Say I am doing a very simple thing: Driving a motor with a low-side N channel MOSFET. Thus VS = 0. Lets say the supply voltage for the motor is 30V. so the circuit is: 30V to +motor. Mosfet drain to -motor. Mosfet source to gnd. Thats it, lets assume the gate is driven by an ideal voltage source.

I want the MOSFET to be in saturation for maximum efficiency. Therefore I must set the gate to some VGS such that VGS-Vth < VDS.

How would I calculate VDS in this situation? The way I see it VDS is going to be determined by the motor current and the RDS(on). So if RDS(on) = .02Ω, and the motor requires 5A, then VDS = 0.1V. Therefore I will want VGS to be very close to Vth such that VGS-Vth < 0.1V.

This makes NO sense to me as you want higher gate voltages to gather more carriers in the channel and thus make it easier to pass current.

I am thinking that in the case of the motor driver, the MOSFET sees 30V and therefore VDS = 30V so your VGS can be something like 10 for saturation... which is how I know the mosfets will work. The motor is a DC short, right?

im looking at the Id/Vd curves on the IRFZ24N datasheet just for a reference.