Unit 4: On Board Electrical components and Payloads - Subjective Questions

Definition: An actuator is a device that converts an electrical control signal into physical movement or mechanical action.

Role in a drone:

• Produces thrust by rotating propellers.
• Changes the position of control surfaces in fixed-wing drones.
• Moves landing gear, camera shutters, release mechanisms, and gimbals.
• Enables the flight controller to translate computed commands into physical actions.

Common actuator types:

• BLDC motors: Rotate propellers to generate lift and thrust.
• Servo motors: Provide precise angular movement for control surfaces and mechanisms.
• Linear actuators: Produce straight-line motion for landing gear or payload deployment.
• Gimbal motors: Stabilize and orient cameras or sensors.

An actuator therefore forms the link between the drone's electronic control system and its mechanical operation.

A Brushless DC motor converts electrical energy into rotational mechanical energy without using mechanical brushes.

Construction:

• Stator: Contains multiple copper windings arranged as phases.
• Rotor: Contains permanent magnets and rotates around or inside the stator.
• Bearings and shaft: Support smooth rotation and transfer torque to the propeller.
• Motor housing: Protects the components and assists cooling.

Working principle:

1. The Electronic Speed Controller energizes the stator phases in a controlled sequence.
2. The energized windings produce a rotating magnetic field.
3. The permanent magnets on the rotor follow this rotating field.
4. Sequential electronic commutation maintains continuous rotation.
5. Changing the commutation rate changes motor speed.

BLDC motors are preferred in drones because they provide high efficiency, high power-to-weight ratio, long service life, low maintenance, and rapid speed response.

Justification: BLDC motors are preferred for multirotors because they deliver high thrust with low mass, respond rapidly to flight-controller commands, consume battery energy efficiently, and withstand repeated speed changes. Their absence of brushes also improves reliability during long and demanding flights.

An Electronic Speed Controller is an electronic circuit that controls the speed and, where supported, the direction and braking of a BLDC motor.

Operation:

1. The flight controller sends a throttle command using a protocol such as PWM, OneShot, MultiShot, or DShot.
2. The ESC interprets the command and switches its power transistors in a precise sequence.
3. This switching converts the battery's DC supply into controlled three-phase pulses for the BLDC motor.
4. The switching frequency and timing determine motor speed and torque.
5. Some ESCs return telemetry such as current, voltage, temperature, and rotational speed.

Additional functions:

• Motor start-up and synchronization
• Active braking
• Current and temperature protection
• Low-voltage protection
• Motor direction configuration

Thus, the ESC acts as the power-control interface between the battery, flight controller, and motor.

ESC selection must consider the complete propulsion system.

Important criteria:

• Current rating: The continuous ESC rating should exceed the motor's maximum expected current, with a suitable safety margin.
• Burst-current rating: It must withstand short current peaks during rapid acceleration.
• Battery voltage: The supported cell count must match the battery, such as 3S, 4S, or 6S.
• Motor compatibility: The ESC must operate reliably with the motor's pole count, size, and maximum speed.
• Control protocol: It should support the protocol used by the flight controller, such as PWM or DShot.
• Firmware and features: Braking, telemetry, bidirectional DShot, and configuration support may be required.
• Cooling and installation: Adequate airflow and heat dissipation are necessary.
• Mass and dimensions: These should suit the drone's payload and frame constraints.

For example, if a motor may draw , choosing an ESC rated comfortably above improves reliability and reduces overheating risk.

A Power Distribution Board receives power from the main battery and distributes it to the drone's ESCs and other onboard electrical systems.

Functions:

• Provides common positive and negative power paths.
• Distributes high current to multiple ESCs.
• May include regulated outputs for the flight controller, receiver, cameras, and sensors.
• May contain voltage and current sensing circuits.
• Simplifies wiring and reduces the number of direct battery connections.

Design considerations:

• Maximum continuous and peak-current capacity
• Supported battery voltage
• Conductor thickness and connector rating
• Heat dissipation
• Protection against short circuits and reverse polarity
• Electrical-noise filtering
• Quality of solder joints and insulation
• Separation of high-current paths from sensitive signal circuits

A correctly rated PDB improves wiring organization, reliability, and electrical safety.

A lithium-polymer (LiPo) battery is a rechargeable battery widely used in drones because of its high energy density and discharge capability.

Construction and working:

• A battery consists of one or more electrochemical cells.
• Each cell contains positive and negative electrodes, an electrolyte, and a separator.
• Chemical reactions release electrical energy during discharge and are reversed during charging.
• Cells may be connected in series to increase voltage and in parallel to increase capacity.

Key characteristics:

• Cell count: Written as 3S, 4S, or similar; a nominal LiPo cell is approximately .
• Capacity: Expressed in or .
• Discharge rating: The C-rating indicates the current-delivery capability.
• Energy: Estimated using , where is nominal voltage and is capacity in ampere-hours.
• Internal resistance: Affects voltage drop and heat generation.

LiPo batteries require careful charging, storage, inspection, and protection against over-discharge or physical damage.

