Construction of a Tricopter Drone capable of being suspended without human intervention

  

Before you start constructing the Tricopter have in mind that it is not an easy thing to accomplish. the degree of difficulty is not same as the simple drones. It needs many hours of adjusting and experimenting to be a reliable flying drone. At the end, you will realise that after many experiments, it is certainly evident that the final model of the tricopter is far from that of the first experiments. Existing external forces that inevitably act on the vehicle in the experimental devices affect both the system that the difference in experimental PID parameters or the control sensitivity from the radio direction is appreciably high compared to those required in the actual final model.

 

tricopter drones

 

However, these experiments allowed the safe exploration and study of objects around the vehicle construction, which contributed significantly to their understanding, so that later problems could be solved in the actual model. For example, the Ziegler-Nichols method applied helped to understand how each parameter of PID affects the tricopter. Telemetry is an irreplaceable tool that offers real-time supervision and control. Also, allowing the user to change the PID parameters, even without stopping flight or some other test, saves too much precious time. In addition, saving telemetry data for later study helps to study them in a user-friendly time, to identify errors and to better understand the situation.

Fine tuning is necessary for the optimal flight of such a vehicle, but quite difficult to achieve. Still, handling such a vehicle is particularly difficult for the novice, uninitiated user. Practicing flight simulators of flying RCTs is very helpful and useful in these situations. As it is a fragile construction, some kind of protectors for the vehicle are proposed, mainly around the motors, as the propellers are extremely easy to destroy in a fall, as well as at the bottom of the vehicle where the battery is located, can become quite dangerous in cases of impact, causing even complete destruction on the vehicle. These protectors should be as light and durable as possible.

Several minor accidents are almost impossible to avoid, so all electronic components must be well protected and insulated. During the development of the tricopter due to some drops, short circuits were created that initially destroyed the first IMU (Sparkfun 9DOF Razor), requiring the purchase of a new IMU, and re-designing the electronic circuits of the tricopter. In a later fall, the ESC (electronic speed controller) of a single motor was destroyed, causing some months to be delayed until the new ones were received and the tricopter was reset.

Quality materials, pieces of construction or electronic parts, have a clear difference with the modest quality, help the project to move faster and suffer less damage. For example, the first inexpensive servomotors did not withstand the great forces that developed at various falls, where they were replaced by a servo, with metal gears, that withstood much more.

In the first stage of construction, 11mm carbon fiber tubes were used for the ends of the tricopter. After several tests, it became clear that the cylindrical tubes are disadvantaged against the squares in terms of their support to the tricopter body as well as the support of the motors at their edges. They were therefore replaced by square aluminum tubes, which had the added benefit of greater fall strength by adding a minimum extra weight. Later, as there was a need for larger edges, for additional protection on the motors and propellers, they were replaced with P-shaped aluminum tubes. These, without losing robustness, allow easier access to the screws supporting the motors as well as the access of their cables.

 

Upgrade Options

The range of possible upgrades in the tricopter is actually huge. Initially, a GPS receiver can give the location of the vehicle on the map as well as assist in its stability. Knowing the real-time position of the vehicle also enables us to develop applications and is the first step in making vehicle use as mentioned above. The most common upgrade of such a vehicle is to place a camcorder on its body. This will allow the user to fly the vehicle outside of his field of vision, as well as capture images and videos from the area where the vehicle is or is being sent.

An additional upgrade is the installation of sensors such as ultrasound or laser, with which can be counted on the distances of the vehicle, and with appropriate mapping of the area on which the vehicle is flying. Finally, depending on the intended use of the vehicle by the user, such materials and sensors can be used, giving you great personalization capabilities and meeting the needs of our basic model of construction.

