# Yaw in Multirotor systems

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1. Jul 28, 2017

### Kyle Broflovski

So I recently developed an interest in quad-rotors and was getting stated with its dynamics. I am particularly intrigued by the yaw motion of a quad-copter which comes into effect as a result of torques of the motors. When the motor torques are variable, we observe the yaw motion as result of a non-zero torque on the system. But I was wondering if we would still observe yaw in vacuum(if we manually suspend the quad in vacuum) by create an imbalance in the the motor torques. What do you guys think?

2. Jul 28, 2017

### Nidum

How could the motors be generating any torque if there is no load on them ?

3. Jul 28, 2017

### Kyle Broflovski

Without vacuum the load for a single motor is the propeller which is being spun to generate thrust. The bigger the propeller the more the torque need to move them. This load will fluctuate if the density of the medium(air) changes. In absence of air, if this load is provided by some other means(like adding some heavy weight to the props), then the quad should yaw, Right?

4. Jul 28, 2017

### CWatters

You would have to accelerate/decelerate the prop using its moment of inertia. Perhaps see the reaction wheels used to steer the Hubble telescope.

5. Aug 1, 2017

### Kyle Broflovski

Is that how MIT's Cubli maneuvers too?

6. Aug 2, 2017

### CWatters

Yes.

You can actually see the flywheels accelerate when the cube is pushed at about 1min 7seconds. Later at around 1m 48s they show how the cube gets up onto an edge and then a corner. In this case it sounds like they spin up the flywheels slowly and then suddenly decelerate them to provide the torque required. They appear to use the same trick when "walking". My guess is they found decelerating the flywheels rapidly is easier than trying to just accelerate them rapidly.