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Motor or ESC failure - Inspire1 meets lake

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After more than a week drying out the bird I thought I'd give her a go and see if I could get my hands on the flight logs. Amazingly the started up, connected to the controller, got satellite reception, everything. I must say I was really surprised :) So I've forwarded the Flight Log on to DJI for what that's worth...
 
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Okay, so I'm very very curious now...

I just started up the Inspire again and ALL the motors run, even the burnt ones I thought caused the crash!:eek: I mean, this thing crashed into the water while powered on and was under for 3 hours! It shouldn't even be able to power up!

I'm really glad I've got the flight logs to DJI cause there's something else going on here.

Any one have any ideas?
 
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Guys, I was suspecting that what took my F550 into the lake was a mistake caused by interference from the lake. After reading this post now I'm sure!

"4 Terrain: In addition, signal distorting factors such as water bodies (reflection of GPS signal causing false readings) and metal cables of cable cars or ski lifts, will adversely impact the accuracy of the GPS."

Source:http://electronics.stackexchange.com/questions/116411/gps-and-barometer-assisted-flight-on-a-mountain
.
...RTFM...
.
(for the n00bs, ReadTheFknManual)
...i haven't read the F550 manual so.. maybe its not in there, in which case common sense should dictate...
.
 
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I do not read the manual, as I mounted my F550 matter all the separate parts. NAZA in the manual does not say anything about it.

Already in the Inspire 1 manual says and I'm glad to hear that. It's a shame that I have been aware of it after losing my F550.
 
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Hi Andy, (sorry, still not had a chance to get over to Freefly!)
Not a problem, Ed.

There are VERY few reported incidents of motor and/or ESC failures on the Inspire platform.
That's reassuring. I've been doing some work with the American Society of Test and Measurement working on operational risk assessment and ESC failures was viewed by the task group as a high-likelihood/high consequence failure.

When the aircraft was designed DJI completely engineered a new propulsion system from the ground up.
It is the first time (to my knowledge) that reverse emf braking has been used on a multi rotor - and boy do we know that works! :p
I might be mistaken but I think Mikrokopter may have done it sooner -- with their BL-Ctrl 3.0. One of the more interesting consequences is that when back EMF breaking kicks in, we were seeing (on my lab dynomometer test bed -- I do independent motor testing) huge voltage spikes from the motor to the ESC caused by the back EMF as the field collapses. Interesting side effect.

From memory, I think the escs are running at about 800hz which is another first.
I'm with you in that I think the tip over caused the initial high current draw whilst the motors were stalled, which burnt off the insulation. The rest was only a matter of time.
Indeed....after that it's just a case of "How do you like your motors, Sir? Well done, or medium?" :)

As an aside the OP asked whether full throttle for long periods of time would cause an issue. The answer to that on the Inspires/E800 propulsion system would be no. It is over engineered for the platform and the AC has a payload capability of 3.4kg. It is only spinning 13 by 4.5 props on 3510 kv350's on a 6S so things are not exactly stretched.
Plus, as the motor is not stalled, I suspect the vent holes on the motor bell and the prop-wash all would aid in cooling both the motor's stator and the ESC.

I genuinely believe in this case the damage was done at the tipover with time then not being on the motors side. :(
Sadly so.
 
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Any and all info is greatly appreciated. The more I can learn about the I1 the happier I am :D
Losing a bird can be a lonely experience, so the good wishes of fellow pilots are also much appreciated.
Thanks you lot!
Editor: One of the more active members over at Freefly requested he have the Member Title of "UAV Grief Counsellor." Not a bad idea to have one on every professional UAV forum. One feels awful when you lose a bird...

Ferdi: I suspect there are only two kinds of copter pilots: those that have lost a bird, and those that have yet to lose a bird. You've joined a fine club with folks who can both empathize and sympathize.
 
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Today I re-calibrated the IMU, then did a 10min hover at an altitude between 5 & 10cm AGL. I wanted to see if I'd have the failure again so that I could send another Flight Log to DJI to help with analysis. I also wanted to run the batts down to 50% for storage until the new unit arrives (hopefully in the not too distant future).

No problems at all. Hovered like a champ. Might be a different story if I actually fly it at 90% throttle... Won't know I guess cause I won't ever trust this bird to fly more than 10cm AGL again though. I'll run all my batts down to 50% and see if I get a failure again.

I'm kinda in awe of this resurrected bird :D
 
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Editor: One of the more active members over at Freefly requested he have the Member Title of "UAV Grief Counsellor." Not a bad idea to have one on every professional UAV forum. One feels awful when you lose a bird...

