Safely disarm your drone and analyze your flight.
After flying, make sure to disarm the drone while you are not operating it. This can be done by moving the left stick to the bottom left until the LEDs on the drone start flashing. At this point the propellers of the drone stop rotating. This prevents unwanted accidental takeoffs. It is also safer to disarm the drone at all times when it is on the ground; when the drone is armed, it could also react to movement when you pick it up, causing your fingers to be cut by the propellers. Regardless, always check that the drone is disarmed before handling it.
When you are done flying the drone, make sure that you disarm the drone on the drone-side as well before handling it: this can be done by pressing and holding the safety switch (on the GPS module), until it starts flashing slower. After this, it is also safer to have the batteries disconnected to prevent draining your batteries while moving the drone. Usually propellers are also taken off the drone after flying.
On-board log files are generated and stored on the SD card. These can be analysed using the tools and procedures shown here:
Important things to check before you fly.
In order to start flying your drone, there are a couple of steps you need to follow. It is important to follow all these steps before every flight.
Please use PPE - Personal Protective Equpiment such as eye protection, heavy clothing that covers exposed skin and closed toe heavy boots while working with any drone.
Make sure you have fully set up your drone. While it is not necessary to check every little setting every time before takeoff, it is a good idea to regularly check your settings, especially after making a lot of changes.
Check out the Flying Regulations in your area whether you are allowed to fly in your area.
Check that you are flying safely by going through the Safety Guidelines.
Arm the drone, which is a two-step process involving both the drone and the RC transmitter:
Arm on the drone-side by pressing and holding the safety switch on the GPS module, until it starts blinking faster.
Arm on the RC transmitter-side by holding the left stick to the bottom right, until the safety switch and RGB LED on the FMU glow solid. At this point the drone is armed!
When the drone is armed, its motors will start rotating immediately! When you test this for the first time, do this without propellers!
Now that the drone is armed, it can be controlled using the RC transmitter. For more tips on things to think about while flying, you can refer to the During flight section. When it is armed, the drone can be disarmed by moving the left stick on the RC transmitter to the bottom left, until the lights on the drone start flashing again (safety switch and RGB LED). More information on what to do when you are done flying can be found in the After you fly section.
It's a good idea to make your own pre-flight checklist and "tick off the boxes" before you arm the drone and go fly. At least include the steps that are mentioned above, with as much details as you need to remember what you need to do exactly.
You can also enable a generic preflight checklist in QGroundControl! Go to the application settings by clicking on the logo on the top left, and the enable "Use preflight checklist". When this is enabled, the home screen will show a checklist with some important steps you should perform before a flight.
Drones are not toys, and should be handled with care to make sure no-one gets hurt. While the local regulations mentioned above improve the general safety somewhat, taking good care of your drone is also required for a safe flight. It is important to do this before every flight, since damaged or loose components can cause the drone to malfunction during flight, leading to loss of control and crashes!
Some general checks that apply to any custom-made drone:
Check whether the propellers are mounted properly. This means that they are spinning in the right direction, and that they are mounted tightly.
DOUBLE CHECK that the propeller nuts are tight and they have not loosened since last use.
Make sure that the propellers can rotate freely without touching any of the frame or wiring.
Check that there are no loose wires that could get in-between the propellers during flight.
Make sure that the battery is tightly strapped to the frame: it should not be able to move at all. If the battery can shift during flight, it causes the drone to get out of balance, or the battery could even detach from the drone!
Check the battery percentage and voltage. Flight-time can drastically decrease when taking off with a lower battery percentage. When the voltage per cell is more than 4V (total voltage for 3S = 3x4 = 12V, total voltage for 4S = 16V) there should be no problem, but when the cell voltage is below 4V you should watch your battery level extra carefully during take-off.
Make sure that you have correctly set up and configured all the settings on the FMU and the RC transmitter.
Ensure you have calibrated and tested all your sensors before flying.
PX4 contains advanced battery measurement features that allow for accurate estimation of battery percentage from measured voltage and current. More information about these features and their setup process can be found at https://docs.px4.io/en/config/battery.html
Drones and robots can be dangerous if safety precautions are not followed:
Be very careful and follow all safety instructions and help prepare additional safety instructions and labels.
Propellers can and will cut severely if not treated with respect. NEVER mount them until after you have calibrated and flight checked the whole system, and are ready to fly.
