Replies to This Discussion

Permalink Reply by Vernon Barry on April 30, 2012 at 2:02pm

Can anyone here contribute to conversation regarding the possibility that bad solder joints could have helped enable the motors to stay in full throttle?

Well, I think one major problem is the use of standard ESCs of which we have no control over the firmware. That said, a Bad solder joint would have to produce a PWM signal (vibrations just right) that is basically impossible.

The ESCs do have a function though of masking what would normally be a momentary loss of input and stay for a second or so at the last throttle position. We actually need this to some extent with our system because the APM puts out PWM pulses only in the main loop which runs reportedly about 200Hz. Thus by basic design of the system, we need the ESC to maintain throttle for short periods of time. This is why there is a rather large push to make our own ESC in which we control the firmware and specifically time functions of input like this. Further, pure digital input would work much better in the system, without the requirement to send out discrete PWM signals. Trust me, this change alone would improve damatically performance of the entire main loop and code.

If you want to prove this to yourself, plug an ESC into the throttle channel of the radio receiver (Remove the prop for safety!!!), Spin it up and then unplug the ESC signal cable and it will continue to run for a short time with obviously no signal input at all.

That said, a bad solder joint ALSO doesn't make a valid input signal to the PPM either, so not exactly what I would consider a remote possiblity of being a cause.  No signal input must equal no throttle. Of course you can do some no prop testing to prove this too, but use a servo on the ouputs of the APM as I stated and proved, the ESCs will mask loss of output from the APM.

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Permalink Reply by Zen on April 30, 2012 at 2:20pm

This is partly what I'm talking about with regard to the provided instruction set. Nothing really explained how to mount the board, where to mount it, or that it couldn't be mounted directly the the PCB.

I will end up with another quad at some point, but it's an investment that apparently can divorce you at will. This EXACT scenario is cause to push safety and law for commercial use. I hate to think about the possibilities, but what if my 5lb 3DR falling from a couple thousand feet landed on someones car? House? Small child? In this instance everything was working brilliantly, and then it wasn't. No failsafe, no tracking, no recovery.  Average joe buys a kit from the internet to investiage possible commercial uses only to find the autopilot doesn't protect against this sort of thing. 

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Permalink Reply by Jeff Taylor on April 30, 2012 at 1:44pm

Hi Zen,

Sorry to hear about your quad! Based on my experience it sounds like the R/C gear lost link and it held the last good data it received which was high throttle. If you're using a Turnigy 9x that would make sense, I've had the 9x drop out at really low range before. Any idea where it could have come down? Maybe you could put up a notice somewhere to contact you if it's found... depending on where/how it landed you might be able to recover a lot of stuff from it.

Jeff

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Permalink Reply by Jeff Taylor on April 30, 2012 at 2:59pm

I can't say for sure because I switched to a spektrum after I had the signal drop I mentioned above over a year ago. That time I was also flying a carbon fiber quad and I thought maybe the CF (which shields RF pretty well) may have been part of the cause.

That said, a lot of people have used the 9x without problems.. whether that's because they keep the quad really close or because they are using ER9x I'm not really sure. Fortunately for whatever reason flyaways like this don't seem to be happening much or at least no one mentions it in the forums if they do.

Usually when people talk about failsafe they mean that the receiver detects loss of signal and goes to a predefined output, not freezing the last known output. Usually then you would set the output to be switching into RTL mode or just killing the throttle so it doesn't fly away. The cheapest solution is probably to switch to the FrSky module mentioned in your link above, that one has a normal failsafe feature that can be set to RTL.

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DeveloperPermalink Reply by Andreas M. Antonopoulos on April 30, 2012 at 10:28pm

Essentially, this is the fixed-wing airplane setting. It is usually combined with a slight roll to go in a circle. If the radio is lost, the engine "coasts" until the battery runs out. The plane just glides in a circle to the ground.

In a copter of course, a stuck full-throttle or even mid-throttle will send it to the moon, and a slight roll (I think the default on mine was 10deg), would send it off to the side too. 

So, you flew a copter with the failsafe settings for a fixed-wing. Again, not blaming you because I did the _exact_ same thing 3 times in the last two months. Apparently I'm not only a newbie pilot, I'm a slow learner because I didn't get it until the third accident. 

