Idea of creating automated aircraft passenger vehicle was developed from entities previous developed for smaller aircrafts.
Drone is aircraft without mechanical moving parts, only moving part is rotor but because it is brushless motor rotor is in magnetic field, and that fact moved the idea that with excellent planning, hardware and software design it is possible to create the most secure flying machine, more secure then car, plane and any other form of transportation.
The main concern of entire development is to have “bulletproof” system that is fully redundant, so that in every moment passenger is safe inside the aircraft. The first question of anyone thinking to fly is about safety and one of the biggest purposes of the document is to show that this is not only possible but also that we have managed to design such system.
The main difference between airplane and drone is a possibility to land vertical and maneuverability. Because of small size and possibility to take off and land from very small space (for e.g. top of the building) drone is in a very big advantage and that is why drone is a future of urban and suburban transportation.
Drone can fly on any legally allowed altitude and with good regulation there can be “infinite” drones on the sky flying on maximum speed and without any path colliding.
Drone is much lighter than standard helicopter, plus it is much quieter. Future production and owning drone like today owning car is possible because of many reasons, the first reason are dimensions and 2nd one is of course production price and access to more widely population. In addition, drone doesn’t pollute environment and like every electric vehicle it is eco-friendly.
Below is a basic introduction and scheme of aircraft hardware with novice explanations
Main part of device is redundant Central computing unit (CCU). CCU has two (2) redundant main computers with controllers and CPUs that communicate among each other and with all sensors, controllers and peripheral systems. Depending of sensors state and calculations system sends signal to each Motor controller that is connected with engine sending PWM signal.
Both main computers communicate with sensors and interface and if data reading shows bad values, redundant system will make sure that device stay active and to perform priority landing. Information about direction, throttle etc. system receives from Interface unit and calculates necessary power of motors. Periphery operations, such as keeping horizontal position and handling with various parasite effects, such as wind etc. are handled directly in CCP, and not over Interface.
Most of information from Sensors that consider integrity of device, such as obstacles avoidance, are handled directly in CCU.
Electronic speed controller (ESC) is a vital part because it controls and regulates the speed of an electric motor. Because of a very strong current (Maximum current of 170A, and max peak current supported of 300A) ESC use very powerful and military grade quality components.
Motor control is based on a six-step commutation sequence. Detection of the magnetic angle of the rotor, to perform the commutation at the correct angle (each step corresponds to an angle of 60 degrees).
Powerful brushless motors connected to ESC controllers are redundant meaning that if any motor have malfunctioning during flight other motor attached on wing is powerful enough to land device safety. Motor and propeller are maximum optimized which generates peak mechanical trust of 79KgF per motor at power of 15.9KW.
Redundant gyro angular sensor is based on the principle of gyroscope, using the real-time output gyroscope angular rate signal, through the high-speed microprocessors to calculate the angular rate, then to calculate the axial deflection angle of up to three simultaneous measurement of axials (X, Y, Z).
Measures of the deflection of moving objects are not influenced by magnetic interference, which can normally measure the yaw angle in the magnetic field regional. Output rate is up to 300Hz, meaning that every 300th of second can send X, Y and Z state. Resolution is 0.1 second of an angle. Connected to main board over RS-232 serial port.
Five radar obstacle avoidance systems. Dual-beam 77GHz millimeter wave radar, with refresh rate (per sensor) of 50ms, distance measuring and scanning up to 120m with accuracy of 0.15m at max speed measurement range of up to 300km/h.
Receives information of up to 50 targets per radar. Not affected by light, weather, environmental, noise, and unmanned aerial vehicle electromagnetic interference.
Altitude and GPS sensors for calculating relative and absolute height are with very small margin of mistake and precise position of aircraft. Altitude sensor is also redundant, and it is highly use during landing, but also for calculating relative height measuring and approximating together with cameras for ground obstacles such as trees, building etc. This is one of the most delicate and sophisticated systems and fast calculations are performed on peripheral CPU.
Main computer is an interface between device and passenger. It has sophisticated system that allows passenger to navigate and monitor all hardware functioning. Main computer has a touch screen with fully UI optimized to easy support commands to main CCU and joystick that enables manual navigation. Passenger can operate drone manually, but it can also flight automatically which is preferable because of optimization and smoothness of flight.
Lithium polymer battery pack of 35KW/h capacity. Extreme high energy density cells (Up to 250Wh/kg). Very high cycle life with more than 2000 cycles.
Fast DC charger rated at 22Kw will charge battery from flat to 80% in less than 2 hours.
In engineering terminology phrase redundancy is used to describe duplication of vital components or functions in assembly in order to increase safety and reliability.
Critical systems can have duplicated or even triplicated parts as a fail-safe backup.
