Boooo...
After a good day out yesterday, I took my small quad out for some full stick action tonight.
And it was all going well until...I think I sheared off a motor. At 20m. So this happened:
Reason I think the bolt sheared, is the fine thread left in the bottom of the motor (I tried to show it in the pic). And the way it just tumbled out the sky. I think you can see it in the logs from the motor logs (crash event starts at 20 with impact at 20.4).
Up until then it was flying well - but if anything a little under powered; feels more "Nissan Micra" than "Nissan GTR". Though it would appear the mounts can't handle it if you drive the Micra like a GTR...
It appears the legs took the brunt - all props and unsheared motors are ok, as is rx/telem, battery GPS and APM. Motors were pretty hot when I picked it up - they'd been working hard.
Vibes until then were good - +/-5 to 6 when doing full sticks, and +/-2 when hovering:
I've attached the flight log, just in case anyone wants to prove my "sheared motor" theory wrong.
Comments
Ok, as way of an update...check out my new mount!
Due to a "senior moment" by me, I managed to only order 1 instead of 4 (remaining three onroute), but not before time...I did a check over of the "trainer" quad tonight as it had now done 1 hour of flight time since the crash. And...worryingly the mounts were loose on 2 motors!
So it's officially grounded until this is resolved. This first one looks promising - blue lactite in all the threads, and the new mount with the "X" bracket as well. It *should* do better. It will also cut down on the vibes too, but TBH I'm only exceed +/-5 briefly when doing full sticks anyway.
@ RD - yeah - motor is a write off. threads pulled off 2 of the holes, wiring snapped, and part of it was "ingested" into the motor base, jamming it solid. I can only imagine the damage to the bottom of the poles. I think the shaft is ok, and the prop is fine, as is the prop mount. But...for safety sake, I've written it off, and am getting a replacement. What I can save will go in the spare bin (the shaft would be especailly useful).
I may try and repair it one rainy afternoon when I'm feeling experimentally brave.
The motors are 2216-11's (900kv). To be honest, they are slightly underpowered for the weight I've got on. A bump to 700kv (hopefully without needing to go to 4S) would probably be good, but as this is my "trainer" quad, I'm not throwing money at it, unless it really needs it. Even the use of t-motors and CF props was a bit overkill.
Ouch! And to make matter worse the wiring was jerked out of the motor. It is probably repairable...probably.
What motors are those? They look quite beefy.
Regarding logging... (short story) I had enabled logging on one of my MRI systems trying to catch a problem. I forgot about it until the service call came in (weeks later) regarding sloooow system performance. Yep. The hard drive was nearly full of logging events. Lesson learned.
-=Doug
That's interesting Nano - funnily enough coming from an IT background I know the impact of logging too verbosely, but it is standard practise when deploying a new service - so I had i all the interesting bits turned on. I was hoping to turn it back to defaults after 2-3 flights and the airframe/PID's were fully optimised.
In the few flights I've done, I can't say I've noticed any performance issues. I do clear down the logs after every flight, as I know filling up the memory with logs can have consequences (just like IT system actually!)
Better do the same for the big quad too!
You live and learn...:-)
PS: You say sheared, but sheared means that the bolt end would still be in the bolt hole. if you mean the thread had stripped, that would be much more likely with a brass bolt than a steel bolt. This could even just be due to over-tightening. With a steel bolt you are more likely to strip the aluminium bolt hole, but the brass bolt it would be the aluminium bolt hole. From the picture bolt hole threads look ok, which is good news, as tapping them to a larger size can be a pain. You should be up and running with some soldering and new bolts in no time.
A good tip is that don't check a bolt is tight by tightening it a little bit, as eventually it will be over tightened. Place a dob of nail varnish (hard wearing paint) on the bolt and joint, if it cracks (i.e moves) remove, reapply loctite, then reinsert.
As Jesse says you need blue Loctite on the threads. And use steel screws not brass. Brass is much softer and is good for use in wood applications where you don't want it to mark the wood.
How many screws do you use to attach the motor to the mount?
I always use all 4.. not sure why an event like this would happen if all four screws are used to attach the motor.
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