public class DifferentialDrive extends RobotDriveBase
These drive bases typically have drop-center / skid-steer with two or more wheels per side
(e.g., 6WD or 8WD). This class takes a SpeedController per side. For four and
six motor drivetrains, construct and pass in SpeedControllerGroup
instances as follows.
Four motor drivetrain:
public class Robot {
Spark m_frontLeft = new Spark(1);
Spark m_rearLeft = new Spark(2);
SpeedControllerGroup m_left = new SpeedControllerGroup(m_frontLeft, m_rearLeft);
Spark m_frontRight = new Spark(3);
Spark m_rearRight = new Spark(4);
SpeedControllerGroup m_right = new SpeedControllerGroup(m_frontRight, m_rearRight);
DifferentialDrive m_drive = new DifferentialDrive(m_left, m_right);
}
Six motor drivetrain:
public class Robot {
Spark m_frontLeft = new Spark(1);
Spark m_midLeft = new Spark(2);
Spark m_rearLeft = new Spark(3);
SpeedControllerGroup m_left = new SpeedControllerGroup(m_frontLeft, m_midLeft, m_rearLeft);
Spark m_frontRight = new Spark(4);
Spark m_midRight = new Spark(5);
Spark m_rearRight = new Spark(6);
SpeedControllerGroup m_right = new SpeedControllerGroup(m_frontRight, m_midRight, m_rearRight);
DifferentialDrive m_drive = new DifferentialDrive(m_left, m_right);
}
A differential drive robot has left and right wheels separated by an arbitrary width.
Drive base diagram:
|_______| | | | | | | |_|___|_| | |
Each drive() function provides different inverse kinematic relations for a differential drive robot. Motor outputs for the right side are negated, so motor direction inversion by the user is usually unnecessary.
This library uses the NED axes convention (North-East-Down as external reference in the world frame): http://www.nuclearprojects.com/ins/images/axis_big.png.
The positive X axis points ahead, the positive Y axis points right, and the positive Z axis points down. Rotations follow the right-hand rule, so clockwise rotation around the Z axis is positive.
Inputs smaller then 0.02 will
be set to 0, and larger values will be scaled so that the full range is still used. This
deadband value can be changed with RobotDriveBase.setDeadband(double).
RobotDrive porting guide:
tankDrive(double, double) is equivalent to
RobotDrive.tankDrive(double, double) if a deadband of 0 is used.
arcadeDrive(double, double) is equivalent to
RobotDrive.arcadeDrive(double, double) if a deadband of 0 is used
and the the rotation input is inverted eg arcadeDrive(y, -rotation)
curvatureDrive(double, double, boolean) is similar in concept to
RobotDrive.drive(double, double) with the addition of a quick turn
mode. However, it is not designed to give exactly the same response.
RobotDriveBase.MotorType| Modifier and Type | Field and Description |
|---|---|
static double |
kDefaultQuickStopAlpha |
static double |
kDefaultQuickStopThreshold |
kDefaultDeadband, kDefaultMaxOutput, m_deadband, m_maxOutput, m_safetyHelperDEFAULT_SAFETY_EXPIRATION| Constructor and Description |
|---|
DifferentialDrive(SpeedController leftMotor,
SpeedController rightMotor)
Construct a DifferentialDrive.
|
| Modifier and Type | Method and Description |
|---|---|
void |
arcadeDrive(double xSpeed,
double zRotation)
Arcade drive method for differential drive platform.
|
void |
arcadeDrive(double xSpeed,
double zRotation,
boolean squaredInputs)
Arcade drive method for differential drive platform.
|
void |
curvatureDrive(double xSpeed,
double zRotation,
boolean isQuickTurn)
Curvature drive method for differential drive platform.
|
java.lang.String |
getDescription() |
void |
initSendable(SendableBuilder builder)
Initializes this
Sendable object. |
void |
setQuickStopAlpha(double alpha)
Sets the low-pass filter gain for QuickStop in curvature drive.
