Safe speed to avoid motor cracks?

[Tim Dawes]

I'm wondering if there is a relationship between flying speed and motor mount cracking.
Any suggestions on what constitutes safe vs aggressive flight?
Its not unusual for me to fly 20-25 mph with rare instances up to 30mph. I try not to make sudden turns or hard braking at those speeds. At slower speeds there are times I'll let go of the sticks if I've lost sight of the P3 or get disoriented. I know that brings it to a quick stop but am not sure that would be considered "hard braking".

 

[gingerbloke]

The plastic just seems to be the wrong sort (it's a bit like the plastic used to make yoghurt pots). I suspect that if you left the phantom in the box and never flew it you'd still get cracks on some

My PV2+ was riddled with it (not warranty covered despite being purchased from a UK DJI dealer) yet neither P3 I've had seem to suffer it (yet!)

 

[Tim Dawes]

The plastic just seems to be the wrong sort (it's a bit like the plastic used to make yoghurt pots). I suspect that if you left the phantom in the box and never flew it you'd still get cracks on some

My PV2+ was riddled with it (not warranty covered despite being purchased from a UK DJI dealer) yet neither P3 I've had seem to suffer it (yet!)

Too funny!

 

[Meta4]

I'm wondering if there is a relationship between flying speed and motor mount cracking.

There's no connection.
Most Phantoms never develop any cracking at all.
All that I've ever had have never cracked despite flying at 35 mph most of the time.

 

[N017RW]

It’s likely DJI uses several vendors for the shells.
Not uncommon for their practices and thus quality to vary amongst them.

 

[solentlife]

I would not want to claim that most P3's do not crac k ... as all the P3's in our club have cracks ... S, A and P.

I don't think speed is anything to do with it ... its CHANGE of thrust as you come in / out of manoeuvres. The motors torque and apparent thrust lines alter and effectively twist / angle the motor against the mount. Its surprising the amount to stress you get from such motors. Asking piddly plastic to live with it is asking a lot IMHO.

Nigel

 

[dazmatic]

I would not want to claim that most P3's do not crac k ... as all the P3's in our club have cracks ... S, A and P.

I don't think speed is anything to do with it ... its CHANGE of thrust as you come in / out of manoeuvres. The motors torque and apparent thrust lines alter and effectively twist / angle the motor against the mount. Its surprising the amount to stress you get from such motors. Asking piddly plastic to live with it is asking a lot IMHO.

Nigel

What he said...

Having worked in a plastics factory and having studied materials as part of my education, plastics are funny things. You could have something well made, with well mixed, good quality plastic that breaks really easily, and really poor low quality plastic that lasts forever.

There are too many variables to say which is good/bad.

For me at least, the most prominent variable is vibration. The motors themselves do not produce any significant vibration, higher frequencies will just get absorbed into the chassis, it's the low frequency vibrations caused by unbalanced propellers that will inevitably cause cracks.

I never used to balance props, but after seeing what happened to one of my birds without balanced props and the headache it caused, I balance them all now.

 

[GMack]

DJI also uses the cheapest Locktite and incorrect products that will cause plastics to crack. B&H Photo sells the DJI branded Loctite online ( dji threadlocker | B&H Photo Video ) and if you read the PDF spec sheets, it is not recommended for plastic. Loctite does make some that are safe around plastic, just DJI doesn't use it (Probably costs $1 more. ha!).

I don't discount their use of cheap plastics either. Had the springs crack the top of the battery case. Any stress seems to crack their cheap plastic and could be due to their vendor too. Hotrodding could be a factor too. Maybe incorrect cleaners that suck out the plasticizers too.

 

[Tim Dawes]

I would not want to claim that most P3's do not crac k ... as all the P3's in our club have cracks ... S, A and P.

I don't think speed is anything to do with it ... its CHANGE of thrust as you come in / out of manoeuvres. The motors torque and apparent thrust lines alter and effectively twist / angle the motor against the mount. Its surprising the amount to stress you get from such motors. Asking piddly plastic to live with it is asking a lot IMHO.

Nigel

I don't know why DJI doesn't imbed a light gauge piece of metal in the inside of the shell under the motors. Seems it would be a simple fix.

 

[solentlife]

I don't know why DJI doesn't imbed a light gauge piece of metal in the inside of the shell under the motors. Seems it would be a simple fix.

I think it needs more than that .... if I was designing it - I would have CF running long the arm out to motor area to support it all. Those arms thin down at a crucial area in my opinion - just before the motor area.

If you ever take a DJI shell apart - you will find out just how little that area can take !

Nigel

 

[dazmatic]

Once again vibration is the killer. Making it rigid isn't really the answer as it'll just effect something else in the chassis.

Remember, It takes energy to crack something like that, energy coming from the motors in the form of vibrations. In an ideal world, dynamically balanced props are the perfect answer. Statically balanced props will suffice.