 

Operating Principles

The tricopter consists of the following main parts:

● The Y-shaped skeleton, on which all other parts are supported
● Three motors, one at each end of the frame, accompanied by the corresponding propellers.
● A servo for changing the rear engine tilt
● Two AVR microcontrollers on separate arduino platforms
● An IMU - Inertial Measurement Unit, with three-axis accelerometer and gyro respectively
● A wireless communication board and antenna
● A battery

 

Features and specifications

The characteristics of the tricopter depend on the user's requirements. An 8-bit microcontroller is sufficient for simple operation, but systems have also been developed in which data processing, control and all the necessary calculations are performed on high-speed terrestrial computers. Regardless of these, there are specifications that must be met by designing and constructing a tricopter to be able to fly satisfactorily, especially when it comes to indoor flights. These specifications are:

● Its small weight. Although it is something that is influenced by many factors, the weight of the tricopter must be kept as low as possible so that it has longer and longer flights. The usual weight of a tricopter is about one kilo. Achieving this goal is done by constructing its skeleton with the lightest and as few materials as possible, without endangering its stability as a whole.

● Flight duration. It usually does not exceed twenty minutes, this time varying according to weight, total battery capacity and type of flight, which can consume the battery faster.

● The flight radius relative to the base station. Depending on the type and power of the selected transmitter and receiver, the tricopter flight range can be changed dramatically.

● Degree of autonomy. This depends on the need for the tricopter in each application, but also the amount of money available for construction. Greater degree of autonomy, involves more, more accurate and more expensive sensors, as well as possibly a more expensive base station. Conversely, if a small degree of autonomy meets the needs of the application, a simple remote control and a fairly expensive IMU, have significantly lower costs.

 

Degrees of freedom and way of movement

To describe the rotational movements of the tricopter we rely on the Euler angles. For the Euler angles we use the letters A, B and C, which correspond to the yaw, roll and pitch. Angle B (roll) corresponds to the axis of rotation affecting M2 and M3. The angle C (pitch) on the axis affecting M2 and M3 combined and M1. Finally, the angle A (yaw) corresponds to the axis affected by the power of all three motors and the slope of M1. The system has a fixed center center of the tricopter with a unit of measurement of degrees.

 

Euler angles

 

Thus, each motor affects the change of all axes, which makes the system quite complicated. Overall, our system has six degrees of freedom, influenced in many cases. For example, the change in the angle B of the X axis is dependent on the power difference between M2 and M3. This change also results in a change in the spin that they apply to the tricopter. Therefore, a change of the Z-axis angle A. Correspondingly happens with the angle C of the Y-axis. Finally, the angle A is influenced by the power of all three motors due to their spin. The stabilization of this axis is achieved by the ability of M1 to alter its slope. The height of the tricopter is adjusted by the power of the three motors.

The control of the tricopter is performed through four variables:

● Throttle: the power of the motor that allows us to control the height of the tricopter.
● Pitch: Proper inclination of the tricopter along the Y axis, resulting in the forward or reverse movement.
● Roll: Proper inclination of the tricopter along the X axis, resulting in the right or left movement.
● Yaw: Reversal of rear engine tilt, resulting in tricopter rotation.

So it seems that we need to control six degrees of freedom with four variables. This makes our system under actuated. Changing the power of a motor changes more than a degree of freedom. This is a very dynamic system with very small, opposing forces. The forces opposing the movement of the tricopter come from gravity, inertia and air resistance.


Gravity opposes the elevation of the tricopter and is the most powerful of the three, making it the main energy consumption for the successful flight of the tricopter. Inertia acts in all directions that the tricopter can move, but mainly in the horizontal, although the speeds developed by such a vehicle are usually not great. Finally, air resistance dampens the linear and rotary movements of the tricopter, but wind gusts can move it or even make it out of balance.

 

Tricopter control algorithm

Checking the tricopter is done using PID controllers for its stability and with user inputs that change the setpoints of the controllers resulting in its movement. In particular, the tricopter tilt angles enter the PID algorithm that maintain stability by keeping the tilt angles at zero degrees or otherwise where the setpoint is set by the user.

The PID algorithm for roll and pitch takes the respective setpoints from the controller, which have already been converted from ms pulse to angles of angles. This variable is subtracted from the actual angle given by the IMU, producing the error. Through this, the PID calculates the appropriate output, which is sent to the motors.

