In considerations of UAV or drone, all parts and equipment are vital to have a smooth and safe flight. Drones with multiple motors are known as multirotors includes Tricopter, Quadcopter, Hexacopter, Octacopter. To understand the basic architecture of building an integrated IoT drone from scratch following parts can be carried out.
Frame is the central hub for a drone. It houses battery, main boards, processors, avionics, cameras, and sensors. To have the best drone for research or target applications, there are some considerations about selecting frame.
Material: In case of frame material, when it is considered as robust, lightweight, and rigid together, carbon fiber is the ultimate king. That is why presently, most of the existing drones are made of Carbon fiber. In case of performance, there is no way around it because of the factors include quality, lay-up, exibility and thickness to the strength of carbon. Besides carbon fiber, there are other three kinds of frames, including plastic frames, wood and metal/fiberglass and pure fiberglass composite.
Shape: The shape of the frame is dictated by the layout of its arms. Following Figure states the different frame shapes of a quadcopter.
There are two types of motors include brushed and brushless. Brushless motors are way more powerful and last longer than brushed motors. In the case of efficiency, brushless motors are typically 85-90% efficient, whereas a brushed DC motor is 75-80%.
Thrust to Weight Ratio: Thrust is the amount of upward force that a motor can produce at the time of full throttle [89]. The amount of thrust a drone generates tells how much the drone can be lifted. The general rule of thumb aims for 2:1 thrust to weight ratio, and the higher ratio, the better obviously.
| Speed | Thrust to Weigh | Uses |
|---|---|---|
| None | less than 1.1 | Paper Weight |
| Poor | 1.1 - 1.2 | Frustration |
| Flyable | 1.2 - 1.5 | Indoor |
| Better | 1.5 - 1.9 | Light Wind |
| Fast | 1.9 - 3.0 | Heavy Wind |
| Turbo | 3.0 - 5.0 | Acro and Racing |
| Rocket | more than 5.0 | Acro and Racing |
| None | less than 1.1 | Paper Weight |
**Size: By determining the frame size, motor size can be obtained how large it should be. Frame size also limits the propeller size, and each propeller requires a different motor to spin it and generate the thrust efficiently KV{Velocity Constant: Motor KV represents the speed at which the motor rotates for every volt applied to the motor. Higher the KV means lower resistance and higher current draw and lower efficiencies. Lower KV means higher resistance and lower current draw, and considerably better efficiencies.
| Frame size (mm) | Propeller size(Inch) | Motor size | Lowest recommended KV | Highest recommended KV | Used Cases |
|---|---|---|---|---|---|
| 150mm and smaller | 3 and smaller | 1306 | 3000 | 4000 | Limited Outdoor/Indoor |
| 150-250 | 4 | 1806 | 2600 | 2800 | Freestyle/Racing |
| 190-220 | 5 and smaller | 2204-2206 | 2300 | 2600 | Freestyle/Racing |
| 220-270 | 6 | 2204-2210 | 1960 | 2300 | Freestyle/Racing |
| 350 | 7 | 2206-2210 | 1450 | 1600 | Long Range |
| 450 | 8 | 2212 | 1000 | 1200 | Long Range |
| 450 and larger | 9 | 2214-2216 | 900 | 1000 | Long Range |
CW and CCW motors: According to the rotational direction, there are two types of motors: clockwise (CW) and counter clockwise (CCW).
A propeller is a structure like rotating fan. Drone propellers provide lift for the aerial vehicle by spinning and creating an airflow, and the consequence creates a pressure difference between the top and bottom surfaces of the propeller. This accelerates a mass of air in one direction, providing lift that counteracts the force of gravity. Propellers always come with a four-digit number like 8045, or 1045, or 6030. Here first two digits represent the propeller's length, and the last two digits present pitch size. Apart from forwarding and backward movement, drones can perform other basic movements through three-dimensional space, and these are described as roll, pitch, and yaw.
An electronic speed controller or ESC is an electronic circuit to vary an electric motor's speed and its direction and possibly act as a dynamic brake. While using a brushless motor, ESC is needed. Brushed motors do not require an ESC, as they operate at DC voltage input. ESC converts DC battery power into 3-phase AC for driving brushless motors.
