Cracking the P3 crack

[Norm Walker]

I think you guys are concentrating too much on the heat issue, which would have an effect, but my thoughts are that vibration would harden the plastic and is probably due to the fail. I have installed quick release prop guards on my bird and even though I don't use them much the bosses that are always fitted really beef up the arms as the plastic is a lot heavier. No way could a motor be ripped out.
I'll still be keeping an eye out for cracks though.

 

[Flyaware]

My god! You guys are amazing! I am concerned about the failure of the plastics and you guys just head out and find the issues and supply half a dozen solutions? This is why this forum is critical. Great work people

 

[Klipkop]

@robinb - Only 29 deg for red and 25 for Yellow. Blue was 20. So it is 30% increase but that was only after 1 minute of hovering. I will do a 20 min flight this afternoon and measure again. If it is not reaching 40 degrees heat will be a non issue and the plastics re-inforcements will work. The type of plastic will also play a major role...

 

[Klipkop]

@Kreso Is this the "new" mount?



@Norm Walker - I hope you are right. The Type of plastic and the max temp will have a huge influence. I am no plastic expert but characteristics like load bearing, tear resistance, Rigidity and tensile strength differs highly between plastics. In some cases will heat actually make "protect" some plastics. See Which type of plastic sheet do I need for my application? | US Plastic Corporation

We probably take it to far, but heck, how else would you cover the bases We grew up with a saying you did not ride a bike without a fall. Hopefully this logic will never apply to the quad world... It will hurt more

 

[geckodrones]

Surely heated plastic would(in general) warp/melt and not snap/crack?

 

[Klipkop]

Further test and photos.
After 30 minutes of flight (2 batteries) in an ambient sunny temperature of around 25 degrees C the max temperature that the motors reached was 38 on the bottom of the plastic.

With my limited knowledge of plastic's I will concur with what a few said in this thread - It is not of such great concern.

I would - if I have a choice between plastic and Aluminium supports, go for the latter, but it's not the end of the world.

Any plastic's experts for an opinion?

 

[dogen]

38 degrees can't be the issue. But I also see the need for something to really make it impossible for the motor to pop out like it did for someone. I wonder if it would be possible to make a mold in some sort of clay, of the problem area. Make a cast with gipsum or something. Then dip it in molten aluminium or something else more suitable (melted plastics of some sort?) just to make a perfect fit in whatever material you like. I love experimenting. I'll see what I come up with, without using a 3d printer.

(I'm not sure about the materials mentioned for mold and cast. I was thinking about the principle of making something to distribute heat and stress)

 

[StevenQX]

Imo the issue is caused by the wobble of the arms that was clearly visible even in the firsts demo video of p3 when begin to be distributed.

 

[N017RW]

Imo the issue is caused by the wobble of the arms that was clearly visible even in the firsts demo video of p3 when begin to be distributed.

I agree and remember seeing that video.
The twisting nature and a poorly designed shell are the root causes.

 

[Lonewolf]

Thermoplastics can be heated and cooled. Thermoset plastics are different. They don't react the same as thermoplastics. Whereas, when thermoset plastic is subjected to high heat it can crack. 38*C is 120*F so, if our birds are made out of Thermoset plastic heat may be the problem.

 

[N017RW]

Many here have heated arms with a hair dryer, etc. to reshape bent arms, thus it would not appear to be a thermoset.
Since these reports were P1 & 2s it's possible P3 is different but wouldn't seem likely.

 

[StumbleBee]

[snip].

Any plastic's experts for an opinion?

]

How about a former plastics expert with an engineering degree in both thermoset and non-thermoset resin molding technology. Back in the early 70's I did some pioneering work for American Standard Lab's in Piscataway, NJ on photoelastic stress analysis of melamines. I then ran a Reliability Test Lab for Mattel, Inc. (toys) for four years until 1977. Lots and lots of experience with polystyrenes, vinyls, polyethelenes and many other thermoplastics, both extruded and molded. I was involved with resolving many cracking issues including on one ill conceived wind up airplane toy (the ZipCord Fighter). Every kid who got one of those on Christmas morning had it shatter to pieces the first time it hit the ground at 20F or less.

Anyway...there are many factors which can cause stress related cracking in molded plastics, including of course residual stress from the molding process itself. Another very important factor is how much regrind (now called recycled) plastic was used along with virgin resin. Often regrind varies greatly (and badly) in composition. Bad regrind equals trouble. And it's intermittent and variable trouble, the worst kind.

To your point about temperature and that you believe the temp's you recorded would not be a problem. It would be. Or at least a strong could be. All plastics contain plasticizers, that's the ''new car" smell we all love, poisonous plasticizers. These naturally exude from plastic and heat greatly accelerates the process. The more these plasticizers are lost the less 'plastic' the plastic becomes, i.e. the more brittle it becomes. Ever see a cracked knob in a car, or a split dashboard? Lost plasticizer. So any heat at all is bad, the more the badder.

 

[dougiemcc]

My quick release prop guard brackets attach directly to the motor bolts, do you think this increases the strength of the mounts?

 

[FredSheldon]

How does this help the guy whose motor and prop ripped themselves right out of the end of the arm? Nothing was left but a shattered plastic stump and some twisted wires.

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.

 

[BuckRogers]

All I see is top to bottom views. Of course it will be red in that view. It has to go through the motor. Lets see a side view to see how hot the plastic really is. This is qualitative too. Need to see some temperature numbers. there's tons of plastics inside an engine compartment of a vehicle and get much hotter than one of these phantom motors. Lets see some figures.

 

[StumbleBee]

My quick release prop guard brackets attach directly to the motor bolts, do you think this increases the strength of the mounts?

Mine do also. What they would do is more widely distribute the stress. The wider the area acted upon by any unit stress, the less strain there is in any part of that area.
In theory then they would seem to lessen the potential for cracking. Thanks to the law of unintended consequences though it could create a worse problem. It could result in a harmonic vibration far worse than the original. This vibration could be transmitted to the next weakest link. Heck, we could have whole arms flying off. Not likely but we are dealing with a complex organism.

 

[N017RW]

Good points about shifting the problem elsewhere.
Without proper analysis a true fix is dubious.

 

[StumbleBee]

Thermoplastics can be heated and cooled. Thermoset plastics are different. They don't react the same as thermoplastics. Whereas, when thermoset plastic is subjected to high heat it can crack. 38*C is 120*F so, if our birds are made out of Thermoset plastic heat may be the problem.

I assure you that our birds are made of a thermoplastic, not a thermoset. Epoxy, melamine and Bakelite are three common thermosets. Polystyrene is probably the most common thermoplastic.

 

[Bobn]

Mine has never been crashed or dropped or fell over. The crack starts on the lower shell between the 2 vents to the right were the battery goes in. Starts at the seam and goes to the top of the sticker on the side of the battery compartment.

 

[Coolhand8]

I did came to the same conclusion too, that the heat and vibration might be the source of the problem.
Although my P3 has no crack yet, I want to find some solution to that as a preventive.
Today, I decided to look around into my other drone. QRX350 from Walkera this time.
And look what I found under the motor...
An aluminium plate 4mm and a carbon plate alike (not sure) 1mm thick.
Did a trial install mod on one of P3's motor. Seems fit fine with some adjustment.
Wanna finish all 4 and fly, but work, family and life caught up...
will report later