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frc::DifferentialDrive Class Reference

A class for driving differential drive/skid-steer drive platforms such as the Kit of Parts drive base, "tank drive", or West Coast Drive. More...

#include <DifferentialDrive.h>

Inheritance diagram for frc::DifferentialDrive:
frc::RobotDriveBase frc::MotorSafety frc::SendableBase frc::ErrorBase frc::Sendable

Public Member Functions

 DifferentialDrive (SpeedController &leftMotor, SpeedController &rightMotor)
 Construct a DifferentialDrive. More...
 
 DifferentialDrive (DifferentialDrive &&)=default
 
DifferentialDriveoperator= (DifferentialDrive &&)=default
 
void ArcadeDrive (double xSpeed, double zRotation, bool squareInputs=true)
 Arcade drive method for differential drive platform. More...
 
void CurvatureDrive (double xSpeed, double zRotation, bool isQuickTurn)
 Curvature drive method for differential drive platform. More...
 
void TankDrive (double leftSpeed, double rightSpeed, bool squareInputs=true)
 Tank drive method for differential drive platform. More...
 
void SetQuickStopThreshold (double threshold)
 Sets the QuickStop speed threshold in curvature drive. More...
 
void SetQuickStopAlpha (double alpha)
 Sets the low-pass filter gain for QuickStop in curvature drive. More...
 
bool IsRightSideInverted () const
 Gets if the power sent to the right side of the drivetrain is multipled by -1. More...
 
void SetRightSideInverted (bool rightSideInverted)
 Sets if the power sent to the right side of the drivetrain should be multipled by -1. More...
 
void StopMotor () override
 
void GetDescription (wpi::raw_ostream &desc) const override
 
void InitSendable (SendableBuilder &builder) override
 Initializes this Sendable object. More...
 
- Public Member Functions inherited from frc::RobotDriveBase
 RobotDriveBase (RobotDriveBase &&)=default
 
RobotDriveBaseoperator= (RobotDriveBase &&)=default
 
void SetDeadband (double deadband)
 Sets the deadband applied to the drive inputs (e.g., joystick values). More...
 
void SetMaxOutput (double maxOutput)
 Configure the scaling factor for using RobotDrive with motor controllers in a mode other than PercentVbus or to limit the maximum output. More...
 
void FeedWatchdog ()
 Feed the motor safety object. More...
 
- Public Member Functions inherited from frc::MotorSafety
 MotorSafety (MotorSafety &&rhs)
 
MotorSafetyoperator= (MotorSafety &&rhs)
 
void Feed ()
 Feed the motor safety object. More...
 
void SetExpiration (double expirationTime)
 Set the expiration time for the corresponding motor safety object. More...
 
double GetExpiration () const
 Retrieve the timeout value for the corresponding motor safety object. More...
 
bool IsAlive () const
 Determine if the motor is still operating or has timed out. More...
 
void SetSafetyEnabled (bool enabled)
 Enable/disable motor safety for this device. More...
 
bool IsSafetyEnabled () const
 Return the state of the motor safety enabled flag. More...
 
void Check ()
 Check if this motor has exceeded its timeout. More...
 
- Public Member Functions inherited from frc::ErrorBase
 ErrorBase (ErrorBase &&)=default
 
ErrorBaseoperator= (ErrorBase &&)=default
 
virtual ErrorGetError ()
 Retrieve the current error. More...
 
virtual const ErrorGetError () const
 Retrieve the current error. More...
 
virtual void ClearError () const
 Clear the current error information associated with this sensor.
 
virtual void SetErrnoError (const wpi::Twine &contextMessage, wpi::StringRef filename, wpi::StringRef function, int lineNumber) const
 Set error information associated with a C library call that set an error to the "errno" global variable. More...
 
virtual void SetImaqError (int success, const wpi::Twine &contextMessage, wpi::StringRef filename, wpi::StringRef function, int lineNumber) const
 Set the current error information associated from the nivision Imaq API. More...
 
virtual void SetError (Error::Code code, const wpi::Twine &contextMessage, wpi::StringRef filename, wpi::StringRef function, int lineNumber) const
 Set the current error information associated with this sensor. More...
 
