✍️ 필사 모드: Introduction to Biotech & Mechanical Engineering -- Engineering Fundamentals for Building Drones

Introduction

Drones are a quintessential convergence technology product sitting at the intersection of modern engineering. Designing and building a single drone requires knowledge from various fields including electrical/electronic engineering, mechanical engineering, software, and recently even biotechnology.

This article uses drone construction as a central axis to cover the fundamental basics of three engineering disciplines.

• Part 1 - Electrical/Electronic Fundamentals (The core power and control of drones)
• Part 2 - Mechanical Engineering Fundamentals (Frame, mechanics, fluid dynamics)
• Part 3 - Biotechnology Fundamentals (Biosensors, DNA, bioinformatics)

  Drone Convergence Engineering System Diagram

   Electrical/     Mechanical      Biotech
   Electronics     Engineering     Engineering

   Motors          Mechanics       DNA
   Circuits        Materials       Cells
   Sensors         Fluids          Bio-
   PID Control     Thermodynamics  sensors

        All converge into the Drone System

Part 1: Electrical/Electronic Fundamentals (Drone Core)

1. Electricity Basics

To make a drone move, you need electricity. Understanding three fundamental physical quantities is the starting point.

Voltage, Current, Resistance

Ohm's Law

The most fundamental law relating voltage, current, and resistance.

  Ohm's Law: V = I x R

  Example: If resistance is 10 ohms and current is 2A
           V = 2 x 10 = 20V

  V = I x R
  I = V / R
  R = V / I

Kirchhoff's Laws

Two essential laws for analyzing complex circuits.

Current Law (KCL): The sum of currents entering a node equals the sum of currents leaving it.

Voltage Law (KVL): The sum of voltage drops in a closed circuit is zero.

2. Circuit Design

Series and Parallel Circuits

Understanding the difference between series and parallel is essential when designing drone power systems.

  Series connection (same current, voltage divides)
  --[ R1 ]--[ R2 ]--[ R3 ]--
  R_total = R1 + R2 + R3

  Parallel connection (same voltage, current divides)
      +--[ R1 ]--+
  ----+--[ R2 ]--+----
      +--[ R3 ]--+
  1/R_total = 1/R1 + 1/R2 + 1/R3

Voltage Divider

Commonly used to convert sensor signals to voltages suitable for microcontrollers.

  Vin --[ R1 ]--*--[ R2 ]-- GND
                |
               Vout

  Vout = Vin x R2 / (R1 + R2)

  Example: Vin=12V, R1=10k, R2=10k
  Vout = 12 x 10000 / (10000 + 10000) = 6V

Filter Circuits

Used to remove noise from sensor data.

• Low-pass filter (LPF): Passes low frequencies only (maintains slow changes, removes noise)
• High-pass filter (HPF): Passes high frequencies only (detects rapid changes)
• Band-pass filter: Passes only a specific frequency range

PCB Design Basics

Beyond prototyping, you will need to design PCBs (Printed Circuit Boards) directly.

• Schematic creation: Using EDA tools like KiCad, Eagle
• Component placement: Separate power, signal, and high-frequency sections
• Routing rules: Thick traces for power, short traces for signals
• Ground plane: Large ground areas to reduce noise

3. Types of Motors

Motors are the core components that spin propellers to generate lift in drones.

DC Motor

The most basic motor that rotates when voltage is applied.

• Simple structure and inexpensive
• Limited lifespan due to brush wear
• Mainly used in small toy drones

BLDC Motor (Brushless DC)

The most commonly used motor in drones.

KV Rating: The key spec for BLDC motors. It represents the no-load RPM per 1V.

• High KV (e.g., 2300KV): Small propeller, fast rotation, racing drones
• Low KV (e.g., 700KV): Large propeller, slow rotation, photography drones

Servo Motor

Used where precise angle control is needed. Applied in drone gimbals (camera stabilizers).

ESC (Electronic Speed Controller)

An electronic device that controls BLDC motors.

  Flight Controller --(PWM signal)--> ESC --(3-phase current)--> BLDC Motor

  ESC roles:
  1. Convert battery DC to 3-phase AC
  2. Adjust motor speed according to PWM signal
  3. Supply power to electronics via BEC (Battery Eliminator Circuit)

4. Sensors

Various sensors are needed for a drone to fly stably in the air.

Accelerometer

Measures acceleration in 3 axes (including gravity). Determines tilt.

Gyroscope

Measures angular velocity (rotation speed) in 3 axes. Quickly detects attitude changes.

  Drone's 3-axis rotation

  Roll (side tilt)        X-axis rotation
  Pitch (front-back tilt) Y-axis rotation
  Yaw (left-right spin)   Z-axis rotation

Barometer

Estimates altitude through air pressure changes. Accuracy is approximately 0.5-1m.

