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New stress cracks. Motor mounts this time.

Discussion in 'Pro/Adv Discussion' started by bighi, Jul 28, 2015.

  1. bighi

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    Yesterday I noticed some wobbling even on a slow descent. I thought that maybe it was wind. Did the usual stress crack check and, low and behold new location. I was very happy that the glued seams on my arms kept all further cracking in check by providing lots of strength in that area. It worked since flight 24. But now at flight 68 comes in cracking at new location. This one just about leaves the motor with lots of movement. A disturbing amount. Enough that I'd say a full motor loss could happen. Gluing is in process as I write this. If it does not work, serious work will be required in that area. I will update on the results but I don't have a very good feeling this time around. I honestly thought that all we had to deal with on the phantom 3 was the two side by side screw holes. Nope. Motor mounts are also a problem. I do have a spare, brand new phantom 3 but I will not use that one until I know exactly what I need to strengthen before flight 1 happens. 20150728_182233.jpg
     
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  2. bighi

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    I'm not going for beauty in the repair this time around. The movement from the motors (two arms) is so much that it gives me the creeps. The arms are left front, right rear. Ten minutes into the wait now. This time I'm leaving a glue line to set. I tell you, if I were to send this thing in for every crack I would not have flown much this summer.
     
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  3. Bigdz

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    Bighi this is what I was dealing with in the beginning. My hair line cracks were never in the hole...
    Crazy glue and a little baking soda or if you don't care how it looks JB weld(it's grey)
     
  4. FredSheldon

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    What if the twisting of the arm was part of the design to relieve stress on the motor mount and by gluing the two halves together you overrode that stress relief.
     
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  5. BuckRogers

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    Mine started at the holes everyone is seeing problems with and progressed to the holes between the motor mounts. Identical to what you are seeing.

    I feel that if you don't repair the shell mount holes, it will cause the motor to move too much in flight because of lack of upper shell support and then the motor mounts go.
     
  6. BlackHawk388

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    In aviation, which we're dealing with aluminum and not plastic, once we find a crack, we would drill an extremely small diameter hole at the head of the crack. Then, fill it with something called Pro-Seal and put a patch over it. For plastic, I wonder if someone caught the crack soon enough, if drilling a small diameter hole to force the crack to stop traveling and then, fill it with the appropriate superglue would work.
     
  7. FASTFJR

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    What was the name of that plastic weld stuff with the UV curing light on it?
     
  8. Oso

    Oso

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    Bondic
     
  9. BlackHawk388

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    Not sure on that one. Was it Epocast?
     
  10. bighi

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    After my earlier repair, the arms were rock solid. For over 40 flights. The today this came up. I'm not opening the shell. In fact, my shell is unopenable as it is. So far the repair looks like its holding after some twisting by hand. Let's see how it goes. These shells really suck to put it mildly. Mind you, the phantom 3 is one incredible machine. And even though I love the design, the plastic quality is truly lacking. To sit there chasing cracks while holding a tube of crazy glue is inexcusable.
     
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  11. BuckRogers

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    Yep, Bondic. And one tube has enough to reinforce all four arms. Mine is holding up really nicely. I may not have to put a new shell on it. But If I do, I'll be sure to reinforce the new one
     
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  12. John Locke

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    I believe this is a problem in the molding of the shell. The plastic formula and the cure timing of plastic parts is a delicate science when molding parts like this. Whoever DJI outsourced the plastics to made a grave error during the manufacturing process. I'm sure dji has 10,000 of these in inventory to use up before any improvement is implemented. That's my feeling about Chinese lack of concern to quality. I'm sure they will eventually figure this out, it will just take time. So if you have cracks but can still fly, wait as long as possible and return your P3 at the end of the warranty period. Maybe they'll has it fixed by them with new plastic.

    I'm wondering if phantom 2s had stress crack problems. If not, I wonder if the plastic was molded by a different company.
     
  13. bighi

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    Phantom 2? Hell, I had one crack from motor mount screw hole up to the seam at 7 flights. Fixed that and the next flight a crack opened up someplace else. If only DJI built a solid shell. Amazing product, crappy structural integrity.
     
  14. FASTFJR

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    Thanks, just ordered 2
     
  15. bighi

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    I think I'm figuring out why some folks never see cracks. Over the last week I've seen three different people flying phantoms of different generations in front of my apartment which is a popular flying spot. All three were doing little flyby's and stuff that barely got into fifty meter distance. In fact I don't think I've seen a single flyer just take off and go. By go I mean take off and away, about a hundred meters up and 1 km away or more if the bird is a 3. Hence, no cracks for these folks flying at what essentially is hubsan x4 micro range. I bet these folks will never see a crack. Maybe damage from crashing into trees cause when you're this close to trees you're bound to hit one once. But I bet most of us seeing the cracks are the high and far pilots. The phantom, of any era, always had it's internals for that capability. But not the fuselage. Beautiful and perfect design but way too thin for the job, period. And the "oh it's a rare occurrence bull crap" that DJI used to spew no longer has any value by what we've seen here. If DJI does not want us doing the high and far, then mention it in the marketing material.

    Anyway, repair is finished. I'm hoping it holds. I have never wanted to open the shell and frankly wasnt required in order to to adress the twin arm screw location issue. This one is different and really could use internal reinforcement. But again I've chosen to do it externally. As I've previously mentioned, invisible wasn't the goal this time due to the extreme nature of motor movement after these two cracks. Unlike the twin arm screw situation, this one cannot be prevented by glue, cable ties or duck tape. You literally have to either open the shell and reinforce the area with epoxy or wait for the crack to happen in order to glue and reinforce.

    I love the phantom 3. Nothing else comes close. But why can't DJI get off its *** and build a thicker, stronger shell already. This was already a problem on the phantom 2. They had every opportunity to make the phantom 3 heavy duty and not so sensitive to screw torque. Though really, on the motor screws, one would go just finger tight on those? And can overtightening explain these screw hole to screw hole cracks I've had? Nah. The shell is too **** thin.
    20150729_092218.jpg
     
    #15 bighi, Jul 29, 2015
    Last edited: Jul 29, 2015
  16. Ken Pascoe

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    Can I ask what the possibilities are of returning a cracked P3 to DJI? I realise the stories of poor services and turn around seem legendary; but it would seem that this is a manufacturing flaw and would surely be under warranty? Am I missing something?
     
  17. bighi

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    Not so much a manufacturing flaw but more of a systemic design flaw. Sort of like the windows on the De Haviland comet which had to be addressed. They tried to chalk it off as overtightening of screws of which the inner 4 near the battery area never had an issue despite being tightened by the same person during assembly. But that tree is no longer bearing any fruit. Anyway, send it in, wait 8 weeks, get a new shell, repeat.
     
    #17 bighi, Jul 29, 2015
    Last edited: Jul 29, 2015
  18. Phantom751874

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    Can't be that. I take off and GO full tilt, 3 miles out 3 miles back.
    No cracks so far. I don't baby it when it's in the air and I've flown in some pretty high winds.
     
  19. ronbo

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    To reinforce the motor mount area why not use removable prop guards, remove the guards but leave on the bases thus distributing the load.