Mesa 5i25/7i76. Looking for some help.

Hello,

I purchased a Mesa 5i25/7i76 combo and have been trying to make it work in my CNC conversion for my lathe. I'm going through the PncConf setup and I now get stuck on the Test/Tune Axis window trying to figure out why I can't get any movements from my X-axis motor.

When I first got my board, only the X-axis motor was hooked up and I was able to move it like I want to in PncConf. I've now finished installing the Z-axis motor, a couple of proximity sensors for home/limit switches and the spindle output connection to the 7i76. I go through the PncConf again and this time as mentioned, the X-axis motor has no movement. The Test/Tune Axis page looks normal and I can see from the changes in rpm number, etc... that it was telling the motor to jog back/forth. I've checked the motor's cables and connections and everything look to be tight and secure.

Kinda scratching my head at this point. Anything else I should be looking for?

One thing to check is that your step pulses are long enough
Often people choose the drives minimum timings when these are in fact just on the edge of not working

Unless the step pulse widths limit your maximum speeds, I would choose a step pulse
length at least double the drives minimum time

Not sure what I did wrong but after several tries I had both X and Z motors moving. Something unusual I've noticed is that my X motor (moves the lathe's cross slide) moves noticeably much faster than my Z motor (moves the lathe's saddle). Both are configured to the same velocity and acceleration (1500 mm/minute and 750 mm/s^2). There is no mechanical binding that I'm aware off that would explain the much slower speed in the Z motor. I'm going to try swapping the motor and see if this "problem" continues.

Going through the setup I also see that you can change the Rapid Speed Following Error and Feed Speed Following Error. I think the default values (10 mm and 1 mm) are just too much for a lathe's precision, so I changed them to 1 mm and 0.1 mm. Do you think these values are practical?

If this is an open loop system, the following error limits only monitor how well the stepgenerator follows
the commanded position and can be set much tighter say .010 mm and .005 mm

Note that if you are using a pncconf generated hal file, you may need to set the PID maxerror setting to 0
to have a properly tuned stepgenerator control loop

Thanks, I will try those values. I still can't quite figure out why my Z motor is so slow compared to the X motor going through the PncConf wizard. My lead screw is 10 x 1 mm (1 mm travel per revolution) and both motors' velocity were set to 1500 mm/minute, which should translate to 25 revolutions per second. Yet the Z motor was spinning at like 1 rev per second. This "problem" seems to have something to do with the motor. These are the Teknic ClearPath SD motors and I've run through their motor programmer software. They're working normally as far as I can tell. I just don't know how to troubleshoot more.

If they are really running slower than commanded by LinuxCNC then you would expect them to carry on moving after the jog stops to make up the lost steps.

Perhaps the two drives are set up for a different electronic gearing (steps per rev)