Ferdi: I suspect there are only two kinds of copter pilots: those that have lost a bird, and those that have yet to lose a bird. You've joined a fine club with folks who can both empathize and sympathize.
Thanks John! Yeah it's a sucky feeling. In Feb I lost a Phantom 2 with GoPro 4 in the ocean. 100% pilot error though. That's why we got the Inspire. Even though we always knew it would go down sooner or later, seeing NZ$5500 tumble out of the sky was still a bit of a shock :eek:
 
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So I hovered the bird and got my 3 remaining TB48 batts down to 50% for safe storage, about 36 mins hovering without a glitch.

The camera also still works, but the gimbal goes nuts. I've ordered new cabling between the bird and the gimbal to see if that solves the crazy behaviour (I doubt it though, but one can hope:p).

Still no word from DJI, although I've had prompt responses whenever I initiated contact via email.
 
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Just to let you guys know DJI will replace/repair my Inspire under warranty. Thus far I've had good service from them. Took 2 weeks from the date of reporting the incident for them to asses and make the call to replace/repair. I asked if they could help with shipping and they said they'd arrange pickup at my address by the courier company. Now the bird is off to Germany.

I'm very happy with the way DJI has treated me thus far.:D
 
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I guess I'll put my 2 cents worth in here.
I have to agree with Wormwood on what he wrote.
If the Inspire dropped into the water on one side (the side with the burned coil windings in the motors), the water would have shorted out the entire electrical system and left the opposite side of the AC dead before it even touched the water. This would explain why those two motors did not have burned coil wires.

I also have to wonder about the AC having issues before this flight. If there were FET and MOSFET issues already, running the AC at near full throttle and near full forward input at the same time, it could have overloaded the already damaged ESC components to the point of total failure and caused the AC to lose motor control on one side. It's pretty obvious that the right side of the AC dropped almost immediately. It did yaw to the right at the same time but that could be due to the left rear motor running faster than the left front motor.

I know that hindsight is 20/20 but if it had been mine, after the tipover, I would have replaced the ESCs and fully dismantled and fully tested all motors before any future flights.

Previous fly away:
Compass calibrations aren't limited to the standard 360 ° calibration. I have had flights where the IMU was checked in the app (not just checking the Mod numbers), the app indicated that an advanced IMU calibration was not needed. Then when I flew it, it would not track straight at all even after I performed the standard 360° calibration for that area. Those 360° calibrations are to help the compass to compensate for the earth's magnetic deviation at any given location. If I calibrate it here and it tracks straight, then drive 500 miles west of here, it would not track straight because of the earth's magnetic deviation (with respect to magnetic north). After moving to a location 500 miles away, I would have to do a calibration so the AC's computer can program the compass to take that new magnetic deviation into account.
As mentioned, that flight where the AC would not track straight even after performing the standard 360° calibration was a firm indication that the compass did need an advanced calibration even though the app indicated that it didn't need it. Even the overall status window (popup page) indicated that the IMU was normal.
I put the AC on a table, leveled it in both the y and x axis and performed an advanced IMU and compass calibration (yes, the compass Mod numbers were right at the 1500 mark before the advanced calibration). The other Mod numbers for the gyro and accelerometers were where they were supposed to be as well. BTW, it did hold well with being level and didn't drift while hovering.
After the advanced calibration was complete, I performed another standard 360° calibration and the AC tracked straight as an arrow in both axis (forward and sideways).
Some people tend to think that the advanced calibration is only for the gyro and accelerometers but it is also for the compass.
Frequent advanced calibrations don't hurt anything. I had one guy to tell me that it could damage it by calibrating it too often. DJI Tech Support says it doesn't. Being an electronics technician and machinist myself, I can't believe that frequent calibrations will hurt it. If anything, it can only help.
Oh, I always do a full advanced and standard calibration after every firmware update. I do hope they get to the point soon where we don't have to update the firmware so often.
Another issue with fly aways is magnetic interference. I always use a teslameter to check for magnetic interference. If it's higher than 100µt, chances are your GPS won't have a clue where it's at!!
I don't use a smartphone teslameter app to test for magnetic interference. They aren't very accurate in my opinion so I use a portable device made especially for that purpose.

