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# How to find torque requirement to rotate antenna?

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#### kalaianand

Hello friends....
I have an small antenna( irregular shape) , mass about 1.5 Kg (about CG), the moment of ineria about spinning axes(Iyy) is 0.0255kg.m^2. product of inertia also known (Ixy, Iyz, Ixz).
Required angular velocity (ω) = 50 deg/sec
angular acceleration (α) = 400 deg/sec^2
The rotation axes is 3mm away from the CG of the antenna. If want to rotate the antenna in the both the direction for every 1hr. How to find the torque and power requirement to rotate it.

Hi.

The same formula applies to rotation as motion in one direction. Mass is replaced with moment of inertia and acceleration is replaced with angular acceleration α

If you're familiar calculating one direction motion, you should get along with this.

thats ok, but still that will help to find the torque requirement.
I can calculate accelerating torque as T = I*α = (moment of inertia)*(angular acceleration).
Suppose i want to rotate the antenna in the one direction, this is not torque required for continuous rotation. Since this accelerating torque is required till the antenna reaches maximum velocity. To make the continuous rotation( with max velocity) this torque is not requred. Also here the effect of CG not considering into the account. So, I guess torque required to rotate any object is not simply I*α (moment of inertia * acceleration).

I'm not sure I do understand the problem. The torque requirement only apply from the moment it start. After that, the motor characteristics will dettermine further acceleration and set speed.
To be able to calculate what the full rotation speed will be, you need to know the motor characteristics AND the friction from the rotation disk all the way to the motor shaft. To be accurate in terms of acceleration, you need to take friction into account too.

Yes! and sticktion and windage of antenna. I would look at what commercial boys do.
Frank

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