Tandem Y never runs two steppers

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07 Jul 2021 21:48 #213992 by hairyMug
Ok, so finally got my X and Z axis working with my 7i96 card, BUT I am at the end-of-my rope attempting to get tandem Y axis working.
I tried:
   1. Using the the PnCConf tool, and specifying a "tandemY" axis BUT when I started LinuxCnc, it just showed 4 joints...
   2. Using the the PnCConf tool, specified a "U" axis and then manually editing the INI to deleting the "U" spec and copy the "Y" axis... No dice...
   3. Used the 7i96 Config tool, but still no dice...
In all cases, LinuxCnc just showed 4 joints and I could select a joint and move the axis but never did I get any config which showed just 3 joints for the X Y Z axis...

I did make sure the KINS entry was XZYY  to correspond to the joints:
        [TRAJ]COORDINATES = XZYY 
        [KINS]KINEMATICS = trivkins coordinates=XZYY  kinstype=B

SO... all I need is to connect the two Y joints; Is it possible OR can I simply connect my two Y drivers to 1 stepper??

Thanks for clues!   

Walt

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07 Jul 2021 21:59 - 07 Jul 2021 22:00 #213993 by PCW
Not sure I understand, 4 joints (and 3 axis) is correct for a XZYY configuration.
Last edit: 07 Jul 2021 22:00 by PCW.

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07 Jul 2021 22:09 - 07 Jul 2021 22:14 #213995 by Clive S

In all cases, LinuxCnc just showed 4 joints and I could select a joint and move the axis but never did I get any config which showed just 3 joints for the X Y Z axis...
Do you have homing switches if so have you tried to home it.  You should see 4 joints then when it is home it should just show 3 (axis)

Can you post the hal and ini files. In the ini file for the tandem axis you need to have

HOME_SEQUENCE = -2 The minus sign tells linux to sync the two motor

Last edit: 07 Jul 2021 22:14 by Clive S.

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07 Jul 2021 22:40 #213996 by hairyMug
" HOME_SEQUENCE = -2 "

This might be the missing link!
What section is that?
When I did a search for "sequence" in INI and HAL files, it did not find that word...

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07 Jul 2021 22:53 #213998 by tommylight
Do you have limit switches on both sides?
If not, do not set a tandem axis, it will not work as it is intended to.
Again if not, set a 3 axis/3 joints machine just select the same axis outputs for two drives.

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07 Jul 2021 23:01 #213999 by hairyMug
Yes, I have a start and end switch in the Y axis , (which are tied together into one input)

>> just select the same axis outputs for two drives. <<

AFAIK, this did not work... Maybe after I find the HOME_SEQENCE setting as Clive mentioned...

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07 Jul 2021 23:16 #214000 by PCW
What tommylight is saying is that if you do not have separate Y and Y2 home switches (so gantry homing cannot work) You should just set the machine up as a standard 3 axis 3 joint machine and have 2 stepgenerators running from the joint that drives the Y axis.

I don't think any configuration utilities can set this up, but it should be pretty easy to add with some copy-pasting/number changing in the main hal file.

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07 Jul 2021 23:43 #214001 by tommylight
Attachments:

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08 Jul 2021 00:19 #214002 by PCW
You can do that in pncconf but it does not setup 2 Y axis stepgens

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08 Jul 2021 00:45 #214003 by hairyMug
I did try this previously and it did not work... Taking your suggestion, I set up a 3 axis config (with 4 steppers) and then created the following to " just select the same axis outputs for two drives." as you had suggested... I did get a display of X Y Z axis BUT NO Joy... It still only runs the one stepper...
So, I went back and created a whole new config (whith the 7i96 config tool) and put in -1 for the homing sequence and (of course), did not work ...

... it should not be this difficult to setup a simple 3 axis with two Y motors...

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