However, if I was a designer, especially for DJI where the drones are used by professionals and novices alike where they will most like use unbalanced props, trying to design for both, I'd include some rudimental vibration dampening on the motors themselves.

 

[solentlife]

I agree that vibration is a killer ... and if you see how much that weakened area can move ....

My suggestion of CF is that it doesn't create such rigidness as metal would ... it still allows some give.

Have a look at 3D planes etc. - see what they put up with ... the CF is a saviour to them.

Nigel

 

[Meta4]

I would not want to claim that most P3's do not crack ... as all the P3's in our club have cracks ... S, A and P.

I don't think speed is anything to do with it ... its CHANGE of thrust as you come in / out of manoeuvres. The motors torque and apparent thrust lines alter and effectively twist / angle the motor against the mount. Its surprising the amount to stress you get from such motors. Asking piddly plastic to live with it is asking a lot IMHO.

If this was the case, all Phantoms would crack up but they don't.
If they all cracked, no-one would buy DJI.
I've only had 6 P3 & P4 series machines and flown them all hard with no cracking ever showing.
The only explanation for the cracking being observed in a minority of Phantoms is that the quality of the plastic or moulding varies.
Most are fine and deal with whatever is necessary but some batches have been released that were not.
This is also supported when you hear of a few users babying their Phantom or taking all sorts of supposed preventative measures and still getting cracks.

 

[solentlife]

If this was the case, all Phantoms would crack up but they don't.
If they all cracked, no-one would buy DJI.
I've only had 6 P3 & P4 series machines and flown them all hard with no cracking ever showing.
The only explanation for the cracking being observed in a minority of Phantoms is that the quality of the plastic or moulding varies.
Most are fine and deal with whatever is necessary but some batches have been released that were not.
This is also supported when you hear of a few users babying their Phantom or taking all sorts of supposed preventative measures and still getting cracks.

As I said - all the P3's in our club have cracked ... that's at least 8 I know personally.

And I never said ALL WILL crack ... I said that all I see have. Its also a common topic on all forums.

Nigel

 

[solentlife]

Lets put a question out then, based on the way society today tends to work ... speed limits on roads, car safety, boats, etc :

Is it better to follow the path of expecting worst and cover the possibilities or assume it will never happen ?

Lets say just odd batches of P's are subject to cracking for whatever reason - what is best ? Ignore and hope you are one of the lucky ones and no cracks or take the cautious path and try to reduce the risk of them ruining your day ?

I know what my answer is - I fitted plates and keep an eye out for them.

My P3S had the later version shell with the raised supports and spider web under the motor to reduce cracking ... she cracked bad ! No crashes or extremes to explain why.

My P3P with same late version shell has signs of cracks starting but the plates are holding it.

People send in AC under warranty for new shells ... funny that there are quite a number of posts saying cracks appeared in the replacement shells ... you'd think if DJI had shells that do not crack - they'd be using those for replacement ?

It has been obvious that the design has a fundamental fault - evident also in the similar designed competing brands - who suffer similar cracks. On another forum a specific question was asked if anyone knew about similar on other brands ... it was confirmed that yes - same happening.

I have no axe to grind on this - only that giving impression that this is an isolated item means many will accept that and then suffer cracks / downtime of their P ... unnecessarily.

Nigel

 

[dazmatic]

I admittedly have purchased aluminium brackets to fit under the motors on my P3P to stiffen and reinforce the plastic arms as a precautionary measure, they help spread the vibrations outwards rather than focused on a single point.

But I also run balanced props that have been balanced on my dubro balancer with a machined balance rod so once again, another precautionary measure.

I have discovered also you can get silicon spacers that sit under the motors themselves, between the motor and the arm in which you run the screws slightly looser but loctite into place. Haven't bought them but that should help absorb any vibrations from the motors.

 

[solentlife]

All measures that reduce to effect on those arms must be good.

The problem with effective measures - you can never actually quantify the results of them unless you specifically test in adverse situation.

Its like the old Rope Cutter arguments on boats propellers ..... the wasted crap about one better than another etc. You never know when it does its job because its unseen incident - same as cracks on a P. All you see is the final ... rope cutter = no rope round prop ... plates = less or no cracks on arms of P3. Whether either would have been same with or without, difficult to prove.

That is why I have a rope cutter on my yacht prop and plates on my P3S and P3P.

Nigel

 

[dazmatic]

Exactly, one of the main complaints I've seen about the P3 is cracks on the arms, hence the investment in plates.

By the way Nigel, it's nice to meet another Nigel!

 

[solentlife]

Cheers .....

I got the name from my Fathers favourite Author .... and I hated it at school - especially when that pop group sang a song with the name !! But later getting older understood how unusual a name it is.

Nigel .....

 

[dazmatic]

Cheers .....

I got the name from my Fathers favourite Author .... and I hated it at school - especially when that pop group sang a song with the name !! But later getting older understood how unusual a name it is.

Nigel .....

My dad liked Formula 1, Mansell, go figure!