How Does A Multirotor do Pure Yaw?

[Eggbeater]

I always wondered how a multirotor performs pure yaw pirouettes? I got collective and cyclic, but yaw? Is it using just the torque of the rotating blades to nose-right and nose-left?

 

[Ttelmah]

For a quad, two motors are rotating in one direction, the other two the other way. Each lifting 25% of the weight. Balanced. It increases the rotation rate on the pair rotating in one direction, and does a corresponding decrease on the other pair. Lift remains balanced (front right, and rear left are now perhaps lifting 30% of the weight each, while front left and rear right are now lifting 20% of the weight each), but the torque being delivered to the pair with the higher lift is now much more.
Same applies for a hex, or octo.
The one that gets complex is the tricopter. Here the third rotor is normally tilted by a servo to counteract it's torque, and this tilt is adjusted. Much more like a helicopter, except only 1/3rd the torque has to be 'balanced' by this, since the other two rotors counteract one another.
Seriously, 'just'. It is easy to underestimate just how much torque the lift motors involve....

Best Wishes

 

[Eggbeater]

Thank you. Good explanantion. So the MR is doing a real balancing act to use counteractive rotational torque to yaw but also regulating the overall motor speeds to also NOT adversely effect the altitude or the cyclic. Makes you appreciate all the work that goes into such designs.

 

[Bartman]

the really impressive thing is when a heli can move into a strong yawing maneuver and stop without jumping up or down in altitude. that wasn't always possible but it's almost expected now.

bart

 

[Eggbeater]

Bartman,
I agree. It's ALL impressive to me. Understanding (and appreciating) somewhat the concepts of algorithims, I can see the complicated math involved in controlling these things. But, as you said, it is the "sudden" or "transitional" aspects that make it even more impressive.


Not to get on a soapbox but this is why I am fundamentally against all of this "killer drone" media fenzy. It stiffles our brain power and dumbs us down. There is so much good that comes from such technology and I wonder how this will play out. I fear it will not be good. Sorry for the sidetrack.

 

[gtranquilla]

The helicopter main rotor/motor tries to rotate the helicopter body in the opposite direction..... that is why the heli needs a tail rotor.....
or another main rotor stacked above or below the main rotor but spinning in the opposite direction.....

However counter-rotating props one a multirotor are typically displaced horizontally but in a symetrical pattern........

In the case of the Muti-Rotor Quadrocopter, for each clockwise rotor there needs to be a counter-clockwise rotor to prevent yaw so there will be two rotating clockwise and two rotating counter-clockwise. If all are rotating at the same speed, then the Quadrocopter will not yaw one way or the other...

Slow two clockwise props down and there will be yaw or speed two clockwise props up and there will be yaw.

I always wondered how a multirotor performs pure yaw pirouettes? I got collective and cyclic, but yaw? Is it using just the torque of the rotating blades to nose-right and nose-left?