Given:

• Cell count
• Nominal cell voltage
• Capacity
• Discharge rating

1. Nominal battery voltage:

2. Stored energy:

3. Theoretical maximum continuous current:

Therefore, the battery has a nominal voltage of , stores approximately , and has a theoretical continuous-current limit of .

Practical limitation: The current should remain below this limit because C-ratings may be optimistic, battery cooling varies, and aging increases internal resistance. A safety margin reduces voltage sag, overheating, cell damage, and the risk of fire.

The ideal flight time can be estimated by:

where is time in minutes, is usable capacity in ampere-hours, and is average current in amperes.

If only a fraction of the battery is safely usable:

For a battery, usable capacity, and average current:

Factors affecting actual endurance:

• Total drone and payload mass
• Propeller and motor efficiency
• Flight speed and maneuvering
• Wind, air density, and temperature
• Battery age and internal resistance
• Voltage reserve required for safe landing
• Power consumed by sensors, computers, and communication systems
• Hovering versus forward-flight conditions

The calculation is only an estimate because current consumption changes continuously during flight.

Charging procedure:

• Inspect the battery for swelling, punctures, damaged leads, or unusual heat.
• Use a charger designed for the correct battery chemistry.
• Select the correct cell count and capacity.
• Connect both the main power lead and balance connector when balance charging.
• Charge in a fire-resistant area and never leave the battery unattended.
• A common conservative charging rate is 1C unless the manufacturer permits otherwise.

Balancing: A balance charger monitors individual cell voltages and equalizes them so that no cell exceeds its safe upper voltage.

Storage:

• Use the charger's storage mode for long-term storage.
• Keep batteries in a cool, dry, fire-resistant location.
• Avoid storing a battery fully charged or deeply discharged.

Handling:

• Prevent short circuits, crushing, puncturing, and excessive heat.
• Allow a hot battery to cool before charging.
• Retire damaged or severely swollen batteries according to local hazardous-waste rules.

These practices reduce performance loss, cell imbalance, fire risk, and premature battery failure.

A balance charger controls charging while monitoring the voltage of individual cells through the battery's balance connector.

Charging stages and modes:

• Constant-current stage: The charger supplies a selected current while battery voltage gradually rises.
• Constant-voltage stage: After the target voltage is reached, the charger holds that voltage while current decreases.
• Balance mode: The charger adjusts individual cells so their voltages remain nearly equal, preventing one cell from being overcharged.
• Storage mode: The charger charges or discharges the pack to a manufacturer-recommended intermediate voltage suitable for storage.

Safety functions:

• Cell-count verification
• Reverse-polarity detection
• Charge-current and time limits
• Overvoltage and temperature protection, where supported

The charger settings must match the battery chemistry, cell count, capacity, and permitted charging rate. Incorrect settings can damage the battery or create a fire hazard.

An RGB camera records reflected visible light in red, green, and blue spectral channels. A lens focuses light onto an image sensor, where pixels convert light into electrical signals. Image-processing electronics then create a color photograph or video frame.

Applications:

• Aerial photography and cinematography
• Visual inspection of structures
• Surveying and photogrammetry
• Mapping and three-dimensional reconstruction
• Traffic, construction, and disaster documentation
• Object detection using computer vision

Important parameters:

• Spatial resolution and sensor size
• Focal length and field of view
• Shutter type and shutter speed
• Frame rate
• Dynamic range
• Camera calibration and geotagging accuracy

Limitations:

• Requires sufficient visible illumination.
• Shadows, glare, haze, and changing light affect image quality.
• It cannot directly measure temperature.
• Motion blur and rolling-shutter distortion may occur.

Stable mounting and correct exposure are essential for useful aerial imagery.

A thermal camera detects infrared radiation emitted by objects and converts differences in received radiation into a temperature-related image called a thermogram. Unlike an RGB camera, it does not depend primarily on visible illumination.

Drone applications:

• Search and rescue
• Fire detection and hotspot monitoring
• Electrical and solar-panel inspection
• Building heat-loss assessment
• Pipeline inspection
• Wildlife monitoring
• Agricultural stress assessment

Key considerations:

• Thermal resolution: Number of detector pixels.
• Thermal sensitivity: Ability to distinguish small temperature differences.
• Emissivity: Different surfaces emit infrared radiation differently.
• Atmospheric effects: Humidity, distance, smoke, and weather can affect readings.
• Reflections: Shiny surfaces may reflect surrounding thermal radiation.
• Calibration: Radiometric measurement requires proper calibration and settings.

A thermal image indicates apparent surface-temperature patterns; accurate interpretation requires accounting for emissivity, environment, distance, and viewing angle.

A multispectral camera records images in several selected wavelength bands, commonly including blue, green, red, red-edge, and near-infrared bands. Each band provides information about how a surface reflects electromagnetic radiation.

Healthy vegetation usually absorbs much of the red light for photosynthesis and strongly reflects near-infrared light. This behavior can be represented by the Normalized Difference Vegetation Index:

where and are reflectance measurements from the respective bands.

Processing steps:

1. Capture overlapping, geotagged images.
2. Apply radiometric calibration using a reference panel and light sensor.
3. Align the spectral bands.
4. Generate an orthomosaic.
5. Calculate an index such as NDVI for each pixel.
6. Classify and interpret the resulting map.

