Raghunathan

a speed feedback has better a step response equal to the step * a constant
i mean when the motor velocity changes the tachometer must follow it without delay
but this is ideal condition- cannot be achieved in real life
thats why i want a tachometer with at least 1000 Hz bandwith
now i think LM2917 has in the order of 10-20 Hz
and this is my problem
LM 2917 cannot follow motor immediately but with a delay - i dont want it

secondly
a speed control loop inside a position loop is never driven with a step - it is driven with a trapezoid
it has acceleration and deceleration ramps
this is required for precision position control
otherwise the system may overshoot