The PI algorithm for the yaw receives its own setpoint by the user, this time its value is preserved in ms pulse, simply by subtracting 1500 ms, a value corresponding to the middle position of the lever. This variable is subtracted from the angular velocity of the Z axis, causing the error. From this value, PI calculates the appropriate output to a value ready to be sent to the servo by varying the inclination of the rear M1 motor, thus adjusting the angular velocity.

 

Design of the Body

Based on the above, the study was conducted for the manufacture of tricopter. Parameters were studied that would affect both the physical construction itself and the necessary code for the successful flight of the vehicle.

Initially, a first body design of the vehicle was made and then transferred to AutoCAD so that the necessary pieces can be cut into a borehole. By choosing PCB as a material for this purpose, we managed to make the central hull of the vehicle light, without sacrificing its robustness. Another possible material to use was plexiglass, which, however, to have the same firmness, had to be thicker and eventually rejected. Thus the final materials selected were dominated by PCB and aluminum. After some possible designs, the simplest and most functional was chosen.

 

tricopter body

 

After research into unmanned flying vehicles of similar capabilities, the selection of the necessary materials began. Appropriate electronics and mechanical parts had to be selected prior to cutting the raw materials of the hull to avoid the need to redesign the vehicle from the start. These parts were chosen in accordance with their necessity for the successful completion of their construction, their cost, their ease of use and their adaptation to the needs of the final product, the quality of construction and proper operation without problems and in some cases their weight and size. Another important part of the choice of materials was the compatibility between them without the intermediary intermediation.

At the same time, the final size of the vehicle was adapted to the needs of the materials it would accommodate and designed to allow us to maintain it in a size that would not burden the cost or give unnecessary weight. It would also be stable and resistant to possible falls, while protecting sensitive materials such as battery and electronic / digital systems, but also allowing work on it with relative ease. The many levels created helped significantly in this. The design was completed and cut and used.

The piece of material with the greatest need in study was the rear system of change in the angle of the relevant motor. As it was the only moving part of the construction, with several fine features and a great risk of destruction in the event of a fall, it had to receive the most attention. There have been several changes during the tests on it, especially after the first fall of the vehicle, where the original construction weakened to withstand the impact. An extensive study was also carried out on the non-material part of the construction.

After the necessary research, the appropriate software was selected to be used to create the necessary programs. Arduino and processing platforms have dominated the ease of use, cross-platform capability and the large active community they have developed. They were used as the end of the construction, although there were tests of other options, such as Atmel's AVR studio for microcontroller programming and Microsoft's Visual Studio for telemetry application programming.

There was also a block diagram of the connection of the materials to each other. This pattern has changed over time when some materials have been replaced. The final is shown in the figure below.

 

block diagram of tricopter

 

Construction Plan

For our drone we will use these two types of microcontrollers Arduino Mega 1280 and Arduino Pro Mini. Arduino for the few ones that don't know, is a computing platform based on a simple motherboard with built-in microcontroller, has inputs/outputs and can be programmed with the Wiring language , Which is a differentiated version of the very successive C++. Arduino can be used to develop independent interactive objects but also to connect to a computer through programs such as Processing, Max / MSP, Pure Data, SuperCollider.

 

An Arduino board consists of an Atmel AVR microcontroller (ATmega328 and ATmega168 in later versions, ATmega8 in the older ones) and complementary components to help the user to program and integrate into other circuits. All boards include a 5V linear voltage regulator and a 16MHz crystalline oscillator (or ceramic resonator in some variations). There is a very well detailed tutorial about Arduino to study here.

 

arduino mega 1280

 

The microcontroller is factory-programmed with a bootloader so that no external programmer is needed. Generally, all boards are programmed via a serial RS-232 connection, but the way this is implemented varies depending on the version. The Arduino serial boards contain a simple reversal circuit for converting between the RS-232 and TTL levels. The Arduino boards currently on the market are programmed via USB, using a USB-to-serial adapter chip such as the FTDI FT232. Some variations, such as the Arduino mini and the unofficial Boarduino, use a USB-to-serial adapter in the form of a board or cable.

