Gents,
Continuing my learning process of LinuxCNC and Mesa cards i've managed (thank you PCW and tommylight!), to start my permanent magnet DC servomotor driven by BTS7960 H-bridges, all hooked up to Mesa 7i95T on the test bench.
forum.linuxcnc.org/configuration-tools/5...-bridges-pmdc-servos
Did some basic PID tuning and motors are not reaching following errors. Ferror is loose however - fine tuning not required at this stage.
On my learning short list now there is two topics:
1) encoder-ratio module
2) Mesa THCAD card. As I'm powering my motors and limit/home switches from old laptop power supply - its voltage sags easily when loading servos so found it good opportunity to practice THCAD and PyVCP by reading power supply voltage and present it on AXIS.
Ad 1) While reading LinuxCNC documentation i found an interesting function ENCODER_RATIO. First thought was "hey! let's do some experiment and slave Z axis servo to X.". Let's say the final idea is to link spindle encoder with rotary/dividing head servo - i can imaging hobbing gears like that:)
Experiment conditions:
- there is three servos available X, Y, Z so three encoders, all the same ppr = 400
- X will be the master, Z will be slave
- i want Z to turn 4 times slower than X
If i understand the documentation right i did the following:
- detached
joint.2.motor-pos-cmd from
pid.z.command
- detached
hm2_7i95.0.encoder.02.position from
pid.z.feedback and
joint.2.motor-pos-fb
- connected
pid.z.feedback and
joint.2.motor-pos-fb with
encoder-ratio.0.error
- decided to use one of the switches for slave axis on/off so detached remote e-stop (will not using it now) input
hm2_7i95.0.inmux.00.input-06-not and hooked it up to
encoder-ratio.0.enable
- connected master axis (X) encoder signals A and B to
encoder-ratio.0.master-A and
encoder-ratio.0.master-B
- connected slave axis (Z) encoder signals A and B to
encoder-ratio.0.slave-A and
encoder-ratio.0.slave-B
- set ratio by stating ppr:
encoder-ratio.0.master-ppr 400 and
encoder-ratio.0.slave-ppr 100
AXIS started with no issues. Checked HAL configuration and what i can see is:
- encoder-ratio.0.master-A and B signals are successfully connected to X encoder
- encoder-ratio.0.enable is ok - turning TRUE when switch is activated by me
And i failed successfully:)
- i can see no change on
pid.z.feedback as well as on
pid.z.output when i move X axis - no change on
encoder-ratio.0.error
I thing i'm not getting fully what manula says about encoder_ratio. i couldn't find any HAL examples showing correct configuration.
What i found is that unfortunatelly
encoder-ratio.0.master-ppr and
encoder-ratio.0.slave-ppr are PARAMETERS, not PINS so no chance to make nice 'change ratio' option in PyVCP (imagine you can input different spindle/slave axis ratio and hob whatever spur gear you want!). The only option i see it close LinuxCNC, edit ppr numbers and re-start LinuxCNC to get ratio i want.
My idea was to have motorized dividing head connected and with just one switch make it move in sync with spindle @ required ratio...So it is basically ELS. Ehmmm those dreams.
Anyway, please! Could you guys look at it and poke me in good direction? I did research and tried by myself before i bother you but, as i said before, failed successfully:)
Thank you.
