Multi-tethered drone error "matching flight task was not able to run"

PX4 Autopilot Simulation šŸŒ
1

Hi all,

Iā€™m attempting to simulate a set of three x500 drones carrying a slung load in Gazebo (see image below) with PX4 SITL.

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The drones are able to take off successfully using offboard control messages from ROS2 (both position and velocity setpoints individually). However, after flying for a while (exact time differs on each simulation), I get the following warning and error:

INFO [commander] Armed by external command
INFO [tone_alarm] arming warning
INFO [commander] Takeoff detected
WARN [failsafe] Failsafe activated
INFO [tone_alarm] battery warning (fast)
ERROR [flight_mode_manager] Matching flight task was not able to run, Nav state: 2, Task: 1
INFO [commander] Landing detected
INFO [commander] Disarmed by landing
INFO [tone_alarm] notify neutral

The failsafe that kicks in results in the drones landing at their current positions.

I donā€™t really understand the root cause of this issue/what is causing the failsafe to trigger and therefore donā€™t know how to fix it. My current hypothesis (given that the error doesnā€™t appear when the tethers arenā€™t present) is that the additional tethered load (although negligible at 0.05 kg - perhaps it is more of the effect of other drones than the weight of the load) is making it difficult for the drones to reach the position/velocity setpoints and so a failsafe is triggered because ā€œsomething appears wrongā€ to PX4. The position (and velocity) setpoints I have selected are physically feasible given the cable length constraints howeverā€¦

Does this error mean anything more to someone else?

What Iā€™ve tried:

  • Removing the cables - the issue no longer appears (drones are able to hover indefinately from ROS2 offboard control commands).
  • Setting SIM_BAT_DRAIN, SIM_BAT_MIN_PCT and BAT1_CAPACITY to max (given the error, thought that the simulated battery could be running out quickly) - this doesnā€™t change anything.
  • Sending offboard position commands from ROS2 and offboard velocity commands from ROS2 - the error appears in both cases.
  • Simulating the ā€œcablesā€ as singular rigid links and as multiple (3 links each) rigid links (thought that perhaps rigid links were preventing drones from reaching the desired setpoints). The error appears in both cases.

I am on commit: a6d2c2cf5e21ecdad8d737c31de81fab128898c5.

Logfile of takeoff in velocity mode showing the error: https://logs.px4.io/plot_app?log=c9cb9702-a3bc-456e-a08e-16ce2b5c7b82.

Thanks in advance for your help!

2

Update: it appears that the issue still occurs even when the tethers are not connected to the dronesā€¦

As there are many bodies in the simulation, the simulatorā€™s real time factor occasionally drops to around 30-50%. Is it possible that this could be causing the error? Perhaps the offboard message isnā€™t being received frequently enough to stay in offboard mode? Iā€™m just confused about the ā€˜battery warningā€™ however as this always appears when the error occurs.

3

Solved. My previous hunch was correct: the drones were dropping out of offboard mode (other warnings were coming from the fallback to position control not working). Setting COM_OF_LOSS_T = 5 (rather than 1) fixes this.

4

hello,
Your Multi-tethered drone is so wonderful. I want to know how to make it and take it off successfully using ROS2. What directory do you put your models in? How to connect a model to a link between models?

5

Hi @suezere - thanks for your interest! The problems I had building this were discussed in this thread. Hopefully that gives you the information you need! I also made a pull request into the PX4 firmware with the edits I had to make to get it to work.

As for model directories and links, the cable and load models went in parallel directories to the x500 model: Tools>simulation>gz>models>[cable or load respectively] and are just regular SDF files. The connections were created in the world file (I just edited the `default.sdfā€™ world file for now) with regular SDF joints after the x500 drones, cables and load are included.

1 Like
6

Thank you for your help @hmer101. Iā€™ve solved the problem and created my own multi-drone model, but when running one of the drones, the droneā€™s position data seems to deviate from real-time with the following warning:

WARN [health_and_arming_checks] Preflight Fail: ekf2 missing data

I would like to know if you have the same problem and how to fix it to get the correct position information of the drone. Thanks again for your help!

7

I did encounter that problem along the way. I believe the problem is caused by incorrect model name assumptions in some plugins discussed in the chain I linked above. The pull request I linked above contains the solution in a modified GZBridge file.