Setting Velocity

Setting Velocity in our Program

Velocity is a closed loop control within the SDK that uses the encoder counts to determine the approximate power/speed the motors need to go in order to meet the set velocity.

To set a velocity, its important to understand the maximum velocity in RPM your motor is capable of. For the Class Bot V2 the motors are capable of a maximum RPM of 300. With a drivetrain, you are likely to get better control by setting velocity lower than the maximum. In this case, lets set the velocity to 175 RPM!

Since RPM is the amount of revolutions per minute, a conversion needs to be made from RPM to ticks per second (TPS). To do this, divide the RPM by 60 to get the amount of rotations per second.

Rotations per second can then be multiplied by COUNTS_PER_WHEEL_REV, to get the amount of ticks per second.

$$TPS = \frac{175}{60} * CPWR$$

Adding Ticks per Second as a Variable

Create a new double variable called TPS. AddTPS the to the OpMode under where rightTarget is defined:

public void runOpMode() {
        leftmotor = hardwareMap.get(DcMotor.class, "leftmotor");
        rightmotor = hardwareMap.get(DcMotor.class, "rightmotor");
        
        rightmotor.setDirection(DcMotor.Direction.REVERSE);
        
        leftmotor.setMode(DcMotor.RunMode.STOP_AND_RESET_ENCODER);
        rightmotor.setMode(DcMotor.RunMode.STOP_AND_RESET_ENCODER);
        
        int leftTarget = (int)(610 * COUNTS_PER_MM);
        int rightTarget = (int)(610 * COUNTS_PER_MM);
        double TPS = (175/60) * COUNTS_PER_WHEEL_REV;
        
        waitForStart();

Changing from Power to Velocity

Exchange the setPower();functions for setVelocity();

Add TPS as the parameter for setVelocity();

waitForStart();

leftmotor.setTargetPosition(leftTarget);
rightmotor.setTargetPosition(rightTarget);

leftmotor.setMode(DcMotor.RunMode.RUN_TO_POSITION);
rightmotor.setMode(DcMotor.RunMode.RUN_TO_POSITION);

leftmotor.setVelocity(TPS);
rightmotor.setVelocity(TPS);

while (opModeIsActive() && (leftmotor.isBusy() && rightmotor.isBusy())){
        
        }

With the velocity set, let's give our program a test run after building!

DcMotor vs. DcMotorEx

With the current state of the code you are likely to get errors similar to the ones pictured below:

This is because the setVelocity();function is a function of theDcMotorEx Interface. The DcMotorEx Interface is an extension of the DcMotor Interface, that provides enhanced motor functionality, such as access to closed loop control functions.

To use setVelocity(); the motor variables need to be changed to DcMotorEx as seen below:

public class HelloRobot_Encoder extends LinearOpMode {
    private DcMotorEx leftmotor;
    private DcMotorEx rightmotor;

public void runOpMode() {
        leftmotor = hardwareMap.get(DcMotorEx.class, "leftmotor");
        rightmotor = hardwareMap.get(DcMotorEx.class, "rightmotor");

Since DcMotorEx is an extension of DcMotor, DcMotor specific functions can be used by variables defined as DcMotorEx.

Full Program

@Autonomous

public class HelloRobot_Encoder extends LinearOpMode {
    private DcMotorEx leftmotor;
    private DcMotorEx rightmotor;
    
    static final double     COUNTS_PER_MOTOR_REV    = 28.0; 
    static final double     DRIVE_GEAR_REDUCTION    = 30.24;   
    static final double     WHEEL_CIRCUMFERENCE_MM  = 90.0 * 3.14;
    
    static final double     COUNTS_PER_WHEEL_REV    = COUNTS_PER_MOTOR_REV * DRIVE_GEAR_REDUCTION;
    static final double     COUNTS_PER_MM           = COUNTS_PER_WHEEL_REV / WHEEL_CIRCUMFERENCE_MM;
    
    @Override
    public void runOpMode() {
        leftmotor = hardwareMap.get(DcMotorEx.class, "leftmotor");
        rightmotor = hardwareMap.get(DcMotorEx.class, "rightmotor");
        
        rightmotor.setDirection(DcMotor.Direction.REVERSE);

        leftmotor.setMode(DcMotor.RunMode.STOP_AND_RESET_ENCODER);
        rightmotor.setMode(DcMotor.RunMode.STOP_AND_RESET_ENCODER);
        
        
        int leftTarget = (int)(610 * COUNTS_PER_MM);
        int rightTarget = (int)(610 * COUNTS_PER_MM);
        double TPS = (175/ 60) * COUNTS_PER_WHEEL_REV;
        
        waitForStart();
        
        
        leftmotor.setTargetPosition(leftTarget);
        rightmotor.setTargetPosition(rightTarget);
        
        leftmotor.setMode(DcMotor.RunMode.RUN_TO_POSITION);
        rightmotor.setMode(DcMotor.RunMode.RUN_TO_POSITION);
        
        leftmotor.setVelocity(TPS);
        rightmotor.setVelocity(TPS);
        
        while (opModeIsActive() && (leftmotor.isBusy() && rightmotor.isBusy())) {
        }
    }
}