility for robots, especially in confined spaces or complex environments.
PID Control: PID control is a widely used control loop feedback mechanism that stands for Proportional, Integral, and Derivative control. This technique helps maintain a desired output in systems by continuously adjusting the input based on the difference between the desired setpoint and the measured process variable. It is integral to effectively managing the performance of various actuators, manipulators, and robots, making it essential for achieving precise control in automation.
Skid Steering: Skid steering is a method used in wheeled and tracked vehicles to control movement by varying the speed of the wheels or tracks on either side of the vehicle. This technique allows for tight turns and maneuverability, making it particularly useful in environments where space is limited. By rotating the vehicle around its center, skid steering enables efficient navigation through obstacles and enhances overall agility.
Terrain interaction: Terrain interaction refers to the ways in which a robot engages with and navigates different types of surfaces and obstacles in its environment. This concept is crucial for understanding how wheeled and tracked robots can optimize their locomotion by adapting to varying terrain conditions, enabling them to move efficiently and effectively across diverse landscapes.
Track tension: Track tension refers to the force exerted on the track of a tracked robot, affecting its ability to maintain traction and stability while moving. Proper track tension is crucial for ensuring efficient movement, reducing slippage, and preventing damage to the track system. The balance of track tension also influences the overall performance of tracked robots in navigating various terrains, making it a key aspect of their locomotion principles.
Tractive Effort: Tractive effort is the force exerted by a vehicle's wheels or tracks to pull or push it forward, essential for locomotion. This force plays a critical role in determining a robot's ability to navigate various terrains and overcome obstacles, influencing factors such as speed, acceleration, and stability.
Trajectory tracking: Trajectory tracking refers to the process of controlling a robot or vehicle to follow a specific path or trajectory over time. This concept is crucial for ensuring that autonomous systems can accurately navigate their environment and reach designated points, while considering factors like dynamics, obstacles, and environmental conditions. Effective trajectory tracking enables robots to perform tasks with precision and can enhance their ability to adapt to changes in their surroundings.
Velocity kinematics: Velocity kinematics refers to the study of the motion of objects in terms of their velocity, which is the rate of change of position with respect to time. In robotics, understanding velocity kinematics is essential for controlling the movement of wheeled and tracked robots, as it allows for precise navigation and maneuvering. This concept encompasses various factors such as speed, direction, and acceleration, which together influence how robots interact with their environment.
Wheel slip: Wheel slip refers to the phenomenon where the wheels of a robot or vehicle lose traction with the surface they are moving on, causing them to rotate without effectively propelling the robot forward. This can lead to a loss of control and reduced efficiency in locomotion, impacting the robot's ability to navigate various terrains. Understanding wheel slip is crucial for optimizing movement strategies in wheeled and tracked robots, ensuring they maintain traction and perform effectively in different environments.