BACKLASH setting not working

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26 Jul 2017 15:12 #96477 by Cpk_Rbt
Cpk_Rbt replied the topic: BACKLASH setting not working

Todd Zuercher wrote: So how can you have any idea if the drives are following the commands it receives?


I realized we forgot to address this question of yours. Each drive is locked into an interpolation loop, and if that unlocks, it sends back feedback to LinuxCNC. We have signals set up to disable the LinuxCNC system if any of the drives leaves "ready for motion" state.


In regards to backlash compensation, it is our understanding that it is basically telling the machine how far to move the motor before the mechanics start moving (e.g. when the gear teeth engage). Is that how LinuxCNC treats backlash compensation, or is there something else going on outside the norm of backlash compensation?
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26 Jul 2017 15:48 - 26 Jul 2017 15:48 #96484 by Todd Zuercher
Todd Zuercher replied the topic: BACKLASH setting not working
Duh! I just realized what your problem is and why you are not seeing any backlash compensation applied to the motors. It is an obvious mistake in your hal file that we should have caught straight off when you posted your hal file. I kind of feel bad for not seeing this before.

You are using the pin axis.N.joint-pos-cmd as the source for your command to your drives. This is WRONG. You need to use axis.N.motor-pos-cmd. The reason is right here in the man page for Motion
axis.N.joint-pos-cmd OUT FLOAT
The joint (as opposed to motor) commanded position. There may be several offsets between the joint and motor coordinates: backlash compensation, screw error compensation, and home offsets.

The simplest fix would be to change these 3 lines in your hal file from this:
net pos0_float axis.0.joint-pos-cmd => lcec.0.1.poscommand
net pos1_float axis.1.joint-pos-cmd => lcec.0.0.poscommand
net pos2_float axis.2.joint-pos-cmd => lcec.0.2.poscommand
to this:
net Xpos => lcec.0.1.poscommand
net Ypos => lcec.0.0.poscommand
net Zpos => lcec.0.2.poscommand
Last Edit: 26 Jul 2017 15:48 by Todd Zuercher.
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26 Jul 2017 16:43 #96491 by Cpk_Rbt
Cpk_Rbt replied the topic: BACKLASH setting not working
Nailed it! Thanks Todd, backlash comp works great now.
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