Because you only indicated that you want to rotate the big pulley by 180 degree.
But you did not say what is the rotating speed so the previous post show you how to calculate the minimum force.
For force large than minimum force, the pulley will have angular acceleration and you call calculate how much time for the system to rotate by 180 degree (But the pulley would not stop, it will continue rotating).

You should clearly indicate what you really want to do with the pulley system.