Designing Your Own Mini Drone

Hey all, I'm a fourth-year Mechatronics Engineering/Computer Engineering double major at RIT and wanted to attempt a project that would encapsulate the essence of mechatronics and I thought a small Arduino-controlled drone would be the best way to learn most facets of Mechatronics.

Keep in mind, this is just the Design phase of the engineering process as I currently lack the actual resources to prototype and test this drone. Once I return to campus, I will be able to rapid prototype the drone and test it. Regardless, I wanted to share what I learned on this journey and how you could design your own drone!

The CAD is heavily inspired off Max Imagination's 3D Printed Drone design

Since this Instructable is solely intended for design, all you really need is design software.

For me, I used:

CAD Software - Autodesk Inventor

Circuit Simulation Software - Autodesk TinkerCAD

Circuit Schematic Software - Circuito.io

But for future rapid prototyping and drone assembly, I will need:

3D Printer - FDM/SLA

Microcontroller - Arduino

1 9V Battery Pack

Drone Motors - Either coreless DC motors or actual stators (since this is a mini build coreless motors would be ideal) 52000 RPM Coreless Motor

Radio Transceiver/Receiver - nRF24L01 module and Antenna (Needed for both Drone and Controller)

Gyroscope and Accelerometer - MPU6050

MultiWii Flight Controller

Motor Driver - Made my own so:

4 NMOS Transistors

4 Diodes

Resistors - Refer to TinkerCAD

Before attempting this project, I knew little to nothing about drone dynamics and design, so background research was especially crucial.

The most common drone designs are quadcopter designs with four rotors and that's because the four-rotor configuration when tuned with PID controls are usually the most stable and have precise maneuvers.

Single rotor designs exert a reactionary torque to the chassis which can be counteracted with a secondary smaller rotor like how helicopters work, but making precise changes to a larger main rotor is very difficult due to the large inertia of the blades.

Dual motor designs resolve the reactionary torque issue by having two motors spin opposite to each other, but the two motors spinning CW and CCW will generate an unwanted net force.

Hence, quadcopters are the most common and I've selected a quadcopter design.

Unidirectional Motor Driver Configuration

Since the purpose of this project is to learn, I wanted to make my own motor driver instead of using Arduino shields/modules. I've made the motor driver circuit schematic above on TinkerCAD.

You can find the link here: Unidirectional Drone Motor Driver - Tinkercad

For quadcopter motors, we only need four unidirectional motors that can be controlled using PWM signals to generate the maneuvers of the drone. NMOS transistors were ideal for this application because they act as efficient PWM switches connecting the motor to ground.

Each NMOS has a PWM pin (i.e. ~3) connected at the Gate, with a 160Ω resistor in series to limit current flow as Arduino's have low current draw. The Source is in series with ground and the Drain serves as the motor's connection to ground.

Simply put, we are rapidly cutting off and on the motor's connection to ground at a desired duty cycle.

However, pulsing the motors will introduce back-emf (as a result of Lenz's Law) which we can redirect using flyback diodes in a parallel pathway from the NMOS Drain to cathode of the battery, avoiding damaging the motor.

I've also attached pull-down resistors in each NMOS from Gate to Source to ensure Gate voltage is zero and there is no accumulation of undesired charge.

Controller Circuit Schematic

For the controller circuit which will be in a separate design process, I've used a separate circuit builder - Circuito.io as TinkerCAD is not extensive enough to include all the components this project will need. The wiring is automatically generated by Circuito.io.

The code is very simple for now as it is hardcoded and is simply a demonstration of how the motors would activate to simulate ascending, descending, forward-backward movement, rolling, and yawing.

I've simulated the motor movement in the TinkerCAD code IDE to verify motor movements.

Example:

Forward Movement = Back motors have to generate more thrust than front motors

Left Yawing = CW motors (front left and back right) have to generate more torque than CCW motors

Left Rolling = Left motors have to generate more thrust than right motors.

I've abstracted all the maneuvers in void functions and placed them in series with a 1 second delay between calling each function so that I can see the motors activate properly.

For the actual drone to function, much more code needs to be implemented to adjust for closed-feedback control for motors and MultiWii.

This CAD design is heavily inspired off of Max Imagination's 3D Printed Drone, but will alter heavily once I get my hands to prototyping.

Since the design can't be validated currently, most of the design choices I've are made are to house the components - specifically the Arduino Nano/Uno R3 and the motor driver, the motors, as well as aesthetic purposes.

The first step is to create a foundational sketch drawing the frame of your drone, I chose the 5" frame.

I've drawn construction geometry as a true X-frame and drawn a center chassis, along with circular mounts for the drone motors.

You can then extrude the frame and mounts to fit your components.

Add a roof housing on top of the frame and then cut out unnecessary material from the design. This way, we can save both prototyping time and allow the drone to be lighter in mass.

Fillets and chamfers are optional but add increased structural integrity to the frame without adding excess unnecessary material.