I have noticed that I have some stress cracks on my P3S and would appreciate some input from anyone who has delt with the same
I have been advised by dji to return the unit and read that some have repaired with weld-on 4, with some success. Have any of u used the reinforcement plates? How have they worked for you
Well I'm thinking of using the weld-on 4 and then adding the reinforcement plates, what do u all think
Here is a pic of my situation
Sorry dji, but I previously posted this in service, but would like to get some input from the others in this forum

I repaired and added plates.

I decided to do this as return to DJI and receiving replacement was too long and second - the replacement would crack also ...

I scratched out the cracks a little to allow the PU glue to get in and fill when expands. Sanded back smooth and then fitted the plates.

That was months ago and all is fine still.

Nigel

What's PU glue and what kinda plates u use?

Did u use any type of lock tight on the screws when you put them back in, if so what type?

PU Glue is sold under various names .... Gorila Glue is the common Modellers name used. It is an expanding single component glue that foams up and expands due to moisture ....

Many modellers use it for building model planes etc. as it has incredible holding power but literally no weight. It can be sanded back and if you use the external grade is fine for outside uses.

I buy from local Hardware Shop at far less cost than Gorila Glue price !!

Some people use Plastic Weld .... Weld Tac ..... Epoxy .....

Main thing is to make sure what you use gets INTO the crack and not just surface. Epoxy and similar tends not to hold too well on plastics. I take a nail or end of a knife and scrape out a V in the crack to get the glue in .. it only needs a slight V ....

You will be supplied replacement bolts with the plates ... because you need slightly longer to allow for plate thickness. If you ever remove the plates - NEVER use those longer bolts for mounting motor as they will be too long without plates
BLUE Loctite (thread locking fluid) is definitely advised to be used ... do not use RED or higher holding power thread lock.
The plates are available on eBay ... here's example :

http://www.ebay.co.uk/itm/Reinfo ... 27eb10d7:g

thanks Solentlife

Hey Solentlife, I read somewhere that the Loctite we should be using is Loctite 425,do u know or have u used this, is it the right stuff?

Sorry forgot to send pic here it is

Have u also heard of this stuff used for the P3S

Here it is, geees

As to other products - I have no idea. Sorry - Latvia is not exactly best place for product choice.

Nigel

Salmonslayer Posted at 2017-6-3 20:18
Here it is, geees

Hello,
Weld-on 4 is an excellent choice. I have repair cracks on three P3S. This glue seeps into the crack and fills the it by melting and bonding from the inside out, just like welding. Beware, a very small amount will do the job. Any excess will melt the  base plastic and leave an ugly scar. About the reinforcement plates, they retard new cracks. As an experiment I added a few internal carbon fiber strips as reinforcement braces in one of my Phantoms. No cracks on this one. This is my "aerobatic" one. Very hard flown hundreds of times. I removed the camera and everything not essential to fly. Very lightweight and agile. Hope this helps.

Thanks solentlif and Thanks Armoni319

Unfortunately the problem is known and common on many other aircrafts too.
I looked at and thoroughly investigated the defect and I came to a definitive conclusion.
There is not any kind of glue that can solve definitively the problem if you do not loose the screws.
Often the compound of the plastic is  not excellent but the main cause is the excessive tightening of the screws.
On many new Dji Phantom and Yuneec Q500 shells I loosened all the screws that were always absolutely overtightened and I narrowed them with just light and correct load.
The defect has never been presented after hundreds of flights.
The Chinese have done great things but have not yet learned how to properly tighten the screws.

Wieg1 Posted at 2017-6-4 22:27
Unfortunately the problem is known and common on many other aircrafts too.
I looked at and thoroughly investigated the defect and I came to a definitive conclusion.
There is not any kind of glue that can solve definitively the problem if you do not loose the screws.

Sorry but I do not agree .... The cracks originate not from over-tightening, but from the thinning down of the plastic shell. The motors are constantly changing thrust causing vibration / stress / twist and torque on a weakened area.

Nigel

I've used Weld On #4 to fix motor mount cracks.  
It is not a glue and will almost immediately become dry  where it is exposed to air. It is very thin and only needs one drop placed on the crack because it soaks in quite well and begins to weld the crack.
Then I installed ABS mounting plates.

Betamace Posted at 2017-6-4 23:53
I've used Weld On #4 to fix motor mount cracks.  
It is not a glue and will almost immediately become dry  where it is exposed to air. It is very thin and only needs one drop placed on the crack because it soaks in quite well and begins to weld the crack.
Then I installed ABS mounting plates.

Exactly ....

OK - I used PU on mine ... but I have no more cracks and the old have not 'grown' .....

The plates are well worth the fitting.

Nigel

solentlife Posted at 2017-6-4 23:01
Sorry but I do not agree .... The cracks originate not from over-tightening, but from the thinning down of the plastic shell. The motors are constantly changing thrust causing vibration / stress / twist and torque on a weakened area.

Nigel

.. so I'm a very lucky
Yesss, vibrations on the stressed plastic due the over tightening of the screws ...
I have two Phantom, two Yunec Q500, one Inspire and after checking the tightening of the screws on my birds and many others of my friends and hundreds of flights I have no cracks.
I never put a drop of glue.
Everyone follows the way he likes.

Given the number of Chinese items and models I and others have ... and I found that generally screws are in fact not tightened enough ... with DJI being one of the few that I have found to be well tightened AND with correct Blue threadlock ... I still disagree.

We will wait for your cracks to appear on your P's - which they WILL .... as to the other models ... be as they may.

Nigel

I ordered metal plates just because I didn't see anyone else using the the AB'S, but would have liked to order the ABS

solentlife Posted at 2017-6-4 23:01
Sorry but I do not agree .... The cracks originate not from over-tightening, but from the thinning down of the plastic shell. The motors are constantly changing thrust causing vibration / stress / twist and torque on a weakened area.

Nigel

Then how do you explain the ones that come out of the box new with cracks.  It is very poor plastic.

First I've ever heard of cracks before flights.

Of course there is always the possibility of a poor installation.

In fact my P3S arrived with signs of it having moved in its box. Gimbal lock laying in bottom of box etc. etc. Given the box design - you wouldn't think it - but it had moved in box.
Having traveled from China to Europe - who knows what tumbles it experienced.

Nigel

I forgot, it is very important, the propellers must be carefully balanced !

Trying to keep this thread limited to REPAIRING OF A P3S that has stress cracks, issues with DJI are well documented and would really appreciate it if it you would add your details on those threads. I have made a decision to repair it myself and greatly appreciate the comments on how that is done and experiences (excluding DJI's poor customer service issues) . Look forward to hearing from more of you with  you experiences with the dreaded STRESS CRACKS .....  

To summarize stress cracks
#1) Most P3S will experience it, unless some action is taken by Captain
#2) Some believe loosening screws reduce or elliminate stress cracks
#3) Weld-on 4 is a recommend ed stress crack sealer but needs to be followed up with arm plates and Loctite (blue not red)
#4) DJI needs to improve it's P3S shells
I think you will all agree the Capt has to make the desition to repair or return after that the above might help someone repair.
Thanks to all for your comments and experiences

Spot on mate !

Cheers
Nigel

Same crack after Weld-on 4 used

I as also used it on this minor crack. In both pic the cracks are hard to seen now, that's because Weld-on 4 really does work on welding the cracks together, I'll report again after I put the guards on and fly it for 50 hours or so

Sorry forgot to add the second one here it is