virtual void SetErrorRange (Error::Code code, int32_t minRange, int32_t maxRange, int32_t requestedValue, const wpi::Twine &contextMessage, wpi::StringRef filename, wpi::StringRef function, int lineNumber) const
 Set the current error information associated with this sensor. More...
 
virtual void SetWPIError (const wpi::Twine &errorMessage, Error::Code code, const wpi::Twine &contextMessage, wpi::StringRef filename, wpi::StringRef function, int lineNumber) const
 Set the current error information associated with this sensor. More...
 
virtual void CloneError (const ErrorBase &rhs) const
 
virtual bool StatusIsFatal () const
 Check if the current error code represents a fatal error. More...
 
- Public Member Functions inherited from frc::SendableBase
 SendableBase (bool addLiveWindow=true)
 Creates an instance of the sensor base. More...
 
 SendableBase (SendableBase &&rhs)
 
SendableBaseoperator= (SendableBase &&rhs)
 
std::string GetName () const final
 Gets the name of this Sendable object. More...
 
void SetName (const wpi::Twine &name) final
 Sets the name of this Sendable object. More...
 
std::string GetSubsystem () const final
 Gets the subsystem name of this Sendable object. More...
 
void SetSubsystem (const wpi::Twine &subsystem) final
 Sets the subsystem name of this Sendable object. More...
 
- Public Member Functions inherited from frc::Sendable
 Sendable (Sendable &&)=default
 
Sendableoperator= (Sendable &&)=default
 
void SetName (const wpi::Twine &subsystem, const wpi::Twine &name)
 Sets both the subsystem name and device name of this Sendable object. More...
 

Static Public Attributes

static constexpr double kDefaultQuickStopThreshold = 0.2
 
static constexpr double kDefaultQuickStopAlpha = 0.1
 

Additional Inherited Members

- Public Types inherited from frc::RobotDriveBase
enum  MotorType {
  kFrontLeft = 0, kFrontRight = 1, kRearLeft = 2, kRearRight = 3,
  kLeft = 0, kRight = 1, kBack = 2
}
 The location of a motor on the robot for the purpose of driving.
 
- Static Public Member Functions inherited from frc::MotorSafety
static void CheckMotors ()
 Check the motors to see if any have timed out. More...
 
- Static Public Member Functions inherited from frc::ErrorBase
static void SetGlobalError (Error::Code code, const wpi::Twine &contextMessage, wpi::StringRef filename, wpi::StringRef function, int lineNumber)
 
static void SetGlobalWPIError (const wpi::Twine &errorMessage, const wpi::Twine &contextMessage, wpi::StringRef filename, wpi::StringRef function, int lineNumber)
 
static const ErrorGetGlobalError ()
 Retrieve the current global error.
 
- Protected Member Functions inherited from frc::RobotDriveBase
double Limit (double number)
 Limit motor values to the -1.0 to +1.0 range.
 
double ApplyDeadband (double number, double deadband)
 Returns 0.0 if the given value is within the specified range around zero. More...
 
void Normalize (wpi::MutableArrayRef< double > wheelSpeeds)
 Normalize all wheel speeds if the magnitude of any wheel is greater than 1.0.
 
- Protected Member Functions inherited from frc::SendableBase
void AddChild (std::shared_ptr< Sendable > child)
 Add a child component. More...
 
void AddChild (void *child)
 Add a child component. More...
 
void SetName (const wpi::Twine &moduleType, int channel)
 Sets the name of the sensor with a channel number. More...
 
void SetName (const wpi::Twine &moduleType, int moduleNumber, int channel)
 Sets the name of the sensor with a module and channel number. More...
 
- Protected Attributes inherited from frc::RobotDriveBase
double m_deadband = 0.02
 
double m_maxOutput = 1.0
 
- Protected Attributes inherited from frc::ErrorBase
Error m_error
 

Detailed Description

A class for driving differential drive/skid-steer drive platforms such as the Kit of Parts drive base, "tank drive", or West Coast Drive.

