Vertical Hovering Fixed-Wing Drone

A control system for achieving stable vertical hovering in fixed-wing drones using PID controllers and motion capture feedback.

Demo Video

Click the image above to watch the vertical hovering demonstration

Project Overview

This project develops control strategies for fixed-wing UAVs to achieve stable vertical hovering, focusing on attitude control and position stabilization. Two platforms were used: Flatty (conventional front-propeller) for validation and Perchug (rear-propeller pusher configuration).

Control Architecture

PID Controller System

The system uses 6 PID controllers for complete hovering control:

1. Roll Control: Maintains constant roll using aileron deflection
2. Altitude Control: Z-position control via throttle command
3. Pitch Control: Cascaded PID (outer: x-position, inner: pitch angle)
4. Yaw Control: Cascaded PID (outer: y-position, inner: yaw angle)

Control Loop Structure

Reference → PID Controller → Actuator → Drone → Sensor → Feedback

Hardware Setup

• Platform: T-Motor AM20 F3P-A (Flatty) / Custom Perchug
• Controller: Arduino Nano IOT 33 with WiFi
• Position Feedback: OptiTrack Motion Capture System
• Actuators: Servo-controlled elevator, rudder, aileron
• Propulsion: Brushless motor with 30A ESC

Key Differences: Flatty vs Perchug

Aspect	Flatty (Front Propeller)	Perchug (Rear Propeller)
Stability	Inherently stable (pendulum)	Inherently unstable (inverted pendulum)
Thrust Vector	Pulls from above	Pushes from below
Roll Control	Full aileron effectiveness	Limited due to reduced airflow
Equilibrium	Zero elevator deflection	Requires elevator offset for COG compensation

Control Challenges

Perchug-Specific Issues

• COG Offset: Thrust vector doesn't pass through center of gravity
• Elevator Compensation: Requires constant offset to counter pitching moment
• Inverted Pendulum: Unstable configuration requiring precise control
• Limited Roll Authority: Reduced airflow over wings affects roll control

Experimental Results

Flatty Platform

• Successfully achieved stable hovering
• Full position and attitude control demonstrated
• Validated PID control methodology

Perchug Platform

• Pitch and yaw control successfully tuned
• Altitude control functional with spinning motion
• Roll control limited but system remains controllable

Tuning Process

1. Pitch Control: Hang drone from wings, tune with ±10° square wave
2. Yaw Control: Similar hanging setup, independent tuning
3. Altitude Control: Tune throttle-to-altitude response
4. Roll Control: Tune while hovering with slack cables
5. Position Control: Final tuning of x,y position loops

Key Parameters

• Thrust Range: ±1% variation around hovering thrust
• Control Frequency: Real-time motion capture feedback
• Elevator Offset: -8° pitch, 4° yaw equilibrium (Perchug)
• Assumptions: Decoupled control, small angular rates, low-speed flight

Future Improvements

• Roll Enhancement: Wing-mounted motors for differential thrust
• Autonomous Operation: Remove motion capture dependency
• Gain Scheduling: Adaptive control for varying flight conditions

Applications

• Prop-Hanging: Traditional fixed-wing hovering technique
• VTOL Operations: Vertical takeoff and landing capabilities
• Research Platform: Control algorithm development and validation