motor spool up time?

[danial stocks]

>If I take an electric motor and run it at 440 rpm, how
>long on average would it take to get it to ramp up to
>880 rpm or down to say, 200 rpm?

This depends on the inertia of the motor [how much the moving parts weigh] 
and the power of the actual motor... ie you can consider that a 4 cylinder 
car can go 100kph as can a 6 cylinder car.. just that the 6 cyl car can 
reach 100kph in a smaller amt of time ie it accelerates quicker.... so a 
highpower very lightweight motor could change speed quite quickly, a lower 
power to weight ratio will take longer.. to slow down quickly you can use 
regenerative braking - the power is disconnected and the mot terminals are 
conn'd across a resistor - the mot becomes a generator and the rotational 
energy is absorbed by heating up the resistor..


is there a reliable
>way to conrol this?
would be possible to control the speed of the motor accurately - need to use 
a feedback system sensing the rotation... you could control it's rate of 
change also, but would have to make it less than the physical limitations of 
the motor for reliable setting.. using brush type 'universal motors' - type 
used in power drills etc you can use something simple like a triac speed 
control - but if you use an induction type motor - common in washing 
machines + industrial equipment - then the speed is controlled by the 
frequency of the ac source - so you have to build a HV variable freq osc ie 
imagine a VCO which puts out 110V 4Amps!
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