Software needed to control a drone:
On the aircraft:
ArduPilot : It is the software (firmware) that runs on our flight controller. It is in charge of managing all the information it receives from outside (physical sensors and radio) and act accordingly on the actuators of the aircraft. Currently it can be downloaded from its official website or even contribute to its improvement (or create its own versions) through GitHub and its official repository. This native firmware can only be used on platforms supported and officially maintained by its creators (despite being Open Source and Open Hardware respectively) such as the APM flight controllers (in its different versions), PX4 FMU or Pixhawk.
- Megapirate-NG: Originally born as a "fork" or repository son of the original Ardupilot allows to use a code virtually identical in functionalities (but always more backward, since you have to always update later on the release of new versions of your "father") with plates that are also OpenHardware created by other people or organizations. The most common combination to use Megapirate-NG is to install it on CRIUS-AIO Pro type plates. They are currently starting to work on 32-bit processor boards, perhaps to carry already the codes used by Ardupilot for their 32-bit Pixhawk and PX4 controllers .
MultiWii: It is another firmware solution, the easiest to configure but the most limited in functions. Can only be installed on clone controllers with low quality components (but enough to mount an economical drone and learn to fly)
In the base station or "ground station":
- Mission Planner: Base station software par excellence. Only available for Windows is the most refined and well-known of the software in charge of establishing a communication via MavLink with the drone and thus allowing to obtain telemetries of flight and the remote configuration of the aircraft.
(Telemetry analysis. In this case it is a Quadcopter with vibration problems)
In other articles, their functionalities will be analyzed in more detail when they have to be used since it is a very extensive software.
- APM Planner: It is the second alternative written in Qt. It is an almost exact copy in functionalities and aesthetics that allows to run on Windows, Linux and MacOS therefore the platform from which we work is no longer a problem.
Other softwares: Not only are there two previous alternatives. Many users have created their own versions of control stations, but mostly the two mentioned above are used. Here is a list of other known applications:
Qgroundcontrol Desktop platform for aircraft control using Mavlink
DroidPlanner Remote control platform for Android that allows us to link to the UAV via Bluetooth or a telemetry radio using an OTG cable on our Android
The next steps are, first of all, to know our flight controller well to prepare it by updating it to the latest stable version of its firmware through Mission Planner.
Flight electronics
Flight electronics for an unmanned aircraft.
If previous pages talked about the main components of a UAV, special emphasis should be placed on the section on all the electronics that govern the operation of a drone.
Let's start with the most important part, the heart of all UAV.
The flight controller.
In general, they all have a similar structure and more or less sophisticated components, but in general, they have:
- Accelerometer to measure the own "inertia" of the movements.
- Gyroscope to be able to measure the angular velocity of the position changes.
- Magnetometer used as a compass that lets you know at any time the direction the drone is pointing.
- Barometric sensor used to know with amazing accuracy the real height of flight.
- GPS to be able to know the exact coordinates in the space of the drone (including theheight)andtobe able to move autonomously.- A processor powerful enough to perform the maximum readings and operationspersecondbasedonall the data it receives (which are not few)With the combination of alltheseelectroniccomponents,yougetenoughinformationfromtheenvironment to make the right decisions about the actuators that should make the flight possible.In this page we will analyze in detail one of the most popular and powerful flight controllers thatexist in the market today (and I repeat, today), the Pixhawk.
As important details highlight the following:
- El pinout de los puertos serie Telem1 y Telem2 es: [+5v; Tx(3.3v) ; Rx(3.3v) ; CTS ; RTS ; GND] (Contando que el cable DF13 tiene el color rojo en el pin1, es decir en +5v)
The serial ports work like the rest of the internal electronics with 3.3v signals, but they are compatible with 5V serial input like the one used by the 3DR telemetry radio, so you do not have to worry about leaving the port when connecting a device to 5V. Yes, the TX ports of the Pixhawk are always 3.3V and the device that we connect must be able to trigger the flanks at that voltage.
- The pinout of the GPS port is: [+5; Tx (3.3v); Rx (3.3v); CAN2TX; CAN2RX; GND]
- The pinout of Serial port 4/5 is: [+5; Tx4 (3.3v); Rx4 (3.3v); Tx5 (3.3v); Rx5 (3.3v); GND] (used to connect for example an OSD)
- The pinout of the I2C port is: [+5; SCL (3.3v); SDA (3.3v); GND]
External sensors:GPS
The GPS unit is responsible for transmitting information about the position on the planet to the flight controller. This connection is made through a standardized serial communication protocol known as NMEA. Simply connect the GPS unit to the controller correctly (taking into account as always that the Tx connectors go to Rx and vice versa in both devices).
Any GPS module with serial output can be used for flight control, but the most common are two models of the uBlox company. Specifically the uBlox NEO-6M (cheaper but somewhat less accurate) and the uBlox LEA-6T (more accurate but much more expensive).
Here we leave you a video to correctly configure a GPS and leave it ready to communicate with a flight controller.
Videotutorial "Configure uBlox NEO-6m" for our drone.
In this new installment of the quadcopter series, I focus on the configuration and installation of the GPS module for the drone. In this case it is a uBlox NEO-6m gps module.