GPS

Determines latitude, longitude, and altitude through satellite signals. Essential for autonomous flight and return-to-home functions.

IMU Sensor Fusion

Combines data from multiple sensors for more accurate attitude estimation.

  Sensor Fusion Flow

  Accelerometer --+
                  +--> [Kalman Filter / Complementary Filter] --> Accurate Attitude
  Gyroscope     --+                                               (Roll, Pitch, Yaw)
                  |
  Barometer     --+--> Altitude Estimation
                  |
  GPS           --+--> Position Estimation

  Accelerometer: Slow but stable (no drift)
  Gyroscope:     Fast but error accumulates over time (drift)
  -> Combining both yields fast and stable results

5. PID Control

The secret to a drone flying stably without wobbling in the wind is PID control.

PID Components

P (Proportional): Controls proportionally to the error.

• Large error = large correction, small error = small correction
• P alone gets close to the target but never reaches it exactly (steady-state error)

I (Integral): Corrects accumulated error.

• If the target is not reached over time, applies increasingly stronger correction
• Too much causes oscillation (overshoot)

D (Derivative): Detects the rate of change of error.

• If error is decreasing rapidly, reduces correction to prevent abrupt response
• Makes the system smoother

  PID Control Block Diagram

  Setpoint -->(+)--> [P] --+
               |            +--> Sum --> Motor Output
  Error    ----+--> [I] --+
               |            |
               +--> [D] --+
               ^
               |
  Current  -->(-)

  Output = Kp x e(t) + Ki x integral(e) + Kd x derivative(e)

PID Tuning Method

1. Start with P: Gradually increase to find appropriate response speed
2. Add D: Increase until oscillation diminishes
3. Add I: Add small amounts until steady-state error disappears

PID Application in Drones

Drones typically run 3 independent PID loops:

• Roll PID: Left-right tilt control
• Pitch PID: Front-back tilt control
• Yaw PID: Left-right rotation control

Each PID loop executes hundreds to thousands of times per second, adjusting motor output in real-time based on sensor data.

Part 2: Mechanical Engineering Fundamentals

6. Mechanics

Newton's Laws of Motion

First Law (Law of Inertia): Without external force, a stationary object stays at rest, and a moving object continues at constant velocity.

Second Law (Law of Acceleration): Force equals mass times acceleration.

  F = m x a

  Drone example:
  Drone weight = 1.5kg, desired acceleration = 2 m/s^2
  Required force = 1.5 x 2 = 3N (gravity separate)

Third Law (Action-Reaction): Every action has an equal and opposite reaction. When a drone propeller pushes air downward, the air pushes the drone upward.

Lift, Drag, Thrust

  Forces acting on a drone

            Lift
              ^
              |
  Drag <------*------> Thrust direction
              |
              v
           Gravity

  Hovering condition: Lift = Gravity
  Ascent condition:   Lift > Gravity
  Forward condition:  Drone tilts, creating horizontal thrust component

Torque

A physical quantity representing rotational force. Counter-torque effect: when a motor spins a propeller in one direction, the body wants to rotate in the opposite direction. That's why quadcopters have diagonal motors spinning in the same direction to cancel torque.

7. Material Mechanics

Stress and Strain

Stress: Force per unit area applied to a material. Strain: Ratio of deformation to original length.

Elasticity and Plasticity

• Elastic deformation: Returns to original form when force is removed (like a rubber band)
• Plastic deformation: Permanent deformation that doesn't return (like paper folding)
• Young's Modulus: An indicator of material stiffness

Frame Material Selection

Comparing representative materials used for drone frames.

Racing drones use carbon fiber, while beginner models typically use ABS + aluminum combinations.

8. Thermodynamics Basics

Engine and Motor Efficiency

According to the first law of thermodynamics (conservation of energy), energy is not created or destroyed, only transformed.

  Energy Conversion Efficiency

  Battery(Chemical) -> ESC(Electrical) -> Motor(Mechanical) -> Propeller(Lift)

  Efficiency at each stage:
  Battery discharge: ~95%
  ESC conversion:    ~97%
  BLDC motor:        ~80-90%
  Propeller:         ~50-70%

  Overall efficiency: 0.95 x 0.97 x 0.85 x 0.60 = approximately 47%
  -> Only about half of battery energy converts to lift

9. Fluid Dynamics

Bernoulli's Principle

The principle that as fluid (air) speed increases, pressure decreases. This is the foundation for how airplane wings and drone propellers generate lift.

Propeller Design

Two key parameters for drone propellers:

Diameter: Propeller size -- larger means more air moved (efficient) but heavier and slower response.

Pitch: The theoretical distance traveled per revolution -- higher pitch means faster speed but lower torque efficiency.

