Drone Flight Physics Question

[PBDawg]

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 right on a vertical axis) since there are no propellers providing sideways thrust (like a bow thruster on a ship). How does a quadcopter rotate?

 

[sar104]

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 right on a vertical axis) since there are no propellers providing sideways thrust (like a bow thruster on a ship). How does a quadcopter rotate?

Conservation of angular momentum. To turn CW it speeds up the CCW props and slows down the CW props, increasing the net CW moment of force on the airframe, and vice versa.

 

[Deleted member 103366]

My physics is too rusty to think about angular momentum but I noticed that on a Phantom the CW and CCW motor are canted tangentially in opposing senses. To my mind they should therefore produce slight and opposing torques around the CoG, when the torques are not in balance the result is yaw. I can't speak about a Mavic yet as my mini is en route.
Well that's my thinking but it is rusty so I will stand correction if I am wrong

 

[Meta4]

My physics is too rusty to think about angular momentum but I noticed that on a Phantom the CW and CCW motor are canted tangentially in opposing senses. To my mind they should therefore produce slight and opposing torques around the CoG, when the torques are not in balance the result is yaw. I can't speak about a Mavic yet as my mini is en route.
Well that's my thinking but it is rusty so I will stand correction if I am wrong

Many drones including earlier Phantoms did not have offset motors and had no problem with yaw control.
Hovering or flying straight, the counteracting torque from CW and CCW motors is in balance.
Yawing is accomplished by varying the motor speed as mentioned i post #2 to allow torque to turn the drone in the desired direction.

The offset motors are to provide more stability in vertical descent.

 

[Andy Mac 230]

It’s all white mans magic...but nobody yet can explain how the humble Bumble Bee gets airborne....lol

 

[Rockycat]

Conservation of angular momentum. To turn CW it speeds up the CCW props and slows down the CW props, increasing the net CW moment of force on the airframe, and vice versa.

Well explained. Love it, shot and sweet.

 

[Dave Maine]

Not magic just basic physics. Has been known for at least 100 years.

 

[Prismatic]

It’s all white mans magic...but nobody yet can explain how the humble Bumble Bee gets airborne....lol

Actually, that myth has been busted for many years.

 

[Prismatic]

My physics is too rusty to think about angular momentum but I noticed that on a Phantom the CW and CCW motor are canted tangentially in opposing senses. To my mind they should therefore produce slight and opposing torques around the CoG, when the torques are not in balance the result is yaw. I can't speak about a Mavic yet as my mini is en route.
Well that's my thinking but it is rusty so I will stand correction if I am wrong

Yeah, but no, that's not how it works. Angular momentum is how it works. This is one of the simplest engineering problems drone engineers have solved. If that's baffling, pretty much every other aspect of drone engineering is way beyond understanding.

Drones rely on technologies that are founded in quantum physics, and Einsteinian relativity, and (of course) Newtonian physics. Few people have a comprehensive command of everything involved, including me. Fortunately, you don't have to understand the Hall Effect to operate a joystick, even though the very existence of that joystick means somebody understands the Hall Effect.

May be best leave it at that, or you'll spend your time studying instead of flying!

 

[buddb55]

I pretty much slept through that class!

 

[Ralph thompson]

Basic classical mechanics, nothing of consequence to do with relativity or quantum physics.

 

[sar104]

Basic classical mechanics, nothing of consequence to do with relativity or quantum physics.

I don't know - have you seen some of the speed records that people have claimed? And so much uncertainty...

 

[jeepcj]

Basic classical mechanics, nothing of consequence to do with relativity or quantum physics.

Yup, just think of a helicopter and WHY it needs a tail rotor...

 

[LazerMan]

Maybe Doc Brown can explain it so we could understand it

 

[Prismatic]

Basic classical mechanics, nothing of consequence to do with relativity or quantum physics.

GPS seems to me of some consequence (relativity). So does the CMOS sensor in the camera (quantum mechanics). You may have assumed more than I said; my comment was not confined to flight mechanics.

 

[Ralph thompson]

I don't know - have you seen some of the speed records that people have claimed? And so much uncertainty...

Along with distance & height records but I’d say they were more Darwinian.

 

[Deleted member 103366]

I am NOT trying to start an argument, be it good natured or a slanging match but......
I have been stirring the little grey cells.
Would the following be correct?
Ignoring "cant of the motors" I am beginning to recollect each motor creates a torque, a pure torque i.e. a couple = pure twist, ( because the wind resistance of the props demands torque rotate the props). This torque/couple is transmitted to the air frame via the motor mounts (remove the motor mount screws and the motors would spin (ignoring that they would 'take off')? and for each motor is the same about all points in space i.e about the centre-of-whatever. The CW motors therefore generate a couple about the relevant centre-of-whatever that acts in one sense, similarily the the two CCW motors generate a couple that acts in the opposite sense, increasing the speed of a motor increases its couple etc.
When the two resultant couples are not in balance the result is yaw.

 

[sar104]

I am NOT trying to start an argument, be it good natured or a slanging match but......
I have been stirring the little grey cells.
Would the following be correct?
Ignoring "cant of the motors" I am beginning to recollect each motor creates a torque, a pure torque i.e. a couple = pure twist, ( because the wind resistance of the props demands torque rotate the props). This torque/couple is transmitted to the air frame via the motor mounts (remove the motor mount screws and the motors would spin (ignoring that they would 'take off')? and for each motor is the same about all points in space i.e about the centre-of-whatever. The CW motors therefore generate a couple about the relevant centre-of-whatever that acts in one sense, similarily the the two CCW motors generate a couple that acts in the opposite sense, increasing the speed of a motor increases its couple etc.
When the two resultant couples are not in balance the result is yaw.

That's correct.

 

[Deleted member 103366]

ta

 

[Ralph thompson]

Agree, action and reaction are equal, applies to angular and linear forces.