Unit 4: On Board Electrical components and Payloads

I. Orientation — On-Board Electrical Architecture

A drone’s electrical system converts stored battery energy into controlled motion, computing, sensing, and payload operation. Reliable flight depends on matching every component’s voltage, current, mass, communication protocol, and electromagnetic characteristics.

• Energy path: Electrical power normally flows from the battery through the Power Distribution Board (PDB) to Electronic Speed Controllers (ESCs), motors, avionics, and payloads.
• Control path: The flight controller reads pilot commands and sensor data, then sends control signals to ESCs, actuators, and the gimbal.
• Power convention: Electrical power and energy are expressed as:
  
  TEXT

    P = V × I
    E = V × Q

  
  where (P) is power in watts (W), (V) is voltage in volts (V), (I) is current in amperes (A), (E) is energy in watt-hours (Wh), and (Q) is capacity in ampere-hours (Ah).
• Payload principle: RGB, thermal, multispectral, and LIDAR payloads collect different forms of spatial or spectral information; their value depends on calibration, positioning, and stable mounting.
• Design constraints: Added mass increases required thrust and energy consumption, while electrical noise, heat, vibration, and poor weight distribution can degrade both flight and data quality.
• Compatibility rule: Maximum battery voltage must remain within the ratings of the ESC, motor system, regulators, flight electronics, connectors, and payloads.

II. Actuators — Converting Commands into Physical Movement

A. Actuators

An actuator converts an electrical control command into mechanical movement or force.

• Types:
  • Rotary actuators: Motors rotate propellers or mechanisms.
  • Linear actuators: Produce straight-line movement for release systems or landing gear.
  • Servos: Combine a motor, gearbox, position sensor, and controller for closed-loop angular positioning.
• Control: A flight controller may command a servo through pulse-width modulation (PWM); traditional hobby servos commonly interpret pulses near 1–2 ms within a repeating frame.
• Performance terms: Torque is measured in N·m, angular speed in rad/s or degrees/s, travel in degrees or millimetres, and response time in seconds.
• Feedback distinction: Open-loop actuators receive commands without confirming position, whereas closed-loop actuators compare actual and demanded positions.
• Drone functions: Actuators operate control surfaces, camera shutters, payload-release hooks, retractable landing gear, and variable-pitch mechanisms.

B. Selection, Applications, and Limitations

Actuator selection balances force, precision, speed, mass, and electrical demand.

• Load matching: Required torque should include a safety margin for aerodynamic load, friction, and acceleration.
• Failure risks: Gear backlash reduces accuracy; stalling produces high current and heat; vibration can loosen mechanical linkages.
• Integration: Supply voltage, signal protocol, travel limits, and fail-safe position must match the flight controller and mission.

III. BLDC Motor — Primary Propulsion Machine

A. BLDC Motor

A brushless direct-current motor produces rotation through electronic commutation of stationary windings around a permanent-magnet rotor.

• Construction: Drone motors commonly use an outrunner design, in which the external rotor rotates around a stator carrying three-phase windings.
• Commutation: The ESC energizes winding phases in sequence, creating a rotating magnetic field without brushes or a mechanical commutator.
• Velocity constant: The (K_V) rating approximates unloaded rotational speed:
  
  TEXT

    RPM ≈ K_V × V

  
  where (K_V) is in rpm/V and (V) is applied voltage. A 900 rpm/V motor at 12 V has an ideal no-load speed near 10,800 rpm.
• Torque relationship: Motor torque is approximately proportional to phase current; increased propeller load therefore raises current and heating.
• Propeller interaction: Diameter, pitch, blade count, and air density determine thrust, torque demand, and efficiency.

B. Selection, Applications, and Limitations

A propulsion motor must be matched to the airframe, propeller, battery, and ESC.

• Selection: Lower-(K_V) motors generally suit larger propellers and higher voltages; higher-(K_V) motors suit smaller, faster propellers.
• Efficiency: Copper loss rises approximately with (I^2R), where (I) is winding current and (R) is resistance.
• Limitations: Excessive current can overheat windings or demagnetize magnets; imbalance and worn bearings create vibration that affects cameras and inertial sensors.

IV. Electronic Speed Controller — Electronic Motor Commutation

A. Electronic Speed Controller

An Electronic Speed Controller switches battery power to regulate a BLDC motor’s speed and torque.

• Power stage: Metal-oxide-semiconductor field-effect transistors (MOSFETs) rapidly switch the three motor phases.
• Command input: ESCs may accept PWM, OneShot, MultiShot, or digital protocols such as DShot; digital signalling improves command consistency and can support telemetry.
• Commutation timing: Rotor position is inferred from back electromotive force in sensorless systems or measured using position sensors.
• Braking: Active braking changes phase switching so the motor decelerates rapidly, improving multirotor control response.
• Rating: Continuous and burst-current ratings must exceed expected motor current at the battery’s maximum charged voltage.

B. Selection, Applications, and Limitations

ESC reliability depends on electrical headroom, cooling, configuration, and wiring.

