Flight Controller Setup and Calibration w/ QGC

• 1: PX4 Firmware
• 2: Airframe
• 3: Sensors
• 4: Radio
• 5: Flight Modes, Arming, and Kill Switch
• 6: Power
• 7: Safety
• 8: Motor Test

sudo apt install libfuse2

1 - PX4 Firmware

Uploading PX4 firmware using QGC

PX4 is firmware that we will be running on the AVR drone. It is an open-source flight stack containing all the software necessary to get your drone into the air.

To facilitate some of the extra functionality required for our drone to fly in stabilized flight mode without a GPS, you will need a custom version of PX4 Bell engineers have developed. Go to the latest AVR PX4 release and download the px4_fmu-v6c_default.<px4 version>.<hash>.px4 file.

In the Firmware screen in QGroundControl you can upload a new version of PX4. To access the firmware screen make sure to click on the Q logo in the top left of the screen and then click on Vehicle Setup > Firmware. You will see the following screen.

Firmware upload screen in QGC

QGC will ask you to plug in your FC using a USB cable. A popup will appear that asks you which firmware you want to use. select “Advanced Settings”, then “Custom firmware file…”

Loading PX4 Pro Stable Release onto FC

Then click “Ok” and select the firmware file you downloaded. Now, you will see a progress bar. This process should take no more than 2-3 minutes.

After the PX4 firmware is successfully loaded you will be presented with the default Vehicle Setup screen. It is necessary to go through the following steps to ensure a reliable and stable first flight.

QGC Vehicle Setup screen right after PX4 firmware load

2 - Airframe

The AVR drone is 500mm in size and is represented by the diagonal distance between motors. If you were to measure the distance it would be close to 500mm. In QGC you will now configure the drone frame, which will provide optimal settings for flight. Select Airframe in the navigation menu.

Airframe Setup screen

Scroll down in the Airframe Setup screen and look for Quadrotor x. Click on the dropdown menu and select S500 Generic as the airframe type. Scroll back up and click the Apply and Restart button in the top right of QGC. You will be asked to confirm that you want to restart. Click Apply and the airframe setting will be saved.

While the FC is rebooting QGC will disconnect for a few moments and then automatically reconnect.

3 - Sensors

The Sensors screen lists most of the sensors that are available to the FC (internal or external). It allows you to start the calibration process for the listed sensors. This step is very important for stable flights. It is required to do the calibration at least once and should be repeated whenever adding new components to the AVR drone or if flight becomes less stable.

Click on Sensors in the navigation menu and let’s walk through the calibration process for each sensor.

Default Sensors screen

Compass

The compass is important for your AVR drone to maintain proper orientation. Click on the Compass button and you will be asked to begin the calibration process. This process requires you to position the AVR drone in a number of set orientations and rotate the vehicle about the specified axis.

Default compass sensor screen before calibration begins.

Click Ok to proceed with the compass calibration. QGC will automatically recognize the orientation of the AVR drone and provide a yellow highlight as shown in the image below.

Begin the process of rotating the AVR drone around the highlighted axis.

Once the orientation is highlighted you can begin rotating the drone until the box is highlighted green. This generally requires one 360 degree rotation around the axis. The image below shows three of the six orientations completed.

Compass calibration in progress

After completing the calibration of all axes click Ok to return to the sensor setup. It is important to reboot your FC prior to flight, but for now we will move on to calibrating the Gyroscope.

Gyroscope

The gyroscope is an important sensor that will be used to keep your AVR drone level when hovering. Now that the compass calibration is complete you will click on Gyroscope to being the process. This will be much easier than compass calibration! Make sure your AVR drone is on a level surface and click Ok.

After a few seconds, the gyroscope calibration will be complete.

Successful gyroscope calibration

Accelerometer

The accelerometer works in conjunction with the gyroscope to keep your AVR drone level along each axis. Click on Accelerometer and then Ok to begin the calibration process.

This process is fairly similar to compass calibration but does not require you to rotate the drone around each axis. You simply need to hold the drone level in each orientation. QGC will detect the orientation, which is denoted by the yellow border.

Accelerometer calibration in progress

Hold your AVR drone steady in each orientation for approximately 5-10 seconds. As you complete each axis the border will turn green in QGC.

Accelerometer calibration complete

Level Horizon

Level horizon is a simple calibration to make sure your FC understands the default level position when powered on. Click on the Level Horizon button and then Ok. This process will take more than a couple of seconds to complete.

Level Horizon calibration complete

Orientations

Given we have mounted the FC in its default orientation (facing up and forward) this calibration is unnecessary.

Nice work! You have calibrated the necessary sensors for your AVR drone to be able to know its orientation and keep level during flight. The following Summary screen shows the successful steps completed in green. Now we will move onto setting up the Radio (aka Transmitter).

Summary screen showing all sensors calibrated and ready for flight

4 - Radio

In the RC Transmitter Setup section we configured the stick and switch channels. Now we will calibrate the endpoints of these channels so they can be saved to the FC. QGC makes this very easy to do and the process can be observed in the following video.

Now that your transmitter has been calibrated using the Radio screen in QGC we will move onto setting up our flight modes.

5 - Flight Modes, Arming, and Kill Switch

The primary goal of the basic assembly is to be able to pilot the AVR drone in stabilized mode. Therefore we will configure SWB (3 position switch) to control which flight mode we’re in. In addition to setting up flight modes, we will also enable a kill switch on SWD (2 position switch). This is VERY IMPORTANT in case the AVR drone needs to be shut down due to a fly-away or complete loss of control. The video below demonstrates this process.

6 - Power

Power Setup

For correct display of battery percentage, you should always specify the correct number of cells in the battery. In our case this will be 4 since we are using a 4 cell LiPo battery. You should also calculate the value for the voltage divider to calibrate the voltage readings coming from the power module. This can be done by measuring the overall voltage with the Venom cell checker. Then you can input the measured voltage into the Calculate Voltage Divider prompt.

These settings will provide you with an accurate battery percentage while the drone is idle on the ground, so you can determine whether it is still safe to take off and when you need to land. PX4 also has a fail-safe that prevents arming when the battery percentage is too low. The video below walks through the power setup.

ESC Calibration

To ensure that all motors correctly respond to commands coming from the FC, you should perform an ESC “calibration”. It makes sure that the ESCs are aware of the minimum and maximum pulse-width modulation (PWM) values that the FC provides. This can be done by pressing the ESC calibration button and following the on-screen prompts. The calibration process requires a USB connection since it involves steps where you have to disconnect and reconnect the battery. The video below covers this in detail.

7 - Safety

Safety Setup

Previously, in the RC Transmitter Setup section, we covered Setting Up Failsafe. In QGC we need to make sure we disable some of the failsafe options, as many of them are related to GPS-enabled drones. AVR is all about indoor navigation in a GPS-denied environment therefore it warrants a different safety configuration. The video below walks through the setup process.

8 - Motor Test

One physical check that must be done to ensure your AVR drone hovers properly is to verify that the motor positions and rotations are correct. We previously covered ESC wiring which should ensure that the FC output is going to the right motor.

We discussed motor rotation when installing the frame arms and learned that the rotation for each motor is important. You may recall the image below and we will refer to it one more time before we run the motor test.

Motor position and rotation diagram

Motor positions and propellers installed with the nose of the AVR drone pointed forward

The video below will walk through the necessary steps to run the position and rotation test.