Aircraft design is limited by its weight. Thus, it’s not possible to duplicate parts and leave them passive.
Battery pack is formed in 4 independent blocks and each block supplies motors with 100V current. System doesn’t prioritize any of blocks and tends to drain battery equally meaning that capacity in each block is going to be more or less quite similar.
In case that one of the blocks fails by any reason system other 3 blocks will take function of failed block and aircraft will proceed with emergency procedure. For e.g. if batteries are very low, at only 10% of capacity and when system notice passenger that aircraft will be landed in order to recharge and in that moment if one block stop working 3 batteries will have ¾ of capacity and system will be able to land with 7.5% of battery capacity from any height without any problem. Even if two blocks collapse there will be still energy enough to land safety.
Motors are also redundant but active. There are in total 8 motors on 4 wings or pair of motors per wing. Each motor is enough to replace a pair of motors for safety landing but the reason why system use both motors per wing all the time is because less of energy is required because propeller spin increase also increase power used but not linear but exponentially so system is more optimized with it use 2 motors that are spinning with less speed. In addition, entire aircraft is quieter on lower RPM.
System uses pair of gyroscopes and has additional gyroscope for backup. It uses couple of inclinometers because of accuracy and data compare in order to eliminate border line results.
There is a fail-safe system that gives information about gyro health status and in case that one doesn’t work or shows bad results it signalizes to main system to use 3rd one and to start emergency procedure.
Gyroscopes are the most important devices and that is the reason why system has 3 of them.
Radar sensors and altitude sensors also comes in pairs and actually there are more radars (5) but redundancy is not a primary idea but the most accurate 3D image as possible.
Altitude sensors also work in pair all the time and there is a fail-safe system that communicates with sensors and signalize if any unexpected results occur.
CCU redundancy is very important. CCUs works in pair but only one communicates with ESCs in the moment. Purpose of working in pair is also for data check and parallel calculations, beside the main purpose which is of course fail of one system which would be fatal.
Software that communicates between CCU is a highly sophisticated and the most important thing of entire development is to make “bullet proof” and theoretically uncompromisable system (!) Passive redundancy, except on lightweight modules (such as additional gyro) is not acceptable.
Aircraft chassis is mainly construct of carbon fiber. Carbon fiber is a light material composed of carbon atoms bonded together to form a long chain. It is extremely strong and benefit of a material in terms of strength to weight ratio and stiffness to weight ratio, compared with steel or aluminum is significant. Particularly in structural design, where in this case added weight may translate into lower performance. Transparent surfaces (windows) are made from 4 to 6mm very hard acrylic, resistant to physical and chemical damages, with much less weight then glass.
In order to save space wings are foldable and below images show dimensions of unfolded and folded aircraft:
Drone flight and stability is based on software, it is not possible to even a lift a drone manually.
Equally spinning propellers won’t lift drone vertically because air has different properties, density and speed, which requires different trust on wings. That is why system needs fast recalculation about device position and to change trust on motors depends of angle and position.
That is why essence of device stability and fly performances is quality software.
CCU is a hearth of system because it receives complete information from all sensors and attached devices and communicates with motors over ESCs. Thus, software that runs on CCU has to be “bullet proof”. There is no OS running on CCU, low level code is executed directly on controller.
Each part of system is paired, because of necessary redundancy. CCU is paired as well, receiving parallel the exact information from sensors and attached devices. Paired software communicates among CCUs and in case that processed data and results are different system performs deep integrity check.
Theoretically not more than 10ms is necessary for system to detect malfunction of some part and automatically inform pilot about it or perform emergency landing if it’s necessary.
Peripheral software has various purposes. Vitality of peripheral software is also very important that is why low level code is also execute on basic controller, but it monitors devices that are not life compromised such as merging signals from all radars and creates 3D image of obstacles in real-time. System also monitors gyroscopes and calculates XYZ-axis but for control purposes only; the same is with GPS devices that are connected on separate PCB that communicates with Main computer.
Main computerMain computer is not redundant and software that runs on Samsung S5p6818 chip under Linux is an interface only. Software is very advance in term of features such as sensor monitoring and displaying, maps and navigation, aircraft status, camera options and recording etc. It is very tested and made of top quality components but the reason why this is only non-redundant system is because aircraft safety is not jeopardized with main computer malfunction.
Code for aircraft stability, landing and other crucial operations is in CCU.
PCBs among each other and sensors communicates over various protocols such as RS232/RS485, CAN/UART, etc. where latency is almost none.
ESC (electronic speed control) is an electronic circuit used to change the speed of an electric motor, its route and also to perform as a dynamic brake. By adjusting the duty cycle or switching frequency of the transistors, the speed of the motor is changed. The rapid switching of the transistors is what causes the motor itself to emit its characteristic high-pitched whine, especially noticeable at lower speeds.