• Sizing: A motor drawing 28 A at full thrust requires an ESC rated above 28 A, with allowance for transients and reduced cooling.
• Firmware settings: Motor direction, timing, startup power, braking, and protocol must suit the propulsion system.
• Risks: Poor cooling, long power leads, voltage spikes, or incorrect settings can destroy MOSFETs or cause desynchronization.

V. Power Distribution Board — Central Power Routing

A. Power Distribution Board (PDB)

A Power Distribution Board divides battery power among ESCs and other on-board systems.

• Distribution: Wide copper traces or bus bars carry high current from the battery connector to multiple ESC outputs.
• Regulation: Some PDBs include battery eliminator circuits or DC–DC converters providing regulated rails such as 5 V or 12 V.
• Monitoring: Current and voltage sensors can report battery usage to the flight controller through analogue or digital interfaces.
• Current requirement:
  
  TEXT

    I_PDB ≥ ΣI_branch

  
  where (I{PDB}) is the board’s required current capacity and (\Sigma I{branch}) is the maximum simultaneous branch current.
• Protection: Fuses, transient suppression, reverse-polarity protection, and capacitors may reduce damage from faults and switching spikes.

B. Selection, Applications, and Limitations

The PDB must safely carry peak propulsion current without excessive voltage drop.

• Layout: Short, thick conductors reduce resistance, heating, and electromagnetic interference.
• Thermal control: High-current boards require airflow and secure solder joints.
• Limitations: An underrated or damaged trace may overheat, delaminate, or interrupt power to several motors simultaneously.

VI. Battery — On-Board Energy Storage

A. Battery

The battery supplies the electrical energy required for propulsion, control electronics, and payloads.

• Chemistry: Lithium-polymer (LiPo) batteries offer high discharge rates, while lithium-ion packs commonly provide greater energy density but lower peak current.
• Cell voltage: A conventional LiPo cell is nominally about 3.7 V and reaches about 4.2 V when fully charged; a 4S pack is therefore 14.8 V nominal and 16.8 V fully charged.
• Capacity: A 5 Ah, 14.8 V battery stores nominal energy of:
  
  TEXT

    E = 14.8 × 5 = 74 Wh

• C-rating: The theoretical discharge limit is (I=C_rQ), where (C_r) is the discharge rating and (Q) is capacity in Ah.
• Configuration: Series connections increase voltage; parallel connections increase capacity and available current.

B. Selection, Applications, and Limitations

Battery choice determines endurance, thrust capability, and aircraft mass.

• Usable energy: Flight planning retains a reserve rather than exhausting the pack, preventing damaging cell undervoltage.
• Condition monitoring: Cell imbalance, swelling, abnormal heat, increased internal resistance, or physical damage indicates an unsafe pack.
• Trade-off: A larger battery stores more energy but adds mass, so endurance does not increase in direct proportion to capacity.

VII. Battery Charger — Controlled Energy Replenishment

A. Battery Charger

A battery charger restores energy using a charging profile appropriate to the battery chemistry and cell count.

• LiPo method: Constant-current/constant-voltage charging first supplies controlled current, then holds the maximum pack voltage while current declines.
• Balance charging: A balance connector allows the charger to measure and equalize individual series-cell voltages.
• Charge rate:
  
  TEXT

    I_charge = C_r × Q

  
  where (I_{charge}) is charging current, (C_r) is the selected charge rate, and (Q) is capacity. At 1C, a 5 Ah pack charges at 5 A.
• Configuration: Chemistry, series-cell count, capacity, and current must be correctly selected before charging.
• Storage mode: A storage program places cells near a moderate state of charge for reduced degradation during inactivity.

B. Selection, Applications, and Limitations

Charging requires supervision and protection against configuration or battery faults.

• Charger rating: Output wattage must support pack voltage multiplied by charging current.
• Safety: Batteries should be charged on a non-flammable surface, away from combustibles, and never when swollen or damaged.
• Limitations: Incorrect cell count, overvoltage, reversed polarity, or inadequate balancing can cause overheating, fire, or permanent damage.

VIII. RGB Camera — Visible-Light Imaging Payload

A. RGB Camera

An RGB camera records reflected visible light in red, green, and blue channels to produce colour imagery.

• Image formation: A lens focuses light onto a CMOS or CCD sensor containing photosensitive pixels.
• Resolution: Pixel dimensions, ground sampling distance, lens focal length, altitude, and sensor size determine visible detail.
• Exposure: Aperture, shutter speed, and sensor gain control brightness; fast shutters reduce motion blur during flight.
• Geotagging: GNSS coordinates and timestamps associate each image with a capture location for photogrammetric processing.
• Products: Overlapping photographs can generate orthomosaics, three-dimensional point clouds, digital surface models, and inspection records.

B. Applications and Limitations

RGB cameras are economical general-purpose payloads but depend strongly on illumination and surface appearance.

• Applications: Mapping, construction monitoring, infrastructure inspection, traffic observation, and visual documentation.
• Capture geometry: Mapping missions often use substantial forward and side overlap so matching software can identify common features.
• Limitations: Shadows, glare, haze, repetitive textures, low light, rolling-shutter distortion, and vegetation concealment can reduce accuracy.

