How does a drone rotate about a vertical axis while in a stationary hover?

[Mavic Air 2]

I am intrigued how my (Mavic Air 2) drone can rotate about a vertical axis while in a stationary hover in still air.

It is obvious how a drone moves in any direction in a straight line - apply forward stick and it tips down at the front to develop a forward thrust, and the stability modules provide the information to maintain stable flight and prevent the drone from climbing or losing altitude while flying in the desired direction.

However, I was hovering my drone indoors after a firmware update to check all was ok and was watching it as I rotated it to the left and to the right on its vertical axis. There is a change to the sound of the motors while it turns, but other than that there is no change in attitude. The drone remains horizontal and stationary. How is that? There does not seem to be any action or reaction to Newtonian forces!

An explanation would be very welcome - Thanks

 

[Deleted member 103366]

Drone Flight Physics Question

I'm asking the following purely out of curiosity. I understand how a quadcopter ascends and descends. I understand how, by applying more or less power to each motor, a quadcopter can fly forward, backward, or left and right. What I don't understand is how such drones can yaw (pivot left or...

mavicpilots.com

 

[sar104]

I am intrigued how my (Mavic Air 2) drone can rotate about a vertical axis while in a stationary hover in still air.

It is obvious how a drone moves in any direction in a straight line - apply forward stick and it tips down at the front to develop a forward thrust, and the stability modules provide the information to maintain stable flight and prevent the drone from climbing or losing altitude while flying in the desired direction.

However, I was hovering my drone indoors after a firmware update to check all was ok and was watching it as I rotated it to the left and to the right on its vertical axis. There is a change to the sound of the motors while it turns, but other than that there is no change in attitude. The drone remains horizontal and stationary. How is that? There does not seem to be any action or reaction to Newtonian forces!

An explanation would be very welcome - Thanks

It uses conservation of angular momentum, although it may be easier to visualize in terms of net torque on the airframe.

It has 2 motors spinning clockwise and 2 motors spinning counter-clockwise which, if all spinning at the same speed, provide a equal transfer of CW and CCW angular momentum to the surrounding air. But if you speed up the CW motors while simultaneously slowing down the CCW motors (so as to maintain total lift), then more CW than CCW angular momentum is being transferred to the air, which results in a net CCW reaction torque on the aircraft, and so the aircraft turns CCW.

 

[Mavic Air 2]

Thank you, sar104, I understand your explanation regarding contrarotating props and the result of varying the speed of individual motors.

 

[ashyt16]

I am intrigued how my (Mavic Air 2) drone can rotate about a vertical axis while in a stationary hover in still air.

It is obvious how a drone moves in any direction in a straight line - apply forward stick and it tips down at the front to develop a forward thrust, and the stability modules provide the information to maintain stable flight and prevent the drone from climbing or losing altitude while flying in the desired direction.

However, I was hovering my drone indoors after a firmware update to check all was ok and was watching it as I rotated it to the left and to the right on its vertical axis. There is a change to the sound of the motors while it turns, but other than that there is no change in attitude. The drone remains horizontal and stationary. How is that? There does not seem to be any action or reaction to Newtonian forces!

An explanation would be very welcome - Thanks

Don't you mean a Horizontal axis?
Vertical is up and down.
X = Vertical Y = Horizontal
Remember X to the left Y to to the sky

 

[Paint Rock Drones]

Don't you mean a Horizontal axis?
Vertical is up and down.
X = Vertical Y = Horizontal
Remember X to the left Y to to the sky

Nope. If you rotate around a vertical axis you are level horizontally.

 

[ashyt16]

Nope. If you rotate around a vertical axis you are level horizontally.

Yep, I was thinking of rotation along the horizontal plane.
Don't think I'd be any good as a real pilot lol.

 

[DoomMeister]

Don't you mean a Horizontal axis?
Vertical is up and down.
X = Vertical Y = Horizontal
Remember X to the left Y to to the sky

X - longitudinal
Y - lateral
Z - vertical

Rotation about X is roll
Rotation about Y is pitch
Rotation about Z is yaw

 

[ashyt16]

X - longitudinal
Y - lateral
Z - vertical

Rotation about X is roll
Rotation about Y is pitch
Rotation about Z is yaw

Contrary to what I posted above (confusing myself now) I always thought X was left to right ( horizontal) and Y was up and down (vertical)
Brain hurts now. I stand corrected. Back to school for me.