The Arduino board has most exposed I/O contacts for use with other circuits. Diecimila, for example, provides 14 digital input/output contacts, of which 6 can produce PWM signals, and 6 analogue inputs. These contacts are available on the top of the board via 0.1 inch female connectors. Various plug-in application boards known as "shields" are also commercially available. Arduino-compatible Barebones and Boarduino boards have male contacts on the underside of the board to allow them to connect with unneeded boards.

 

arduino pro mini

 

Two Arduino microcontrollers are used in our Drone. The first is an Arduino Pro Mini which, through the I2C protocol, accepts sensor values ​​and uses a quaternions-based DCM filter to convert these values ​​to the tricopter's 2-axis tilt angles and sends them through a serial port to the Arduino mega. The second is an Arduino Mega 1280, which adopts the tilt angles, applies code for three PIDs, one for each axle and sends the appropriate values ​​to the three brushless motors of the vehicle, as well as the servo motor that defines the angle of inclination of the M1. It is also responsible for identifying commands from remote control as well as sending telemetry to the computer via the serial port.

The reason why two microcontrollers were used is the lack of specific arduino mega sockets to read sensor values ​​as these receptors are responsible for the hardware interrupts used to read the values ​​from the redirection.

 

Sensors

The board used in the final version of the vehicle is the Drotek which uses the MPU-6050 chip. It is a board that incorporates a three-axis digital gyro, a three-axis digital accelerometer as well as a microcontroller, all in a closed architecture chip. The built-in microcontroller takes measurements from the sensors and applies a digital DCM filter to give the exact tilt angle on each axis. The sensor communicates with the second microcontroller of the tricopter with the I2C protocol by sending values ​​that the microcontroller analyzes and gives us the angles of inclination of the X and Y axes as well as the gyroscope value for the Z axis.

 

MPU-6050 sensor

 

In the early stages of construction, Razor 9DOF was used by Sparkfun. This particular sensor included a separate three-axis accelerometer, a two-axis gyroscope for the front/rear and lateral inclination, one axis gyroscope for horizontal rotation, and a three-axis magnetometer. It also contained an ATMEGA 328 microcontroller that received the values ​​from all sensors and with a DCM filter it calculated the angles of the X and Y axes. Then it sent through the serial port the values ​​of the angles of these two axes and the gyroscope for the horizontal rotation, as well as the magnetic direction of the vehicle. The Razor 9DOF has to be replaced when the vehicle has suffered a serious damage that has rendered it inoperable.

 

Razor-9DOF

 

Gyroscopes

Gyroscopes are angular velocity measuring devices. The usual unit is the degrees per second. Historically, the gyroscopes began as a game, but in the course of time scientists began to work on this subject, discovering its potential, developing it into a navigational, aviation and civilian and civilian tool for sustainability and stability.

The instruments that originally used gyroscopes were bulky and heavy. Industries, however, slowly built smaller and smaller appliances weighing only a few grams. Nowadays gyroscopes meet in the form of MEMS - Microelectromechanical Systems. There are plenty of companies that manufacture and distribute MEMS boards, others with gyroscopes and other IMU or AHRS types, including accelerometers and magnetometers, as well as on-board microcontrollers. On these boards you can meet MEMS with one, two or three axes gyroscopes, with the latter gaining ground on the market due to the offer of totally more integrated possibilities at very low weight and cost.

 

gyroscope

 

An important feature of a gyroscope and its selection criterion for the intended application is the choices it offers with regard to its analysis. This is expressed in degrees or radians per second, which corresponds to how fast the sensor can perceive. Typically, for use on multicopters, preferred values ​​are between ± 100◦ / s and ± 300◦ / s. The MPU-6050 used in the tricopter has four sensitivity settings that the user can select: ± 250◦ / s, ± 500◦ / s, ± 1000◦ / s and ± 2000◦ / s.


The main disadvantage of the gyroscopes, is the phenomenon of slip or drift. This phenomenon prevents the exclusive use of gyroscopes for vehicle stability, since after some time the deviation of the measurements will change the originally considered zero point, resulting in the necessary setpoint for maintaining stability. This is shown by laboratory measurements being carried out and while the sensing output value should remain zero during the resting state, there is a slow, gradual change in time. Complementing the measurements with those of an accelerometer and the appropriate filters, we can greatly reduce this slip.

