I won't say that you are wrong, but when I worked at Lesson, all the rotors were balanced on the same machines, they used the same bearings, and for the most part even used the same small parts. So to say that the motor is balance for one speed vs another is a farce, in reality many 2 and 4 pole motors use the same rotor, they just had more poles in the stator and were rated for HP acordingly. Manufacturing something like a motor is done on a mass scale, you use what you can common between them, when the girls on the build line did that on the 48 & 56 frame motors they had about a 12 drawer bulk bin, thats all they needed.
I have no idea what you are talking about with the speed ratio thing 20:1 in relation to what? When you say a constant torque motor, are you talking about a AC servos? thats like comparing apples to watermelons, they are both round and juice and thats about it? Your application is either constant torque like in a mill or belt system or constant HP which is on processes like involute pumps for hydraulics. The motor can be designed to suit that but they are not stuck in that use by an means. The drive would be more likely to be consdiered a CP or CH style, most now are both, typipcally the more you pay the better it is esp at vectoring. Vectoring is well suited to AC servos, as they have an armature, you have a greater control of torque over a broader speed range, but again the motors and drives are entirely different.
A true "vector" 3 phase motor in the higher horsepower range cost as much as some peoples homes, and have encoders, and carefully matched drives which are tuned to that motor. I don't know about AC servos, but AC 3 phase motors flat line there torque at or above name plate, it does not drop, but it may seem like it and out near the breakdown area it very well may drop. 3 phase motors need a change in votlage for more torque at a given frequency, the drives can fool the motor to a ceratin extent, esp on the lower then nameplate area(vectoring and torque boost), but higher you can only gain so much before begin to saturate the motor.
chris  |