Pluto Servo -- Progress...Sort of Still need some help

[TZak]

Here is an update on the pluto servo problems that I have been having hopefully someone out there can offer me some tips.

As far as the encoder goes it's counting fine. The motor is still not servoed correctly but I think I may have found out why. The problem is I'm not sure that the scale is correct, here is what is happening.

I have first had this machine setup in MM, I have a 500pluse encoder. I have tried getting the input_scale correct I had is set for 400, one turn of the motor is 5mm given my mechanical setup, however that is where I run into problems getting a servo on the motor. At this setting the motor is oscillating like crazy and I can't get a correct servo. The problem discussed in an earlier post.

Now when I change the units to INCH and dramatically increase the input_scale to 10,000 the motor has a good servo however there is a large deadzone. About 1/8 the revolution of the motor. However this causes another problem of the fact that that the scaler is way of. So the motor is turning probably 10-20 more then it really should for the correct distance.

And when I use the increment button on AXIS to move the motor .100 it actually is moving on .100mm not inches. How can I change that.

I know in the INI file that I'm using under the [TRAJ] section the LINEAR UNITS =1.0 But in the config for each AXIS it is set to INCH. I have tried to change the LINEAR_UNITS section however the system fails at that point. I'm not sure if this is causing a conflict with two different units or something??


Now I'm not sure if any of this makes sense but hopefully someone can shed some light on the subject and help out.

[acondit]

TZak,

Have you actually calculated the correct steps per unit?

A 500 pulse quadrature encoder is actually 2000 counts per revolution. So it would seem that the correct figure should be (2000 * (25.4/5))= counts per inch or 10,160 cpi.

I believe that in the trajectory planner section of your ini file you should have the line:
LINEAR_UNITS = inch
and
SCALE = 10160
or for metric
LINEAR_UNITS = mm
and
SCALE = 400

I also have a line in the "Part program interpreter" section in mine that reads:
RS274NGC_STARTUP_CODE = G17 G20 G90
which sets it to XY axis, Imperial mode and absolute movement. If you are doing a lathe the G17 should be changed to G18. Mine used to have a G21 which would cause it to always come up in metric mode even though it was configured for inch mode in the LINEAR_SCALE.

I am not using servos so I don't know if this will help or not.

Alan

[TZak]

Alan

Thanks for the reply.

It seems as though the scale values that you have given me are ones I have already used. I know that the metric value of 400 was correct. This however caused problems with the motor. It would still have the problem of the motor not servoing properly depending on the scales used. I'm not sure you have any info on this since you are not using servo motors.

I will also try changing the startup code to reflect the units being used.

Thanks for the advice none the less.

[acondit]

Your welcome, I would like to know how how resolve the problem. I have several servo motors, I just haven't built any drivers for them yet.

Alan

[acondit]

Have you tried the linuxcnc.org irc list? They are usually really helpful.

Alan