Cracking the P3 crack

[Klipkop]

I was thinking (being in manufacturing myself) there could be a few reasons for the cracking problem on the P3.

- Flight fatigue and stress over time
- Off Balance motor due to rotor damage

But look at this, a FLIR image of a P3 after about 1 minute of hovering

Heat buildup from the motor is NOT good for the plastic. Combine that with vibration and over a period of time you get brittle arms. I saw a number of 3d printed re-inforcing plates - this could in fact increase the heat issue What we actually need is machined aluminium plates, those will acted as a heatsink as well..

Any thoughts?

 

[StevenQX]

I agree. That's why I will not buy the uav renforcement plates. 4 piece of plastic for 25$ is not cheap and moreover those plates should be, as you wrote, in light metal so aluminium is perfect.

 

[jcknows0]

Bondic has worked for me. The arms near motor mounts do feel hot after a flight, in a way the P2 never did (always thought it was because of active braking). I could not see how reinforcement plates would have solved this issue. Glad to see a more in depth look at the problem.

 

[Jeff48920]

I was thinking (being in manufacturing myself) there could be a few reasons for the cracking problem on the P3.

- Flight fatigue and stress over time
- Off Balance motor due to rotor damage

But look at this, a FLIR image of a P3 after about 1 minute of hovering

View attachment 30029

Heat buildup from the motor is NOT good for the plastic. Combine that with vibration and over a period of time you get brittle arms. I saw a number of 3d printed re-inforcing plates - this could in fact increase the heat issue What we actually need is machined aluminium plates, those will acted as a heatsink as well..

Any thoughts?

This is very interesting. Do you really think aluminum plates will sufficiently shed heat buildup or will they too, simply heat up even more/? I am not an engineer by any stretch of the imagination but it would seem to me that the plates would have to be machined with many cooling slots to keep the heat disapating properly.

 

[DJi Newbie]

Do you think someone can make aluminium ones in 2D? if so make me a DXF file and ill make them and try!

 

[N017RW]

It's all about surface area in contact with the air or other fluid.

Adding plates would not cause additional heating but you need to conduct that heat to the plates.
Are four small screws sufficient?

Slots, fins, etc., add surface area increasing [heat] dissipation efficiency.

 

[StumbleBee]

It's all about surface area in contact with the air or other fluid.

Adding plates would not cause additional heating but you need to conduct that heat to the plates.
Are four small screws sufficient?

Slots, fins, etc., add surface area increasing [heat] dissipation efficiency.

Take a second look at that FLIR photo. The screws are much cooler than the motor area. Either they dissipated heat quickly, or they did not conduct much heat at all.

 

[StumbleBee]

I was thinking (being in manufacturing myself) there could be a few reasons for the cracking problem on the P3.

- Flight fatigue and stress over time
- Off Balance motor due to rotor damage

But look at this, a FLIR image of a P3 after about 1 minute of hovering

View attachment 30029

Heat buildup from the motor is NOT good for the plastic. Combine that with vibration and over a period of time you get brittle arms. I saw a number of 3d printed re-inforcing plates - this could in fact increase the heat issue What we actually need is machined aluminium plates, those will acted as a heatsink as well..

Any thoughts?

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.

 

[Chris Vedeler]

I was thinking (being in manufacturing myself) there could be a few reasons for the cracking problem on the P3.

- Flight fatigue and stress over time
- Off Balance motor due to rotor damage

But look at this, a FLIR image of a P3 after about 1 minute of hovering

View attachment 30029

Heat buildup from the motor is NOT good for the plastic. Combine that with vibration and over a period of time you get brittle arms. I saw a number of 3d printed re-inforcing plates - this could in fact increase the heat issue What we actually need is machined aluminium plates, those will acted as a heatsink as well..

Any thoughts?

Very interesting image! It matches exactly where mine failed. And I agree with you regarding prolonged exposure to heat on the plastic.

However, I think the bottom line is the plastic that holds the motors is inadequate for the power of the P3 motors. They may have gotten away with this form factor with the P1 and the P2 with the weaker motors, Heat of course makes things worse and I wonder if the P3 motors get more hot than its older siblings as well.

The dissipation of heat is an issue of course, but the aluminum housing of the outside of the motor itself is a heat sink and should do a fair job of that as it is exposed to the wind of the prop and is above the plastic. I think aluminum would be better than plastic as a reinforcing material, but I think the main concern isn't heat dissipation but strength.

