# Torque required to reduce the speed of a rotor?

Hi,

I'm currently trying to find out how to calculate the torque required to slow a rotor down from a high rotational speed to a low rotational speed. I know the inertia of the rotor, the 2 rotational speeds and the time it needs to take to slow the rotor down.

Is there a method or formula I can use to determine the torque required for this operation?

Any help would be greatly appreciated.

Mark.

## Answers and Replies

Dear Mark

You are so close to the answer. By this I mean that you have all the physical properties required to calculate the Torque. The key is to remember that any rotational problem is analogues to linear problems and you can utilize Newton's second law to calculate the torque.

Firstly I assume you want to decelerate the rotor at a constant speed:

alpha (rotational acceleration) = (omega_2 - omega_1) / (time required for braking)

(remember the unit of omega is rad/s)

And then slot it into:

T = I * alpha

to obtain the torque required for constant deceleration of the rotor.

Regards

Janik Bessinger