Stress cracks

After sanding. I think I sanded too far because I may have re-exposed the crack on the end of one. So I've reglued. But the other spots came out great. Kind of hard to see in the pic though.
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Also make sure you read up about the screws because I've heard problems with the screws either being too long and causing problems hitting the motors or over tightening them and cracking more

THIS. Definitely make sure not to obstruct the motors. I, too, had stress cracks on my P3P, which I actually think was because the previous owner had installed a set of removable prop guards. Seems the additional weight and stress from the guards could have exacerbated cracking.
 
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Glued, sanded, reglued a couple spots, and strong arms installed. Hopefully this is the end of that issue, but what I didn't think about, is that it now doesn't fit in the case. So I need to enlarge the holes where the motors go.
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Glued, sanded, reglued a couple spots, and strong arms installed. Hopefully this is the end of that issue, but what I didn't think about, is that it now doesn't fit in the case. So I need to enlarge the holes where the motors go.

Yes, I had to do this with my P3P backpack case with foam insert. I used a heat knife to make it as clean as possible.

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Yes, I had to do this with my P3P backpack case with foam insert. I used a heat knife to make it as clean as possible.

View attachment 117450
That's the same backpack I have. How much did you have to take out? I haven't started but was hoping maybe an 1/8 inch or so. I don't have a heat knife so I may just try a utility knife.
 
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That's the same backpack I have. How much did you have to take out? I haven't started but was hoping maybe an 1/8 inch or so. I don't have a heat knife so I may just try a utility knife.

Based on your photo, I suspect that the profile of my prop guards is wider than your reinforcement plates, and I'm not exactly sure how much I ended up taking off. Your best bet may be to set the Phantom down in the foam as far as it will go, then draw a line on the foam around the edge of your plates. Then cut right up to those lines. I'm actually currently selling my pack and other P3P accessories; listed in the classifieds here on the forum. I had two of the exact same DJI backpacks, and modified one but kept the other stock, in case I ever took the prop guard mounts off, which I ended up doing.
 
My Phantom 3 Standard "Plus" :D weighs about 1350 grams. After about 200 km of flight distance, I noticed cracks under 2 motors. I am using now reinforcement plates like the ones in the link below and there are no more issues. This will add 16-20 grams of weight. Probably you can find them on eBay as well. Bellow is an aliexpress link. The only problem is that can take a while for items from aliexpress to arrive.

 
+1 for the owoda plates shown by capt ko. I have put them on 3 phantom 3’s so far. However, the Ali express set shown above are 50 percent cheaper! wow.
 
Huh? Joking or 1 of a kind?
Not meant as joke. Something I saw on a YouTube video. The presenter DJI "expert" seemed to know what he was talking about so I just accepted as fact. Could be wrong but it would explain why the P3's crack like eggshells and my P4P v2 is difficult to even scratch.
 
The different in P3 and P4 cracking frequencies are due to arm design and structure. While there could also be slight composition differences in the material, the shells are both still plastic. Definitely not metal of any kind, as weight and magnetic inference issues would be introduced.
 
Just my two cents; I widen the crack a bit with a hobby knife and fill it with baking soda, then I hit it with the glue. If you add baking soda to the glue, it doesn't get into the crack as well... where the added strength is needed.
 
I've had cracks round the motor mounts on my elderly P3P for around 4 years, but they don't appear to have got any worse UNTIL a recent close inspection with flexing the rotor arms by hand revealed this crack beside the shell screws. The photos are of the same arm, the second one is with the arm flexed. This is an alarming development, and will need to be repaired. I'll pop off the top shell, (YouTube is useful here) remove the motors and use Plast-aid, working from the inside and forming a 'puddle' of well diluted Plast -aid around the cracks, flexing the arms while it's still liquid to ensure it works into the cracks. IMHO, Plast-aid has to be better than superglue and baking soda, as it actually fuses into the shell material. Both the rear arms are in the same condition, so I'll repair them all.
This way I don't need to completely dismantle the P3, but I do get a robust and neat repair. I'll let you know how I get on..
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