Cracking the P3 crack

[StumbleBee]

I just bought a new p3 shell a and I'm going to make a mold then lay up carbon fiber shells. I'll post here when I'm done

Please post the weight of the OEM shell, and your carbon fiber shell prototype.

 

[Dirby]

aluminum might cause a radio problem

 

[Chuck Young]

I just bought a new p3 shell a and I'm going to make a mold then lay up carbon fiber shells. I'll post here when I'm done

I would like to see how you do that. I will be following the same path if my bird develops cracks. I am convinced CF is definitely the way to go.

 

[Wibble]

I just bought a new p3 shell a and I'm going to make a mold then lay up carbon fiber shells. I'll post here when I'm done

What resin will you use? Will you vacuum bag?
How much weight saving will there be over glass cloth?
I have never used CF but I have made all sorts of Fibreglass parts over the years. Is CF much harder to work with?

 

[Phil Tuggle]

Sounds to like I should pick up a small sheet of aluminum and cut out a few pieces and mount them to the arms?? Do you think this will help?

Depends. Where? How?

 

[cheebs]

On the cheap (but decent) Quanum Nova, HK/Cheerson use an aluminum disc with a center hole and the 16/19mm holes, between the motor and the frame. This sounds like a great stress relief for the plastic motor mounts, and doubles as a heat sink for the motors. Maybe something like that for the P3?

 

[johnp44]

It's very unlikely that the motor just ripped itself out during normal flight. It had to have been involved in a crash or very hard landing. Just my opinion.

I saw the pictures of it and I disagree, it was a massive failure that looked like it followed right along crack lines that had developed. I had a P2 almost reach that stage but I replaced the shell long before it reached the point that his did. My other P2 had a failure where the screws that hold the motor in the bottom shell had two of the mounts totally separated from the bottom shell. It also wasn't far from becoming a motor departing in flight. No one seems to be concerned except the people who have had these problems, that is until it happens to them. Consider yourselves lucky. But I agree 100%, everyone is entitled to their opinion.

 

[FredSheldon]

I saw the pictures of it and I disagree, it was a massive failure that looked like it followed right along crack lines that had developed. I had a P2 almost reach that stage but I replaced the shell long before it reached the point that his did. My other P2 had a failure where the screws that hold the motor in the bottom shell had two of the mounts totally separated from the bottom shell. It also wasn't far from becoming a motor departing in flight. No one seems to be concerned except the people who have had these problems, that is until it happens to them. Consider yourselves lucky. But I agree 100%, everyone is entitled to their opinion.

The op had admitted that he had a crash soon after buying the quad. I think the damage was started at that time but he did not open it up to see if any damage occurred.

 

[mikedaniels]

That FLIR post may show the smoking gun. After a minute? Imagine 20 minutes later on a hot day. That in combo with high frequency vibration is too much stress for the plastic.
I am liking the idea of a heat sink -or radiator- but I'd be putting them around the exposed top barrel area of each motor. That'd put them in the prop wash and have metal to metal contact for better heat transfer.

I think the new motors have a larger base. Maybe better for heat dissipation.

 

[Mako79]

Sounds to like I should pick up a small sheet of aluminum and cut out a few pieces and mount them to the arms?? Do you think this will help?

Like this (don't laugh)...

I have the UAV strong arms arriving (not sure when as im in Aus). The UAV strong arms adds assurance to the shell and motors. I have done the aluminium method as prevention for motors only. You can always add cable ties for the shell but I think its more critical for the motors as the shell has (pain in the ***) clip sections and will keep the shell intact.

I've done an addition 40minutes of flights and the cracking has ceased with the 0.35mm aluminium mod. The aluminium is installed on the non-cambered screws (look closely and you will see 2 that are even and the other 2 are higher and lower. The reason for this was to get the perfect length screws (incorrect length will damage the motor). I really think the mod I have done is enough to prevent motors from separating as it will distribute the pressure like a washer and act as contingency.

If you do decide to do the mod, just take note that the motors are rotated differently to accommodate the cambers. One side will be 16mm from screw to screw and the other will be 19mm from screw to screw. So you will need 2 x 16mm and 2 x 19mm plates.

