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Flywheel Mechanism

Shooters are used in FRC games when you need to score in high places but are not allowed to physically reach up to the scoring position. A flywheel is the most common method of scoring an object that needs launched. The flywheel mechanism is built for high-speed rotating wheels (shooters, launchers). It focuses on velocity control and supports duty cycle output for testing.

1690 shooter flywheel2910 shooter flywheel

Common Use Cases​

  • Shooter wheels
  • Catapult/flywheel launchers

Typical Controls​

  • Velocity control for stable RPM.
  • Motion profile velocity control for faster spin-up times (TalonFX only).
  • Duty cycle for simple open-loop testing.

Constructor Parameters​

The FlywheelMech constructor requires the following parameters:

  • logging_prefix - String prefix for logging (typically from getSubsystemKey())
  • mech_name - Optional name for multiple instances (pass null if only one flywheel)
  • motor_configs - List of MotorConfig objects, leader first
  • gear_ratio - Gear ratio as motor rotations / mechanism rotations
  • wheel_inertia - Moment of inertia of the wheel in kg·m² (used for simulation)
  • wheel_radius - Radius of the wheel in meters (used for simulation)

Example Construction​

// In your subsystem constructor
flywheel_ = new FlywheelMech(
    getSubsystemKey(),           // Logging prefix
    "Flywheel",                   // Mechanism name
    List.of(
        CONSTANTS.SHOOTER_LEADER_MOTOR_CONFIG,
        CONSTANTS.SHOOTER_FOLLOWER_MOTOR_1_CONFIG,
        CONSTANTS.SHOOTER_FOLLOWER_MOTOR_2_CONFIG,
        CONSTANTS.SHOOTER_FOLLOWER_MOTOR_3_CONFIG
    ),
    CONSTANTS.FLYWHEEL_GEAR_RATIO,           // Gear ratio
    CONSTANTS.FLYWHEEL_INERTIA,              // Wheel inertia (kg·m²)
    CONSTANTS.FLYWHEEL_WHEEL_RADIUS_METERS   // Wheel radius (m)
);

Common Methods​

Control Methods​

  • setTargetVelocity(velocity_rad_per_sec) - Standard velocity control
  • setTargetVelocityMotionProfile(velocity_rad_per_sec) - Velocity control with motion profiling
  • setTargetVelocityWithFF(velocity_rad_per_sec, feedforward) - Velocity control with arbitrary feedforward
  • setTargetDutyCycle(duty_cycle) - Open-loop voltage control (-1.0 to 1.0)

Feedback Methods​

  • getCurrentVelocity() - Returns current velocity in radians per second
  • getLeaderCurrent() - Returns leader motor current draw in amps

Tips​

  • Use a spin-up command that waits for a velocity tolerance before shooting.
  • Log actual vs target velocity to tune control.
  • Motion profile velocity control can reduce spin-up time significantly.
  • Multiple motors can be configured as leader-follower for more power.
  • Use feedforward to compensate for back-EMF and improve velocity tracking.
  • Convert between linear and angular velocity: v = ω × r where r is wheel radius.