ESC-Motor Wiring: A Brushless ESC has three wires coming out from it which directly plugs or gets soldered onto the three wires coming from the motor. Following figure illustrates that connecting any three wires will make the motor to spin. But the direction in which the motor rotates depends on the order in which the wires are connected. Matching the three wires from top to bottom will make the motor spin clockwise and swapping any two wires will make the motor to spin in anti-clockwise direction.
LiPo battery is always the auto best choice for drones as its attributes of high capacity and high output current. The nominal voltage of a LiPo cell is 3.7v, and cells are put together in series to increase the voltage, the number of cells used in a LiPo pack is shown by a number followed by the letter S.
| Number of Cells | Battery Voltage | Applications |
|---|---|---|
| 1S | 3.7 | Indoor whoops |
| 2S | 7.4 | 30-75mm micro brushless |
| 3S | 11.1 | 100-220mm brushless |
| 4S | 14.8 | 220mm brushless |
| 5S | 18.5 | 220mm brushless and larger |
| 6S | 22.5 | 220mm brushless and larger |
A Power Distribution Board is also known as PDB what distributes thee essential power from the battery to the drone ESC.
Flight controller is the ultimate brain of any drone. It is an essential hardware hub of circuit boards with particular sensors such as gyroscopes, accelerometers, and several other insignificant but valuable sensors such as barometer, compass and so on. With these functions, one of the primary functions of a flight controller includes receiving and processing the input signals from the receiver and executing appropriate commands given by the users. Some major ight control firmware's widely used in flight controllers include Beta ight, Ardupilot, PX4 Flight Stack, LibrePilot, KISS and RaceFlight.
My aim was to build a drone that can be integrated with IoT as an IoT edge. So, preferences were for a freestyle-based frame which can be crashed with a limited chance of a total write-off.
Considering the factors, I selected Holybro X500 True X shape drone frame of 500mm wheelbase.
I used short shaft brushless 2216 KV880 motors for this drone. The 22 is the width of the stator in mm, and the 16 is the height of the rotor in mm.
Considering all aspects of motor, I selected 1045 propeller. My propeller is 10 inches in diameter. Again, the last the pitch is 4.5 inch.
Battery is the only power source of a drone from where motors strain power. I selected 8000mAh 4s 14.8v 15C specification LiPo battery.
For my drone. I chose BLHeli S 20A ESC with Current: 20A, Burst Current(10S): 30A, LiPo cells: 2-4S.
ESC drains power from the battery through power distribution board or PDB where all the main electrical components will connect. The main things that need to be soldered with PDB are ESCs and battery connector. Our motor current rating is 30A. That means at functional running 4motors will drain 120A of current. In my drone, Power Management PM07 board has been used as PDB, which is developed decidedly for Holybro X500 drone power distribution by Holybro. I have done some solderings on PM07 board so that ESC, battery and other components can be connected easily with plug and play avalibilities. Following Figure illustrates PM07 pdb after soldering.
To connect PDB with battery and ESC, connectors are needed. For plug and play purpose I used XT60 male and female connectors and 10CM Jumper Wire Cable Wire Jumpers Set for Male to Female, Male to Male, Female to Female.
Pixhawk is an autopilot and supports many additional sensors like barometer, magnetometer, accelerometer, and gyroscope. It's a flight control hardware and autopilot software
used in the drone industry. Pixhawk is suitable for running the drone automatically. It is more flexible and reliable when compared to other copter controllers.
For remote controller purpose I used RadioLink AT9S PRO 10 channels 2.4GHz RC. There are two signal working modes, PWM and SBUS&PWM signal output to connect with autopilot. On reciever end, to connect with flight controller telemetry R9DS - RadioLink 9/10 channels should be binded with RadioLink AT9S PRO.
Firmware and software update and configuaration for drone control, QGeoundControl or QGC setup is needed using QT creator.
PX4 is an open source flight control software for drones and other unmanned vehicles. Pixhawk 4 flight controller's airframe, sensors, radio, flight modes, power, ESC and other aspects need to be callibrated in PX4 stack.
The overall mentioned procedue is the process how to build an autonomous drone from scratch. I built this drone for an embedded IoT system. I used this drone as an IoT edge of real-time drone sensory data monitoring and customization with AWS cloud computing for IoT applications. The embedded IoT drone project is summarized here: https://github.com/Shakir74/IoT_Drone