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Calasada 25-10-2016 20:23
Efficient Swerve Drive
 
Our team has been testing out swerve drive off-season (possibly) for next year. We have code that can successfully drive smoothly, but there are a few kinks we still need to work out to make it even more smooth. One of those that we are currently having trouble on is making the wheels drive backwards when we move backwards to spin the module in the most efficient way possible. We have tried a few rudimentary solutions that have failed miserably. Our modules are the AndyMark Swerve & Steer modules. Practically all of our swerve code is contained in the subsystem, pasted below. The "swerveDrive" method is used to take 3 values from the controller and output 8, 4 for steering and 4 for wheel speeds. Any help would be appreciated! :)


Code:
/**
 *
 */
public class SwerveDriveBase extends Subsystem {
        private CANTalon frontRightWheel;
        private VictorSP frontRightSwivel;
       
        private CANTalon frontLeftWheel;
        private VictorSP frontLeftSwivel;
       
        private CANTalon rearRightWheel;
        private VictorSP rearRightSwivel;
       
        private CANTalon rearLeftWheel;
        private VictorSP rearLeftSwivel;
       
        private AHRS navSensor;
       
        private Encoder frontRightEnc;
        private Encoder frontLeftEnc;
        private Encoder rearRightEnc;
        private Encoder rearLeftEnc;
       
        private PIDController frontRightPID;
        private PIDController frontLeftPID;
        private PIDController rearRightPID;
        private PIDController rearLeftPID;
       
        private final double p = 0.05;    //0.015;
        private final double i = 0.0025;    //0.005;
        private final double d = 0.005;    //0.125;
       
        //TODO: Adjust value during testing. Some of this code is copied from 2016 Season Code, this value will change
        final private double ENCODER_TICKS_FOR_ADJUSTER_TRAVEL = 875.0;
       
        public class PIDOutputClass implements PIDOutput {
                public VictorSP motor;
               
                public PIDOutputClass(VictorSP motor) {
                        this.motor = motor;
                }
               
                @Override
                public void pidWrite(double output) {
                        motor.set(output);
                }
        }
       
    public SwerveDriveBase() {
            super();
           
            frontRightEnc = new Encoder(new DigitalInput(2), new DigitalInput(3));
        frontLeftEnc = new Encoder(new DigitalInput(0), new DigitalInput(1));
        rearRightEnc = new Encoder(new DigitalInput(6), new DigitalInput(7));
        rearLeftEnc = new Encoder(new DigitalInput(4), new DigitalInput(5));
           
        PIDOutputClass frontRightPIDOutput = new PIDOutputClass(new VictorSP(RobotMap.FRONT_RIGHT_SWIVEL));
        PIDOutputClass frontLeftPIDOutput = new PIDOutputClass(new VictorSP(RobotMap.FRONT_LEFT_SWIVEL));
        PIDOutputClass rearRightPIDOutput = new PIDOutputClass(new VictorSP(RobotMap.REAR_RIGHT_SWIVEL));
        PIDOutputClass rearLeftPIDOutput = new PIDOutputClass(new VictorSP(RobotMap.REAR_LEFT_SWIVEL));
       
            //Intstantiating PID Controllers with p, i, d, Encoder, Victor
            frontRightPID = new PIDController(p, i, d, frontRightEnc, frontRightPIDOutput);
            frontLeftPID = new PIDController(p, i, d, frontLeftEnc, frontLeftPIDOutput);
            rearRightPID = new PIDController(p, i, d, rearRightEnc, rearRightPIDOutput);
            rearLeftPID = new PIDController(p, i, d, rearLeftEnc, rearLeftPIDOutput);
           
            frontRightPID.setInputRange(-180, 180);
            frontLeftPID.setInputRange(-180, 180);
            rearRightPID.setInputRange(-180, 180);
            rearLeftPID.setInputRange(-180, 180);
           
            frontRightPID.setContinuous();
            frontLeftPID.setContinuous();
            rearRightPID.setContinuous();
            rearLeftPID.setContinuous();
           
            //Makes sure navX is on Robot, then instantiates it
            try {
                navSensor = new AHRS(SPI.Port.kMXP);
            } catch (RuntimeException ex ) {
                DriverStation.reportError("Error instantiating navX MXP:  " + ex.getMessage(), true);
            }
           
            frontRightWheel = new CANTalon(RobotMap.FRONT_RIGHT_WHEEL);
            //frontRightSwivel = new VictorSP(RobotMap.FRONT_RIGHT_SWIVEL);
           
            frontLeftWheel = new CANTalon(RobotMap.FRONT_LEFT_WHEEL);
            //frontLeftSwivel = new VictorSP(RobotMap.FRONT_LEFT_SWIVEL);
           
            rearRightWheel = new CANTalon(RobotMap.REAR_RIGHT_WHEEL);
            //rearRightSwivel = new VictorSP(RobotMap.REAR_RIGHT_SWIVEL);
           
            rearLeftWheel = new CANTalon(RobotMap.REAR_LEFT_WHEEL);
            //rearLeftSwivel = new VictorSP(RobotMap.REAR_LEFT_SWIVEL);
    }

    public void initDefaultCommand() {
        setDefaultCommand(new SwerveDrive());
    }
   
