On the importance of being thorough when setting up your UAV

Yesterday, I was preparing for a rather simple auto mission. I set everything up, did a last minute change to CH7_OPT, then positioned my IRIS on a nice place for takeoff. I armed in LOITER and raised the throttle. The IRIS lifted off to about 50cm and started drifting to the right.I tried to steer against with no effect. I switched through modes but couldn't get back control. The IRIS bounced off a tree, then another tree and finally got stuck in a hill. Still no reaction to sticks, mode, nothing. I didn't have stabilize mode configured as flight mode, so I jumped to my GCS, switched to STAB through AP2 and finally, the throttle went zero and I could disarm.

What has happened? Logfile analysis revealed that all THR_* PIDs were zero. Some more testing turned out that APM Planner 2 apparently doesn't always correctly refresh the extended tuning page, so when I did the last minute change to CH7_OPT, I accidentally also wrote the zero THR_* PIDs to the vehicle. Of course, with all those zero, the IRIS couldn't do anything with my control inputs in any mode in which the altitude hold controller was active.

That whole thing could have gone much worse. I only broke the 2 front props but without the trees to bounce off from, the IRIS could have made it to the street or somewhere else.

This is a textbook example why it is extremely important to be thorough when setting up your vehicle.

  • When changing the configuration, always double check all parameters you are writing! Not only the ones you changed but the whole screen!
  • Always have stabilize configured as a flight mode for your TX switches! It can be the last resort to save your vehicle or - more important - prevent it from causing harm to property or people!
  • When using copter 3.3 or higher, it's a good idea to have the new motor kill function configured on a switch. Better dump the copter somewhere than let it go out of control.

Views: 1053


3D Robotics
Comment by Chris Anderson on June 13, 2015 at 6:53am

Good analysis. Thanks for sharing that and the excellent advice. 

Comment by Marc Dornan on June 13, 2015 at 8:16am
Not having stabilize as an option seems so important, and I have read this a few times her in crash stories, that I wonder if this could not be added in bold to the wiki.Also I might add you should always take off in stabilize. Loiter is not something to use near the ground. Either take off or landing. It is an absolute no no imho.
Comment by Stefan Gofferje on June 13, 2015 at 8:38am

@Marc:

I agree. I even wonder if it would make sense to reduce the number of freely configurable flight modes to 5 and have STAB fixed to position 1 or 6. Or at least have MP/AP2 output a warning if no switch position is configured for STAB, like "WARNING: You have no switch position configured for mode stabilize. Having a switch position configured to mode stabilize is important, because... Are you sure you want to write this configuration?"

I normally always have STAB set up on all my copters so, that I can switch to it with one flick, basically as a "panic button". It was just another oversight in this case and as I was planning to do a really short mission, I wasn't too concerned about that.

Comment by James Slizewski on June 13, 2015 at 9:38am

Great advice. Thank you for posting this. 


MR60
Comment by Hugues on June 13, 2015 at 11:43am

Before launching your ship in any auto mode,  first take off in stabilize to have a feel of the behaviour and ensuring the ship is reacting normally to the sticks, then secondly switch to loiter to check the GPS controlled mode and then thridly switch to Auto. If you follow this sequence you will avoid these situations.

Have always stabilize mode set as one of your flight modes and preferably position it in one of the extreme switches positions so that in panic mode you won't miss it.


T3
Comment by Thorsten on June 13, 2015 at 2:02pm

Hugues, 

I fully agree!

Stabilize is my number one flight mode. After any change I make - no matter of soft- or hardware - I test the copters in stabilize first before switching to any other mode. Only in a series of mapping missions I take off in Auto. 

Comment by Charlie on June 13, 2015 at 11:58pm

Jezz... and they are selling this things in BestBuy. I understand not having alarms on the open/diy version of the software... but in an IRIS? Common... a range and alarm in the defaults should be common sense on the manufacturer. Being a 4 year apm/pixhawk user recently move to Vector for plane and A2 for hexa... I still can't understand why it does not branch to a closed more detailed developement, leaving the open source for the diyers. Or thats the Solo?

Comment by Felixrising on June 14, 2015 at 4:00am

Good advice. I've also lost configuration after (wrongly) assuming that the parameters were all loaded properly in MP2 before making a change and writing them back. If you don't have a backup of the parameters, it is a crap way to spend the next hour re-configuring and re-tuning your multirotor.

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