P3 is heavier on rear end ( battery side )

Ideally, if you had 4 scales like the one pictured, you could place one motor on each scale and see if any difference showed there. Then again, not many people have 4 scales? Unless you know people who are into that kind of stuff. Just a thought.
Made a crude arrangement by inverting and resting the top on a block and started adding coins to see what gets me best balance.
ImageUploadedByPhantomPilots1455392769.240141.jpg
 
You seem to have a good understanding of its inner control system.

Also I agree with your finding that one motor has more sag and nose is up. This is due to unbalanced weight distribution. You are right controls will adjust the angles during flight by adjusting the motor speeds depending upon the stick values. Doing this rear motors will spin faster than needed if there was a perfect balance.

I m looking at the best solution to get near balance at its expected CG.
You seem to have a good understanding of its inner control system.

Also I agree with your finding that one motor has more sag and nose is up. This is due to unbalanced weight distribution. You are right controls will adjust the angles during flight by adjusting the motor speeds depending upon the stick values. Doing this rear motors will spin faster than needed if there was a perfect balance.

I m looking at the best solution to get near balance at its expected CG.

Might be better to look at making the P3's more Aero-Efficient.
 
Guys, guys, guys,
The P3 is not tail heavy !!
I the world of Aviation ALL AIRCRAFT have a CG RANGE,
An aircraft can fly tail heavy or nose heavy,
An aircraft does not fly well at perfect zero CG,
Its preferred to fly an aircraft on either side of the zero CG,
Its more stable in that configuration.
Its crazy talk to add weight to the Phantom,
Don't you think our Chinese friends have this figured out??
Forget about this CG thing.
 
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If the weight that was added to the front was additional battery weight, it would be a win-win



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Guys, guys, guys,
The P3 is not tail heavy !!
I the world of Aviation ALL AIRCRAFT have a CG RANGE,
An aircraft can fly tail heavy or nose heavy,
An aircraft does not fly well at perfect zero CG,
Its preferred to fly an aircraft on either side of the zero CG,
Its more stable in that configuration.
Its crazy talk to add weight the Phantom,
Don't you think our Chinese friends have this figured out??
Forget about this CG thing.

Tail heavy aircraft are dangerous...if they stall without engines it is not recoverable. For a quad I don't think it matters....but ideally it would balance in the dead center...
 
Tail heavy aircraft are dangerous...if they stall without engines it is not recoverable. For a quad I don't think it matters....but ideally it would balance in the dead center...

To far tail heavy out of range is dangerous of course.
We dispatch aircraft all day long that are within the CG range toward the aft of that range.
Getting back to the thought of adding nose weight to the P3...no way.
 
Not quite, by adding weight to the front you have balanced it so the load on the motors will be more similar. However if you add weight the back is still lifting the same weight so getting through power at the same rate, the front will be lifting more weight so will be getting through power quicker. Net result, shorter run time.

I disagree, as the motors (front and back) are linked by a rigid frame the rears will indeed spin faster than the front, but as a result the front will spin slower as they are being "pulled up" by the rears.
I completely agree that a balanced load would be preferable (or maybe nose heavy if you're flying forward rather than hovering.
However I think this needs to be done by re-distributing the existing weight rather than adding more.
This is however just theory in my head and I'd be happy to be proved wrong.

Forward vs reverse flight time comparison woul be interesting. Probably best using waypoints for the route then changing the direction the camera faces between the 2 flights.
 
Being slightly off center allows greater PID loop stability. Anyone who understands PID gain will agree that a little bit of error from set point (0 or level) allows it to stabilize with ease.


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Being slightly off center allows greater PID loop stability. Anyone who understands PID gain will agree that a little bit of error from set point (0 or level) allows it to stabilize with ease.


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Dave you are correct, exactly what I said,
Please take no offense, but the correct nomenclature is "off CG"
There is no way In going to mess with the CG of my Phantom.
 
No offense taken, I come from a process control engineering background, the loops I tune or construct are mainly level, pressure, temperature, speed. From the quads view, it sees a set point (CG, level, whatever :) and adjusts motor voltages to bring it to set point, balancing many factors. Having a slight offset allows certain elements of the gain to behave more predictably.


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Adding weight will reduce flight time. All you will achieve in making the front motors work as hard as the back motors is higher total power required in all attitudes.
 

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