There are several types of ESC depending on the power rating. As example 25A or 30A versions. But the main purpose of this custom made ESC is to make it more powerful than the traditional ESCs found on the market.
So, one of the main questions knock at the first, why we need to use custom made ESC, where you can find several type of ESCs in the market.
The answer is really simple. We need to make robust military grade product which can support the powerful motor that we are using in this project.
There are two major part that we have to keep in mind to complete the ESC
Here are some insights about the hardware and firmware.
One of the main concerns to make the custom ESC is to use military grade product and failsafe (~) hardware design.
With the traditional working principle, in this hardware a powerful microcontroller will be incorporated. The main concern of this custom-made ESC is to feed power in most efficient way to the chosen motors.
To work the hardware correctly and efficiently, firmware is the key thing.
The firmware can be divided into two main parts.
The ESC will work with the PWM signal.
Like the traditional system, the ESC works with the 50Hz PWM signal. The pulse width modulation will vary from 1ms to 2ms.
The 1ms pulse width will stop the motor and the 2ms pulse width will rotate the motor at 100% speed.
There are several types of ESCs are available in the market. But by viewing the importance of the safety, the power limit and the efficiency, it becomes very important to make the custom designed ESC. The ESC is able to deliver enough power to drive the motor. The main goal is to make a military grade product which will failsafe (~) and much more efficient than the available ESCs for the chosen motors.
Max current of 200A (Peak current 300A)
Voltage 40-100V
Signal frequency above 50-500Hz
Length / Width / Height 150 x 74 x 44mm
Weight 640grams
ESC has protections from Over-load, Over-heat, Over-current, Abnormal input values protection, Throttle lost protection and stall protection.
Goal is to reach almost theoretical optimization of a brushless direct-current (BLDC) motor and propellers attached; to test various combination of attached propellers and to see which produces the most efficient solution.
Fundamental Physics Electric motors transform power from the electrical domain to the mechanical domain using magnetic interaction. In a BLDC motor, this magnetic interaction occurs between coils of wire on the stator (stationary part), permanent magnets on the rotor (rotating part), and the steel structure of both. A single wire carrying current in a uniform magnetic field sees a force exerted on it, called the Lorentz force:
F = IL x B
Where I is the vector current flowing through the wire (direction is important), L is the length of the wire, and B is the magnetic field vector
The direction a propeller rotates when viewed from aft facing forward:
| RPM | Angular speed [rad/s] |
Linear speed of Tip 50" Prop 60 | |||
| 50" Prop | 60" Prop | ||||
| [m/s] | M speed | [m/s] | M speed | ||
| 500 | 52.359878 | 33.249 | 0.097 | 39.898 | 0.116 |
| 1000 | 104.719755 | 66.497 | 0.194 | 79.796 | 0.233 |
| 1500 | 157.079633 | 99.746 | 0.291 | 119.695 | 0.349 |
| 2000 | 209.439510 | 132.994 | 0.388 | 159.593 | 0.465 |
| 2500 | 261.799388 | 166.243 | 0.485 | 199.491 | 0.582 |
| 3000 | 314.159265 | 199.491 | 0.582 | 239.389 | 0.698 |
The max. speed of 50“and 60“propeller is subsonic.
Therefore, no need for additional modification of the Airfoils as transonic region is out of reach.
However, the compressibility of air will occur at:
Beyond this speed-limit the air will be gradually compressed, therefore more turbulent and noisy
T: Thrust [N]
D: Propeller Diamater [m]
Q: Torque [Nm]
n: Rotations [rev/s]
ρ: Density [kg/m3]
V: Freestream [m/s]
Thrust Power ratio can be used as a comparison value among different propellers that indicates what thrust is provided at specific RPM.
