Help with the big picture

DMM has been unable to resolve the issue. I don't want to run step/dir. So I've returned the DMM stuff and will be buying something different.

@pcw, What hardware would you recommend for maximum compatibility with my 5i25/7i77 control? I'm willing to throw a bit more money at this to minimize the F*ck-around-factor.

Thanks

PCW post=282030 userid=481
For step/ dir, the default setup and timing should work though you
obviously need a different daughtercard

7i77 can't handle step/dir to drive a servo's driver ?

7i77 can drive velocity mode servos, those are +-10V input drives, also known as analog drives.
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If you already have 5i25/7i77 you can get a 7i85S (there are 7i85 and 7i85S, one is step/dir the other is SSerial, do check that) and can be used to drive any stpper/servo drive in position mode with step/dir signals.

tommylight wrote:

7i77 can drive velocity mode servos, those are +-10V input drives, also known as analog drives.
-
If you already have 5i25/7i77 you can get a 7i85S (there are 7i85 and 7i85S, one is step/dir the other is SSerial, do check that) and can be used to drive any stpper/servo drive in position mode with step/dir signals.

Thanks for precisions, Tommylight. While this time, I had a look to these two ways of driving servos.
Finally, most of people use 7i77 for this kind of retrofit, and the step/dir way is not really more attractive than the analog way, specially if you work in a closed-loop way with encoders. Maybe the PID-Tuning could be a little bit touchy.

I'll go the analog way, so.

It does not matter if you use analog or step/dir with LinuxCNC, granted you close the loop in LinuxCNC, everything works perfectly.
Step/dir is easier to setup and tune with less chances of "run away" or mishaps.

andypugh wrote:

If you are using the 7i77 then you pretty much have to use analogie voltage control.
Position control with analogue voltage is a terrible idea, so not that.

Torque control and Speed control can both work, but speed control is likely to be much easier to tune.

I was recently introduced to a very simple and effective way to control an axis under speed control.

Set up the PID for position control, in the usual way.
Connect pid.N.command-deriv to joint.N.vel-cmd

Set P I and D to zero, and adjust the pid.N.FF1 value until the axis speed and commanded speed match exactly.

Then you should find that all you need is a very small amount of P gain to bring things under control.
 

Is this method a better alternative from classic method?
(increase P until oscillation then reduce P to 70% then eliminate cruise ferror with FF1 and fix start-stop error with little FF2)
Can you give an example for a hal file generated by pncconf ?