Why is there a hole in the big pulley
If there is a hole on a big pulley to look at the need of use, generally drag in order to save energy, as far as possible to reduce the weight of the pulley, so on the pulley has a hole, but in some devices, in order to increase the pulley inertia, need to turn into solid pulley, so in the device lost power and to enter into another drag force moment, because of the large inertia of the pulley, basic no change speed
Try to minimize weight and save energy on the basis of ensuring strength
That's because you need to keep the belt in place, and it's easy to scale, and you can also reduce the weight of the belt
