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‫Welcome back, starting from this lecture, we will start driving the fundamental formulation for the

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‫dynamics equations for six degrees of freedom system that we will later use on our specific quadcopter.

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‫So if kinematics was a branch of mechanics which studied the motion of a body or system of bodies without

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‫forces or talks, without considering them, then dynamics.

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‫Thus consider forces and talks.

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‫One crucial assumption that we will have is that our drone is a rigid body.

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‫So what does it mean if you look at the drone from the side and you apply some thrust to it with the

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‫propellers like this, then this is what will really happen.

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‫The rods from the center of the drone to the propeller will slightly bend upwards.

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‫The bending is very small and you will probably not see it in real life, but nevertheless, it's there.

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‫And if you want to perform structural analysis on the body of the drone, meaning that you want to find

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‫at which laws the rules break or you want to assess the stiffness of the rods, then you have to take

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‫that bending into account.

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‫And they are equations for that as well.

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‫However, for controlling the drone, you don't need to take it into account so you can ignore bending

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‫and make your life much simpler for yourself.

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‫If you ignore bending, then you treat the drone as a rigid body.

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‫It means that when you apply thrust, then your drone looks like this.

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‫That's not the reality, but it's good enough for control purposes.

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‫The same thing with a beam attached to a wall.

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‫If you're on the edge of the beam, then it will slightly bend downwards.

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‫In fact, it will bend downwards even if you are not there because there's force of gravity acting on

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‫it.

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‫However, let's ignore that for now.

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‫But if bending is very small and not even visible, then we neglect it and we treat the beam as a rigid

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‫body.

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‫Then it looks like this and that's how we will treat our drone as a rigid body.