Magnetometer
Employing a second magnetometer independent of the one of the flight controller allows us mainly an advantage: to get away as much as possible from the battery, distribution cables and ESCs that cause the interferences that can bring us more than one headache. Without going into many details to explain it, the continuous current flowing through the distribution cables in large quantities (we speak of draining the battery in some multicopters up to 80 amps) is such that the magnetic field it generates can cause serious problems in the magnetometer , that uses the magnetic field of the earth together with the declination information (thanks to the GPS) to know where the north is.
Typical rookie mistake! try to solve the problem of interference in the "mag" (see graphs below) using aluminum foil or any other "metal" as insulation from electromagnetic interference. A tip, review well the knowledge about magnetism and electromagnetism. It is not the same continuous current or very low frequency as alternating current. We could only avoid the interference generated by our cables through a Mu-metal (very expensive), at the cost of losing also the magnetism of the earth, so it is not a solution either.
In the following graph it is observed how with the changes in the accelerator (green line) the value of mag_field (in red) changes more than 30% of its original value, which can cause problems as common as deviation in orientation or famous "toilet bowl" or spiral movement in Loiter mode
The best advice I can give is to mount the magnetometer in an elevated position, as far as possible from any metal object or through which current flows.
Drums
The battery is one of the most carefully chosen electronic elements. Mainly LiPo batteries are used and the voltages they offer along with their capacity and weight is the choice that everyone should make.
Battery: Nominal voltage or "cells"
As a general rule, for multirotors it is convenient to opt for 3S, 4S, 5S or 6S batteries. The letter "S" indicates the cells in series, knowing that each cell has a nominal voltage of 3.7v, we obtain nominal voltages of 11.1; 14.8; 18.5; 22.2 volts respectively. It is best to use a battery with the highest possible voltage to reduce the necessary current and therefore obtain greater efficiency. The problem is in the electronics of the motor controllers and the motors themselves, that few are prepared to work above 4S and their prices soar. For non-professional multicopters, it is normal to work in the range of 3S or 4S where the electronics and motors are reasonably priced. In the case of airplanes, the general rule is to work with 3S or even 2S in some cases.
Battery: Capacity or "mAh"
Simply, the more capacity more autonomy, right ?. Well, no. It turns out that in the case of aircraft, the weight of the aircraft itself, the efficiency of engines and propellers, ESCs, and many other variables make the choice of battery capacity must be somewhat reasoned. I explain:
Let's suppose that we have a quadcopter with a 3S 4000mAh battery that has a 10-minute flight autonomy. If we add another battery in parallel we get a quadcopter with a total battery of 3s 2P 8000mAh, should I fly approximately 20 minutes? Well, the normal thing is that it does not exceed 15 with luck.
The explanation for this phenomenon is in the weight. Adding more capacity is not always productive if the remaining characteristics of the aircraft remain constant. The higher the weight, the greater the energy consumption and therefore there comes a time when adding more batteries (this is the heaviest element of the aircraft) can be counterproductive.
The best way to find the "sweet spot" where capacity and autonomy are optimal I have found in this fantastic simulator, that being realistic, it is surprising the ability and accuracy that has to obtain estimates of flight time: Simulator
Engines that use this type of aircraft are not "normal" DC motors. As the exact operating system is complex enough to explain in one line, Google is your friend to learn more about brushless motors.
The point is that we need to convert the continuous current of the battery with a "constant" voltage to a source of variable voltage and reversible direction for each pole of the motor. It may seem somewhat complex to understand, but again I repeat, it is a matter of looking for information on how the engines of aeromodelling (or brushless in general) work.
The electronic device responsible for carrying out said conversion is the so-called motor controller, motor speed controller or simply ESC (from its acronym in English Electronic Speed Controller) and has an appearance similar to this:
The characteristics that we want to know about an ESC is its maximum amperage and its maximum input voltage.
For multirotors the normal amperages range from 25 to 40 amps (in normal sized aircraft).
For fixed-wing airplanes are normal values from 10 to 100 amps (it is something very dependent on how big the plane or the engines it is).
As for the maximum input voltage, the most common values are ESCs that allow batteries of 4S maximum, triggering something the price for those who support batteries of 5S and 6S. But remember that the higher the voltage of the battery, the lower the value of amps to move the same mass ... "P = V * I"
Motors
Those in charge of transmitting the necessary energy to the propellers to support the aircraft.
The most important characteristics of a brushless motor like these are:
- Maximum input voltage: is determined by the battery and is usually indicated in volts or "S"
- Speed or "Kv": it is the speed at which they manage to turn given a tension. It is measured in 1000Rev / Volt. Therefore, a 1000Kv motor will rotate at 2000RPM with an input voltage of 2v.
- Maximum amperage: it is related to the maximum power that develops.
As a recommendation, going back to the recommendation of the batteries, the interesting thing is to get an engine, in the case of multicopters, with the lowest possible Kv accompanied by a battery of the highest possible voltage. With this we achieve great speeds with little amperage, thus allowing thinner cables and less weight.
Finding the perfect relationship between the weight of the aircraft, the motors, the battery and the propellers is a mystery and here plays a fundamental role the capacity (especially economic) that we have to try all possible combinations.
As an example, for the same aircraft (a quadcopter) with a 3S battery, the two equivalent combinations with which a stable flight is achieved are:
- 1000Kv motor with 10 × 4.5 "propellers
- 850Kv motor with 11 × 5 "propellers
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