The generator I have in mind puts out 120 Volt single phase AC current, at a maximum of 14 Amps. Can I hook up a 120 Volt to 48 Volt AC transformer, followed by a full-wave bridge rectifier, and get DC power clean enough to put in the motor controller for the motor? Will I need other components in the circuit?
If you peak-rectify an AC voltage, it will be sqr(2) higher (minus the diode voltage drops) as the caps charge to the peak voltage and the AC voltage is RMS.
For 48DC, you need: (48+2xdiode drop)/sqr(2)
Assuming the diode drop (for a single diode) at the current in question is say 1.5V (you need to check a datasheet or measure), you'd need:
(48+2x1.5)/sqr(2) = 51/1.41 = 36VAC
The current OTOH will decrease by sqr(2).
As I understand your setup, it's: 120V @ 14A max -> 120V:36V transformer -> diode bridge -> cap -> motor control and this equates to...
Max current: (14A x 120 / 36) /sqr(2) = 33A
This will give a DC with some ripple, depending on the value of the cap. The cap needs to be huge for this - at least 66,000µF (and with a 60V+ rating) following the rule of thumb saying 2,000µF/A, which should give a ripple of around 3V).
How much ripple your controller can handle, you have to see in its datasheet/manual.