This is useful for compensating for translational skew when translating and rotating a - * swerve drivetrain. + * holonomic (swerve or mecanum) drivetrain. However, scaling down the ChassisSpeeds after + * discretizing (e.g., when desaturating swerve module speeds) rotates the direction of net motion + * in the opposite direction of rotational velocity, introducing a different translational skew + * which is not accounted for by discretization. * * @param vxMetersPerSecond Forward velocity. * @param vyMetersPerSecond Sideways velocity. @@ -134,7 +137,10 @@ public class ChassisSpeeds implements ProtobufSerializable, StructSerializable { * along the y-axis, and omega * dt around the z-axis). * *
This is useful for compensating for translational skew when translating and rotating a - * swerve drivetrain. + * holonomic (swerve or mecanum) drivetrain. However, scaling down the ChassisSpeeds after + * discretizing (e.g., when desaturating swerve module speeds) rotates the direction of net motion + * in the opposite direction of rotational velocity, introducing a different translational skew + * which is not accounted for by discretization. * * @param vx Forward velocity. * @param vy Sideways velocity. @@ -157,7 +163,10 @@ public class ChassisSpeeds implements ProtobufSerializable, StructSerializable { * along the y-axis, and omega * dt around the z-axis). * *
This is useful for compensating for translational skew when translating and rotating a - * swerve drivetrain. + * holonomic (swerve or mecanum) drivetrain. However, scaling down the ChassisSpeeds after + * discretizing (e.g., when desaturating swerve module speeds) rotates the direction of net motion + * in the opposite direction of rotational velocity, introducing a different translational skew + * which is not accounted for by discretization. * * @param continuousSpeeds The continuous speeds. * @param dtSeconds The duration of the timestep the speeds should be applied for. diff --git a/wpimath/src/main/java/edu/wpi/first/math/kinematics/SwerveDriveKinematics.java b/wpimath/src/main/java/edu/wpi/first/math/kinematics/SwerveDriveKinematics.java index 45c3f3bb23..4979a7be10 100644 --- a/wpimath/src/main/java/edu/wpi/first/math/kinematics/SwerveDriveKinematics.java +++ b/wpimath/src/main/java/edu/wpi/first/math/kinematics/SwerveDriveKinematics.java @@ -274,6 +274,10 @@ public class SwerveDriveKinematics * reduce all the wheel speeds to make sure that all requested module speeds are at-or-below the * absolute threshold, while maintaining the ratio of speeds between modules. * + *
Scaling down the module speeds rotates the direction of net motion in the opposite direction + * of rotational velocity, which makes discretizing the chassis speeds inaccurate because the + * discretization did not account for this translational skew. + * * @param moduleStates Reference to array of module states. The array will be mutated with the * normalized speeds! * @param attainableMaxSpeedMetersPerSecond The absolute max speed that a module can reach. @@ -300,6 +304,10 @@ public class SwerveDriveKinematics * reduce all the wheel speeds to make sure that all requested module speeds are at-or-below the * absolute threshold, while maintaining the ratio of speeds between modules. * + *
Scaling down the module speeds rotates the direction of net motion in the opposite direction + * of rotational velocity, which makes discretizing the chassis speeds inaccurate because the + * discretization did not account for this translational skew. + * * @param moduleStates Reference to array of module states. The array will be mutated with the * normalized speeds! * @param attainableMaxSpeed The absolute max speed that a module can reach. @@ -318,6 +326,10 @@ public class SwerveDriveKinematics * reduce all the wheel speeds to make sure that all requested module speeds are at-or-below the * absolute threshold, while maintaining the ratio of speeds between modules. * + *
Scaling down the module speeds rotates the direction of net motion in the opposite direction + * of rotational velocity, which makes discretizing the chassis speeds inaccurate because the + * discretization did not account for this translational skew. + * * @param moduleStates Reference to array of module states. The array will be mutated with the * normalized speeds! * @param desiredChassisSpeed The desired speed of the robot @@ -365,6 +377,10 @@ public class SwerveDriveKinematics * reduce all the wheel speeds to make sure that all requested module speeds are at-or-below the * absolute threshold, while maintaining the ratio of speeds between modules. * + *
Scaling down the module speeds rotates the direction of net motion in the opposite direction + * of rotational velocity, which makes discretizing the chassis speeds inaccurate because the + * discretization did not account for this translational skew. + * * @param moduleStates Reference to array of module states. The array will be mutated with the * normalized speeds! * @param desiredChassisSpeed The desired speed of the robot diff --git a/wpimath/src/main/native/include/frc/kinematics/ChassisSpeeds.h b/wpimath/src/main/native/include/frc/kinematics/ChassisSpeeds.h index 396b33a618..90eef5d1e4 100644 --- a/wpimath/src/main/native/include/frc/kinematics/ChassisSpeeds.h +++ b/wpimath/src/main/native/include/frc/kinematics/ChassisSpeeds.h @@ -59,7 +59,11 @@ struct WPILIB_DLLEXPORT ChassisSpeeds { * y-axis, and omega * dt around the z-axis). * * This is useful for compensating for translational skew when translating and - * rotating a swerve drivetrain. + * rotating a holonomic (swerve or mecanum) drivetrain. However, scaling down + * the ChassisSpeeds after discretizing (e.g., when desaturating swerve module + * speeds) rotates the direction of net motion in the opposite direction of + * rotational velocity, introducing a different translational skew which is + * not accounted for by discretization. * * @param vx Forward velocity. * @param vy Sideways velocity. @@ -94,7 +98,11 @@ struct WPILIB_DLLEXPORT ChassisSpeeds { * y-axis, and omega * dt around the z-axis). * * This is useful for compensating for translational skew when translating and - * rotating a swerve drivetrain. + * rotating a holonomic (swerve or mecanum) drivetrain. However, scaling down + * the ChassisSpeeds after discretizing (e.g., when desaturating swerve module + * speeds) rotates the direction of net motion in the opposite direction of + * rotational velocity, introducing a different translational skew which is + * not accounted for by discretization. * * @param continuousSpeeds The continuous speeds. * @param dt The duration of the timestep the speeds should be applied for. diff --git a/wpimath/src/main/native/include/frc/kinematics/SwerveDriveKinematics.h b/wpimath/src/main/native/include/frc/kinematics/SwerveDriveKinematics.h index 276f9a8818..41f56510e9 100644 --- a/wpimath/src/main/native/include/frc/kinematics/SwerveDriveKinematics.h +++ b/wpimath/src/main/native/include/frc/kinematics/SwerveDriveKinematics.h @@ -335,6 +335,11 @@ class SwerveDriveKinematics * the absolute threshold, while maintaining the ratio of speeds between * modules. * + * Scaling down the module speeds rotates the direction of net motion in the + * opposite direction of rotational velocity, which makes discretizing the + * chassis speeds inaccurate because the discretization did not account for + * this translational skew. + * * @param moduleStates Reference to array of module states. The array will be * mutated with the normalized speeds! * @param attainableMaxSpeed The absolute max speed that a module can reach. @@ -370,6 +375,11 @@ class SwerveDriveKinematics * the absolute threshold, while maintaining the ratio of speeds between * modules. * + * Scaling down the module speeds rotates the direction of net motion in the + * opposite direction of rotational velocity, which makes discretizing the + * chassis speeds inaccurate because the discretization did not account for + * this translational skew. + * * @param moduleStates Reference to array of module states. The array will be * mutated with the normalized speeds! * @param desiredChassisSpeed The desired speed of the robot