Another disadvantage of gyroscopes is their sensitivity to vibrations. This can be a problem in a tricopter, as the three motors, taking into account the change of one's inclination, can create vibrations in the body of the vehicle. To reduce this noise, the MPU-6050 is mounted between a soft shock absorbing material that protects it from of the vibration.

 

mems gyroscope axis

 

Accelerometers

The Accelerometer is a sensor that measures acceleration, that is, the change in speed in time and is a vector value (it has direction and size).

Accelerometers measure in units g, one g is equal to the acceleration of gravity, ie 9.81m / s². Accelerometers have evolved from simple tubes with an air bubble into integrated circuits. Accelerometers can measure: vibrations, impacts, tilt and motion of an object.

 

analogue accelerometer designed by Sandia National Laboratiories

 

Accelerometer Types:

There are several types of accelerometers. What differentiates the species is the sensing element and its operating principles.

Capacitive capacitive meters measure a change in electrical capacity in relation to acceleration. This accelerometer detects the change in capacity between a static state and a dynamic position. Piezoelectric accelerometers use materials such as crystals, which produce electrical voltage from an applied force. This is known as piezoelectric effect.

The strain gauge works by measuring the difference in electrical resistance of a material when it deforms slightly when some force is exerted.

Hall Effect accelerometers measure voltage changes resulting from changing the magnetic field around the accelerometer.

Magnetostatic accelerometers operate by measuring changes in magnetic field resistance. They are quite similar in structure and function to Hall Effect accelerometers, but they only measure changes in resistance rather than voltage.

Heat transfer accelerometers measure changes in temperature transfer due to acceleration. A heat source is located in the center of a cavity, and the thermoresistances are shared on the walls. In zero acceleration mode the heat gradient will be symmetrical. With any acceleration, the heat gradient becomes asymmetric due to heat transfer.

MEMS Based Microsystems (MEMS): MEMS technology is based on a set of tools and methodologies used to form small structures with micrometer scale dimensions (one millionth of a meter). This technology is now used to build ultra-modern accelerometers.

Uses of accelerometers:

From industry to education, accelerometers have many applications. These applications range from activating the airbag to monitoring nuclear reactors. There are a large number of practical applications for accelerometers. Accelerometers are used to measure static acceleration (gravity), object tilt, dynamic acceleration, knocks on an object, speed, orientation and vibration of an object. Accelerometers are becoming increasingly ubiquitous. They are now in mobile phones, computers, and even in laundries.

 

adxl335

 

Choosing an accelerometer:

When choosing an accelerometer for an application, the first factors to take into account are:

 

1. Dynamic Range: is the +/- maximum acceleration range that can be measured before deforming or locking the generated signal. The dynamic range is usually measured in g.

2. Sensitivity: Sensitivity is the scale factor of a sensor or system, which is measured in terms of the change in the output signal per change in the measurable input. Sensitivity refers to the ability of the accelerometer to detect motion. The sensitivity of the accelerometer is usually determined in millivolts per g (mV / g).

3. Frequency response: Frequency response is the frequency range for which the sensor will detect movement and will report a true output. The frequency response is usually defined as a range measured in Hertz (Hz).

4. Sensitive axis: Accelerometers are designed to detect acceleration with respect to one axis. Single Axis Accelerometers can only detect entrances at the same level. Three-axis accelerometers can detect inputs at any level and are needed for most applications.

5. Size and Mass: The size and mass of an accelerometer can alter the characteristics of the object under consideration. The mass of the accelerometers should be significantly less than the mass of the system being measured. The drawback of accelerometers when they are applied to flying vehicles such as the tricopter of this paper is that when the vehicle moves horizontally, the accelerometer of the analog shaft will exhibit non-zero values ​​just as when inclined to the same side. The accelerometer itself as a sensor can not know what is going on, the use of the gyroscope helps it, so one sensor corrects the weaknesses of the other.

