how much power do they require and how much room do they take up?
If you are talking about the truck (traction) motors on a locomotive, then whole power system! diesel engine, generator, exciter generator, truck motors, can range anywhere from seven hundred horsepower for a switch engine up to several thousand horsepower for a line haul locomotive. The traction motors get their power from the generator which is connected to the diesel engine. There is no direct mechanical connection from the diesel engine to the wheels. All the diesel engine does is turn the generator. The power from the generator is what running the traction motors which in turn drives the wheels of the locomotive. That is where the term diesel over electric comes from. In short the diesel engine drives the generator. The power from the generator drives the traction motors. The traction motors drive the wheels. The wheels drive the locomotive. The amount of power the generator puts out is controlled by two things. How fast it is turning (number of RPM and how much excitation voltage it's fields are being excited with by the exciter generator. Both the RPM's and the excitation voltage is controlled by the engineer. The advantage of using diesel over electric is they can tandem several locomotives together to pull long trains and be able to control them all from the lead engine. (Locomotive) As far as size Look at the trucks on the locomotive. The area between the wheels is pretty muchly taken up by the traction motors. Here is another fact. The generator is a DC generator and the traction motors are DC motors. Most of the time they are series wound DC motors for better starting torque since they are always coupled to a load. Here is another fact from the been there done that file! Traction motors are nasty and dirty to work on like when you have to change brushes and seat the new brushes and horne the commutator
