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Do the tips of your props line up?
1236 8 2016-7-15
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mochorm
lvl.3
Flight distance : 940148 ft
Canada
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Was hovering in place yesterday and noticed that on the left side of my P3P the blade tips are not even on the horizontal plane, there is about a 2-3mm difference in height between the front and back blades. While looking at the right side they look to be bang on even with the horizontal plane? And you can still see the difference when the Xcopter is stationary.

Moved props around with the same result, put new props on,  motors are all tight, no stress cracks on housing.

Curious if this is normal or something is not quite right with my P3P?


TIA

IMG_2127_07-15-2016.jpg
IMG_2128_07-15-2016.jpg
2016-7-15
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Cetaman
Captain
Flight distance : 2494390 ft
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United States
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Aloha TIA,

     Cool, you noticed it.  Not everyone notices the differences in thrust angles of each motor.  These differences are to protect the Phantom from Vortex Ring State (VRS) while descending.  Starting with the Phantom 2 v.3, these changes in the motor angles have allowed for safe and improved downward speeds.  The earlier Phantoms discovered that quadcopters suffer from the same physics as full scale helicopters when descending.  This was often called the wobble of death (or some other colorful term).  No matter what size your quadcopter (or helicopter), if you put it into a fast descent in calm winds, your copter would experience VRS.  VRS caused the crashes of the Stealth H-60 in the Bin Laden raid and the testing of the V-22 Osprey.

     With the introduction of the Phantom 3, DJI started to include the change in motor angles in their manual drawings.  The Phantom 4 manual has a very obvious angle for its motors off of vertical.  If you go back and look at the same manuals P2 v.3 - P3 - P4, you will also see an increase in descent speeds due to the change in motor angles.  DJI handled the issue initially by decreasing descent speeds in the software and then increasing the descent speeds safely when they compensated with motor angles in their newer designs.

*  *  *

     Now, back in the dark ages before the success of DJI, Wikipedia tried to post issues of VRS in small, indeed micro, helicopters, quadcopters, etc. on the same pages as full scale helicopters.  But the full scale helicopter advocates could not see and understand that this problem could affect such small vehicles.

     These helicopter advocates would delete any post that tried to tie VRS to micro copters so that there was no way to inform the operators of micro copters, including the new DJI consumers, of this danger.  Now, flying full scale helicopters is a very demanding job, but we are all susceptible to the laws of physics.  In this case the bridge is the "Physics of Scale".  

     FYI, if you have a debate with others in Wikipedia, there is a back-door to a room where discussions take place to get, and keep, the real world on the pages of Wikipedia.  This is a very good tool for setting the record straight.

     If you choose to go there, you will discover a familiar voice arguing about the "Physics of Scale" to the extent that all the crashes of micro quadcopters were recognized by the full size helicopter advocates that kept deleting references to our problem.  Some videos demonstrating this phenomenon by pioneers of quadcopter flight and saving the copter from crashing in predictable ways were also included.  The evidence was compelling.

     Due to this effort, you can now find VRS noted in direct reference to our quadcopters.  On the full scale helicopter page there is also a reference that small quadcopters also experience this problem.  

     Yes, there are differences in the angles of each motor in your Phantom.  And you can descend faster and safer than your Phantom's predecessor because of it.

Aloha and Drone On!
2016-7-16
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mochorm
lvl.3
Flight distance : 940148 ft
Canada
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Thanks for the reply Cetaman, I realize the motors are canted.

However it would seem to me that the tips of the props should be on the same horizontal plane. As you pointed out there are several pictures in the manual and if one looks the tips of the blades they are on the same horizontal plane.
In the pictures I posted you can see on the right side the tips are on the same plane as where on the left side they are not. Also if you turn the props towards each other and look from the front and back, the front tips are off plane very slightly and the back equal. It's as if the front left motor is slightly out of whack. i.e. if I were to move that motor just a hair the prop tips would all be on the same plane.

I was hoping someone would have a look at their P3P to see if all the tips are all on the same plane.
2016-7-16
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endotherm
Captain
Flight distance : 503241 ft

Australia
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Probably manufacturing tolerances, nothing to worry about.  One arm could be very slightly twisted, could have happened in a hard landing or during assembly.  I notice your arm has slight puckering on the stickers across the two shell halves, which is a sure sign of some twisting.   If a canted motor is going to cause drifting to one side the others will compensate by spinning faster and the "bad" one would be slowed.  The blades will be flexing a lot more than the difference during flight anyway.  Others have noticed these differences by placing the inverted aircraft (without blades) on a perfectly flat table and noticing all 4 motor spindles aren't touching.

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2016-7-16
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endotherm
Captain
Flight distance : 503241 ft

Australia
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I just checked my P3A with a brand new set of props.  My aircraft has all 4 motors perfectly flat as per the inverted test.  I noticed a small variation between the tips, just like yours.  When I spin one prop through 180 degrees, the low blade tip becomes high.  This happens on all props.  I suspect the center hub which screws onto the motor is not perfectly perpendicular to the plane of the blades.  Some are worse than others.  Again, I wouldn't worry and if it were badly out of tolerance there would be some serious vibrations happening in flight.  I tested these props and they are nicely balanced out of the packet.  The result of having the props ever so slightly skewed is that the downdraft will be almost imperceptably conical (tapering outwards) instead of perfectly parallel.  A slight breeze is more likely to be a greater concern than a misshapen downdraft.
2016-7-16
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guns&cameras
lvl.2

United States
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I'm not sure if anyone, or if it's even possible, to measure a type of stress test. I have seen a test on maximum weight being lifted from a craft...anyway, there has to be quite a bit of torque/flex from arm to arm as the velocity of each prop increases and decreases to control flight. Remember, these are just plastic. Hmmm, I wonder if anyone has created a mold for a CF frame...THAT would be beautiful...expensive, but beautiful...
2016-7-16
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AG0N-Gary
Captain
Flight distance : 700846 ft
United States
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Also, ANY amount of breeze will cause the quad to lean slightly to compensate to keep it in the same location.
2016-7-16
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mochorm
lvl.3
Flight distance : 940148 ft
Canada
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Thank you very much for your efforts endotherm!
It's the engineer in me that see's a deviation and needs to know why My motors are also perfectly flat! And the deviation of the tips is more noticeable when hovering in front of me, that's what tweaked me to begin with.

I noted the stickers as well! I figured it may be due to the way I carry the P3P to the park, I just hold onto one of the arms while walking.
Other than that I've had a few tip overs during the first week of ownership, trying to use the CSC command after landing The manual should be updated to remove the reference to using the CSC after landing. I was bound and determined to use both methods to shutdown the bird, when in fact holding down the throttle is all that is ever needed.

She fly's good so that's all that matters in the end.
2016-7-16
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DJI-Paladin
DJI team
Flight distance : 2408 ft

Hong Kong
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Hello mochorm, if your drone and the motors work well in the air, you don't need to worry about that.
2016-7-17
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