    //Small, simple tank drive method
    public void tankDrive(double leftValue, double rightValue) {
            if (DriverStation.getInstance().isFMSAttached() && DriverStation.getInstance().getMatchTime() < 4) {
                    setBrake(true);
            } else {
                    setBrake(false);
            }
           
            frontRightWheel.set(rightValue);
            rearRightWheel.set(rightValue);
           
            frontLeftWheel.set(leftValue);
            rearLeftWheel.set(leftValue);
    }
   
    //Method for calculating and setting Speed and Angle of individual wheels given 3 movement inputs
    public void swerveDrive(double FBMotion, double RLMotion, double rotMotion) {
            //Swerve Math Taken from: https://www.chiefdelphi.com/media/papers/2426
            //FBMotion = (FBMotion*(Math.sin(getNavSensor().getAngle()))) + (RLMotion*(Math.cos(getNavSensor().getAngle())));
            //RLMotion = -(FBMotion*(Math.cos(getNavSensor().getAngle()))) + (RLMotion*(Math.sin(getNavSensor().getAngle())));
           
            double L = 1.0;
            double W = 1.0;
            double R = Math.sqrt((L*L) + (W*W));
           
            double A = RLMotion - rotMotion*(L/R);
            double B = RLMotion + rotMotion*(L/R);
            double C = FBMotion - rotMotion*(W/R);
            double D = FBMotion + rotMotion*(W/R);
           
            double frontRightWheelSpeed = Math.sqrt((B*B) + (C*C));
            double frontLeftWheelSpeed = Math.sqrt((B*B) + (D*D));
            double rearLeftWheelSpeed = Math.sqrt((A*A) + (D*D));
            double rearRightWheelSpeed = Math.sqrt((A*A) + (C*C));
           
            double t = 180/Math.PI;
           
            double frontRightAngle = Math.atan2(B, D)*t;
            double frontLeftAngle = Math.atan2(B, C)*t;
            double rearLeftAngle = Math.atan2(A, C)*t;
            double rearRightAngle = Math.atan2(A, D)*t;
           
            double max = frontRightWheelSpeed;
            if(max < frontLeftWheelSpeed) {max = frontLeftWheelSpeed;}
            if(max < rearLeftWheelSpeed) {max = rearLeftWheelSpeed;}
            if(max < rearRightWheelSpeed) {max = rearRightWheelSpeed;}
            //I'm so sorry Jake
           
            if(max > 1) {
                    frontRightWheelSpeed /= max;
                    frontLeftWheelSpeed /= max;
                    rearLeftWheelSpeed /= max;
                    rearRightWheelSpeed /= max;
            }
           
            //Set Wheel Speeds
            frontRightWheel.set(frontRightWheelSpeed);
            frontLeftWheel.set(frontLeftWheelSpeed);
            rearLeftWheel.set(rearLeftWheelSpeed);
            rearRightWheel.set(rearRightWheelSpeed);
           
            //Set Wheel Angles
            setFrontRightAngle(frontRightAngle);
            setFrontLeftAngle(frontLeftAngle);
            setRearLeftAngle(rearLeftAngle);
            setRearRightAngle(rearRightAngle);
           
    }
   
    //Turn on/off brake mode
    public void setBrake(boolean brake) {
            frontRightWheel.enableBrakeMode(brake);
           
            frontLeftWheel.enableBrakeMode(brake);
           
            rearRightWheel.enableBrakeMode(brake);
           
            rearLeftWheel.enableBrakeMode(brake);
    }
   
    //Returns navX sensor ?
    public AHRS getNavSensor() {
            if (navSensor != null) {
                    return navSensor;
            } else {
                    return null;
            }
    }
   
