Hi,
I am running AC3.1.5 on a 450 size quad and have had quite a good experience until now. Here is what happened.
I took the quad to my other apartment for the first time which is on the 3rd floor. Tried to arm it on the balcony but it would not arm as the GPS pre-Arm check was failing. Since I was not planning to use any GPS related features and would be flying indoors, I disabled the GPS pre-arm check in MP.
Copter Armed took off hovered for a few seconds and then al hell broke loose. The quad came directly towards me. moving the sticks had no effect on the quad and it was pretty close so I had no choice but to stick my hand out and stop it.One of the props hit my forehand and broke leaving me with a 6 inch gash in my forearm. Since I still had the TX in my other hand i killed the throttle but no luck because by then it was already in RTL (Failsafe kicked in)and heading to some incorrect location that it thought was HOME.
Looking at the logs both the GPS & the Geofence Failsafes kicked in together. It was a false Geofence failsafe because of the incorrect GPS location it registered and a completely incorrect home location too. Actual Home was about 30mts Off.
Logs are attached below however a few points I noted:
1. If I skipped the GPS Pre-Arm - Shouldn't all functionality GPS (especially fail safes) be disabled?
2. The GPS Failsafe kicked in first.My GPS failsafe is set to LAND. However the GeoFence Kicked in also and caused RTL failsafe to activate. Now if the GPS failsafe has kicked in and subsequently the GeoFence failsafe has kicked in then why did the GeoFence RTL take priority? The RTL would be useless without a GPS lock. In this case shouldnt the GPS Failsafe have overridden the GeoFence Failsafe? Also, I never noticed the LAND command that I have set for GPS failsafe. It directly went to RTL.
3. When RTL Kicked in, the Quad came straight at me. I have the RTL height set at 80mts. Shouldnt the quad have gone up before moving towards what it believed was home. Could this be cause I armed from the third floor.
So coming to my question - Is this the expected behaviour or is there a bug in there that needs fixing?
What I wanted to do was fly indoors without any GPS functionality. What is the checklist I should have followed to ensure the indoor flight was safe without interference from the GPS?
Attached are both the telemetry & dataflash logs. Please note that I take off only towards the end of the logs. at about the 75-80% progress of the logs. There are a couple of ARMS' DISARMS but please look at the last ARM which is when I actually take-off.
Any help - Guidance would be grateful. If you'll wanna see the gash in my hand let me know.. Ill post a few pics. :-)
Replies
Yip, I agree with Rob. Plan for the worse and be pleasantly surprised if it doesn't happen.
I did actually get one of those really small rtf hobby king toys to start with and I still have it but it just refuses to fly stable. Something is wrong with the gyros on that. Getting fed up with it I bought the 450 quad.
I agree that one should start small in this however the point I am trying to bring up is that of one has intentionally disabled the GPA prearm it means he knows he is flying in a bad GPS area and will not use any GPS enabled auto modes. In this situation having GPS enabled failsafes kick in does not provide any benefit. The geofence failsafe in this situation as Maj pointed out is a time bomb waiting to blow. If you have armed with a bad GPS position your home location is always going to be wrong. In this situation the geofence failsafe should be disabled automatically. This is what I feel.
Hi Arsheesh,
Didn't mean to say that I didn't think the specific condition you are addressing wasn't to blame, clearly it was.
But it is also true that the APM/Pixhawk firmware is in a continuous and very rapid state of evolution and that is mostly a good thing.
But the fact is that because they do so much so fast, that there is also a continuous condition where a lot of things do not actually work in the most reasonable fashion.
Certainly I am willing to accept the risks and dangers inherent in dealing with this continually really powerful but often troublesome combination.
The developers are very talented people, but the test process is actually a lot of unpaid testers and - every body else.
Lots of stuff falls through the cracks all the time.
I am afraid it is simply an aspect of dealing with the bleeding edge (and as you have now experienced first hand why they call it the bleeding edge.)
There are a lot of small quadcopters out there that give a less than exemplary showing for themselves.
The two I mentioned have proven to be reliable and constant performers.
My complaint is that overall I feel on the DIYDrones site and particularly on the wiki people are mislead into thinking that things are more consumer friendly than they turn out to be.
Both from the physical safety aspect and from the state of development of the flight controllers.
Even yourself as an experienced fixed wing flyer was unable to deal with a flight controller caused problem (going pear shaped) in a sufficient manner to prevent personal injury.
Where does that leave the "Newbe"?
Although I am not prepared to recommend it for a Newbe, the new Blade 200QX is getting rave reviews and my friend Oliver has demonstrated it to be a very accomplished acrobatic flyer that is rock solid in the air.
I have no doubt it is still possible to achieve a small level of injury with it, but short of hitting yourself in an eyeball, I believe that a band aid would fix any problems.
I think it is perfectly reasonable for people to use an APM or Pixhawk, but you really do need to understand that the dynamics of its evolution for the time being at least are not without risk.
