Lesson 6.2: Using for Loops to Repeat Robot Actions Cleanly

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Technical Context

Repetitive mechanical tasks — such as pulsing an intake or cycling a scoring mechanism — are prone to "logic bloat" if written line-by-line. Using a for loop ensures code efficiency and allows the programmer to adjust the number of iterations (e.g., 3 gear-clearing pulses) in a single parameter change rather than rewriting blocks of code.

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When a for Loop Is Better Than Repeating Code

The for loop follows the syntax for(initialization; condition; update). It instantiates a local int counter that increments after each pass. In FTC robotics, this is frequently used to cycle mechanisms for a fixed number of iterations rather than relying on inconsistent time-based logic.

The three parts of the for header do distinct jobs:

• Initialization — runs once before the loop starts, creating the counter (e.g., int i = 0)
• Condition — checked before every iteration; the loop stops when this is false (e.g., i < 5)
• Update — runs at the end of every iteration, advancing the counter (e.g., i++)

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Annotated Code

package org.firstinspires.ftc.teamcode;

import com.qualcomm.robotcore.eventloop.opmode.LinearOpMode;
import com.qualcomm.robotcore.eventloop.opmode.Autonomous;
import com.qualcomm.robotcore.hardware.DcMotor;

@Autonomous(name="Pulse_Demo")
public class PulseDemo extends LinearOpMode {

    @Override
    public void runOpMode() {
        DcMotor scoringMotor = hardwareMap.get(DcMotor.class, "scoring");

        waitForStart();

        // Example: Pulsing a scoring motor 5 times
        for (int i = 0; i < 5; i++) {
            scoringMotor.setPower(1.0);
            sleep(100); // 100ms on-pulse
            scoringMotor.setPower(0.0);
            sleep(100); // 100ms pause between pulses

            telemetry.addData("Pulse", i + 1);
            telemetry.update();
        }
    }
}

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Fill-in-the-Blank Practice

1. In the for loop header, the __________ section is executed exactly once before the loop begins.
2. To repeat a block of code exactly 10 times starting at i = 0, the condition should be written as i < __________.
3. The __________ statement is executed at the end of every iteration, typically used to increase the counter.

Show answers

1. initialization (e.g., int i = 0)
2. 10
3. update (e.g., i++)

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Template Challenge

Robot Scenario: Your robot needs to "flick" a servo named "delivery" three times between position 0.0 and 1.0 to ensure a game element has been released.

package org.firstinspires.ftc.teamcode;

import com.qualcomm.robotcore.eventloop.opmode.LinearOpMode;
import com.qualcomm.robotcore.eventloop.opmode.Autonomous;
import com.qualcomm.robotcore.hardware.Servo;

@Autonomous(name="Triple_Flick")
public class TripleFlick extends LinearOpMode {

    @Override
    public void runOpMode() {
        Servo delivery = hardwareMap.get(Servo.class, "delivery");

        waitForStart();

        // INSERT CODE HERE: Create a for loop that runs exactly 3 times
        {
            // INSERT CODE HERE: Set position to 1.0, sleep 200ms, then set to 0.0
        }
    }
}

Show answer

for (int i = 0; i < 3; i++) {
    delivery.setPosition(1.0);
    sleep(200);
    delivery.setPosition(0.0);
    sleep(200);
}

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