# Rotating around the yaw axis

Hi,
I’m a student at NTNU in Ålesund and I’m working on my bachelor thesis. In my thesis, I’m using an octocopter, and I’m currently working on the theory part of the report.

I haven’t managed to figure out exactly how a multicopter rotate around its yaw axis. Because there seem to be a lot of confusion going around the internet on how a multicopter turns around the yaw axis. YouTube videos, web pages and even books don’t seem to agree on which engines must spin faster in order to make a multicopter turn. Some sources seem to think that for a multicopter to turn CW the CW engines must spin faster than the CCW engines. And equally as many sources claim that the CCW engines must spin faster to turn CW.

Take these two YouTube videos for example:
This one claim to increase RPM on CCW in order to make the copter spin CCW: How Do Quadcopters and Multicopters Fly? - YouTube

And this video claim the CW engines need to spin faster in order to turn CCW due to torque: How Do Quadcopters Fly? - YouTube

Can anyone help me clarify this subject? And do anyone know about any good sources I can use as a reference in my report regarding this problem?

Regards

i am trying to explain how i think it is:
an easy imaginable example is an single blade (just a normal) Helicopter!
the main blade is turning for example CW, and it’s easy to imagine that if you hold the props tight with your hands, the helicopter will start to spin (instead of the rotor) - but in the opposite direction - CCW!
so every spin induces a spin in the opposite direction on your motor/copter!

if anyone can explain it better or correct me, please go on!

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@panky that is correct - Newton’s Third Law - every action has an equal and opposite reaction.

@kenneth.f It’s functionally the same reason a traditional helicopter needs a tailrotor for anti-torque control. Otherwise fuselage spins opposite direction of main rotor. A quick google for that should yield a picture to help. Single engine prop fixed-wing aircraft suffer from similar torque issue that can be offset with roll trim and/or engine offsets. Likely beyond scope of what you are looking for here.

The vast majority of Multicopters use fixed pitch blades and vary RPM for control - differential thrust for roll/pitch and differential torque for yaw. And it’s all subject to Newton’s Laws. Again, in this case, Third.

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Thanks for the answer @panky and @coby!

This makes absolute sense. I just wanted to clarify this before writing about it in my report With all these misleading sources it’s easy to get confused

Regards