| RPM | Angular speed [rad/s] |
Thrust [N] |
Thrust [KgF] |
Torque [Nm] |
Density? [kg/m3] |
Rotations [rev/s] |
Propeller Diameter [inch] |
Propeller Diameter [m] |
Freestream [m/s] |
Torque Coefficient [CQ] |
Power Coefficient [QP] |
Advance Coefficient [Cj] |
Thrust Coefficient [CT] |
Propeller Efficiency |
Machanical Power [W] |
Power Efficiency [kgF/W] |
| 1000 | 104.720 | 97.139 | 9.905 | 8.789 | 1.196 | 16.667 | 60 | 1.524 | 5 | 0.003217999 | 0.020219286 | 0.196850394 | 0.054203219 | 0.528 | 920.382 | 0.0108 |
| 1500 | 157.080 | 250.021 | 20.495 | 20.526 | 1.196 | 25.000 | 60 | 1.524 | 5 | 0.003340168 | 0.020986894 | 0.131233596 | 0.062004816 | 0.388 | 3224.217 | 0.0079 |
| 2000 | 209.440 | 472.446 | 48.176 | 36.890 | 1.196 | 33.333 | 60 | 1524 | 5 | 0.003376721 | 0.021216562 | 0.098425197 | 0.065905800 | 0.306 | 7728.224 | 0.0062 |
| 2500 | 261.799 | 763.480 | 77.854 | 57.791 | 1.196 | 41.667 | 60 | 1.524 | 5 | 0.003385530 | 0.021271913 | 0.078740157 | 0.068163063 | 0.252 | 15129.648 | 0.0051 |
| 3000 | 314.159 | 1122.863 | 114.501 | 83.223 | 1.196 | 50.000 | 60 | 1.524 | 5 | 0.003385691 | 0.021272925 | 0.065616798 | 0.069617053 | 0.215 | 26145.277 | 0.0044 |
| RPM | Angular speed [rad/s] |
Thrust [N] |
Thrust [KgF] |
Torque [Nm] |
Density? [kg/m3] |
Rotations [rev/s] |
Propeller Diameter [inch] |
Propeller Diameter [m] |
Freestream [m/s] |
Torque Coefficient [CQ] |
Power Coefficient [QP] |
Advance Coefficient [Cj] |
Thrust Coefficient [CT] |
Propeller Efficiency |
Machanical Power [W] |
Power Efficiency [kgF/W] |
| 1000 | 104.720 | 69.477 | 7.085 | 6.110 | 1.196 | 16.667 | 60 | 1.524 | 5 | 0.002237112 | 0.014056188 | 0.196850394 | 0.038767921 | 0.543 | 639.838 | 0.0111 |
| 1500 | 157.080 | 190.715 | 19.448 | 14.616 | 1.196 | 25.000 | 60 | 1.524 | 5 | 0.002378442 | 0.014944190 | 0.131233596 | 0.047297021 | 0.415 | 2295.876 | 0.0085 |
| 2000 | 209.440 | 368.720 | 37.599 | 26.456 | 1.196 | 33.333 | 60 | 1524 | 5 | 0.002421646 | 0.015215651 | 0.098425197 | 0.051436115 | 0.333 | 5540.932 | 0.0048 |
| 2500 | 261.799 | 598.486 | 61.029 | 41.473 | 1.196 | 41.667 | 60 | 1.524 | 5 | 0.002429584 | 0.015265527 | 0.078740157 | 0.053432492 | 0.276 | 10857.606 | 0.0056 |
| 3000 | 314.159 | 881.638 | 89.902 | 59.713 | 1.196 | 50.000 | 60 | 1.524 | 5 | 0.002429254 | 0.015263451 | 0.065616798 | 0.054661210 | 0.235 | 18759.392 | 0.0048 |
| RPM | Angular speed [rad/s] |
Thrust [N] |
Thrust [KgF] |
Torque [Nm] |
Density? [kg/m3] |
Rotations [rev/s] |
Propeller Diameter [inch] |
Propeller Diameter [m] |
Freestream [m/s] |
Torque Coefficient [CQ] |
Power Coefficient [QP] |
Advance Coefficient [Cj] |
Thrust Coefficient [CT] |
Propeller Efficiency |
Machanical Power [W] |
Power Efficiency [kgF/W] |
| 1000 | 104.720 | 56.846 | 5.797 | 4.863 | 1.196 | 16.667 | 50 | 1.270 | 5 | 0.004430543 | 0.027837925 | 0.236220472 | 0.065774317 | 0.558 | 509.252 | 0.0114 |
| 1500 | 157.080 | 149.065 | 15.200 | 11.362 | 1.196 | 25.000 | 50 | 1.270 | 5 | 0.004600711 | 0.028907122 | 0.157480315 | 0.076656609 | 0.418 | 1784.739 | 0.0085 |
| 2000 | 209.440 | 281.569 | 28.712 | 20.432 | 1.196 | 33.333 | 50 | 1.270 | 5 | 0.004653756 | 0.029240411 | 0.118110236 | 0.081448161 | 0.329 | 4279.268 | 0.0067 |
| 2500 | 261.799 | 455.235 | 46.421 | 32.103 | 1.196 | 41.667 | 50 | 1.270 | 5 | 0.004679703 | 0.029403443 | 0.094488189 | 0.084277582 | 0.271 | 8404.546 | 0.0055 |
| 3000 | 314.159 | 670.868 | 68.410 | 46.377 | 1.196 | 50.000 | 50 | 1.270 | 5 | 0.004694754 | 0.029498011 | 0.078740157 | 0.086248392 | 0.230 | 14569.764 | 0.0047 |