 

[wotblake]

While I agree aluminum would be better, it's not as easy as 3D printing to get a product out quickly to consumers. The UAV strong arm kit works great - I use it. Adds a ton of strength.

I agree. That's why I will not buy the uav renforcement plates. 4 piece of plastic for 25$ is not cheap and moreover those plates should be, as you wrote, in light metal so aluminium is perfect.

 

[Klipkop]

@StumbleBee - I will investigate the temp difference with the screws in more FLIR photo's Good point...
@Chris Vedeler - Thicker support would have made a huge difference - I agree. What the FLIR showed me is that it is not only vibration but a combination of factors.

I need to calibrate the camera and take actual temp readings over time. My hypothesis is that Aluminium support will be a) stronger and b) handle heat dissipation better. It is also a flat area on the bottom so laser cutting a 3mm plate will not be that difficult.

I will hopefully do a drawing and test them with some silicone paste in between. It will be nice if we can get some DJI engineers in on it....

 

[Jeff48920]

Just saw a water jet CAM machine that can cut like crazy. It fully cut a 7 inch 90 tooth three spoke gear from a billet of aluminum in about 6 minutes. If that can be done think how fast played could be cut once a CAD design had been drawn.

 

[FredSheldon]

Hey, Just zip them up and go out and enjoy your quad. Life's too short to worry about things you have very little control over. They will crack if they want to, All you can do is try to hold things together if they do

 

[StumbleBee]

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.

 

[FredSheldon]

Without knowing the entire history of his unit it would be hard to determine what fix might have prevented what happened. It's possible that just a single tip over while landing could create enough of a shock when the prop hits something and stops suddenly to crack the motor mounts. I know mine did so but I was in grass and not on something hard. Still the sudden stoppage has got to create some stress on the motor mounts, arms.

 

[TeeJayN]

...However, I think the bottom line is the plastic that holds the motors is inadequate for the power of the P3 motors. They may have gotten away with this form factor with the P1 and the P2 with the weaker motors, Heat of course makes things worse and I wonder if the P3 motors get more hot than its older siblings as well......

Well said - and there is an additional factor to add to the equation - the P3's dynamic braking. It is so easy to repeatedly observe the P3 violently jerk back to stop it's forward movement with the P1 and P2 being tame by comparison. Yes, you can adjust the P3 braking but even at it's lowest setting it's still relatively easy to see violent attitude changes. These sharp attitude changes come from sudden motor torque which has to cause huge, repeated, stress on the arms and motor mounts. Combined with previously mentioned design factors, IMHO, it's unchecked disaster waiting to happen.
If DJI doesn't make a design change to correct this, I believe we should consider the P3 shell to be a wear item that needs to be replaced at a safe repeating interval.

 

[ZX10R203]

What about adding a small heat sink under each arm where the motors are mounted and cut them down to size?

even something like this to match each mounting screw:

 

[geckodrones]

Hey, Just zip them up and go out and enjoy your quad. Life's too short to worry about things you have very little control over. They will crack if they want to, All you can do is try to hold things together if they do
View attachment 30045

I don't understand how that design will help at all? The cracks happen right where the motors attach to the frame.

 

[StumbleBee]

What about adding a small heat sink under each arm where the motors are mounted and cut them down to size?
even something like this to match each mounting screw:

I like that design idea, but sandwiching a plastic shell between it and the motor provides an effective heat barrier. The screws are never going to carry the amount of heat which that sink could dissipate. I think that if you made the center hollow and put it around the upper motor housing it would be extremely effective. Anyone ever touch the motors after some spirited flying? They will almost give you a first degree burn.

 

[robinb]

I was thinking (being in manufacturing myself) there could be a few reasons for the cracking problem on the P3.

- Flight fatigue and stress over time
- Off Balance motor due to rotor damage

But look at this, a FLIR image of a P3 after about 1 minute of hovering

View attachment 30029

Heat buildup from the motor is NOT good for the plastic. Combine that with vibration and over a period of time you get brittle arms. I saw a number of 3d printed re-inforcing plates - this could in fact increase the heat issue What we actually need is machined aluminium plates, those will acted as a heatsink as well..

Any thoughts?

What is the temperature of the yellow/ red areas ?