stouffeg. (The following is intended purely as a thought provoke rather than a black&white suggestion)
It depends on what you are going to use to 'control' the motor. Let me explain this general statement.
The standard induction motor has been around for over 100years and essentially has not changed in design too much. One of the reasons is that (standard)motors are designed to be able to withstand the energy required to start Direct on line (DOL) and therefore the mass of the motor is relatively high, the inertia of the rotor is high and therefore the acceleration/deceleration time is that much longer. The advent of motor/motion control technology should in theory change that. If all motors were designed to run on variable speed drives, for example, then the physical size of a motor would be considerably smaller due to the improved control of the current during start up. (typically a DOL motor demands 5 to 6 times the current to start due to the immediate appliance of full volts, whereas a variable speed will pull only 1 to 1.5 times). You can see this in the development of servo motor technology. In this business the acceleration times are critical, as can be seen with the following comparison of a 'standard' induction motor, a standard induction motor with force ventilation and a dedicated servo motor. EG: a motor rated 8NM at 2800rpm.
Std motor= Mass 29kg; Inertia 55 x 10(-4)kgm(sq); accel time would be 0.2secs
Std motor+force vent fan=Mass 22kg; Inertia 38 x 10(-4)kgm(sq); accel time would be 0.14 secs
Servo Motor=Mass 10.1kg; Inertia 3.4 x 10(-4)kgm(sq); accel time would be 0.013 secs
So, to effectively 'do the same job' the motor dimensions change considerably depending on a) what is going to control them and then b) based on this information you can design the motor accordingly.
Now this is a special case in that servo drive systems need to have the provision to accelerate quickly and therefore are designed this way. However, this technology is moving into the realms of 'standard' induction motors that are only suitable for use on VSD's. Companies such as ABB, Siemens and Baldor (to name a few) have such technology now to provide a motor with quite impressive power to mass ratios. I personally have used this method when trying to offer an AC variable speed drive solution as a replacement to a DC solution on the main drive for a plastic injection machine. The DC motor (225kW)had a power to mass considerably smaller than a 'standard' induction motor. Offering a motor that is only designed for VSD operation realised a motor that was both very compact, low rotor inertia and, as it was AC, virtually maintenance free compared to the DC motor.
Maybe not what you were looking for but I trust of use.
