Arducopter Non-Simulated Motor Failure Test!

I took my new Pulsar H-8 Octocopter for a test flight tonight.  I'm getting ready for more flights with the Nex5 camera, so I wanted to give it a bit of a shakedown run. For this flight it has a Contour camera mounted just for fun.  Previous to this flight, some of the bearings sounded and felt a little iffy...  and now we know why!

One of the motors failed and came apart in flight.  It appears that when it came off, it actually hit another propeller, stopping it.  The H-8 now had two adjacent props stopped which isn't good.  It does a flip, but then miraculously recovers after the second motor re-starts.  I've never seen a better example of Arducopter stability and fault tolerance.  In the past, I've disabled motors by removing the props to test the performance, but it's just not the same as the real thing.

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Comment by Dany Thivierge on July 16, 2013 at 10:47pm

Not too bad then!  I hate the walk of shame... :)   (happen quite often to me still after all these years!) 

Robert post more picture of your Pulsar H-8 for us to see here instead of looking around in the other threads. 

Again great code (3.0.1) and redundancy on an octo! 


Comment by leonardthall on July 16, 2013 at 11:56pm

That is an amazing bit of footage!!!

Comment by Graham Dyer on July 17, 2013 at 12:21am

"Ominous screeching sound" - LOL... yeah, that's NEVER good!

Comment by Shaw Innes on July 17, 2013 at 1:33am

It's not great that your motor failed - but that shot of the prop shooting off into the sunset is priceless! :)

Comment by Peter on July 17, 2013 at 2:52am

So was it happy chance or "stability and fault tolerance"?

Comment by Rob_Lefebvre on July 17, 2013 at 3:39am

Peter, I think it was a bit of both.  Obviously the code was able to handle it.  In fact, once it righted itself, I'm quite sure it could have flown back.  I actually couldn't really feel much of a problem, but since there was a nice place to land, and I was a little freaked out at the near miss, I decided to just put it down immediately.

However, it was also happy chance because, a second motor was stopped momentarily.  So it really had to save itself.  It righted itself from upside-down, with only about 50 meters of altitude.

Dany,  I'm kind of keeping this one under wraps for now.  It's a pretty good design, and I don't want to give away all my ideas on it. ;)

I do need to figure out what happened here though.  I'm pretty sure that the mounting pads for 4 of the motors need to be post-weld machined for flatness.  The bearings on them felt wonky right upon installation. I suspect what happened is that bearing failed, and the vibration caused motor shaft to shear off at the circlip. 

Comment by R. D. Starwalt on July 17, 2013 at 5:00am

'Wow' indeed!

I cannot help think that the 99.9% rule applies to the mass quantities of motor components in the hobby field now. In that I mean that all parts are 99.9% good. That 0.1% is nearly unacceptable in most professional environments and as the microaviation industry blossoms, my money is on regulatory agencies (if not insurance underwriters) requiring flight certified components if any airspace over people or insured property is used.

Well done AC3.0.1 (and Robert's airframe ideas probably helped some too)!


Comment by Rob_Lefebvre on July 17, 2013 at 6:08am

Yeah, again, I think that this is probably mostly my fault.

But still, they probably should never have failed in this manner.  My first Octo, I used 35mm motors, but these are 28mm.  They're tiny, and look a bit silly swinging 12" props.  But that's what they're "rated" for.  Even though they are low KV, and can put out 300W, I suspect the bearings and shafts, etc. are not up to the task.  Maybe they'd be fine if everything is perfect.

I would prefer the motor would hold together until the bearing seized, and then it would just stop.  Though maybe that would cause the ESC to burn up, and it's a 4-in-1, causing loss of the entire thing?

I dunno.

Though it's obvious I was pushing my luck flying with these motors that didn't feel right.  It was subtle, but I knew something wasn't right.  I'm just glad the Nex wasn't on board.

Now the question is... These are Turnigy NTM 2830-800 motors.  They are out of stock.  But I do have 1 spare.  But I think 3 others need new bearings now.  Have the circlips been damaged though, or will they be damaged when I replace the bearings?  Do trust these motors at all anymore anyway?  Maybe I should get some from a more reputable brand before flying with the $600 camera too much.

The only good part of the whole thing is, Arducopter performed brilliantly.

Comment by Josh Potter on July 17, 2013 at 6:58am

Is that stock rate I settings or a higher value?  Do you think it could fly with 2 less motors on stock rate I values?

Comment by Rob_Lefebvre on July 17, 2013 at 7:28am

Good question Josh, I can't remember and will have to check.  My guess is that it's stock Imax of 2500.  

The ability to fly with 2 more motors gone... it depends.  If the other motor on the same arm hadn't restarted, I'm sure it would have crashed.  It really depends on where the motor failures are.  I have flown a "round" Octo with 3 motors stopped, but I got to select which motors to disable, and did so in a balance fashion.  I got it off the ground, but it wasn't pretty.  Best case, if it was just the right motors, I think you could have a controlled crash.  If it was adjacent motors, then it's going in.


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