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Elevator Mechanism

Elevators pop up commonly in FRC and are used to move mechanisms in a compact linear fashion. This is usually to reach higher places with a mechanism, reach far out from your frame perimeter, or even climb on a field element. The elevator mechanism controls a linear translation system, such as a carriage that moves vertically. It supports position, velocity, and duty cycle control with unit conversions built in.

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Common Use Cases​

  • Vertical lifts
  • Telescoping mechanisms
  • Vertical climbers

Typical Controls​

  • Position control for set heights.
  • Motion profile position control for smoother movements with controlled acceleration.
  • Velocity control for smooth motion.
  • Duty cycle for manual control.

Constructor Parameters​

The ElevatorMech 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 elevator)
  • motor_configs - List of MotorConfig objects, leader first
  • gear_ratio - Gear ratio as motor rotations / mechanism rotations
  • drum_radius - Radius of the drum/pulley in meters
  • carriage_mass - Mass of the carriage in kg (used for simulation)
  • min_height - Minimum height in meters (used for simulation)
  • max_height - Maximum height in meters (used for simulation)
  • is_vertical - Boolean indicating if elevator is vertical (affects gravity compensation)

Example Construction​

// In your subsystem constructor
elevator_ = new ElevatorMech(
    getSubsystemKey(),                // Logging prefix
    "Elevator",                       // Mechanism name (optional)
    List.of(CONSTANTS.ELEVATOR_LEADER_MOTOR_CONFIG,
            CONSTANTS.ELEVATOR_FOLLOWER_MOTOR_CONFIG),
    CONSTANTS.ELEVATOR_GEAR_RATIO,    // Gear ratio
    CONSTANTS.ELEVATOR_DRUM_RADIUS,   // Drum radius (m)
    CONSTANTS.CARRIAGE_MASS,          // Carriage mass (kg)
    CONSTANTS.MIN_HEIGHT,             // Min height (m)
    CONSTANTS.MAX_HEIGHT,             // Max height (m)
    true                              // Is vertical
);
// Set initial position (for zeroing)
elevator_.setCurrentPosition(CONSTANTS.ELEVATOR_HOME_POSITION);

Common Methods​

Control Methods​

  • setTargetPosition(position_m) - Standard position control in meters
  • setTargetPositionMotionProfile(position_m) - Position control with motion profiling
  • setTargetPositionWithFF(position_m, feedforward) - Position control with arbitrary feedforward
  • setTargetPositionMotionProfileWithFF(position_m, feedforward) - Motion profile with feedforward
  • setTargetVelocity(velocity_mps) - Velocity control in meters per second
  • setTargetDutyCycle(duty_cycle) - Open-loop voltage control (-1.0 to 1.0)

Feedback Methods​

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

Calibration​

  • setCurrentPosition(position_m) - Sets the current position (for zeroing/homing)

Simulation​

  • applyLoadForce(force_n) - Applies external load force at the carriage (simulation only)

Tips​

  • The mechanism automatically handles gravity compensation for vertical elevators.
  • Use motion profile control for smoother movements with large height changes.
  • Always set an initial position using setCurrentPosition() after construction to establish a known zero point.
  • Keep distances in meters for consistency.
  • Use feedforward control to improve tracking performance on demanding trajectories.
  • For multiple elevators (e.g., left/right sides), provide unique mech_name values to distinguish them in logs.