Robotics Flashcards
What is a singularity in robotics?
`A singularity is a point along a cartesian path where a robot loses a degree of freedom. Moving near a singularity can cause odd motion like massive velocities or accelerations.
What is a Jacobian matrix?
The Jacobian matrix relates the velocities of a robots joints to the velocity of its end effector.
joint velocities = inverse jacobian * end-effector velocity
Describe Roll, Pitch, and Yaw
Roll, Pitch, and Yaw describe the orientation of an object relative to a fixed coordinate frame.
Describe Euler Angles
Euler angles describe a 3D rotation as a sequence of rotations about a sequence of axes. They can be extrinsic, i.e. the reference axes remain the same throughout the operation, or intrinsic, where the axes change as the frame rotates.
Describe Quaternions
A mathematical representation used to describe rotations in 3D space. They allow continuous rotation handling without gimbal lock which can occur in euler angles.
What are Inverse Kinematics?
Inverse kinematics are used to find the joint angles required to achieve a given end-effector pose
What are Forward Kinematics?
Forward kinematics take a set of joint angles and compute the end-effector pose
What is a homogeneous transform?
A homogeneous transformation matrix describes a transform between two coordinate frames. It combines the rotation matrix and the translation vector.
It looks like H = | R T |
| 0 1 |
Difference between stepper and servo motors?
Stepper motors are a type of BLDC motor that drive a toothed rotor in “steps” by sequentially energizing stator coils. Since steppers move single “step” each pulse, they can be used precisely without an output position sensor.
Servo motors are also often BLDCs, but they require position sensors to be controlled precisely.
Describe PID control and its use in robotic systems
PID stands for proportional, integral, and derivative and is a control system methodology. Its used with a closed-loop system where a state variable is set to a desired value and then monitored. The proportional gain adapts the control signal based on the magnitude of the state variable error, the integral gain based on the cumulative error, and the derivated based on the rate of change of the error.
What are Kalman Filters?
Kalman filtering is an algorithm that uses a series of measurements including statistical noise and other error to estimate the value of a state variable
What is Sensor Fusion?
Sensor fusion takes data from multiple sensors such as lidar and camera or imus and accelerometers and combines them produce a more accurate state estimate.
What is SLAM?
SLAM is simultaneous localization and mapping. It’s a technique used by autonomous systems to build a map of their environment while also determining their location within that environment. It often uses Monte Carlo Localization (AKA Particle Filtering).
What is A* and how does it work?
A* is a path finding and graph traversal algorithm that finds the shortest path between two points in a graph using a heuristic function (which is used to estimate cost of moving from a node to the goal) to explore the search space.
What is ROS?
ROS is robot operating system, it is a middleware that supports different forms of messaging and integrates a number of powerful robotics tools for things like simulation, and visualization.
What are Publishers and Subscribers in ROS?
Publishers send messages of certain types out onto the ROS network using a topic. Subscribers listen to specific topics and can handle them with callbacks.
How does ROS2 differ from ROS1?
ROS1 used a master node to keep track of all nodes and topics whereas ROS2 uses a discovery system built into DDS.
What is a URDF?
A URDF is a Universal Robot Description File. It is used to define a robot for use in different applications. It defines things like geometry, kinematics, joint limits, and even STL files for visualization.
What are ROS Services?
ROS services are another form of message. Unlike publishers and subscribers, services use a client / server model.
What are DH parameters?
Denavit-Hartenberg parameters are a standard method to describe the kinematics of a robot using 4 parameters to define the transformation between consecutive joints
What are ROS actions?
ROS actions are used to manage long-running operations which can be pre-empted and monitored as they progress. They are useful for robotic operations like a cartesian move that may take some time to complete. They are comprised of a Goal, Feedback, and a Result.
What is the ROS2 Daemon?
The ROS2 daemon is a service that runs in the background and keeps track of the ROS2 participants it discovers on the network. It informs CLI introspection tools like ros2 topic list
What is the bandwidth of a robotic system?
Bandwidth of a robotic system is the frequency range in which the system can respond effectively. The cutoff is typically considered -3Db.
What is Monte Carlo Localization?
AKA particle filter localization is an algorithm used by robots to estimate their pose using a known map. The robot generates guesses (particles) of where it might be and compares those guesses against what it senses. It throws away the least accurate guesses, and therefore over time, the guesses should converge on the real pose.
What is Gimbal Lock
Gimbal lock occurs when two axes of a 3D system align and thus the system loses a degree of freedom. It can occur with Euler angles.
What are some methods to compute IK?
Simple arms can be solved analytically. Gradient Descent and Inverse Jacobian are numerical methods used for more complex arms.
What is Gimbal Lock?
Gimbal lock occurs when two axes of a 3D rotation become aligned, thus removing a degree of freedom. This can occur with Euler Angles, but is fixed by using Quaternions.
What are some methods for computing IK?
IK for simple robotic arms can be computed analytically, but numerical methods like Gradient Descent or Inverse Jacobian are used for more complex robots.