  Propeller notation: Diameter x Pitch (inches)

  Example: 5045
  -> 5-inch diameter, 4.5-inch pitch

  Racing drones:   5-inch, high pitch (5045, 5051)
  Camera drones:   10+ inches, low pitch
  Micro drones:    3 inches or less

Part 3: Biotechnology Fundamentals

10. DNA and Genes

Recently, drones are increasingly intersecting with biotechnology through environmental monitoring, wildlife tracking, and sample collection. Understanding biotech basics opens doors to these convergence fields.

Central Dogma

The core concept explaining the flow of biological information.

  Flow of Biological Information (Central Dogma)

  DNA  --Transcription-->  RNA  --Translation-->  Protein

  DNA: Genetic information storage (blueprint)
  RNA: Information carrier (messenger)
  Protein: Actual function performer (machine)

DNA Structure

DNA consists of 4 types of bases (A, T, G, C) in a double helix structure.

• A-T: 2 hydrogen bonds
• G-C: 3 hydrogen bonds
• Human genome: approximately 3 billion base pairs (approximately 700MB as data)

CRISPR Gene Editing

CRISPR-Cas9 is a revolutionary technology that can precisely cut and modify genes.

Applications:

• Genetic disease treatment
• Crop improvement
• Virus-resistant organism development
• Synthetic biology

11. Cell Biology

Mitochondria

The cell's energy factory that produces ATP (adenosine triphosphate).

  Energy Production Process

  Glucose (C6H12O6)
       |
  [Glycolysis]           --> 2 ATP
       |
  [Citric Acid Cycle]    --> 2 ATP
       |
  [Electron Transport]   --> 34 ATP
       |
  Total approximately 38 ATP + CO2 + H2O

  Mitochondria have their own DNA
  -> Maternal inheritance (inherited only from mother)

Stem Cells

Undifferentiated cells with the ability to become various cell types.

• Totipotent stem cells: Can differentiate into all cell types (fertilized egg)
• Pluripotent stem cells: Can differentiate into most cell types (embryonic stem cells, iPSC)
• Multipotent stem cells: Can differentiate into limited cell types (hematopoietic stem cells)

Used in regenerative medicine, drug testing, and disease modeling.

12. Bioinformatics

Genome Analysis

The field of analyzing large-scale biological data using computers.

  Genome Analysis Pipeline

  [Sample Collection] -> [DNA Extraction] -> [Sequencing]
       |
  [Raw Data] -> [Quality Check] -> [Alignment/Mapping]
       |
  [Variant Calling] -> [Annotation] -> [Interpretation/Reporting]

  Key tools:
  - FASTQ: Raw sequencing data format
  - BWA/Bowtie: Sequence alignment tools
  - GATK: Variant calling tool
  - BLAST: Sequence similarity search

AI in Bio

Areas where artificial intelligence is driving innovation in biotechnology:

• Protein structure prediction: AlphaFold predicts 3D protein structures
• Drug discovery: AI searches for and optimizes candidate molecules
• Genome interpretation: Deep learning analyzes the meaning of genetic variants
• Medical imaging: CNNs automatically read X-rays and MRIs

13. Biosensors

Sensors that use biological elements to detect chemical substances or biological signals.

Blood Glucose Sensor

The most widely used biosensor, used daily by diabetes patients.

  Blood Glucose Sensor Working Principle

  Blood (glucose) --> Glucose oxidase (enzyme)
                          |
                    H2O2 generated
                          |
                    Current generated at electrode
                          |
                    Blood glucose concentration calculated from current

  Continuous Glucose Monitor (CGM):
  - Sensor inserted under the skin
  - Automatic measurement every 5 minutes
  - Real-time monitoring via smartphone

Wearable Biosensors

Devices worn on the body to monitor health status in real-time.

  Drone + Biosensor Convergence:
  - Drones collecting biosensor data at disaster sites
  - Drone transport of remote patient health data
  - Environmental pollution monitoring drones with biosensors

Conclusion: Drone Building Roadmap

A step-by-step roadmap for building drones based on everything covered.

  Drone Building Roadmap

  [Step 1: Theory]
    - Learn electrical/electronic basics
    - Understand mechanical engineering fundamentals
    - Get hands-on with Arduino/Raspberry Pi

  [Step 2: Component Selection]
    - Frame (carbon/ABS)
    - Motor + ESC + propeller matching
    - Flight controller (FC)
    - Battery (LiPo)
    - Receiver/transmitter

  [Step 3: Assembly]
    - Frame assembly
    - Motor/ESC mounting and wiring
    - FC installation and sensor calibration
    - Receiver connection

  [Step 4: Software]
    - Firmware installation (Betaflight, ArduPilot)
    - PID tuning
    - Flight mode configuration

  [Step 5: Test Flight]
    - Indoor low-altitude test
    - Outdoor hovering test
    - Axis control verification

  [Step 6: Advanced Features]
    - GPS-based autonomous flight
    - Camera/gimbal mounting
    - Biosensor integration
    - Telemetry system

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