|
void |
setQuickStopThreshold(double threshold)
Sets the QuickStop speed threshold in curvature drive.
|
void |
stopMotor() |
void |
tankDrive(double leftSpeed,
double rightSpeed)
Tank drive method for differential drive platform.
|
void |
tankDrive(double leftSpeed,
double rightSpeed,
boolean squaredInputs)
Tank drive method for differential drive platform.
|
applyDeadband, getExpiration, isAlive, isSafetyEnabled, limit, normalize, setDeadband, setExpiration, setMaxOutput, setSafetyEnabledaddChild, free, getName, getSubsystem, setName, setName, setName, setSubsystempublic static final double kDefaultQuickStopThreshold
public static final double kDefaultQuickStopAlpha
public DifferentialDrive(SpeedController leftMotor, SpeedController rightMotor)
To pass multiple motors per side, use a SpeedControllerGroup. If a motor needs to be
inverted, do so before passing it in.
public void arcadeDrive(double xSpeed, double zRotation)
xSpeed - The robot's speed along the X axis [-1.0..1.0]. Forward is positive.zRotation - The robot's rotation rate around the Z axis [-1.0..1.0]. Clockwise is
positive.public void arcadeDrive(double xSpeed, double zRotation, boolean squaredInputs)
xSpeed - The robot's speed along the X axis [-1.0..1.0]. Forward is positive.zRotation - The robot's rotation rate around the Z axis [-1.0..1.0]. Clockwise is
positive.squaredInputs - If set, decreases the input sensitivity at low speeds.public void curvatureDrive(double xSpeed, double zRotation, boolean isQuickTurn)
The rotation argument controls the curvature of the robot's path rather than its rate of heading change. This makes the robot more controllable at high speeds. Also handles the robot's quick turn functionality - "quick turn" overrides constant-curvature turning for turn-in-place maneuvers.
xSpeed - The robot's speed along the X axis [-1.0..1.0]. Forward is positive.zRotation - The robot's rotation rate around the Z axis [-1.0..1.0]. Clockwise is
positive.isQuickTurn - If set, overrides constant-curvature turning for
turn-in-place maneuvers.public void tankDrive(double leftSpeed, double rightSpeed)
leftSpeed - The robot's left side speed along the X axis [-1.0..1.0]. Forward is
positive.rightSpeed - The robot's right side speed along the X axis [-1.0..1.0]. Forward is
positive.public void tankDrive(double leftSpeed, double rightSpeed, boolean squaredInputs)
leftSpeed - The robot left side's speed along the X axis [-1.0..1.0]. Forward is
positive.rightSpeed - The robot right side's speed along the X axis [-1.0..1.0]. Forward is
positive.squaredInputs - If set, decreases the input sensitivity at low speeds.public void setQuickStopThreshold(double threshold)
QuickStop compensates for the robot's moment of inertia when stopping after a QuickTurn.
While QuickTurn is enabled, the QuickStop accumulator takes on the rotation rate value outputted by the low-pass filter when the robot's speed along the X axis is below the threshold. When QuickTurn is disabled, the accumulator's value is applied against the computed angular power request to slow the robot's rotation.
threshold - X speed below which quick stop accumulator will receive rotation rate values
[0..1.0].public void setQuickStopAlpha(double alpha)
The low-pass filter filters incoming rotation rate commands to smooth out high frequency changes.
alpha - Low-pass filter gain [0.0..2.0]. Smaller values result in slower output changes.
Values between 1.0 and 2.0 result in output oscillation. Values below 0.0 and
above 2.0 are unstable.public void stopMotor()
stopMotor in interface MotorSafetystopMotor in class RobotDriveBasepublic java.lang.String getDescription()
getDescription in interface MotorSafetygetDescription in class RobotDriveBasepublic void initSendable(SendableBuilder builder)
SendableSendable object.builder - sendable builder