I will let you know how this progress...

 

[gtpark]

Wow, it is sad the things owners have to do because DJI won't provide a well designed lower frame!

 

[AlexSP]

I just bought a new p3 shell a and I'm going to make a mold then lay up carbon fiber shells. I'll post here when I'm done

I´m doing the same. The hardest part is perfecting the shell mold beacuse it has lots of vents and the angles must be 100% due to the motor anchoring angles and PB fixings. But it will sure be lighter, stiffer and stronger.

I´ll also try reinforcements on the arms and around motor support on another new shell using kevlar strips instead of CF (harder to cut but easier to lay up and glue inside the shell). My original shell is still perfect after lots of flying, so I´m not messing with it unless of course it starts cracking.

 

[mikeCtv]

I just bought a new p3 shell a and I'm going to make a mold then lay up carbon fiber shells. I'll post here when I'm done

I would like to buy one when you are ready. I am sure you will become very rich making these. Good luck and keep me posted.

 

[mikeCtv]

I´m doing the same. The hardest part is perfecting the shell mold beacuse it has lots of vents and the angles must be 100% due to the motor anchoring angles and PB fixings. But it will sure be lighter, stiffer and stronger.

I´ll also try reinforcements on the arms and around motor support on another new shell using kevlar strips instead of CF (harder to cut but easier to lay up and glue inside the shell). My original shell is still perfect after lots of flying, so I´m not messing with it unless of course it starts cracking.

Buy a shell on line and use that, if it turns out to be good people like myself will buy it from guys like you. I bought my P3P as a tool for my photography business I can't be worried about it dropping out of the sky because of the motor falling out from crack motor mounts

 

[mikeCtv]

Like this (don't laugh)...

I have the UAV strong arms arriving (not sure when as im in Aus). The UAV strong arms adds assurance to the shell and motors. I have done the aluminium method as prevention for motors only. You can always add cable ties for the shell but I think its more critical for the motors as the shell has (pain in the ***) clip sections and will keep the shell intact.

I've done an addition 40minutes of flights and the cracking has ceased with the 0.35mm aluminium mod. The aluminium is installed on the non-cambered screws (look closely and you will see 2 that are even and the other 2 are higher and lower. The reason for this was to get the perfect length screws (incorrect length will damage the motor). I really think the mod I have done is enough to prevent motors from separating as it will distribute the pressure like a washer and act as contingency.

If you do decide to do the mod, just take note that the motors are rotated differently to accommodate the cambers. One side will be 16mm from screw to screw and the other will be 19mm from screw to screw. So you will need 2 x 16mm and 2 x 19mm plates.

I will let you know how this progress...

I bought the strong arms too, thinking preventative measures. But here is what happened. I am not knocking them but IMO the problem might be bigger than that. Bad plastic or bad mold injections on a batch of shells, I think they are going to crack no matter what. I am however looking into Plast-aid mentioned at this Forum. It voids the warranty but I don't want to worry about crack that can lead to a crash. I am a pro photog and can't deal with down time or a law suit.

 

[AlexSP]

Buy a shell on line and use that, if it turns out to be good people like myself will buy it from guys like you. I bought my P3P as a tool for my photography business I can't be worried about it dropping out of the sky because of the motor falling out from crack motor mounts

Yes that´s exactly what I´m doing. Besides using 2 cracked shells borrowed from friend´s P3s I ordered 2 new shells and will experiment differently with both. I´ve been looking into this issue on every shell I have access to, since mine´s still intact 2 months in with lots of flights. IMHO the best solution may be just add some structural reinforcements to the arms and core on the inside. It becomes one with curing, and only adds a few g of weight.

Not just the tips as some suggest, the shell is basically a monocoque structure (i.e. the shells ARE the structure). So it should be looked as a whole. If strenght is added only to the failure point (s) and/or around it, the stress in other parts might increase and lead to failure in other areas of the body with time. I´m also adding small kevlar strips to the outside area of the shell tips (near the motors) in order to help in case of crashes.

