6 Motor Failures. What is this noob doing wrong.

[Nocteel]

So here's the long story condensed down as much as I can. I have just built my first multirotor and have been grounded due to motor failures more than I've been flying so far. First I suppose should be my specs:

Flame Wheel F450
DJI 30A ESCs
NAZA + GPS
DJI 2212-920 and Twister T450-880

There are two motors listed because that's what I've had on it so far.

I bought most of the parts as a kit from Atlanta Hobby after spending a month or so trying to learn as much as I can. At the time they where offering a ARF kit with the Twister motors instead of the stock DJI. Since these where a bit more torquey and not that much more as far as the cost of the kit. I went for it knowing that I would eventually be putting a GoPro on it. Shortly after I finished the build and before I really had it off the ground (just testing motor direction and hovering for programming testing) I noticed one of the motors making an odd sound. After a quick inspection I found one of the motors had started to separate and the barrings where grinding. (By separating I mean the bell had slid up the shaft and lifted off the base.) I contacted Atlanta Hobby and they immediately shipped me 2 replacement motors (not sure if that was intentional or not). I replaced the bad motor and after one flight found the replacement was also bad but this time the bell was actually directly binding on the base. So after replacing the replacement I was able to fly for about 10 or so flights before I had a catastrophic failure of the replacement replacement motor. From about 30 ft up one arm dropped which threw it into a nasty spiral and into the pavement. After a few four letter words I checked over the wreckage and noticed that in addition to the fully bound motor 3 of the others where just starting to bind as well. Same as the first replacement where the bell was touching the base. Again I contacted Atlanta Hobby and simply asked what I was doing wrong and they responded by not only sending 4 DJI motors and a replacement arm for the one that broke but told me that they where looking into the MFG for what was going wrong. I was told in a later email that there had been a MFG defect with that batch of Twister motors causing the binding and that I should just keep using the DJI motors till they sorted it out and ship me four new Twisters. This leads me to two days ago when I'm flying and again loose control. This time from closer to 80 ft up. Having more stick time under my hat this time I'm able to at least direct it away from the ocean where it had started heading and land it in a empty lot. (Ok so the "landing" was pure luck since I was aiming for the road where I might have been able to find it. I was only about a 100 yards off.) Again the survey of the crash finds a failing motor but this time it's on the DJI and looks more like the very first failure where the bell is pulling away from the base and the bearings are grinding. The way I understand it this is not the same issue that caused the original recall and since it has happened twice now on two different brands I'm wondering if it's me or my build.

So after all that my questions are this: My 4 new motors should be here in a few days. How do I keep them in the air? Is it something I'm doing or is it just pure bad luck that I keep having these things happen.

There are a few other details but this post is already too long so I'll leave it here and/or add on later if needed.

I'll be thankful for any help I can get. With this much money hovering over my head I'd like it to stay there.

 

[ProPilotWannaBe]

I definitely am not qualified to help you debug this issue, but I do know the first question that someone will be asking is what battery type/size are you using? I'm guessing 3S or 4S, but you might want to put that information out there for those ESC/motor savvy people out there to help you debug the issue.

 

[olof]

Just curious, you mention the ocean so is it possible some salt mist/spray/beach sand may have had contact with the MR?

It is strange that you are having bearing failures.

One thing I do after every flight is check the temp of each motor, usually about 95-105 F, I measure with an IR thermometer. If you have hot motors something is wrong and if one starts running hotter, it is an indication that motor is going bad. Or that your CG is off.

Make sure they all sound the same before takeoff.

Make sure your CG is in the middle, pick up by opposing on arms one finger under each to check. If CG is off the MR will still fly but one or two motors will work much harder (and they will get hotter).

On my 450 I use 4000 3S Lipos, it is a very good match, even with a GoPro attached. Any heavier would be too much. On my 550 I use 6400 3S or dual 4000's and a Yun-1 gimbal. On my S800 I run dual 6000 6S Lipos, and a ZenMuse Gimbal.

I have hundreds of flights on these and no motor problems on any of them. They are all stock DJI parts except I use Graupner E-props on the smaller MR's.

 

[tstrike]

Wonder if your using to long of a motor mount screw and it's going into the windings.

 

[Nocteel]

Yes, duh battery. Knew I forgot something. I am using 3s liPo 3650 and 4400 batteries. (45C if that also makes a difference.)

This was actually the first time flying close to the beach. (Well closer than about 2 miles away) I try to avoid flying when there is strong wind off the water anyway. I suppose there is always salt in the air here, and I figured I'd be replacing parts a bit faster than average but I find it hard to believe that it would take affect like this after only a few weeks.

I do check everything over before and after every flight. The twister motors never really did heat up much more than ambient temp and the DJI motors would get warm to the touch but not hot. (Don't have an IR thermometer.... yet) Also they would be evenly warm after a flight.

My CG is about as close to perfect as I can get it. On a side note I have also been checking prop balance as well.

As far as mount screws, they are the stock screws that came with the frame.

