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How to use Bondic on stress cracks ?

Discussion in 'Pro/Adv Discussion' started by jephoto, Sep 28, 2015.

  1. jephoto

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    I posted this 9 hours ago in the help forum. But no answers.
    Thought I'd put it here as well:

    ImageUploadedByPhantomPilots - DJI Phantom Forum1443485775.774541.jpg OK then. Just discovered my first stress crack on my P3.
    Hoping I wouldn't, but here we are.

    Lots of you talk up this Bondic as a good solution. About to order it from Amazon - $21.95 for a starter kit
    http://www.amazon.com/Bondic-Anything-Waterproof-Resistant-Plastic/dp/B00QU5M4MG
    What they say is :

    THE BONDIC PRINCIPLES
    • Bondic works best on rough surfaces and even better with undercuts
    • Bondic solidifies only by exposure to UV light (LED included)
    • Bondic works best in layers (the maximum thickness of one layer is 1- 1.5 mm)
    • Bondic works best when the surface is clean and free of grease
    • Bondic is solvent free, which is one reason why it doesn't dry out
    • Bondic is a liquid plastic welder that should be used with the principle of welding and not gluing


    Obviously where it is I can't rough up the surface or use layers. How have you all effectively applied the Bondic to a crack like this??
     
  2. bobmyers

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    You might consider these also-- a little more insurance
    Strong Arm reinforcement plates
     
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  3. envisionabove

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    Thats a nasty one compared to what most of us have hair line cracks going from screw to screw,if mine looked like that I would send it in. Hmm just used some wet and dry sandpaper and put it on my hair line cracks.

    Hit it with the black light and done. I plan on sending it in when I hear back if they are getting birds back faster. I hope doing the bondec does not void it I have a shell but it does not look like the newer ones I am seeing now.
     
  4. Shammyh

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    I tried repairing my P3 with a combo of gorilla super glue and bondic. While it fixed the broken screw mount rather well, it did not stop the stress cracks from spreading.

    I decided to give up, bought a new shell, and swapped all the electronics. Took about 4 hours from beginning to end, without any particular hurry or urgency. Probably do it in half the second time.

    You just need to be careful and gentle with certain parts, and make sure you're logging what goes where. And don't over tighten screws.

    While my new shell has the "x brace" reinforcement, I fully expect to have to do it again in the next 6 months or so, possibly in perpetuity. I do run DJI CRP props, which probably doesn't help, but I think all P3Ps are probably afflicted to some degree. Just a question of when.

    So my $0.02, don't throw good money after bad. Buy a replacement shell and diy, or send it to DJI for replacement.
     
  5. mirrorimage

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    $85 for a brand new Phantom 3 shell on Amazon. It's much better than spending money on dangerous bondic
     
  6. Chuck Young

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  7. jephoto

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    Got them. Will put them on after I repair the crack.
     
  8. Evel_Knievel

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    I don't know because I haven't seen the "strong arm reinforcement plates" but I personally think the following removable prop-guards will do almost the same thing plus you get removable prop guards:

    http://www.amazon.com/gp/aw/d/B00TJ...SummitLink&dpPl=1&dpID=41367hqMP4L&ref=plSrch

    Agreed, it's not quite as elegant....looks like the strong arm plates give you two more holes so they may be a little better...I guess it would depend on thickness etc.
     
  9. Darmie

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    So, these are best to put on before the cracks? do they stop from getting them? is that the idea?
     
  10. bobmyers

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    With the cracking issues, you could be proactive-- and if they develop at least you are limiting the problem and preventing the chance of a motor coming completely loose. One case o f that was reported. I have the snap on prop guard mounts on mine which uses the four motor bolts, otherwise, I would use the strong arm plates from UAV as a preventative measure at the least.
     
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  11. J0ck0

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    it's a free replacement from DJI. why not just have them replace the shell? i just got my RMA and shipping label this weekend. nothing will work as good as a new shell...
     
  12. dlbyers

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    My problem is, I don't trust DJI's service techs based on some of the stories I've read on this forum. Saw one returned a week or so ago with net new cracks in a supposedly new shell. With that combined with the extended down-time it will be worthwhile to me just buy a shell and replace myself. My only concern with this solution is that I'm not adding my phantom cracks to DJI's data/analytics.
     
  13. J0ck0

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    i understand your concern, but it will come with a warranty if you have them do it. no guarantees if you do it yourself. i'll take the couple of weeks of downtime if it means i have the peace of mind knowing that they did it and it is covered.
     