I did a lot of that kind of work on my RC models, from cars to copters and drones. I´m using a cracked shell from a friend´s P3A to mold a 100% CF shell but it´s very time and labor consuming, and I´m still far from being satisfied with the results. CF is awesome but the shell body has lots of angles, vents and recesses, it´s pretty hard without industrial tools. The P3 is indeed a precision instrument.

So far from what I´ve done and seen, I´d say the best solution may be to just build "better" shells using the existing plastic ones from DJI (the original) with very precise and well executed internal reinforcements. Faster, cleaner, cheaper (the shells aren´t that expensive, and if you think a "better" shell might last longer then it´s a good investment). Also nicer looking and still stiffer and stronger than the plastic original, without any potential compromises in performance - as it keeps the specs of the original!

I´ll keep posting as I make advancements.

 

[mikeCtv]

Yes that´s exactly what I´m doing. Besides using 2 cracked shells borrowed from friend´s P3s I ordered 2 new shells and will experiment differently with both. I´ve been looking into this issue on every shell I have access to, since mine´s still intact 2 months in with lots of flights. IMHO the best solution may be just add some structural reinforcements to the arms and core from the inside.

Not just the tips as some suggest, the shell is basically a monocoque structure (i.e. the shells ARE the structure). So it should be looked as a whole. If strenght is added only to the failure point (s) and/or around it, the stress in other parts might increase and lead to failure in other areas of the body with time. I´m also adding small kevlar strips to the outside area of the shell tips (near the motors) in order to help in case of crashes.

I did a lot of that kind of work in my RC models, from cars to copters and drones. I´m using a cracked shell from a friend´s P3A to mold a 100% CF shell but it´s very time and labor consuming, and I´m still far from being satisfied with the results. CF is awesome but the shell body has lots of angles, vents and recesses, it´s pretty hard without industrial tools. The P3 is indeed a precision instrument.

So far from what I´ve done and seen, I´d say the best solution may be to just build "better" shells using the existing plastic ones from DJI (the original) with very precise and well executed internal reinforcements. Faster, cleaner, cheaper (the shells aren´t that expensive, and if you think a "better" shell might last longer then it´s a good investment). Also nicer looking and still stiffer and stronger than the plastic original, without any potential compromises in performance - as it keeps the specs of the original!

I´ll keep posting as I make advancements.

Thanks Alex, good luck I will look forward to your advancements.

 

[AlexSP]

@mikeCtv:

Impressive pictures. That shell is kaput. My friend´s got the same type on his plus a few more on one arm, midway through the core of the AC. His body center also has minor cracks wich lead me to believe the plastic used had problems in the mix or contamination in the molding. Mine has more flying hours than his and is holding strong. I see no other logical explanation to this.

Happens a lot, it´s only detectable when in use and something comes up like this. I used to mold "bubles" (bodies) for RC models from plastic and it happened a lot, but then we had no QC or preset formulas, everything was quite experimental (and still is for us hobbyists but the good part is once we get the hang of it, the solution is definitive and it leads to serious upgrades over time).

On his shell I sealed the cracks and glued the small parts using a thin superglue. Then I cut layers of fine, ultra-tough and tight-knit kevlar fabric and layered around the screw bases and bottom part of the tip under the motors using epoxi to the inside part of the tips. Only one layer of this fabric for each tip is enough since it´s super-strong. Then I aded strips along the arms and also around some areas of the main body. That won´t add weight, bulk or interfere with anything. We were able to assemble all the parts back and it´s under testing.

This past weekend he flew in heavy wind for hours and it held up perfectly. We´ll open it this thursday and see. On the outside it´s 100% fine, let´s see how the epoxi holds. I´ll test some more as I work on the CF projects. I am documenting everything so if it all goes fine I might be doing tutorials on possible solutions for cracked and non-cracked shells (though I´d still go for a brand new, reinforced shell rather than a fixed one, regardless of how it holds up).

 

[Meta4]

Wow, it is sad the things owners have to do because DJI won't provide a well designed lower frame!

You do know that DJI will replace the shell for anyone unfortunate enough to develop cracking?