Help with a bipolar driver.

Hello guys,

I am in need of a little help. I have just finished building the
PAP8ABL bipolar driver from Laurent Fouga's website. I intend to use
it with size 34 double stack bipolar motors.Details are 1.8 deg. 4.6
amp per phase and 0.55 ohms per phase. However for testing purposes I
decided to use a motor salvaged from an old printer. The details are
1.5 ohms and 2.1 volts. The driver steps the motor without the
chopper enabled but maxes out on current, pulling about 6 amps and
the motor gets very hot very quick. When the chopper is enabled I
cannot 'tune' the motor to any set current say 2 amps. If I turn the
pot fully one way the motor will turn freely and when I turn it fully
the other way , the current maxes out. About halfway the motor makes
a chopping sound but becomes highly unstable. It tends to spin
rapidly one way or the other. If it does settle , when I step the
motor using turbocnc it starts to spin rapidly again. No matter how
much I adjust the pot it remains unstable.

I read somewhere that the minimum Ohms per phase should be above
1.6ohms. Would this be the cause of my problems . If it is does any
one know a way round this .

Hope someone can help me with this problem.

Cheers Dave.