IX. Thermal Camera — Infrared Temperature Mapping

A. Thermal Camera

A thermal camera detects emitted infrared radiation and represents apparent surface-temperature differences.

• Detector: Uncooled microbolometers commonly measure long-wave infrared energy, often in approximately the 8–14 μm region.
• Radiometry: Radiometric cameras preserve temperature-related values for each pixel; non-radiometric models primarily provide visual contrast.
• Emissivity: Temperature estimation depends on surface emissivity, atmospheric transmission, reflected radiation, range, and viewing angle.
• Resolution: Thermal arrays usually have fewer pixels than RGB sensors, making altitude and field of view especially important.
• Interpretation: A bright or dark thermal region indicates different detected radiance, not automatically a specific fault or material.

B. Applications and Limitations

Thermal imaging reveals heat patterns invisible to an RGB camera.

• Applications: Solar-panel inspection, roof heat-loss surveys, electrical hotspot detection, firefighting support, and search operations.
• Timing: Early morning, evening, or controlled operating conditions may improve thermal contrast.
• Limitations: Glass, polished metal, rain, wind, solar heating, and incorrect emissivity settings can produce misleading apparent temperatures.

X. Multispectral Camera — Narrow-Band Spectral Measurement

A. Multispectral Camera

A multispectral camera captures several discrete wavelength bands to distinguish materials by spectral reflectance.

• Bands: Typical payloads include blue, green, red, red-edge, and near-infrared channels, although exact wavelengths vary by sensor.
• Vegetation index:
  
  TEXT

    NDVI = (NIR − Red) / (NIR + Red)

  
  where (NIR) and (Red) are reflectance values in the near-infrared and red bands; values are dimensionless.
• Calibration: Reflectance panels and incident-light sensors help compensate for illumination changes.
• Registration: Bands must be spatially aligned so that each pixel represents the same ground location.
• Data product: Calibrated mosaics support comparison across fields, dates, and treatment zones.

B. Applications and Limitations

Multispectral data supports material and crop analysis beyond normal colour vision.

• Applications: Crop-stress assessment, irrigation planning, vegetation classification, disease scouting, and environmental monitoring.
• Interpretation: An index identifies spectral variation but does not independently diagnose nutrient deficiency, disease, or water stress.
• Limitations: Clouds, shadows, changing sunlight, poor calibration, mixed pixels, and canopy structure can distort measurements.

XI. LIDAR Sensor — Active Three-Dimensional Ranging

A. LIDAR Sensor

A LIDAR sensor emits laser pulses and measures their return to calculate distance and generate three-dimensional point clouds.

• Range equation:
  
  TEXT

    d = cΔt / 2

  
  where (d) is range, (c) is the speed of light, and (\Delta t) is the pulse’s round-trip travel time.
• Scanning: Mechanical or solid-state mechanisms direct pulses across the scene, producing points with (x), (y), and (z) coordinates.
• Georeferencing: GNSS supplies position, while an inertial measurement unit supplies orientation; accurate timestamps combine these observations.
• Returns: A pulse may produce multiple returns from canopy, branches, and ground, assisting terrain extraction beneath partial vegetation.
• Specifications: Range, accuracy, scan rate, field of view, wavelength, and point density determine mission suitability.

B. Applications and Limitations

LIDAR provides direct geometric measurements under varied lighting conditions.

• Applications: Topographic mapping, forestry, corridor surveys, stockpile measurement, building modelling, and obstacle detection.
• Advantages: It does not depend on sunlight and can capture fine three-dimensional structure.
• Limitations: Payload cost, mass, processing volume, GNSS outages, reflective surfaces, water, fog, and calibration errors can reduce data quality.

XII. Gimbal — Payload Stabilization and Pointing

A. Gimbal

A gimbal supports and actively or passively stabilizes a payload while controlling its viewing direction.

• Axes: A three-axis gimbal corrects roll, pitch, and yaw; two-axis designs usually omit active yaw stabilization.
• Feedback loop: Inertial sensors measure angular disturbance, and a controller commands brushless gimbal motors to oppose it.
• Operating modes: Follow mode tracks aircraft heading smoothly, lock mode maintains a fixed direction, and target-tracking mode points toward a selected subject.
• Mechanical balance: Positioning the camera’s centre of mass near each rotation axis reduces motor torque and electrical consumption.
• Integration: Trigger, video, telemetry, and pointing commands may pass through dedicated cables, slip rings, or serial interfaces.

B. Applications and Limitations

A correctly configured gimbal improves image sharpness, survey geometry, and target observation.

• Applications: Stabilized filming, nadir mapping, oblique inspection, thermal search, and LIDAR orientation control.
• Configuration: Motor strength, control gains, axis limits, and damping must suit payload mass and inertia.
• Limitations: Poor balance causes heat and oscillation; excessive vibration causes blurred imagery; restricted axis travel, wind load, and landing-gear obstruction limit viewing angles.