Example Code for PID Control and Vehicle Speed Detection

Introduction

The Maqueen Plus V3 is equipped with magnetic induction encoders on both drive wheels, enabling precise measurement of real-time rotational speed and traveled distance. Leveraging this data, the robot supports closed-loop PID control for accurate motion execution—such as moving a specific distance or rotating a precise angle.

Key Features:

• Distance control accuracy: ±2 cm
• Angle control accuracy: ±5°
• Real-time speed output: in centimeters per second (cm/s) — functions like a digital speedometer

This capability enables reliable autonomous navigation, consistent turning, and performance monitoring—essential for competition robots or educational projects requiring repeatability.

Example 1: PID Control (Non-interruptible Mode)

Introduction

In non-interruptible mode, the program blocks further execution until the PID-controlled movement (distance or rotation) is fully completed. This simplifies logic but offers no mid-action flexibility.

Use Case: Simple sequences where actions must complete before proceeding (e.g., “move 50 cm, then turn 180°”).

Program Description

• Move forward 50 cm using PID distance control
• Turn 180° in place using PID angle control

Note: Due to mechanical tolerances, wheel slippage, and surface friction, the robot may not return exactly to the starting point. Repeated cycles will accumulate error.

Hardware Preparation

• Maqueen Plus V3
• micro:bit
• Flat, consistent surface for testing

Sample Code

View on MakeCode

Result

The robot executes the full forward-and-turn sequence without interruption, demonstrating basic closed-loop motion control.

Example 2: PID + Laser Ranging Stop (Interruptible Mode)

Introduction

Interruptible mode allows ongoing PID motion to be stopped early based on external conditions—in this case, obstacle detection from the Matrix Laser Ranging Sensor. A flag variable (x) ensures commands are only issued when the robot is not already in motion, preventing command conflicts.

Advantage: Enables responsive, sensor-driven behavior while maintaining PID precision when uninterrupted.

Program Description

• Start PID-controlled forward motion for 500 cm (effectively “drive until stopped”)
• Continuously check laser distance at x4, y6
• If obstacle < 20 cm → stop PID motion, set flag x = 1
• When obstacle removed → resume forward motion, reset x = 0

Critical Design Note:
Without the flag variable, re-triggering PID during active motion causes undefined behavior. The flag acts as a state guard.

Sample Code

View on MakeCode

Result

The robot halts immediately upon detecting a close obstacle and resumes when clear—ideal for dynamic environments.

Example 3: Read Real-Time Speed

Introduction

This example reads and outputs the instantaneous speed of each wheel via serial communication. Speed is reported in centimeters per second (cm/s), providing real-time feedback similar to a vehicle speedometer.

Program Description

• Continuously read left and right wheel speeds
• Print values to serial monitor every 100 ms

Sample Code

View on MakeCode

Result

Observed Speeds:

• Left wheel: 29.4 cm/s
• Right wheel: 14 cm/s

Application Ideas:

• Diagnose wheel imbalance or motor issues
• Implement speed synchronization for straight-line driving
• Log performance data for tuning PID parameters