significant ?   see  Part 1


......... Let's try to exaggerate the angle of the tail rotor. See image below.

In order to maintain the current altitude, an increase in the quadcopter engine speed (rotational speed) of rotors 3 and 4 (rear motors) is necessary since it generates less lift due to their inclination on the sides but, as and as the battery discharges, they are no longer able to maintain their rotational speed. The electronics no longer have a choice, it must command a reduction in the speed of rotation of the motors 1 and 2 in order to maintain the attitude. The drone then loses altitude and, even with full throttle, the drone continues to descend because its priority is to maintain the attitude. All this in conjunction with the remaining power in the battery. The weaker the battery, the less engines 3 and 4 manage to maintain their rotational speed and the cycle continues until there is no longer enough power to remain in flight.

This is what I understand. Simple question of logic.

You can say that replacing the propellers solves the problem. I do not believe. It is a false impression. You return to fly with full charge batteries but, in principle, the same behavior should return sooner or later.

Unfortunately, I will have to stop my involvement in this forum. More urgent things to settle but I will continue to read you as often as I am allowed.

Good flights and that the planet heals as soon as possible!

Yes, the drones are designed that way, and your front props are tilted back. It seems that all of the Mavic drones are this way, and probably all drones in this class. The uncommanded descents occurred even with fully charged batteries. And there were only a handful of drones having this issue. I don't think the design is the cause.

The only fix I can see would be to replace the two rear arms.

JGFly Posted at 4-29 06:47
The only fix I can see would be to replace the two rear arms.

Fix of what?

Deucalion Posted at 4-29 06:27
Yes, the drones are designed that way, and your front props are tilted back. It seems that all of the Mavic drones are this way, and probably all drones in this class. The uncommanded descents occurred even with fully charged batteries. And there were only a handful of drones having this issue. I don't think the design is the cause.

..........I took a look at 2 other cheap drones (Holy Stone) that I have and the 4 motors on each of them are all perfectly horizontal with respect to the ground therefore, I am not completely convinced.........

From Significant part 1 - post #9

JGFly Posted at 4-29 06:55
..........I took a look at 2 other cheap drones (Holy Stone) that I have and the 4 motors on each of them are all perfectly horizontal with respect to the ground therefore, I am not completely convinced.........

From Significant part 1 - post #9

edit - i have been corrected. Phantoms "LOOK" like the props are flat. But in any case if some are not and they work, surely this is not the root cause.

lee82gx Posted at 4-29 07:12
The phantom series also do not have tilted / no horizontal rear props.

Thank you for the information

Cheers

lee82gx Posted at 4-29 07:12
The phantom series also do not have tilted / no horizontal rear props.

No, that isn't true...

https://phantompilots.com/threads/p3p-–-motors-mounted-at-an-angle.57817/

If you look into It deeper, a lot of designs use this approach. Airplane wings for example. The wheels on your car. It provides better control and stability.

Deucalion Posted at 4-29 07:19
No, that isn't true...

https://phantompilots.com/threads/p3p-–-motors-mounted-at-an-angle.57817/

I stand corrected!

FYI    Motor angle explanation

.........It's straightforward mathematics/physics - if you tilt the motor from vertical the total thrust from the motor/prop doesn't change but there is now a "sideways" thrust vector (the effect you wanted - it's why you tilted the motor) - so there must be correspondingly less vertical lift. If you tilt the motor to 90 degrees, you'll have 100% "sideways" thrust and 0% vertical thrust. At 45 degrees you'll have 50% "sideways" thrust and 50% vertical thrust, i.e. you've reduced the "lift efficiency" by 50%.

If you put a 5mm thick shim under one side of a 40mm diameter motor (for example), you induce a tilt of approximately 7.15 degrees from vertical, equating to about 8% loss in vertical thrust.

For what we've seen from analysis in this and other (external) forums (including .dat analysis with commercial software) the indicators point at a supervened maximum rpm reached with the rear motors.

That means the rear motors are spun at max rpms (for the propellers not producing enough uplift), unfortunately the combination of increased pitch down (for advancing) and diagonal vector thrust provided mostly by the rear propellers isn't enough to maintain altitude... I highly doubt it could be called a stall, but actually that's what happens and the drone plummets to the ground quite quickly.

Another read, especially post 1 and 2

dihedral .....

m80116 Posted at 4-29 08:08
For what we've seen from analysis in this and other (external) forums (including .dat analysis with commercial software) the indicators point at a supervened maximum rpm reached in the rear motors.

That means that the rear motors are spun at max rpm (because the propellers do not produce enough uplift), unfortunately the combination of increased pitch down (for advancing) and diagonal vector thrust provided mostly by the rear propellers isn't enough to maintain altitude... I highly doubt it could be called a stall, but actually that's what happen and the drone plummets to the ground quite quickly.

Just to be clear, the drones did not descend while the propellors were maxed out. The FW reduced the RPM on all the motors and descended the drone in a controlled state, except you could not override it at all.

As I can understand (read on different forum) the small inclination of the engines would increase the stability of the drones but what I can't understand is that the modification of the rotor angle is on 2 arms (rear) only. ???

Other interesting readings


https://oscarliang.com/tilted-angle-motor-mounts-racing-quadcopter/

JGFly Posted at 4-29 08:35
As I can understand (read on different forum) the small inclination of the engines would increase the stability of the drones but what I can't understand is that the modification of the rotor angle is on 2 arms (rear) only. ???

Other interesting readings

That would be a question for the guys @ DJI...

Flycaster Posted at 4-29 11:29
That would be a question for the guys @ DJI...

Indeed !

