A Axis setup

Hi
looking for some ideas on the strange behaviour of my A axis setup
I've justed added the driver, a DM542A from Longs motors
Set up Linuxcnc and mapped a couple of spare output pins on parport 0 to the Step and Dir on the stepper driver
Also added a 5volt feed to the stepper driver

The green LED is lit and the red LED is not lit

I can jog the A axis through gmoccapy, but its anything but smooth and its faster moving in one direction than it is in the other
I did a quick and dirty test and it appears that one rev of the motor clockwise is 50 units on the display, but 25 units the other way completes the 1 rev anti clockwise

Does it matter that the 5 volts is not from the BOB, its 4.6 volts, so I though this would be fine, but can run a wire from the BOB to the stepper driver.

I may well have something wrong in Linuxcnc, but why would it jog 2x as far in one direction than it does in the other

Any help much appreciated

Cheers,
Paul

What's the 5V feed to the stepper driver? - sorry, don't understand that. I'm assuming that you're using the BoB to switch the "-" inputs to the driver with a common 5V supply to the "+" - in which case, so long as the 5V supply has a common earth with the BoB it'll be fine.

Faster in one direction than another?, strange - step/dir means that the step generation is independent from the direction signal.

Random thoughts - what's the frequency of the thread that your parport is driven by? (I'm doubting that Linuxcnc will stretch any performance requirements of the driver). here's a thought - slave the step input to your A-Axis to another known axis and confirm the behaviour (different rates/direction) - that'd tell us there's something amiss with the driver.

I finally got bacck to this today, because my A axis arrived, UPS lost the first one, God knows how you loose a 7.2Kg parcel
I replaced the 5 volt feed to the stepper driver with one from the BOB and all works perfectly now.
I also installed a push on push off switch to the power feed on the driver so that it can be turned off when not using the A axis

Paul