 

[sar104]

Contrary to what I posted above (confusing myself now) I always thought X was left to right ( horizontal) and Y was up and down (vertical)
Brain hurts now. I stand corrected. Back to school for me.

There is no standard mathematical convention for 3-D cartesian axes, other than the right-hand rule. In aerospace applications, however, there is a convention, which is right handed with x forwards, y right, and z down:

​

 

[ashyt16]

There is no standard mathematical convention for 3-D cartesian axes, other than the right-hand rule. In aerospace applications, however, there is a convention, which is right handed with x forwards, y right, and z down:

View attachment 138073​

So in conclusion it's neither X nor Y axis, but Z axis in this case as far as aeronautical terms go?

 

[sar104]

So in conclusion it's neither X nor Y axis, but Z axis in this case as far as aeronautical terms go?

That's correct. Rotation around the vertical z-axis is rotation in the horizontal (xy) plane.

 

[Daytona500]

whew! glad we got that straight

 

[The Admiral]

I just love this site. There are sooo many knowledgeable people out there who are willing to explain stuff, and sort out drone stuff as well

 

[DoomMeister]

There is no standard mathematical convention for 3-D cartesian axes, other than the right-hand rule. In aerospace applications, however, there is a convention, which is right handed with x forwards, y right, and z down:

View attachment 138073​

Thanks for the graphic!

 

[BrianH55]

Contrary to what I posted above (confusing myself now) I always thought X was left to right ( horizontal) and Y was up and down (vertical)
Brain hurts now. I stand corrected. Back to school for me.

Would you pass me a few of those ibuprofen?

 

[SkyPath Studios]

I am intrigued how my (Mavic Air 2) drone can rotate about a vertical axis while in a stationary hover in still air.

It is obvious how a drone moves in any direction in a straight line - apply forward stick and it tips down at the front to develop a forward thrust, and the stability modules provide the information to maintain stable flight and prevent the drone from climbing or losing altitude while flying in the desired direction.

However, I was hovering my drone indoors after a firmware update to check all was ok and was watching it as I rotated it to the left and to the right on its vertical axis. There is a change to the sound of the motors while it turns, but other than that there is no change in attitude. The drone remains horizontal and stationary. How is that? There does not seem to be any action or reaction to Newtonian forces!

An explanation would be very welcome - Thanks

From what I understand your asking, two opposite motors (ccw or cw), speed up and the others slow down. This imbalances the drone, in a good way, and causes it to rotate. Hope this helps.

 

[Deleted member 103366]

The following is from a yaw-test, indoors, with a Mavic 2 Zoom. I tried the same thing with a Mavic Mini but the motor speeds are so much higher that they and the automated motorspeed adjustments conceal the variations of motorspeed due to commanded yaw.

 

[Jonathan Burnett]

I have a related question; I'm on my third Mavic 2 Pro (each replaced with a new one under warranty) and they all experience this undesirable rotation about the vertical axis when I hover for long periods shooting hyperlapses. Not all flights have this problem but many do. I've always thought the issue was wind but it happens even on what seem to be calm days (but who knows what's at altitude).

I just wish there was a way to counter it or even better, have the Mavic MAINTAIN its orientation. It does a great job of maintain POSITION but the rotation (yaw) is ruining many of my hyperlapses.

Oh and almost all of the time, the rotation is in the clockwise direction (more than 9 out of 10 occurrences).

 

[sar104]

I have a related question; I'm on my third Mavic 2 Pro (each replaced with a new one under warranty) and they all experience this undesirable rotation about the vertical axis when I hover for long periods shooting hyperlapses. Not all flights have this problem but many do. I've always thought the issue was wind but it happens even on what seem to be calm days (but who knows what's at altitude).

I just wish there was a way to counter it or even better, have the Mavic MAINTAIN its orientation. It does a great job of maintain POSITION but the rotation (yaw) is ruining many of my hyperlapses.

Oh and almost all of the time, the rotation is in the clockwise direction (more than 9 out of 10 occurrences).

Impossible to say what is causing that without a DAT file for one of those flights.