One other issue that I've noticed with some pilots (drones and sport RC) is that they will for some reason be standing at their electric model and spin the props while it's powered off. I watched one guy spinning the heck out of all of his props just for fun (maybe it was a nerve problem, I don't know). I tried to explain that when you spin a prop by hand, you are producing electricity and it has to go somewhere! Guess where it goes. It feeds right straight into the ESC but backwards and does damage it!! I'm not saying that's what happened in this case, it was just a warning for those who didn't know that spinning a prop by hand will damage an ESC.
I decided a while back to hook a brushless motor and ESC up to my bench voltage meter and oscilloscope and spin the motor just to see what would happen. It didn't take too many times for it to destroy the FETs in the ESC!!!
It's a good idea to pull up on the motors and pull on them sideways to check for bearing wear but never spin one by hand. Spinning them by starting the motors and listening to them without props is the best way to check for bearing noise. Just spinning them a little still produces voltage. DJI's checklist even says to start the motors to listen for bearing noise.
On my next trip to the flying field I ran across the guy that was spinning his props, he said that his drone crashed because one of the motors just quit right after takeoff. He was ranting about not knowing what happened and was even blaming the manufacturer for a faulty ESC or motor and said he was going to make them pay for the damages. I just walked away while shaking my head.

These brushless motors are 3 phase AC (alternating current just like the AC voltage in your house). They will produce high voltages!! The faster you turn it, the higher the voltage.
If you ever read about being careful to never over rev your brushless motor, that's why. If you take a single rotor electric helicopter and put in a dive with the collective stick at neutral, then give it positive collective when you flare it out before it hits the ground, the rotor and motor will spool up to way more than the battery and ESC is designed for. That over rev just damaged your ESC by feeding too much voltage back into it.
ESCs are nothing more than precision inverters, they take one positive and one negative wire from a DC voltage source and turn it into 3 phase AC power (alternating current). 3 phase AC motors will produce much higher speeds and power than a brushless DC motor.
The gimbal on your Inspire has DC brushless motors because they will produce much higher torque at very slow speeds (much faster than a servo but much slower that a prop motor).
Gimbal motor controllers are strictly DC.

I go so far as you use a portable spectrum analyzer to record any activity on the 2.4GHz band. I record about 10 minutes worth while walking around as close as I can to the area I will be flying at.

Am I going overboard? Maybe. But I can honestly say that in four years and over 800 flights I've only had two crashes. One was determined to be a radio jamming system on heavy equipment (used as a theft deterrent device) which is why I now use a portable spectrum analyzer everytime I intend to fly. Yes, there have been a few times that I decided not to fly as a result of obvious radio interference. The other crash was totally my fault, I was trying to squeeze just a few more flights out of a set of heavily used 18 month old lipos with high internal resistance, yes, it was a really dumb thing to do but I guess we all need a reality check once in awhile eh?
Becoming too complacent is not a good idea!! Being a licensed private pilot since 1987 has taught me that one well!
I've never had a crash in a manned aircraft but I did have an engine failure and set it down in a field. I didn't physically check the fuel like I was supposed to, I just looked at the guage but it was wrong! At the time the engine quit, it showed that I still had 1/2 of a tank on each side.
I did have a fly away once but it didn't crash, I managed to get it back after putting it in manual mode and flying it back (that was my S800). That one turned out to be very strong magnetic interference which is why I now always use a portable teslameter.
I started out with a 700 class single rotor with a front mounted servo based gimbal, no GPS or self leveling gyro, then I bought the S800, then the S1000 and now the Inspire Pro. The fly away was with the S800 and manual mode is the same as no self leveling gyro at all which means if you aren't careful, you'll flip it upside down in a heartbeat. Man, will that beast fly like a bat out of H*LL in manual mode :-O Lol Good thing I have lots of experience in flying single rotor 3D helis.
Yep, When I was learning to fly 3D aerobatics, I crashed quite a few times!!

Ok, that was way more than 2 cents worth :-D
But I do hope this info helps somebody to prevent a highly unwanted crash (as if anybody wants to crash). Although, I did watch a guy at our field crash an old Raptor 90 on purpose while we were filming it. It was flat worn out, never been crashed and the owner wanted to retire it. He said that he decided that he wanted it to go out with a BANG! Lol

Edit:
Updated Information:
NOTE: Recent research has revealed that DJI did not install Schottky diodes at the output of the ESC to the motor to prevent Back EMF (BEMF = Back Electro Magnetic Field, which is voltage generated by the motor feeding back into the ESC). DJI actually uses this Back EMF (BEMF) to help regulate the speed of the motor and the braking system more accurately.
 
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