I will continue trying to find an answer by myself and maybe a solution. For example `` angled motor mounts '' ???

WHO DARES NOTHING, WINS NOTHING

Cheers!

JGFly Posted at 4-29 11:48
Indeed !

I will continue trying to find an answer by myself and maybe a solution. For example `` angled motor mounts '' ???

A solution to what? I don't understand what the problem is you are trying to solve?

Deucalion Posted at 4-29 12:18
A solution to what? I don't understand what the problem is you are trying to solve?

Ha Ha Ha,  your'e funny Deucalion  

P.S. This is my last day  as an active member on the forum. Don't know how long. (Too much busy at home with Childrens and grandchildrens)

Cheers !  Have a good flight !

JGFly Posted at 4-29 12:27
Ha Ha Ha,  your'e funny Deucalion  

P.S. This is my last day  as an active member on the forum. Don't know how long. (Too much busy at home with Childrens and grandchildrens)

Well, if you run your solution by DJI, I think they will ask the same thing. A solution of what?

Deucalion Posted at 4-29 12:29
Well, if you run your solution by DJI, I think they will ask the same thing. A solution of what?

Why motor issue only on tail rotors, especially the left one ???.

I'm this kind of individuals who can't sleep very well when unable to find the source of the problem and also the solution.

When somethings stop working, I open and try to fix it. I am made like this and it is not at my age that I am going to change LOL. You know, the funniest thing is that I almost did not fly my Drone (less than 30 minutes since January, spread over 11 connections including only 2 takeoff to test the commands and my parameters and not over 50 fts height in the parking lot of the building. No time to do more). snif snif

Even I find myself complicated, but when I find a solution or a potential solution and I can help someone, it makes me extremely happy. I like to help others. Now Going to lunch and do not know when I'll come back.

It was nice to talk (writing) to you all.


P.S. Even if it's a coding or programming problem, it's not bad. The bright side is that I learn a lot.

Cheers!

as and as the battery discharges, they are no longer able to maintain their rotational speed.
This is what I understand. Simple question of logic.
This assumption is incorrect.
DJI drones don't lose the ability to fly as the battery runs down.
Try for yourself and you'll see that the drone can climb and fly as fast at 30% as it did with a fully charged battery.

JGFly Posted at 4-29 06:47
The only fix I can see would be to replace the two rear arms.

How could you perform yaw with all straight propellers? You need angled props...

virtual Posted at 4-30 00:37
How could you perform yaw with all straight propellers? You need angled props...

Many drones don't have offset motors and they yaw without any problem.
DJI Phantom and Phantom 2 series had vertical motors.

virtual Posted at 4-30 00:37
How could you perform yaw with all straight propellers? You need angled props...

No, yaw happens naturally as result of the physics of spinning props.  That's why two motors spin in the opposite direction - you control the yaw of the aircraft by adjusting the relative speed of the opposing motors.  The angle of the props changes the physics a bit, but the principle remains the same, whether they are straight up and down or angled.

Labroides Posted at 4-29 20:43
as and as the battery discharges, they are no longer able to maintain their rotational speed.
This is what I understand. Simple question of logic.
This assumption is incorrect.

Not totally incorrect but I would like to believe you (to verify). But that does not change the fact that the drone must maintain   
A T T I T U D E     at the expense of the    A L T  I T U D E     (if not, the drone will sting towards the ground)  therefore, necessarily, since the engines (even with Full throttles) fail to lift the rear of the drone (since one or two propeller(s) is or are damaged), the front motors will have to reduce the rotational speed in order to maintain the ATTITUDE and, necessarily, the drone will lose ALTITUDE.

Am I correct ? (in general)

Anyway, there are so many possibilities (they have all been reported on this forum by you and several others) but the point I raise just adds to the various attempts to explain these infamous '' Uncommanded descent ''.

Cheers !

P.S. again, this is a traduction via Google and a correction of Google by me (Google not always very acccurate)

virtual Posted at 4-30 00:37
How could you perform yaw with all straight propellers? You need angled props...

Agree with @Laboides and @011111110  wrote.

Also, see my post #5

Cheers!

JGFly Posted at 4-30 05:26
Not totally incorrect but I would like to believe you (to verify). But that does not change the fact that the drone must maintain   
A T T I T U D E     at the expense of the    A L T  I T U D E     (if not, the drone will sting towards the ground)  therefore, necessarily, since the engines (even with Full throttles) fail to lift the rear of the drone (since one or two propeller(s) is or are damaged), the front motors will have to reduce the rotational speed in order to maintain the ATTITUDE and, necessarily, the drone will lose ALTITUDE.

Not totally incorrect but I would like to believe you (to verify).
It's very easy to check for yourself.

Am I correct ? (in general)
This forum isn't the place where you'll get proper discussion on the technical aspects of DJI drones.
But you will get plenty of wrong guesses.

To save you some trouble, you'll find some answers to your problem here:
https://mavicpilots.com/threads/mavic-mini-uncommanded-descent-tests.86237/unread

Labroides Posted at 4-30 05:49
Not totally incorrect but I would like to believe you (to verify).
It's very easy to check for yourself.

Thanks for the shortcut seems very interesting !

JGFly Posted at 4-30 06:10
Thanks for the shortcut seems very interesting !

Many thanks @Labroides, I like  this thead !

Cheers !

Quote '' Yes. In this situation the rear motors are unable to generate enough lift for the aircraft to perform nominally, and the very high motor speeds are probably making the prop deformation worse. ''

In  the following post,  Mavic Mini uncommanded descent tests

He is right. Another behavior which amplifies the problem.