Circumventing Safety Features

I recently encountered an interesting problem when configuring all three drones simultaneously with the Skybrush drone management software.

I would power up all three drones and connect them to the network I configured for them. All three would appear on my laptop. After double-checking that they were actively connected, I manually rebooted each one and confirmed the connection using the Skybrush software.

With propellers removed, pre-arm checks approved. I would go and arm each drone.

"Arming" is the last step before takeoff for a drone. "Pre-Arm" ensures all safety checks (foreshadowing) are completed but does not start up motors. Arming, on the other hand, starts the motors at a low rpm and listens for control inputs (i.e., throttle up) for takeoff. It disarms if no input is provided within 10 seconds of the motors spinning.

But here's where the problem occurred. Only one drone would go into arming mode, while the other two reported an "unknown" error and blinked red.

After some research and trial and error, I discovered that the drone reported an "RC Not Found" error to the ground station.

Now, that's strange; it should be configured to ignore whether or not it had an RC connection for Pre-Flight. I went into QGroundControl and manually configured it to ignore pre-flight checks for the RC. After a quick reboot, I tried again.

Still, no luck, except the behavior changed slightly. After the blinking red error, I tried arming the drones again... and they all spun up! But Skybrush still showed them as reporting an error. This is not ideal for my case, but as the classic saying goes, a different error is still in progress.

After more research, I found a forum post with someone asking a similar question and a super helpful user linking to a page about configuring ArduPilot with autonomous flight software like SkyBrush.

It ended up being two parameters that affected my problem.

• FS_THR_ENABLE - Allow arming without checking for RC

• ARMING_CHECK - Disable RC failsafe for pre-arm checks

Setting those two and a quick reboot resulted in all three drones being able to go into pre-arm, then arming mode, and ready for takeoff. The corrected values are:

FS_THR_ENABLE0ARMING_CHECK1048510

The longer string for ARMING_CHECK signifies which failsafe options to disable; Arducopter gives you 19 total options for failsafe, from Compass to Battery Levels. A complete list is provided here.

And finally, here's a quick reference list I had ChatGPT create based on the parameter's instructions:

Bit Check Value Description 0 All 1 Enables all checks 1 Barometer 2 Ensures the barometer is functioning correctly 2 Compass 4 Verifies compass calibration 3 GPS lock 8 Requires a valid GPS lock before arming 4 INS 16 Checks Inertial Navigation System (IMU) health 5 Parameters 32 Confirms parameters are set correctly 6 RC Channels 64 Ensures RC signal is valid 7 Board voltage 128 Monitors voltage levels of the flight controller 8 Battery Level 256 Verifies battery level is sufficient 10 Logging Available 1024 Checks if logging is available 11 Hardware safety switch 2048 Requires safety switch to be engaged 12 GPS Configuration 4096 Verifies GPS is configured correctly 13 System 8192 Checks system-level health 14 Mission 16384 Ensures a valid mission is loaded 15 Rangefinder 32768 Checks rangefinder sensors 16 Camera 65536 Verifies camera is functioning correctly 17 AuxAuth 131072 Checks auxiliary authorization systems 18 VisualOdometry 262144 Monitors visual odometry sensor health 19 FFT 524288 Verifies Fast Fourier Transform data availability