I have added a warning about failsafe to the wiki here:

http://code.google.com/p/arducopter/wiki/AC2_First

"failsafe modes for signal loss.."

and another warning about avoiding high altitude and speed before testing auto modes and failsafes, here:

http://code.google.com/p/arducopter/wiki/AC2_Safety

"Avoid flying at high speed or high altitude"

and 

"Avoid sudden or extreme control deflections"

(this last one unrelated to your accident, but very much a part of mine ;-))

Hey, sorry about your lost copter again, but at least we can use this experience to help future droners. Thanks for posting it.

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DeveloperPermalink Reply by Andreas M. Antonopoulos on April 30, 2012 at 1:57pm

Ugh!

What a horrible experience, so sorry!

i have crashed my quad 3 times, each time because of too much altitude + wind + loss of control - it seems to be the recipe for disaster. 

I know this will not be much comfort, but it is precisely because of this scenario that I worked on porting "geo-fencing" to the ArduCopter. The goal is to have an automatic fence that does not allow your copter to go too far and will automatically return it if it does (if GPS is working). 

I'm considering putting "Property of X - reward if found" on the bottom of the quad, in case it gets lost. Then again, I am wondering if that note just provides someone with contact details for a lawsuit if it damaged property or worse when landing.

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ModeratorPermalink Reply by Alex on April 30, 2012 at 2:17pm

Best thing is to buy a cheap GPS GSM tracker of ebay, then if something bad happens, you can always use that to locate your lost UAV

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ModeratorPermalink Reply by Gary Mortimer on April 30, 2012 at 2:37pm

Bad solder won't induce runaway ESCs, not setting a failsafe will! 

What was the expected behaviour of the throttle channel in the event of a loss of signal?? 

If you can't answer that before you fly then you should not be flying, also make sure you test that function, props off before your first test flight. Its non negotiable. Setting of failsafes is very radio dependant so consult your manual!

Harsh words I know and a hard lesson learnt. Console yourself in the knowledge that 5 years ago multicopter levelling only boards started at $1000 

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Permalink Reply by Zen on April 30, 2012 at 2:33pm

So to be clear - I bought the kit from DIY, as-is, and what came with it is what I used.

I specifically bought this kit BECAUSE of all the safety/auto shit that's included, but didn't enable or investigate for any maiden flights.

Now that I know what's possible I would say that it's a requirement to geo fence during initial flight testing. That way if failure at least it'll be contained. I would also state that after initial testing and "burn-in" is done and everything appears to be safe, that telemetry is the next requirement. That way if fail at least you have an idea as to where to look for your shit.

I don't think anyone except the guy who was with me knows how far this thing went. It was literally almost completely out of sight, both in height and distance. Without last know coordinates we wouldn't even know where to begin looking. Someone also mentioned a liability issue, and you're spot on... It's kind of scary thinking that UAV's can just fly away on their own and drop from the sky.

RTL on signal loss, geo fencing, telemetry, gps transponders, etc all sound cool but seem 100% necessary to me. How does one know if their aircraft is 100% reliable? How much testing and air time need to be done before you're comfy knowing all is well? Sounds like you never can be 100% certain, which to me sounds like safety should be 100% required.

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ModeratorPermalink Reply by Gary Mortimer on April 30, 2012 at 2:56pm

You did'nt enable the simplest failsafe, the one included with the radio. Every RC flyer should have the throttle channel set to close in the event of loss of signal.

Its a building block of RC flight, nothing to do with autopilots.

Yes your quad would drop like a rock but at least you would find the bits.

By having a flyaway you have no idea what your quad hit when it fell. Perhaps if it had your name and address on it somebody might come knocking on your door with a claim.

Of course UAS can fly off, its your responsibility to make sure it does not. 

The amount you spend on the radio gear, is directly proportional to what you stand to loose with what you are flying. $50 radios are great for $50 machines.

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Permalink Reply by Jake Stew on April 30, 2012 at 4:22pm

   Bummer dude.  I have to say that I have read quite a few stories like that.  This sport just isn't plug-n-fly yet, it really is for developers and tinkerers at the moment.

   If it's any consolation, a lot of people crash and burn their first few times.  Thanks for bringing up the potential 9x problem though.  I've got one and should probably do a lot more testing of failure conditions.

   It's too bad the autopilot didn't have more sophisticated failure handling.  But I don't know how much you can  really expect the autopilot to do when flying in manual mode.

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Permalink Reply by Crispin on April 30, 2012 at 5:16pm

Bummer to hear but, go look for it.  I've found mine after what seemed hopeless fly-away, a friend 3 times.  

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