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Servos

package com.seattlesolvers.solverslib.hardware

ServoEx

The ServoEx class allows for more methods and actions than the normal servo class in the SDK. You can change the position of the servo relative to the last position or set it to an absolute position. You can either specify a position within the range of the servo's motion or have it rotate a certain number of specified angle units.

It serves as a successor to the ServoEx interface and SimpleServo class, which have now been Deprecated. A copy of the original ServoEx interface documentation can be viewed here.

Constructors:

1. Regular (no Angle Control)

ServoEx(HardwareMap hwMap, String id)

ServoEx servoEx = new ServoEx(hardwareMap, "servoEx");

2. Angle Control (with Min and Max angle)

ServoEx(HardwareMap hwMap, String id, double min, double max)

MIN_ANGLE and MAX_ANGLE are the minimum and maximum angle positions in degrees you would like to set the servo. This functionally serves as the servo's effective range. If you want to change the effective range at any point, you can do the following:

// change the effective range to a min and max in DEGREES
servo.setRange(MIN_ANGLE, MAX_ANGLE);

// change the range to a min and max in RADIANS
servo.setRange(MIN_ANGLE, MAX_ANGLE, AngleUnit.RADIANS);

// return the effective range
double degreeRange = servo.getAngleRange();

// return the effective range in RADIANS
degreeRange = servo.getAngleRange(AngleUnit.RADIANS);

3. Angle Control (with Range and AngleUnit)

ServoEx(HardwareMap hwMap, String id, double range, AngleUnit angleUnit)

This is similar to the 2nd constructor, except that you specify the angular range (from when the servo is set to 0 to 1). As such, you also need to define the AngleUnit (Degrees or Radians) for that range.

Utility Methods:

You can use setInverted() invert the servo's direction as well:

// invert the servo
servo.setInverted(true);

// get if the servo is inverted (true if inverted, false if not)
boolean isInverted = servo.getInverted();

To turn to positions and angles, utilize the following methods:

  • rotateByAngle: turns the servo a number of angle units relative to the current angle

  • turnToAngle: sets the absolute angle of the servo

  • rotateBy: turns the servo a relative positional distance from the current position

  • setPosition: set the absolute position of the servo (from 0 to 1)

Power Caching

Additionally, as an Ex class, ServoEx supports caching. If the power set to that hardware is less than an adjustable threshold, it will not send a write to it to help with loop speeds. The default threshold, which is called cachingTolerance , is 0.0001.

You can use .setCachingTolerance to adjust cachingTolerance it as needed.

ServoEx servoEx = new ServoEx(hardwareMap, "servoEx");

servoEx.setCachingTolerance(0.0001);

CRServo

The CRServo class is just a motor object intended to be used for a continuous rotation servo. Its general purpose is to be used in SolversLib classes that require a Motor input. It works just like a regular motor, without any of the encoder stuff. As such, it extends the Motor class, and can be used in a CRServoGroup.

CRServo crServo = CRServo(hardwareMap, "CRServo");

crServo.set(0.5);

CRServoEx & AbsoluteAnalogEncoder

The CRServoEx class is an advanced wrapper for continuous rotation servos (CRServos), adding key features for enhanced control and integration, including:

  • Absolute analog encoder support (e.g., for Axon servos)

  • Optimized positional control using PIDF (required for absolute encoder)

  • Power caching for improved loop performance

  • Custom PWM range support

It it extends CRServo, which in turn extends the Motor class, and can also be used in a CRServoGroup.

The AbsoluteAnalogEncoder class is an advanced wrapper for Analog input AnalogInput absolute encoders, which are most commonly seen on servos with a 4th wire (like Axon Servos). It is best used in conjuction with CRServoEx .

Constructors (AbsoluteAnalogEncoder)

1. Basic AbsoluteAnalogEncoder

AbsoluteAnalogEncoder(HardwareMap hwMap, String id)

// Example
AbsoluteAnalogEncoder encoder = new AbsoluteAnalogEncoder(hardwareMap, "absoluteEncoder");

This defaults to a range of 3.3, and an AngleUnit of Radians. If you do not know what you need, this is most likely it (and is functional for Axon servos).

2. Advanced CRServo

AbsoluteAnalogEncoder(HardwareMap hwMap, String id, double range, AngleUnit angleUnit)

// Example
AbsoluteAnalogEncoder absoluteEncoder = new AbsoluteAnalogEncoder(hwMap, "encoder", 3.3, AngleUnit.RADIANS)

This allows you to set your own range and AngleUnit if necessary. These constructors are used automatically in the designated CRServoEx constructors below as well.

  • angleUnit: Angle unit for moving servo to position (AngleUnit.DEGREES or AngleUnit.RADIANS)

  • analogRange: Voltage range for the encoder (e.g., 3.3V or 5V, depending on hardware)

    • Default: 3.3V

  • encoderID: Name of the absolute encoder in hardware map

Constructors (CRServoEx)

1. Basic CRServo (Raw Power)

CRServoEx(HardwareMap hwMap, String id)

  • No encoder required; runs in RawPower mode by default. This is similar to CRServo , with a few extra features.

