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I am a beginner in Electronics. I am trying to make a small robot controlled by an Arduino. The problem is that I do not know how to calculate the power required to rotate a structure with a servo motor placed on its axis (see picture below).

My servo motor is a Dynamixel MX-28 T with an average stall torque of 2.5 Nm at 12 V. The product page for the servo can be found here and the specification sheet for it is here.

Do you think it is possible to rotate it using this servo motor?

Informations:

Structure weight: 2,2 kg (2200 g) (include battery-arduino-servo)

Structure Dimension: 900mm/120mm/120mm (see picture below)

Structure type: Aluminum

Servo weight: 72 g

total weight 2.2 kg will be distributed fairly. 1.1 kilo on the top and on the bottom 1.1 kilo

(click for full resolution)

enter image description here

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With the structure (and masses) being distributed perfectly even on both sides of the servo, the servo will not require any additional force to rotate the structure since the mass on one side is always balanced out or negated by the mass on the other side.

You will still have to overcome friction forces and depending on how you mount and use the servo (directly connected to the driving shaft of the servo or not), you may have to take into account whether your servo's motor shaft can handle such radial forces (and maybe axial forces too depending on your application).

So yes, it is possible to rotate the structure with the servo.
But in order to know how fast you can accelerate or decelerate the structure, you will have to use its moment of inertia.

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If the structure is ballanced around the pivot point, as you seem to indicate, then in theory it only takes enough torque to overcome whatever friction or other external resistances there are. There is no inherent torque required just to move a mass.

It does take a minimum torque to accellerate a object. To know this minimum torque, you have to decide what the object's moment of inertia is about the pivot point, how fast you want it to rotate, and how long you are willing to wait to get it to that speed.

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