    //Methods taken from ShooterBase in 2016 Code to help calculate angle
    public Double getFrontRightEncPercent() {
            return Math.abs(frontRightEnc.getDistance() / ENCODER_TICKS_FOR_ADJUSTER_TRAVEL);
    }
   
    public Double getFrontLeftEncPercent() {
            return Math.abs(frontLeftEnc.getDistance() / ENCODER_TICKS_FOR_ADJUSTER_TRAVEL);
    }
   
    public Double getRearRightEncPercent() {
            return Math.abs(rearRightEnc.getDistance() / ENCODER_TICKS_FOR_ADJUSTER_TRAVEL);
    }
   
    public Double getRearLeftEncPercent() {
            return Math.abs(rearLeftEnc.getDistance() / ENCODER_TICKS_FOR_ADJUSTER_TRAVEL);
    }
   
    public double getFrontRightAngle(){
                if (frontRightEnc != null) {
                        return (getFrontRightEncPercent());
                } else {
                        return -1.0;
                }
        }
   
    public double getFrontLeftAngle(){
                if (frontLeftEnc != null) {
                        return (getFrontLeftEncPercent());
                } else {
                        return -1.0;
                }
        }
   
    public double getRearRightAngle(){
                if (rearRightEnc != null) {
                        return (getRearRightEncPercent());
                } else {
                        return -1.0;
                }
        }
   
    public double getRearLeftAngle(){
                if (rearLeftEnc != null) {
                        return (getRearLeftEncPercent());
                } else {
                        return -1.0;
                }
        }
   
    //Methods to set Angles of wheels, enables PID then sets its setpoint as the input
    public void setFrontRightAngle(double angle) {
            frontRightPID.enable();
            frontRightPID.setSetpoint(angle);
            System.out.println("out angle: " + frontRightPID.getSetpoint());
    }
   
    public void setFrontLeftAngle(double angle) {
            frontLeftPID.enable();
            frontLeftPID.setSetpoint(angle);
            System.out.println(angle);
    }
   
    public void setRearRightAngle(double angle) {
            rearRightPID.enable();
            rearRightPID.setSetpoint(angle);
    }
   
    public void setRearLeftAngle(double angle) {
            rearLeftPID.enable();
            rearLeftPID.setSetpoint(angle);
    }
   
    //General Methods for moving any motor
    public void frontRightDrive(double value) {
            frontRightWheel.set(value);
    }
   
    public void frontRightTwist(double value) {
            frontRightSwivel.set(value);
    }
   
    public void frontLeftDrive(double value) {
            frontLeftWheel.set(value);
    }
   
    public void frontLeftTwist(double value) {
            frontLeftSwivel.set(value);
    }
   
    public void rearRightDrive(double value) {
            rearRightWheel.set(value);
    }
   
    public void rearRightTwist(double value) {
            rearRightSwivel.set(value);
    }
   
    public void rearLeftDrive(double value) {
            rearLeftWheel.set(value);
    }
   
    public void rearLeftTwift(double value) {
            rearLeftSwivel.set(value);
    }
   
}

kylelanman 26-10-2016 00:18
Re: Efficient Swerve Drive
 
The trick to a smooth swerve and optimal control is to limit rotating the module as much as possible. If you think about it you should never have to rotate a swerve module more than 90 deg for a given action. The exception is for a smooth change over time like a tornado maneuver where the robot is spinning while traveling in a given direction. At any rate from a single step perspective a 90 degree limit is key. If the desired angle is more than 90 degrees and less than 270 degrees than it is going to be optimal to command the module to the desired angle + 180 and then reverse your motor speed.

We have handled this in the past using the following code.

Code:
//C++
if (fabs(desiredAngle - currentAngle) > 90 && fabs(desiredAngle - currentAngle) < 270) {
    desiredAngle = ((int)desiredAngle + 180) % 360;
    speed = -speed;
}
Here is our entire SwerveModule implementation from 2015.
https://github.com/Frc2481/frc-2015/...erveModule.cpp

Poseidon5817 26-10-2016 09:13
Re: Efficient Swerve Drive
 
What we did in 5817's swerve code last year is this:

1) Added a method that lets us feed the wheel a degree value rather than an encoder position value.
2) Let's pretend the wheel is at 30 degrees east of North. If you want to get to 180 degrees South, the code will check and see whether it is faster to go clockwise or counterclockwise to 180.
3) The code then adds 180 to the angle (which in this case will equal 0/360 degrees) and with the two prior values in mind, checks whether it is even faster to go clockwise or counterclockwise to the new angle.
4) Now you have four angles: regular clock and counterclockwise, and reversed clock and counterclockwise.
5) Compare the four values and see which is the shortest and command the wheel to go to that position.
6) If the direction you chose goes to the reversed position, multiply the wheel power output by -1.

Hopefully this helps, I can share the code itself if you would like.

frodobaggins05 03-11-2016 19:54
Re: Efficient Swerve Drive
 
Thanks for your help Poseidon5817 We fixed


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