 

[Electro 2]

Seems to me the message is clear here, no more "Twister" motors. If the failures were all on one arm, maybe a bad ESC. If not, and they are randomly dropping, lose 'em.

 

[Nocteel]

That was what I was thinking until the DJI motor failed. It's been different arms as well. Can a bad ESC cause motor bearings to fail?

 

[OneStopRC]

I have been using DJI motors for months, never had a bearing failure but did replace one as it was sloppy. Never had one fail on me like you are describing, could not under stand why they would be failing like that. What props are you using? and what ESC's are you using?

Seems like you are not having much luck at all with this, never have I heard of anything like this!. Do your DJI motors get hot after a few minutes? Something is odd with all this....

 

[Nocteel]

ESCs are the 30A DJI ones and the props on it now are, again, the stock 10in DJI. With the twister motors I was running 10x4.7 APC. Now here's something I didn't mention in the original post. The 10x4.7s are the ones that came with the kit but in doing more digging after all this has happened I noticed that the Twisters are rated for 12x6. Could running them with the smaller props with less bite be a cause? I did once fly the DJI motors with the 8 inch DJI props as an experiment. (Liked the way if flew but I had an almighty 2 min battery life.) Maybe that's it?

I would love for someone to tell me that I'm doing something wrong. I'm having a hard time believing that my luck has just been that bad.

 

[OneStopRC]

Sorry, did not notice where you mentioned the props before. You could have damaged them running the 8" on the 3S battery, you would probably have been running them motors hard to get them to give you lift. As I said, I have never seen issues like this, not with the DJI motors anyway.

Unfortunately, you can't run the 12" props with the standard DJI arms, but rctimer make some longer ones that should allow you to go to 12" props.. see here http://www.rctimer.com/index.php?gOo=goods_details.dwt&goodsid=845&productname=

 

[ProPilotWannaBe]

Deanot, you may be right. However, I used 3S and 4S with 8" props for the first 3 weeks I had my F450. Though now I run with 10" (DJI 10x3.8) on 3S all the time.

 

[OneStopRC]

That is what I run on my DJI motors, 10" on 3S or 8 on 4S. Waiting on getting some 9" while I get the funding for lower KV motors and bigger props, hoping to go to 12" with the longer 800mm Arms.

 

[Nocteel]

Hadn't seen the longer arms but I had been looking at some aluminum extender plates I came across. What is the min clearance required between props? Is it just "don't let them hit anything/each other" or are there other factors involved?

 

[OneStopRC]

I heard bad things about the metal plates, people have complained they are pretty heavy... Just what I have read around in places.... I wanna do the extended arms option, some on here have done it and love it.

 

[Nocteel]

I might play the guinea pig and order both and report back. Then again by my measurements the 12 in props should clear each other by 1.5 cm on the unmodified arms. Is that too close? I don't see how they would be able to hit each other without something else moving and I can't imagine that the arms deflect that much in flight. But that's just the noob in me talking again. Would that close of a clearance cause unwanted flight characteristics or funky efficiency sapping turbulence?

Thanks for all the feedback so far.

 

[SMP]

Did the extensions on a 550 using Aerial Media Pro extensions and Tiger 2814 motors and 12" Wooden Xoars. The bird is a friggen rocketship now, unfortunately its also a vibration monster. My guess is the plastic arms flex with this much torque.

 

[OneStopRC]

Not sure on the clearance of a 450, my 550 has about 3/4" with 10" props... wow SMP, that sucks, up until now I had heard good stuff about them. How bad is that vibration?

 

[SMP]

Not sure on the clearance of a 450, my 550 has about 3/4" with 10" props... wow SMP, that sucks, up until now I had heard good stuff about them. How bad is that vibration?

Hi Deanot, the extensions work fine I think it may be more to do with my application.. I'm fitting it with a brushless gimbal which are extremely sensitive to vibration. Currently the Gimbal is mounted using M10 vibration dampers which are not working well. Will be trying MUCH more vibration damping and hopefully that will resolve it.

 

[OneStopRC]

Hi Deanot, the extensions work fine I think it may be more to do with my application.. I'm fitting it with a brushless gimbal which are extremely sensitive to vibration. Currently the Gimbal is mounted using M10 vibration dampers which are not working well. Will be trying MUCH more vibration damping and hopefully that will resolve it.

Cool, hope your issue gets resolved doing this. Would be interested to find out if you get it resolved.

 

[Eggbeater]

Before changing and adding more equipment right now, did you ever check the mounting bolts as suggested? The bolts should not protrude into the motor case at all and even a slight recess is good. Just use Loctite. The bolts can physically touch the windings or cause interference. Checking the heat of motors/esc's all around should tell you something whether it's per arm or all arms. I'd check these things first but my initial reaction was cheap bearings. And that can span across many motor brands. Many manufacturers use the same parts sources. But something could be causing the bearings to get over-stressed. That's where the bolts and heat comes in. Interesting case. Other suggestions about sources like battery size etc are good ideas. But don't think I'd be looking into changing something else like exotic arm extensions and prop experiments (which can work well) until I got the basics to work first. You'd just be creating more variables to consider. EGG