mini-drone-altitude-control

Arduino-based altitude control circuit for a mini-drone using an ultrasonic sensor and PID controller.

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Table of Contents

• Overview
• Hardware Components
• Circuit
• How It Works
• PID Controller
• Configuration
• Setup & Usage
• Serial Monitor Output

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Overview

This project implements a closed-loop altitude control system for a mini-drone. An ultrasonic sensor measures the drone's current height, a potentiometer sets the target height, and a PID controller adjusts motor speed via two ESCs to maintain the desired altitude.

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Hardware Components

Component	Description
Arduino Uno	Microcontroller
Ultrasonic Sensor (HC-SR04)	Measures altitude via echo signal
ESC x2	Electronic Speed Controllers for motor control
Brushless Motors x2	Drone propulsion
Potentiometer	Sets target altitude
Push Button	Start/stop control

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Circuit

Component	Arduino Pin
Ultrasonic Trigger	Pin 7
Ultrasonic Echo	Pin 8
ESC 1	Pin 9
ESC 2	Pin 10
Push Button	Pin 3
Potentiometer	A0

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How It Works

1. Start — Press the button to arm the drone. The ESCs go through a calibration sequence on startup.
2. Liftoff — Motor speed ramps up gradually for a smooth takeoff.
3. Altitude sensing — The ultrasonic sensor fires a 10µs pulse and measures the echo return time, which is converted to a distance in centimetres.
4. Target setting — The potentiometer maps to a target height between min_height (10cm) and max_height (50cm).
5. PID control — The controller computes the error between target and measured height and adjusts the PWM signal sent to both ESCs every 100ms.
6. Stop — Press the button again to trigger a controlled landing.

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PID Controller

The control output is calculated as:

output = (Kp × error) + (Ki × errSum × SampleTime) + (Kd × dErr / SampleTime) + PWM_offset

Parameter	Value	Description
Kp	3	Proportional gain
Ki	0	Integral gain
Kd	0	Derivative gain
SampleTime	100ms	Control loop interval
PWM_offset	50	Hover offset to keep drone airborne

The PWM signal is clamped between 0 and 180 to stay within safe ESC range.

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Configuration

The following constants can be tuned at the top of the sketch:

const int min_height = 10;  // minimum target height in cm
const int max_height = 50;  // maximum target height in cm
const int ramp_time  = 40;  // motor ramp up/down speed in ms
int SampleTime       = 100; // PID update interval in ms
double Kp = 3;              // proportional gain
double Ki = 0;              // integral gain
double Kd = 0;              // derivative gain
int PWM_offset       = 50;  // hover PWM value

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Setup & Usage

1. Wire the components according to the circuit table above.
2. Open mini_drone_altitude_control.ino in the Arduino IDE.
3. Select Arduino Uno as the board and the correct COM port.
4. Upload the sketch.
5. Open the Serial Monitor at 9600 baud to observe the ESC calibration sequence.
6. Press the button to start the drone.
7. Adjust the potentiometer to change the target altitude.
8. Press the button again to land.

Warning: Test in a safe, open area. Keep hands clear of propellers during operation.

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Serial Monitor Output

ESC calibration process
Starting...
Now writing maximum output
Now writing minimum output
Press button to start minidrone

Target distance: 30
Measured distance: 28
Error: 2
PWM: 56
Button Status: 1

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Reference

Ben Finio, Science Buddies, 2021.

Author

Patricia Munginga, 2023