  14. Phil Tuggle

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    Two really important things:
    (1) In using any adhesive on the shell, you ***MUST*** clean the area and roughen the intended bonding surfaces. If there are already cracks, make certain you roughen there too. Look up "abrasive pen" online - about 8-15 USD - and these work great for tiny locations. The injection molding process almost universally has a worker spray a water-based mold release into each cavity every few cycles, especially with complex parts; so, you must make sure none remains on the part....or you are wasting your time.
    (2) Use an adhesive - like marine epoxy - or a laminate, but NOT Bondic. Bondic is wonderful as a filler or wrapped bandage, but it is not an adhesive. Even the company states this.

    Just my 3.5 cents.

    Oh, also can someone please post a photo or link of what this new "x-Brace" design looks like, please? I searched but could not find it termed that way. Thanks.
     
    #14 Phil Tuggle, Sep 29, 2015
    Last edited: Sep 29, 2015
  15. Shammyh

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    Hence why I used the super glue for bonding, then used Bondic to layer over (after the glue had cured) for strength. Guess I didn't explicitly make that clear.

    My issue wasn't that the glue didn't hold, or the Bondic broke, it was that the stress cracks continued through the lower part of the shell after my work, unabated by my fixes.
    I'll take some high res photos over the weekend, and you can see what I mean. In fact, if anything, the added rigidity seemed to have accelerated the pace of the cracks.

    I was hoping that the glue and bondic would have applied the force/torque of the motor over a larger area, hence, less cracking and safer arms.

    However, it appears that the added rigidity somehow transferred MORE energy from the motors into the arms and motor mounts.
    Even if the screw holes don't break, and the motor mount is solid, my whole arm itself was starting to show signs of fatigue/stress cracks.

    I probably could have flown it for another dozen or so flights before actual failure, but as I'm often flying over populated areas, I played it safe and grounded the P3P until I could replace the shell.

    So basically... mechanical engineering fail on my part. Also why I'm not terribly surprised that other's "DIY fixes" (and even "strong arms kit") don't seem to be holding up too well over time.
    If your mounts and screw holes don't break, the plastic itself in the arm just doesn't seem to be up to dissipating the energy transferred to it from the motor.

    That's why my conclusion is basically... keep a very close eye on the cracks and replace the whole shell rather than repair.

    Again, I still have my old shell, so will post some pics when I can, and let other's analyze/critique my work.
     
  16. Chuck Young

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    I have to go with @Phil Tuggle on these repairs @Shammyh

    Bondic only bonds because it fills tiny voids in the surface, it does not actually form a covalent chemical bond with the surface. I typically use MEK to clean the surface before I scuff the surface and then use a long cure epoxy or what I have found recently is a type of bisphenol resin used for carbon fiber and it is great.

    Again I would not use Bondic for any permanent fix at all.
     
  17. jephoto

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    Ok. You've seen the crack I need to fill. What brand specifically is the long cure epoxy you use?
     
  18. jephoto

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  19. fastsmiles

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    jephoto
    The Strong Arm kit is ideal for strengthening and repairing that area. Several people have reported cracks beginning under prop guard plates, even the four hole kind. NO reports have come in about new cracks forming under the Strong Arm Reinforcement Plates or about them not holding up over time.
     
  20. Chuck Young

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    The Real Carbon Fiber Cloth Plain weave kit and epoxy resin

    I would get a batch of that, Scuff the surface
    http://www.amazon.com/Scratch-Brush...x0a5RzL&dpSrc=sims&preST=_AC_UL160_SR160,160_

    Clean the thing real well with MEK, Make sure you only clean the surface, it will etch and could dissolve the plastic. I just checked and it will eat the plastic so be careful to only clean the surface. Let the MEK evaporate in a clean environment for a couple hours.

    Cut you some small patches of the CF cloth. Mix a small amount of the resin, mix precisely very precisely. Put down a thin but even layer of the epoxy (make sure to make it slightly larger than your CF patches) and let get tacky to the touch, time can vary depending on how well you measured the resin and hardener, keep testing until a nice fingerprint remains. Put down the fiber patch on the resin. Mix resin/hardener, put on top of patch and repeat the entire process until you are satisfied, 3-4 layers will probably be fine. 24-48 hours later you have a permanent fix.

    I laid two layers of that ebay fiber under the weight of a book in a ziplock bage it measured 0.05" Just measured the dry CF, if they sent the same 3Kplain weave, it is 0.01" thick.
    You really should have nitrile gloves and a respirator, good ventilation.

    Not easy but a good fix for sure.