How to sequence a PID motor return-to-zero after shooting using State Machines in FTC Java?

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Summary

The issue at hand is how to sequence a PID motor return-to-zero after shooting using State Machines in FTC Java. The goal is to have the spindexer automatically return to encoder position 0 after shooting, without interrupting the shooting motion or overriding the PID loop. Key concepts include using state flags and state machines to manage the different states of the spindexer.

Root Cause

The root cause of the issue is the lack of a clear state machine to manage the different states of the spindexer. The current implementation uses a single boolean flag shot to switch between different behaviors, but this is not sufficient to handle the complex sequence of events required. Causes of the issue include:

  • Insufficient use of state flags
  • Lack of a clear state machine
  • Inadequate handling of concurrent events

Why This Happens in Real Systems

This issue occurs in real systems because of the complexity of concurrent events and the need for precise control over the spindexer. In FTC robotics, the spindexer must be able to shoot game pieces and then return to a safe position, all while avoiding collisions and maintaining control. Real-world factors that contribute to this issue include:

  • Limited processing power and resources
  • Complexity of the control loop
  • Need for precise timing and synchronization

Real-World Impact

The real-world impact of this issue is significant, as it can affect the performance and reliability of the robot. If the spindexer fails to return to the correct position, it can cause collisions or game piece jams, leading to penalties or disqualification. Impacts of this issue include:

  • Reduced robot performance
  • Increased risk of collisions or game piece jams
  • Potential penalties or disqualification

Example or Code

// Example state machine implementation
enum SpindexerState {
    IDLE,
    SHOOTING,
    RETURNING_TO_ZERO
}

SpindexerState currentState = SpindexerState.IDLE;

// In the control loop
if (gamepad1.bWasPressed()) {
    if (currentState == SpindexerState.IDLE) {
        currentState = SpindexerState.SHOOTING;
        // Start shooting sequence
    } else if (currentState == SpindexerState.SHOOTING) {
        currentState = SpindexerState.RETURNING_TO_ZERO;
        // Start returning to zero sequence
    }
}

// Update the spindexer position based on the current state
if (currentState == SpindexerState.RETURNING_TO_ZERO) {
    target = 0;
    pid.reset(getRuntime());
}

How Senior Engineers Fix It

Senior engineers fix this issue by implementing a clear state machine to manage the different states of the spindexer. They use state flags and concurrent programming techniques to ensure that the spindexer returns to the correct position after shooting, without interrupting the shooting motion or overriding the PID loop. Key strategies include:

  • Using a finite state machine to manage the spindexer states
  • Implementing concurrent programming techniques to handle multiple events
  • Carefully synchronizing the control loop to avoid conflicts

Why Juniors Miss It

Juniors may miss this issue because of limited experience with concurrent programming and state machines. They may also overlook the importance of precise control and synchronization in the control loop. Common mistakes include:

  • Insufficient use of state flags and state machines
  • Inadequate handling of concurrent events
  • Failure to synchronize the control loop correctly

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