 

Motors

The vehicle has three three-phase DC Brushless outrunner motors that drive three propellers. The Brushless DC motor is a Permanent Magnet Synchronous Motor, and it is powered electronically using a three-phase power inverter (Electronic Speed ​​Controller or ESC). These motors have the best performance as they minimize losses due to lack of friction; the "carbon brushes" known to classic DC motors do not exist in DC Brushless motors.

 

The selection of these engines was based on comparative tests between different engines that featured the chosen ones.

 

A20-22L motor

 

Electronic Speed ​​Controller

For each engine in our vehicle, we need a circuit that converts 12 volts of DC to three-phase alternating current frequency to turn the motors to the turns we want. These circuits receive a squared servo pulse from our microcontroller and output exactly the appropriate three-phase voltage required per case. In our case we use 3 controllers, up to 20A, one for each brushless motor. In the first design phase of Tricopter, an ESC of up to 40A resistance was chosen for maximum durability, but was ultimately unprofitable due to size and weight.

 

skywalker 20a Speed ​​Controller

 

A servomotor precisely controls the inclination of the rear motor to compensate for the torque and to change the direction of the vehicle. Servomotors are essentially servo-actuators with closed feedback circuitry to preserve precisely the desired angle. They have a gearbox to provide enough torque to maintain the angle even when relatively large forces are exercised.

 

md933 servo motor

 

Pulse Width Modulation

Pulse width modulation (PWM) is a technique for controlling analog circuits with the digital outputs of a microcontroller. PWM is used in a wide variety of applications ranging from measurements and communications to power control.

By controlling analogue circuits in a digital way, cost and energy consumption can be drastically reduced. Also, many microcontrollers already include onchip PWM controllers, making it easy to implement.

In short, PWM is a way of digitally encoding the level of an analog signal. Through the use of high resolution meters, the square pulse cycle is configured to encode a specific analog signal level. The PWM signal is still digital because at any given time, the DC signal is either "1" (on) or "0" (off). The voltage or current source is supplied to the analog load via a recurring series of pulses "0" and "1".

The following figure shows three different PWM pulses. In the first part of the image we see a pulse with a 10% duty cycle, ie the pulse is "1" for 10% of the total pulse time. Correspondingly in the next 2 pieces we see pulses with 50% and 90% duty cycle.

The pulse frequency varies depending on the application. For the intensity of radiation of a incandescent lamp a frequency of 10Hz is sufficient. Most loads require much higher frequencies for the PWM pulse. Servo motors used in modeling as well as ESC bushless motors need a specific PWM range to operate. The frequency must be 50Hz, ie have a 20ms period and a 5-10% duty cycle. At 5% duty cycle, they are left at the left and 10% are at the right end, ie with 1ms and 2ms respectively. The long empty time throughout the pulse period allows for a very easy multiplexing of up to 9 servo signals on a communication channel, allowing money to be saved. Signals resulting from servo signal multiplex are called PPM (Pulse Position Modulation).

 

Propellers

In our vehicle we use 10 inch long propellers, and 4.5 inches per rotation, 2 right-handed and one left-handed to reduce the total torque to ⅓, with all the propellers being in the same direction of rotation.

 

propelers

 

Initially, propellers with 8 inches long and 6 inches tilter per revolution were placed in the vehicle. Unfortunately, such helicopters with a large slope relative to their length do not fit into helicopters, as they generate winds that absorb substantially the most energy from the engine. The result of this is that there is not enough thrust to be able to offset the weight of the weight, so the vehicle loses abruptly height without any obvious reason for the observer / pilot. The relevant term in aviation is "stalling".

 

Remote direction

A radio-directional system consists of a transmitter and a receiver, and is responsible for transferring the operator's instructions to the vehicle. It has eight "analog" channels, that is, it can send up to eight square pulses to various motors, servomotors, etc. To meet the vehicle's handling needs, five of the eight available channels are used, one to control the power of the motors, For the direction, two for the inclination of the horizontal axes, and finally we send the status of a switch, which can be switched off at any time in the event of an emergency. There are two ways to communicate with the receiver, PCM (Pulse code modulation), and PPM (pulse position modulation).

