I have seen Hz defined in different ways, if $$\Omega = 1 \ \text{Hz} = 1\frac{\text{cycle}}{\text{s}} $$ Here $1 \ \text{cycle} =$ a full turn of the rotor $= 2\pi$

If I wish to express this a rpm:

By definition $ 1 \ \text{rev} = $ a full turn of the rotor = $2\pi$

So, $$1 \ \text{Hz} = 1\frac{\text{cycle}}{\text{s}} = 1\frac{\text{rev}}{\text{s}} = 1\frac{\text{rev}}{\text{s}} \cdot \frac{60 \ \text{s}}{\text{min}} = 60 \ \text{rpm}$$ I wonder if this is true because I saw a different transformation from Hz to rpm: $$\omega = 24 \ \text{Hz} = 24 \ \text{Hz} \left( \frac{1}{s}\frac{\text{rev}}{2\pi}\frac{60 \ \text{s}}{\text{min}} \right) = 231 \ \text{rpm}$$ He has that "random" pi factor. In here, omega is the angular speed of the rotor, so 24 turns per second.