Multiwii pro jittery after big crash

[dod22]

Hi everyone so I've built a FT H-quad in June and couldnt have done it without @CraftyDan and others. I've gone through at least 10 frames since then first built out of wooden then aluminium square tubing. So here's my current problem

-The last time i was in the air was with a DIY aluminium frame and it fell from about 100 meters (prop came off no locktite I'm a bad person I know), luckily it landed flat so 4 new props and it seemed fine physically. I tried to take off again just after the big crash and it did this jittery thing where one motor would surge randomly.

-I then didn't touch it for about a month (masters thesis got in the way of flying time) and rebuilt it with the same guts but on a SK450 frame and 10X4.5 props instead of the 11 inches ones I had before.

-But not the jitteryness is so bad it wont take off, I've uploaded a video so you can see (sorry about the quaility its terrible but its late and I've been working on this for too long)

I think I've done all the obvious trouble shouting
-ESCs are calibrated using the board
-ACC and Mag are calibrated
-Batterys fully charged
-Plugged in and take off on a level surface

Any help would be greatly appreciated, thanks

https://www.youtube.com/watch?v=qnMNggfDiuc&list=UUo5rbeSybDd5FzthchzAQKQ&index=1








Sk450 frame
DT750 motors
10X4.5 props
30a Plush ESC
Multiwii Pro from Hobbyking board with 2.2 software

 

[joshuabardwell]

For what it's worth, ACC doesn't do anything unless you are flying in Angle or Horizon mode. MAG doesn't do anything unless you have it activated or are in heading-free mode. So if you are in Acro mode, then only Gyro matters. Dumb question: does the gyro show 0,0,0 when the quad is stationary? Do the numbers correctly change when you rotate the quad along each axis? It's possible that the hard crash damaged the gyro. Although these are solid-state components, they do have mechanical parts (very tiny ones) and can be subject to damage in hard crashes. It's unlikely, but it should be ruled out.

Next step is physical inspection of the motors. Bent shaft, bad bearing, etc...

Disconnect the ESC's from the FC and plug them, one at a time, directly into the throttle channel on the receiver. Power up, throttle up, and confirm that all motors throttle up smoothly and correctly. Confirm that they all begin to spin at about the same point. A bearing dragging would cause the motor to need more throttle to start spinning. If you have an amp-meter, plug it in-line with your battery and measure amp draw at full throttle for each motor. A motor with a bent shaft or damaged bearing will have more current draw.

If none of this indicates a problem, I would probably spring $15 to try another flight controller.

100 meters is a pretty hard fall. It'd be amazing if something didn't break!

PS: It doesn't seem like you have any bad ESCs from the video you posted. They usually cause motors to jitter and/or not spin up at all.

PPS: Check all relevant solder joints. If an ESC's power was intermittent, you would hear it beeping as it came back online. But if an ESC's signal lead was intermittent, it's possible it could cause motor surging. It's a long shot, but worth keeping in mind.

 

[dod22]

Hi Joshua thanks for the advice

One thing I forgot to mention, if I throttle up slowly everthings fine and normal till about 60% throttle then it starts to surge.

-The sensor graph on the multiwii GUI all looks normal, a bit of vibration when the motors are running but nothing huge.
-I've just swapped out two of the ESCs for new ones and it had no effect.
-if i hold the quad and tilt it one way it tried to fight me to level itself so I presume the gyro is doing something.
-I'm pretty confident all my solder joints are good cause u basically had to resolder everything when moving from the
big H-quad frame to the SK450.
-Its not bearing drag cause the motors do the same surging thing when I dont have any props on and the motors arent screwed into the mounts.


I found this forum post where the guy seems to be having the same problem as me but the thread was never solved

http://www.multi-rotor.co.uk/index.php?topic=7224.0
https://www.youtube.com/watch?v=X1CufoA_bUA

 

[RichB]

I vote for bent motor shafts or some other physical issue that is causing vibrations at speed.

 

[jhitesma]

Have you ruled out a problem with the motor? A shorted winding or broken winding wire that makes intermittent contact could be causing what you describe.

 

[dod22]

Rich and Jhites I think ye might both be right. I reloaded the board with 2.3 and swapped out one of the motors (I only had 1 unused motor on hand), it seems to work now it will just about get in the air but its now randomly surgy and odd motors apart from the new one. Also one of the motors started to spark last night and I had a look its wirings are fraid.

Looks like I'm have to order new motors, its kinda amazing they lasted this long these motors have seem some serious crashes since i built my H-quad in June.


Thanks for all yer help once again.

 

[jhitesma]

Brushless motors are simple, but unfortunately not bulletproof

What motors are you running out of curiosity?

If you're good with your hands you could always try rewinding them. I rewound two of my 24g HK motors on my knuckle quad - it only took me an hour or two one evening even though I had to do one of them twice There are a number of good articles on the main FT site and youtube videos showing how to rewind motors. It's not that difficult. Basically you just unwind them paying attention to how many wraps are around each stator and what winding pattern/direction is used. Then put fresh wire back on the same way. Radio Shack here in the states carries magnet wire that will work on some motors - but you may have to order some depending on the size of wire in your motors.

Other than a dented bell there isn't that much on a brushless motor that isn't repairable. Bent shafts can be replaced, loose magnets can be reglued, bearings can be replaced (though it's a lot easier to replace them before they fail completely!) and windings can be re-wound.

 

[dod22]

I'm running DT750s, I found this crazy detailed post about rewinding them on rcgroups http://www.rcgroups.com/forums/showthread.php?t=1892195 . I might give it a go if I can get my hands on the wire.

I had it up in the air earlier for a few minutes before one of the motors stuttered for too long and sent me to the ground. I'll probably end up ordering a new set of dt750s and have the dodgy ones as a rewinding project. How many turns did u have on each stator that rcgroups post says 100 per stator for the dt750s.

 

[joshuabardwell]

The DT750 is a fine motor, but I think you can do a lot better these days. For example, 2212 980kv.

 

[jhitesma]

I don't recall exactly how many turns there were on the 24g motors but I think it was in the 12-16 turn range. Was really easy.

I'd also agree with looking into better motors if you're going to replace them. The Sunnysky 2212's are amazing, and there are some rctimer and the sunny Sky angel 2212's as well that are cheaper but not quite as nice as the x series Sunny's. Switching to something with a bolt on prop adapter and more protected wiring will help prevent further motor damage from crashes in the future.