In PCM, the value of each variable is sent as a digitally encoded number. Each manufacturer uses its own encoding, with a different degree of accuracy, eg 9bit for 0-511, 10bit for values ​​between 0-1023 or even 11bit for values ​​of 0-2047. The PCM includes a check sum at the end to verify that all values ​​have been taken correctly. In the event of a transmission error, there is a safety valve to give a predetermined value, or the last valid value.

 

turnigy 9xr pro transmitter and receiver

 

In PPM the values ​​of the variables are sent as variable length pulses in the series. It is what was used in this diploma because the cost difference was significant without much difference in performance and the fact that due to the low cost this particular remote control set was highly tested and reliable.

 

The Skeleton of the Tricopter

The vehicle skeleton is made of aluminum and fiberglass sheets coated with copper (PCB). The sheets are laid in layers so that they fit between all the electronic components of the vehicle and large holes have been opened in them to reduce the weight but also to optimally distribute the cables between the different layers. The ends of the vehicle are made of aluminum for maximum durability and weight minimization. At these ends are the three motors with propellers. At the rear end to compensate for the torque and to change the direction of the vehicle, there is a bearing mechanism for the inclination of the respective motor.

 

tricopter completed

 

The shifting mechanism has been built into a machine shop for maximum durability and precision for this important piece of construction. It consists of two bearings mounted on an aluminum base holding the shaft on which the rear engine is supported.

 

servo up view

 

 

servo side view

 

Battery and Charger

LiPo batteries are a relatively new type of battery. Their many advantages have established them in the field of remote-controlled modeling. Proper knowledge of the right type and correct and safe use is required. Wrong and careless use can be very dangerous.

LiPo batteries consist of elements connected in series to give the desired voltage (Volt, V). Each element has a nominal voltage of 3.7V. Data series can give multiple voltage values ​​of 3.7. So there are batteries with 1cell and 3.7V, 2cell and 7.4V, 3cell and 11.1V, 4cell and 14.8V coke. A fully charged LiPo cell has a maximum voltage of 4.2V. So a fully charged 3cell battery will have a voltage (3x4,2V) of 12.6V.

Care must be taken when unloading the battery so that no components fall below 3V. If this happens, the battery may become obsolete. It is recommended to use speed controllers (ESC) suitable for LiPo. When the voltage drops below the specified voltage, they gradually reduce the speed of the motor rotation or completely shut down the power, depending on how they are set to operate. There are still suitable beacons that when the voltage drops below a limit, they alert you by emitting a distinctive sound.

 

zippy flightmax 3000mah battery

 

In addition to their voltage, LiPo batteries are also characterized by the power they can give. This is measured in "C". So we have batteries 15C, 20C, 25C and so on. To find out how much current a battery can deliver, multiply the C number with the Ampere battery. So a LiPo 5000mAh and 30C can give 5x30 = 150A. However, as the battery is discharged, the current stored is reduced. So when it is at 50% of its charge, the example battery will have a load of only 2500mAh. So then it can only give 2.5x30 = 75A.

There are special chargers for charging LiPo. They take care, among other things, that battery cells have the same load. They do so called balancing. LiPo batteries are good when they are not going to be used directly to charge up to 80% of their capacity. Many chargers have an appropriate storage program. Another value that characterizes LiPo is the charging current. This is also expressed by C and calculated in the same way as the discharge current. So set the charger accordingly.

 

iMAXB6 charger

 

LiPo may be tricked by their size, but they have large amounts of energy stored inside. So if they are short-circuited or overcome, then they can become very dangerous. They must always be handled with care and according to the manufacturer's instructions.

 

Voltage divider for battery measurement

To know the voltage of the tricopter battery in real time, a voltage divider was built and used. The voltage attenuator is necessary as the Arduino analog inputs can be measured as 5V while the tricopter battery runs between 9V and 12.6V. This value is divided by 3 and thus, through a proportional input of the arduino, the battery voltage is measured. This value is sent by telemetry to display on the computer screen so that the user is informed at all times of the battery status.

 

voltage divider

 

Files to download

 

Source code in Processing

Source code in Arduino Mega:

Source code in Arduino Pro Mini: