kinematics::DiffDriveKinematics Class Reference

Represents the kinematics of a differential drive. More...

#include <DiffDriveKinematics.h>

Public Types
enum class	PreferredVelPreservation { Proportional , PreferXVel , PreferThetaVel }
	Proportional: The xVel and thetaVel are scaled an equal amount. More...

Public Member Functions
	DiffDriveKinematics (double wheelBaseWidth)
	Create a new DiffDriveKinematics with the given wheel base width.
navtypes::pose_t	wheelVelToRobotVel (double lVel, double rVel) const
	Given the left and right wheel velocities, find the robot velocity in the robot's reference frame.
wheelvel_t	robotVelToWheelVel (double xVel, double thetaVel) const
	Given the robot velocity in the robot's local reference frame, find the left and right tangential wheel velocities.
navtypes::pose_t	getLocalPoseUpdate (const wheelvel_t &wheelVel, double dt) const
	Calculate the pose update in the local reference frame assuming the left and right wheels have constant velocity.
navtypes::pose_t	getPoseUpdate (const wheelvel_t &wheelVel, double heading, double dt) const
	Calculate the pose update in the global reference frame (map space) assuming the left and right wheels have constant velocity.
navtypes::pose_t	getNextPose (const wheelvel_t &wheelVel, const navtypes::pose_t &pose, double dt) const
	Calculate the next pose of the robot in the global reference frame.
navtypes::pose_t	ensureWithinWheelSpeedLimit (PreferredVelPreservation preferred, double xVel, double thetaVel, double maxWheelSpeed) const
	Ensure that the given xVel and thetaVel translate to a wheel speed less than or equal to the max wheel speed.

Detailed Description

Represents the kinematics of a differential drive.

This class can be used to calculate various velocities and pose updates using the mathematical representation of the drivebase.

Member Enumeration Documentation

PreferredVelPreservation

enum class kinematics::DiffDriveKinematics::PreferredVelPreservation

strong

Proportional: The xVel and thetaVel are scaled an equal amount.

This keeps the linear and theta velocity at equal proportions to their original values but their output wheel speed is below the max allowed.

PreferXVel: The theta velocity is scaled and the x velocity is maintained. This preserves linear velocity over theta velocity meaning we lose turning ability.

PreferThetaVel: The x velocity is scaled and the theta velocity is maintained. This preserves the ability to rotate the rover by scaling down the linear velocity so that the calculated max wheel speed is below the set max wheel speed allowed.

Constructor & Destructor Documentation

DiffDriveKinematics()

kinematics::DiffDriveKinematics::DiffDriveKinematics ( double wheelBaseWidth )

explicit

Create a new DiffDriveKinematics with the given wheel base width.

Parameters

wheelBaseWidth

The width of the wheelbase. The units themselves don't matter, as long as you're consistent.

Member Function Documentation

ensureWithinWheelSpeedLimit()

pose_t kinematics::DiffDriveKinematics::ensureWithinWheelSpeedLimit	(	PreferredVelPreservation	preferred,
		double	xVel,
		double	thetaVel,
		double	maxWheelSpeed ) const

Ensure that the given xVel and thetaVel translate to a wheel speed less than or equal to the max wheel speed.

Scales them if they do not.

Parameters

preferred	Choose proportional if x velocity and theta velocity should be scaled proportionally to each other, choose PreferXVel if linear velocity is preferred, or choose PreferThetaVel if turning is preferred.
xVel	The xVel used to calculate the wheel speed
thetaVel	The theta veloicty used to calculate the wheel speed.
maxWheelSpeed	The current max possible wheel speed. This is the value that the calculated velocity will be checked against.

getLocalPoseUpdate()

pose_t kinematics::DiffDriveKinematics::getLocalPoseUpdate	(	const wheelvel_t &	wheelVel,
		double	dt ) const

Calculate the pose update in the local reference frame assuming the left and right wheels have constant velocity.

Parameters

wheelVel	The velocities of the wheels.
dt	The elapsed time in seconds for which the update is calculated. The robot has been moving at the specified velocity for this much time.

Returns

The pose update in the robot's local reference frame.

getNextPose()

pose_t kinematics::DiffDriveKinematics::getNextPose	(	const wheelvel_t &	wheelVel,
		const navtypes::pose_t &	pose,
		double	dt ) const

Calculate the next pose of the robot in the global reference frame.

(map space)

Parameters

wheelVel	The velocities of the wheels.
pose	The current pose of the robot, in the global reference frame.
dt	The elapsed time in seconds for which the update is calculated. The robot has been moving at the specified velocity for this much time.

Returns

The next pose of the robot in the global reference frame after having moved at the specified velocity for the specified time.

getPoseUpdate()

pose_t kinematics::DiffDriveKinematics::getPoseUpdate	(	const wheelvel_t &	wheelVel,
		double	heading,
		double	dt ) const

Calculate the pose update in the global reference frame (map space) assuming the left and right wheels have constant velocity.

Parameters

wheelVel	The velocities of the wheels.
dt	The elapsed time in seconds for which the update is calculated. The robot has been moving at the specified velocity for this much time.

Returns

The pose update in the global reference frame.

robotVelToWheelVel()

wheelvel_t kinematics::DiffDriveKinematics::robotVelToWheelVel	(	double	xVel,
		double	thetaVel ) const

Given the robot velocity in the robot's local reference frame, find the left and right tangential wheel velocities.

Parameters

xVel	The x velocity in the robot's reference frame.
thetaVel	The rotational velocity around the z-axis. In rad/sec.

Returns

Struct with fields lVel and rVel, representing the left and right velocities.

wheelVelToRobotVel()

pose_t kinematics::DiffDriveKinematics::wheelVelToRobotVel	(	double	lVel,
		double	rVel ) const

Given the left and right wheel velocities, find the robot velocity in the robot's reference frame.

Since this is a non-holonomic drivebase, the y velocity will be 0.

Parameters

lVel	The tangential velocity of the left wheel.
rVel	The tangential velocity of the right wheel.

Returns

The robot velocity in the form [xVel, yVel, thetaVel] in the robot's local reference frame. thetaVel will be in units rad/sec.

---

The documentation for this class was generated from the following files:

• src/kinematics/DiffDriveKinematics.h
• src/kinematics/DiffDriveKinematics.cpp