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:

class Robot {
public:
frc::Spark m_frontLeft{1};
frc::Spark m_rearLeft{2};
frc::SpeedControllerGroup m_left{m_frontLeft, m_rearLeft};
frc::Spark m_frontRight{3};
frc::Spark m_rearRight{4};
frc::SpeedControllerGroup m_right{m_frontRight, m_rearRight};
frc::DifferentialDrive m_drive{m_left, m_right};
};

Six motor drivetrain:

class Robot {
public:
frc::Spark m_frontLeft{1};
frc::Spark m_midLeft{2};
frc::Spark m_rearLeft{3};
frc::SpeedControllerGroup m_left{m_frontLeft, m_midLeft, m_rearLeft};
frc::Spark m_frontRight{4};
frc::Spark m_midRight{5};
frc::Spark m_rearRight{6};
frc::SpeedControllerGroup m_right{m_frontRight, m_midRight, m_rearRight};
frc::DifferentialDrive m_drive{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 to the 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 SetDeadband().

RobotDrive porting guide:
TankDrive(double, double, bool) is equivalent to RobotDrive::TankDrive(double, double, bool) if a deadband of 0 is used.
ArcadeDrive(double, double, bool) is equivalent to RobotDrive::ArcadeDrive(double, double, bool) if a deadband of 0 is used and the the rotation input is inverted eg ArcadeDrive(y, -rotation, false)
CurvatureDrive(double, double, bool) 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.

Constructor & Destructor Documentation

frc::DifferentialDrive::DifferentialDrive ( SpeedController leftMotor,
SpeedController rightMotor 
)

Construct a DifferentialDrive.

To pass multiple motors per side, use a SpeedControllerGroup. If a motor needs to be inverted, do so before passing it in.

Member Function Documentation

void frc::DifferentialDrive::ArcadeDrive ( double  xSpeed,
double  zRotation,
bool  squareInputs = true 
)

Arcade drive method for differential drive platform.

Note: Some drivers may prefer inverted rotation controls. This can be done by negating the value passed for rotation.

Parameters
xSpeedThe speed at which the robot should drive along the X axis [-1.0..1.0]. Forward is negative.
zRotationThe rotation rate of the robot around the Z axis [-1.0..1.0]. Clockwise is positive.
squareInputsIf set, decreases the input sensitivity at low speeds.
void frc::DifferentialDrive::CurvatureDrive ( double  xSpeed,
double  zRotation,
bool  isQuickTurn 
)

Curvature drive method for differential drive platform.

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.

Parameters
xSpeedThe robot's speed along the X axis [-1.0..1.0]. Forward is positive.
zRotationThe robot's rotation rate around the Z axis [-1.0..1.0]. Clockwise is positive.
isQuickTurnIf set, overrides constant-curvature turning for turn-in-place maneuvers.
void frc::DifferentialDrive::InitSendable ( SendableBuilder builder)
overridevirtual

Initializes this Sendable object.

Parameters
buildersendable builder

Implements frc::Sendable.

bool frc::DifferentialDrive::IsRightSideInverted ( ) const

Gets if the power sent to the right side of the drivetrain is multipled by -1.

Returns
true if the right side is inverted
void frc::DifferentialDrive::SetQuickStopAlpha ( double  alpha)

Sets the low-pass filter gain for QuickStop in curvature drive.

The low-pass filter filters incoming rotation rate commands to smooth out high frequency changes.

Parameters
alphaLow-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.
void frc::DifferentialDrive::SetQuickStopThreshold ( double  threshold)

Sets the QuickStop speed threshold in curvature drive.

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.

Parameters
thresholdX speed below which quick stop accumulator will receive rotation rate values [0..1.0].
void frc::DifferentialDrive::SetRightSideInverted ( bool  rightSideInverted)

Sets if the power sent to the right side of the drivetrain should be multipled by -1.

Parameters
rightSideInvertedtrue if right side power should be multipled by -1
void frc::DifferentialDrive::TankDrive ( double  leftSpeed,
double  rightSpeed,
bool  squareInputs = true 
)

Tank drive method for differential drive platform.

Parameters
leftSpeedThe robot left side's speed along the X axis [-1.0..1.0]. Forward is positive.
rightSpeedThe robot right side's speed along the X axis [-1.0..1.0]. Forward is positive.
squareInputsIf set, decreases the input sensitivity at low speeds.

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