OUTPUT_SCALE doubt

Hello all,

I'm using the 5i25+7i77 plug and ready mesa cards to manage a 3 Axis (XZA) machine.
By default the value for OUTPUT_SCALE is 10 in a pncConfig application. But I'm little unsure if this value is correct or not and also on the meaning of it.

I'm using a 10V servo driver to command the motors. Following the documents and searching a little in the source code of the h2m driver I saw that the system is using the "hm2_5i25.0.7i77.0.1.analogoutN-minlim" and "hm2_5i25.0.7i77.0.1.analogoutN-maxlim" to clip the value of dc between this limits, and after is divided by "hm2_5i25.0.7i77.0.1.analogoutN-scalemax" (Set to OUTPUT_SCALE) this makes the dc value between -1 and +1. (would this be done by MAX_OUTPUT value in the config file?).

But reading the documentation on-line I saw that somebody have the OUTPUT_SCALE set to 1 (or -1). In the integrator manual defines the OUTPUT_SCALE like the units increment per volt in the servo-driver. And in the hostmot2 driver manpage seems unclear the use of hm2_5i25.0.7i77.0.1.analogoutN-scalemax.

Then my question which is the real use of the OUTPUT_SCALE and hm2_5i25.0.7i77.0.1.analogoutN-scalemax?.

Sorry by my bad English.

Regards,

Luis Bellot

There's a preliminary sserial manual in master:

git.linuxcnc.org/gitweb?p=linuxcnc.git;a...hb=refs/heads/master

unfortunately the 7I77 section is unfinished, however all sserial analog outputs have the same basic scaling/limiting parameters

Default scaling for analog outputs is volts (that's why scalemax is 10 for 10V full scale). If you set scalemax to 500 you would need a analog output value of 500 to get 10V full scale.

The minlimit and maxlimit parameters bound the output but do not offset or change the scaling.

For velocity mode PID use I like to set scalemax to the drives machine units (inches or mm) per second at 10V in. This normalizes the PID loop so FF1 can be set to 1.

Forgot to mention one important point. If your encoder scale and direction (in DRO) are correct but PID feedback is backwards (motor runs away), you can fix this by reversing the output polarity by changing the sign of scalemax (so -10 instead of 10 for example)

Thanks a lot for your answer.

Thinking about your answer and reading again the documentation I got an idea how it works.

I'm planning to make some documentation about it an I'll be happy to share it with all linuxcnc users.

Regards,

Luis Bellot