stepper driver frequency help .

[max_imum2000]

hello
i recently build alan picstep driver
i set it up to 1.6amps and powerd it with 30volts
i used a 1.6amp 2.7volt bipolar stepper.

i didnt use a computer
i just used a small pic 16F628A circuit that generated a pwm frequency to feed the step signal
i tied the enable to ground .

now the problem
the max frequency i can feed to the driver before the motor stall is 18khz. then it stalls ( i tried it up to 20khz) (50% duty cycle)
i tried changing the input voltage (lower it to 12V) but there were no effect on the motor speed at all, just a lower noise from the motor.
the motor speed is not high at all, i estimate it to be about 200rpm or something like that.

am i missing something here ?
i know that the frequency can go much higher than that but the motors stops and make a hissing noise.

i dont know if this is important or not but i replaced the 1uf capacitors on alan circuit with electro caps. ( i dont have any mkt on hand), also replaced the 2.2nf with 2.6nf

i will appicate any help here

thank you

[pminmo]

http://www.pminmo.com/wiki/index.php?title=Performance

[max_imum2000]

thanks phil
i sow the link
and since i am using 30volts and 1.7amps and i am using bipolar motors not unipolar i can only think of using microstepping rather than full step
i hope that will solve the speed problem

[max_imum2000]

hi again phil
well
i just removed both jumpers on picstep board to switch to least microstepping
and the speed was even lower !!
now the max frequancy i can feed is about 2khz !!!
i tried 1/4 1/2 steps
but still the same problem

what am i doing wrong !!!

[max_imum2000]

i raised the voltage to 35volts, and the amps to about 1.9amp
still the same
any ideas please ??

[pminmo]

What kind of speed are you expecting? 18khz at full step would be 90 rps, and you're not going to get anything near that with a conventional driver. A lot of factors go into speed. 2K at full step is 10 rps which is pretty respectable.