Randy clearly realizes the circumstance you found yourself in is a less than optimal situation and will no doubt undertake to correct it, but even so, there are a lot of things that a user can do wrong or set up wrong that will inevitably result in a situation similar to that which you experienced.
A small and intrinsically safe quadcopter can go a long way to allowing you to learn how to respond when some future circumstance requires you to do so.
And for a lot of newbes, learning how to fly a quadcopter and all the intricacies of the APM/Pixhawk at the same time can be an overwhelming experience that leaves them no longer interested in the hobby at all.
Even experienced RC pilots perhaps.
I used to fly closer to myself and others than I do now and not because I am a worse pilot.
A big towel also might have helped and is recommended on my safety page either on the DIY wiki or on my site.
(Unfortunately nobody reads the safety page until after they needed to).
I think the future of quadcopters is in the ultralights under a pound and even under a half pound, but with stabilized 1080P video.
Intrinsically very safe but with very high performance, at that size using lithium batteries is feasible so flight times in excess of 20 minutes are also feasible.
There are still problems with getting adequate brushless motors in this size (bearings and low speed torque), but that is the future.
The bigger, even Phantom sized ones are too hazardous (and too many completely incompetent people are using them) (not talking about you) but that will force the copters to go tiny in order to get public and legal acceptance.
Best,
Gary
I completely agree with you and by no means am I complaining. I do this knowing the risks and try to be as careful as possible. I've learnt from this and obviously will take a lot more precaution when flying in the future.
As you have rightly pointed out its in a continuous state of evolution and there are some risks associated with that. Which is perfectly acceptable and we do this because we all love the hobby. But as you have stated, the real danger is that not everybody realizes that "its not perfect" just yet.
Ill have a look at the smaller quads you have called out. The only problem I see there is being able to source them in India. Its very difficult and importing this stuff is a major major challenge because of customes..
Arshish,
Really sorry about your injury. Hope you're better soon.
1) skipping the GPS pre-arm check does not disable the features that rely on the GPS including Loiter, RTL, Auto flight modes GPS failsafe and fence. All it does is turn off the pre-arm checks for the GPS including checking that the hdop value is below 2.0 and the vehicle does not appear to be moving.
2) The vehicle took off in stabilize mode so despite many GPS failures this would not trigger the GPS failsafe (because the vehicle wasn't in a flight mode that required the GPS). It looks like the GPS recovered however but it's position when it recovered was outside the fence so the RTL was triggered. With such bad GPS values both the home position and the vehicle's current position (according to the GPS could be quite inaccurate).
3) the hdop was still very bad (7.0) when the RTL was triggered meaning the vehicle would have had very had horizontal velocity and position estimates which could make it fly in any direction.
So I guess in summary, the contributing factors to the accident are:
On the software side we need to improve the autopilot so it can recognise when #1 happens. Something similar can happen when the compass is very far off. https://github.com/diydrones/ardupilot/issues/572. This is on the list for AC3.2 but it's a slightly difficult problem. We will try and put something in though.
#2 could have been avoided if the fence had been disabled at the same time as the gps arming check. I don't think we want to directly link these two in the arducopter software but it's possible the ground station (if it was being used) could take care of checking this.
Again, very sorry about your accident. I'll try and do my part to help improve the safety of the system, I guess on your side you'll obviously be careful going forward about disabling safety checks and always maintaining a safe distance from the copter.
Randy: "Again, very sorry about your accident. I'll try and do my part to help improve the safety of the system, I guess on your side you'll obviously be careful going forward about disabling safety checks and always maintaining a safe distance from the copter."
I most definitely will.. Thank you again! :-)
One last question.. Does the APM have a "Hardcoded Fence" at 400M? I read somewhere that the DJI has a 400M height limit coded in. If that is the case, even if we disable the Fence in Mission planner, could this problem re-occur?
No, absolutely not. There is no hard-coded 400m limit in Arducopter.
The #1 best way to fly in GPS denied environments, at this point, is to simply disconnect the GPS. "Kill it with fire, it's the only way to be sure."
Is it safe enough to just disconnect the GPS physically, or is it advisable to change any of the params as well? And what would the behaviour be, in both the above cases, if by chance the flight mode changes to one that uses the GPS? Thanks.
The reason I disabled the precheck was because I wanted to hover in stabisile indoors.this is a very valid use case where I intentionally did not want to use any GPS related functionality. It is very unlikely that someone would also remember to disable the geofence failsafe. I feel the geofence failsafe should be disabled in this scenario by default.
Also.. I think I have read somewhere that there is a hard coded maximum geofence enabled by default? 400m? Or is that just on the DJI? If this is indeed the case then even if one remembers to disable the geofence in such a scenario there is a possibility that this could happen again.
So to simplify the question - how do I safely just fly in stabilise in areas where I know the GPS signal is not stable / bad? As in just fly it like a normal quad without any autopilot features..
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