On the software side, PX4 also provides a lot of safety features, which can improve the safety of your flights. More on these safety features can be found here
Things to keep in mind during the flight of your drone.
There are multiple modes in which you can control a drone. For each of these modes, there are different things to keep in mind. Some things apply to any flight mode, while others apply only to the more advanced flight modes. More information about the different available flight modes can be found here:
Always watch your environment during flight. Next to people and animals getting in your flight area, the weather is also very important. A sudden gust of wind can quickly blow your drone out of the sky, or out of sight! If you notice that you are unable to keep the drone stable, land it immediately to avoid damage to the drone or its surroundings.
While you can technically fly a drone by yourself, it is always safer to have someone else with you. They can keep track of your surroundings, and watch the telemetry information of the drone, while you can be more focused on flying the drone.
During flight it is important to keep track of the battery percentage and voltage of your drone; when the voltage gets too low, the drone will become less mobile, and eventually it will crash! Note that the lower the cell voltage, the quicker the battery will deplete. Especially at a cell voltage below 3.7 V (3S = 11.1 V, 4 S = 14.8 V), the battery percentage will drop pretty quickly.
When you lose control of the drone, always make sure that it is safe to stop the motors mid-flight; do not engage the kill switch immediately! However, when the drone is about to hurt someone, you should enable the kill switch as soon as possible.
When the kill switch is used to turn off the drone, be aware that the drone is not immediately disarmed! You have to do this manually. If you don't, and turn off the kill switch again, the motors will turn on again!
Make sure to leave the kill switch on until you have disarmed the drone and unplugged the batteries.
Assisted flight modes are flight modes in which the drone uses more sensors in order to keep position when it does not receive any command. An example of an assisted flight mode is altitude control, in which the drone regulates its height in the air using a barometer or its height above the ground using a distance sensor. Position control is another assisted flight mode, in which the drone also keeps its horizontal position using GPS or a flow sensor.
During assisted flight modes, more sensors are being used by the drone. When one of these sensors fails, the drone will turn on its fail-safe (https://docs.px4.io/en/config/safety.html) mode, which can sometimes mean that you have to manually bring the drone to the ground. This means that you should always be watching the state of the drone to be able to react appropriately. In some cases, this means switching to another flight mode!
During autonomous flight, the drone essentially controls itself. The drone can fly missions using GPS which you can configure using QGroundControl, or you can put the drone in offboard flight mode. When in offboard flight mode, a companion computer will provide commands to the drone.
Even though the drone controls itself, this does not mean that you do not have to watch your drone: during autonomous flight you should still keep clear sight on the drone, and be ready to take over when the drone loses control of itself.
This means switching back to an assisted flight mode or to full manual mode, or flipping the kill switch. Make sure you know which modes are available and how they work, and think about what you would do in case something goes wrong.
When something goes wrong in offboard flight mode, you should first turn of the offboard flight mode. You should set up an offboard switch on your RC transmitter, so you can use the controller to decide whether you are in control, or the companion computer.
It is also possible to set up failsafe actions for when offboard mode fails, both with and without RC connection. Before flying in offboard mode, it is highly recommended to set up these offboard failsafes, to avoid non-expected behaviour during flight.
When you need to monitor or control the companion computer connected to the FMU during flight, you should also have someone else fly the drone.
More information about autonomous flight using offboard control can be found here:
Some options to improve the flight characteristics of your drone.
As is often the case, practice makes perfect. When you are flying a drone for the first time, it's not going to be easy and you will make mistakes. As you grow more confident and get more familiar with the controls and the different flight modes, you will be able to fly quicker and more aggressive.
While the default values should be a good starting point, the controllers that are part of PX4 are not perfectly tuned for every drone. Some improvements are always possible, but are probably not needed unless you are using the drone in more extreme situations, or when you are doing more advanced flying.
The default PID values for the S500 airframe preset are listed below:
The PX4 user documentation has a multicopter tuning guide that will be useful if you decide to do your own PID tuning.
You may want to try using GPS as the primary altitude source instead of the barometer (pressure sensor). The result is still fused between the two. Depending on your GPS accuracy it might improve the altitude control of your drone. To set GPS as the primary altitude source, set parameter EKF2_HGT_MODE to GPS.
Tips for (safely) flying a drone.
This section provides important information about safely flying a drone. It is split up in things you should do before you fly, things to keep in mind while you're flying, and things to check afterwards.
It is recommended that you check all three sections before your first flight.