2. Positional Control with Encoder

CRServoEx(HardwareMap hwMap, String id, AbsoluteAnalogEncoder absoluteEncoder, RunMode runmode)

// Example
CRServoEx crServoEx = new CRServoEx(hardwareMap, "crServoEx", encoder, CRServoEx.RunMode.OptimizedPositionalControl)

  • hwMap: FTC HardwareMap instance

  • id: Configuration name of the CRServo

  • absoluteEncoder: Instance of AbsoluteAnalogEncoder (must be initialized separately)

  • runmode: Mode to run (see below)

Warning: If you have set the runmode to OptimizedPositionalControl, regardless if you want angle-based control, you must use a valid AbsoluteAnalogEncoder and also set the PIDF (see below for more information). Failing to do will result in an error being thrown.

3. Advanced Encoder Configuration

CRServoEx(HardwareMap hwMap, String id, String encoderID, double analogRange, AngleUnit angleUnit, RunMode runmode)

Instead of passing an AbsoluteAnalogEncoder in, this overloaded constructor has parameters to create one inside of the instance of the CRServoEx.

  • Allows specifying encoder parameters:

    • encoderID: Name of the absolute encoder in hardware map

    • analogRange: Voltage range for the encoder (e.g., 3.3V or 5V, depending on hardware)

      • Default: 3.3V

    • angleUnit: Angle unit for moving servo to position (AngleUnit.DEGREES or AngleUnit.RADIANS)

      • Default: If not specified, defaults to AngleUnit.RADIANS unless overridden

    • runmode: See below

Using a CRServoEx RunMode

Like the Motor's RunMode, the CRServoEx RunMode is a method of running the CRServoEx when power is supplied. However, there are only two modes: OptimizedPositionalControl, and RawPower.

// in CRServoEx.java

/**
 * The mode in which the CR servo should behave.
 */
public enum RunMode {
    /**
     * Mode in which the CR servo takes the shortest path to reach a specific angle
     * Requires PIDF tuning (see below) + absolute encoder
     */
    OptimizedPositionalControl,
    /**
     * Default mode in which the CR servo is controlled with raw power
     */
    RawPower
}

OptimizedPositionalControl

  • Requirements: An absolute encoder and PIDF coefficients.

  • Behavior: When you call .set(angle), the servo will move to the target angle using the shortest path.

    • Example:

      
AbsoluteAnalogEncoder encoder = new AbsoluteAnalogEncoder(hardwareMap, "absoluteEncoder");
CRServoEx crServoEx = new CRServoEx(hardwareMap, "crServoEx", encoder, CRServoEx.RunMode.OptimizedPositionalControl)

crServoEx.setPIDF(new PIDFCoefficients(0.001, 0.0, 0.1, 0.0001));
crServoEx.set(Math.toRadians(90)); // move to 90 degrees (in radians)

    • If PIDF not set, positional control will throw an error.

RawPowerMode

  • Acts like a normal CRServo's RawPower.

PIDF Control

For positional control, you must set PIDF coefficients:

s_crServoEx.setPIDF(new PIDFCoefficients(double P, double I, double D, double F));

  • These coefficients will be used by the internal PIDF controller to compute the necessary power to reach the target angle smoothly and quickly.

Important: These PIDF coeffecients are used in SolversLib's PIDF class for the calculations. As such, you should tune it as if you were to tune a normal PIDF.

Power Caching

Finally, like MotorEx , CRServoEx supports power caching. If the power set to that hardware is less than an adjustable threshold, it will not send a write to it to help with loop speeds. The default threshold, which is called cachingTolerance , is 0.0001.

You can use .setCachingTolerance to adjust cachingTolerance it as needed.

CRServoEx s_crServoEx = new CRServoEx(hardwareMap, "s_crServoEx");

s_crServoEx.setCachingTolerance(0.0001);

Example: Full Setup

AbsoluteAnalogEncoder encoder = new AbsoluteAnalogEncoder(hardwareMap, "absoluteEncoder");
CRServoEx crServoEx = new CRServoEx(hardwareMap, "s_crServoEx", encoder, CRServoEx.RunMode.OptimizedPositionalControl);
crServoEx.setPIDF(new PIDFCoefficients(0.8, 0.02, 0.1, 0.0));
crServoEx.setCachingTolerance(0.0002);

crServoEx.set(Math.toRadians(135));

Additional Methods

  • .setRunMode(RunMode runmode): Change runmode after construction.

  • .setAbsoluteEncoder(AbsoluteAnalogEncoder encoder): Switch encoder instance.

  • .getAbsoluteEncoder(): Get associated encoder.

  • .getCachingTolerance(): Retrieve current tolerance.

  • .getController(): Get extended controller instance.

  • .getServo(): Get underlying SDK CRServo object.

  • .getDeviceType(): Returns device type (string).

  • .setPwm: Sets the PWM range for the servo using

For more details, refer to the Javadocs within CRServoEx.java. The class supports method chaining for convenient setup and configuration.

CRServoGroup

The CRServoGroup is like a MotorGroup, but for CRServo/CRServoEx. A CRServo group object takes several CRServos and runs them in parallel like a single CRServo. CRServo groups have one leader and a set of followers. For any group, there must be a leader, but the number of followers can be zero. This makes creating different drive profiles simpler. The constructor for a CRServoGroup is as follows:

CRServoEx myCRServos = new CRServoGroup(leader, follower1, follower2, ...);

The number of followers is variable. The other methods of the CRServoGroup are the same as the ones found in CRServo. You can very simply treat a CRServoGroup object like a single CRServo object. The flywheel sample in the examples folder shows a few other methods you can utilize with the MotorGroup.

Warning: CRServo/CRServoEx should use a CRServoGroup (this) instead of a MotorGroup

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