Applications: Crop-health monitoring, irrigation planning, disease detection, nutrient assessment, land-cover classification, and environmental surveys.

The appropriate payload depends on the mission. RGB provides visual detail, thermal reveals temperature patterns, and multispectral sensing identifies spectral differences not clearly visible to the human eye. Multiple sensors may be combined when complementary information is required.

LIDAR, or Light Detection and Ranging, measures distance by emitting laser pulses and detecting their reflections.

Operating sequence:

1. A laser source emits a short pulse toward a target.
2. The pulse travels to the target and is reflected.
3. A receiver detects the returning light.
4. Electronics measure the round-trip travel time.
5. The sensor combines repeated measurements with its position and orientation to create a point cloud.

The distance is calculated by:

where is target distance, is the speed of light, and is the measured round-trip time. Division by two is necessary because the pulse travels both to and from the target.

When mounted on a drone, LIDAR data are combined with GNSS and inertial measurements to assign three-dimensional coordinates to points. The resulting point cloud can represent terrain, buildings, vegetation, and other objects.

Advantages:

• Produces accurate three-dimensional point clouds.
• Measures object height, distance, and shape directly.
• Operates without normal daylight because it has an active laser source.
• Some systems obtain multiple returns through vegetation gaps.
• Supports detailed terrain and structural models.

Limitations:

• Higher cost, mass, and power consumption than many cameras.
• Accuracy depends on GNSS, IMU, calibration, and synchronization quality.
• Rain, fog, dust, and highly reflective or absorbent surfaces can reduce data quality.
• Large point-cloud datasets require significant storage and processing.
• Eye-safety requirements must be observed.

Applications:

• Topographic and corridor surveying
• Forestry and canopy analysis
• Power-line inspection
• Construction monitoring
• Mining and stockpile measurement
• Flood modeling
• Archaeological mapping
• Obstacle detection and autonomous navigation

Mission altitude, scan angle, pulse rate, overlap, and flight speed must be selected to achieve the required point density and accuracy.

A gimbal is an electromechanical platform that supports and stabilizes a camera or sensor while allowing controlled rotation.

A three-axis gimbal stabilizes movement about:

• Roll: Rotation about the longitudinal axis
• Pitch: Up-and-down camera tilt
• Yaw: Left-and-right camera direction

Main components:

• Three gimbal frames or axes
• Brushless gimbal motors
• An inertial measurement unit containing gyroscopes and accelerometers
• A gimbal controller
• Camera mounting plate and vibration isolators

Working:

1. The IMU detects angular movement and vibration.
2. The controller compares the measured orientation with the desired orientation.
3. It computes corrective commands.
4. Gimbal motors rotate in opposition to the drone's movement.
5. Closed-loop correction maintains a stable line of sight.

Proper mechanical balance is essential because an unbalanced payload increases motor current, heat, vibration, and stabilization error.

Payload mass: Additional mass requires greater thrust, increases motor current, reduces acceleration, and shortens flight time. It must remain within the drone's rated payload capacity.

Center of gravity: The combined center of gravity should remain close to the intended balance point. An offset causes some motors to work harder, reducing stability and efficiency.

Vibration: Motor and propeller vibration can produce blurred images, rolling-shutter distortion, unstable video, and noisy sensor measurements. Balanced propellers, secure motor mounts, vibration isolators, and suitable shutter settings reduce these effects.

Gimbal balance: The payload should remain nearly stationary at different gimbal angles when the motors are unpowered. Proper balance reduces gimbal motor torque and improves smoothness.

Integration checks:

• Verify clear propeller and landing-gear clearance.
• Secure cables without restricting gimbal motion.
• Recalibrate the flight controller and gimbal when required.
• Perform a low-altitude test flight.

Correct payload integration improves endurance, controllability, safety, and data quality.

Proposed architecture:

1. The main battery feeds a correctly rated connector, anti-spark arrangement if required, and Power Distribution Board.
2. High-current PDB outputs supply the ESCs, which drive the BLDC motors.
3. A regulated power module supplies the flight controller and measures battery voltage and current.
4. Separate regulated rails supply the gimbal, RGB camera, LIDAR, GNSS, and onboard computer according to their voltage requirements.
5. Signal interfaces connect sensors and actuators to the flight controller or companion computer, with a suitable common reference where required.

Power budget:
The required electrical power is:

Each regulator and conductor should be rated above its expected continuous load and capable of handling startup or transient currents. Battery endurance should be estimated using propulsion and payload consumption together.

Protection and reliability:

• Use fuses or current-limited branches where appropriate.
• Provide reverse-polarity and overvoltage protection.
• Filter noisy ESC power and isolate sensitive sensors.
• Select connectors and wire gauges for expected current.
• Provide cooling for ESCs and regulators.
• Secure and insulate wiring against vibration and abrasion.
• Keep power cables away from GNSS, compass, and sensitive data lines.

Before flight, verify voltage levels, current draw, polarity, sensor communication, electromagnetic compatibility, center of gravity, and failsafe behavior.