Help with homing issue
25 Jul 2018 07:31 #114794
by curtisa
Replied by curtisa on topic Help with homing issue
Have you tried watching the DRO/velocity readouts and backplot in Axis while it is homing? Does Axis show the Z-axis starting and stopping as it travels towards the homing switch, or is it just the motor itself doing the jerky motion? I'd almost suggest you have a hardware or wiring error of some kind from the way the Z axis is moving in that video.
I had weird homing behaviour when I built my first machine that I couldn't get my head around for a while. My axes would jog around fine, but would do odd things when homing, like not backing off a limit switch when tripped or Axis continuing to show movement after the steppers had stopped. It wasn't until after several hours of playing with settings in the INI file that I realised I hadn't powered the breakout board from the external 5V supply
I had weird homing behaviour when I built my first machine that I couldn't get my head around for a while. My axes would jog around fine, but would do odd things when homing, like not backing off a limit switch when tripped or Axis continuing to show movement after the steppers had stopped. It wasn't until after several hours of playing with settings in the INI file that I realised I hadn't powered the breakout board from the external 5V supply
![:whistle: :whistle:](/media/kunena/emoticons/whistling.png)
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25 Jul 2018 15:53 #114811
by MAG45
Replied by MAG45 on topic Help with homing issue
I set stepgen_maxaccel to 8, nothing changed though.
Axis DRO is following stop and go movement of the axis. I can manually enter gcode on each axis and get smooth consistent travel.
I did find that if i keep pressing home button after it errors that after 5 to 10 tries it will eventually click the switch and move to home.
I was asked about the kernal by someone, this is what i found, not sure if it was what was needed
drive.google.com/open?id=10qYVz1ET4bnv7KjTFOoc2763QwO72sfvOA
Axis DRO is following stop and go movement of the axis. I can manually enter gcode on each axis and get smooth consistent travel.
I did find that if i keep pressing home button after it errors that after 5 to 10 tries it will eventually click the switch and move to home.
I was asked about the kernal by someone, this is what i found, not sure if it was what was needed
drive.google.com/open?id=10qYVz1ET4bnv7KjTFOoc2763QwO72sfvOA
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29 Jul 2018 01:13 #115041
by andypugh
Replied by andypugh on topic Help with homing issue
You are using stepgens in PID mode (which generally works better) but and your settings are what suit the typical 1mS servo thread. Is there any chance that your servo thread is running faster or slower than that?
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29 Jul 2018 12:26 #115056
by MAG45
Replied by MAG45 on topic Help with homing issue
I am not even sure what a servo thread is or how to check it.
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30 Jul 2018 12:51 - 30 Jul 2018 12:59 #115133
by andypugh
Replied by andypugh on topic Help with homing issue
The servo thread rate will be in the INI file.
The LinuxCNC realtime system has one or two "threads". All systems will have the "servo-thread" which typically runs every 1mS. Systems that use the parallel port typically also have a "base-thread" that runs every 50uS or thereabouts.
Every HAL module has one or more "functions" that are called every time the thread runs. Each function runs in strict sequence, reading the input HAL pins and writing to the output HAL pins.
So, your PID calculations are run every time the servo thread runs, and the PID parameters are set up on the assumption that the servo-thread runs at 1mS.
The LinuxCNC realtime system has one or two "threads". All systems will have the "servo-thread" which typically runs every 1mS. Systems that use the parallel port typically also have a "base-thread" that runs every 50uS or thereabouts.
Every HAL module has one or more "functions" that are called every time the thread runs. Each function runs in strict sequence, reading the input HAL pins and writing to the output HAL pins.
So, your PID calculations are run every time the servo thread runs, and the PID parameters are set up on the assumption that the servo-thread runs at 1mS.
Last edit: 30 Jul 2018 12:59 by andypugh.
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