Post PnCConf velocity & acceleration tweaking
03 Oct 2013 22:20 #39506
by ruffle
Post PnCConf velocity & acceleration tweaking was created by ruffle
Just in case anyone else gets stuck in the same hole as myself...
If you feel the need to tweak MAX_VELOCITY or MAX_ACCELERATION for an axis in your INI file after generating it with PnCConf, you will also need to change the corresponding values in your HAL file or you may well end up with 'Following errors'.
For example, if you change My_mill.ini like so:
make sure you also change My_mill.hal like so:
The observant amoungst you might notice that the actual values are different. The ones in the HAL file have to be larger than the ones in the INI file. PnCConf uses a multiplier of 1.25
This applies to PnCConf Beta 1.
HtH
If you feel the need to tweak MAX_VELOCITY or MAX_ACCELERATION for an axis in your INI file after generating it with PnCConf, you will also need to change the corresponding values in your HAL file or you may well end up with 'Following errors'.
For example, if you change My_mill.ini like so:
[AXIS_0]
...
MAX_VELOCITY = 40.0
MAX_ACCELERATION = 350.0
...make sure you also change My_mill.hal like so:
# Step Gen signals/setup
...
setp hm2_5i25.0.stepgen.00.maxvel 50
setp hm2_5i25.0.stepgen.00.maxaccel 437.50
...The observant amoungst you might notice that the actual values are different. The ones in the HAL file have to be larger than the ones in the INI file. PnCConf uses a multiplier of 1.25
This applies to PnCConf Beta 1.
HtH
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04 Oct 2013 02:35 #39511
by BigJohnT
Replied by BigJohnT on topic Post PnCConf velocity & acceleration tweaking
If something is set in the .hal file the .ini entries are not used which can be very confusing to a new user.
If you don't see something like:
www.linuxcnc.org/docs/html/config/ini_co...b_custom_variables_a
Also note that once the configuration is made by Pncconf it is done and does not come into play when running a configuration.
JT
If you don't see something like:
setp hm2_5i25.0.stepgen.00.maxvel [AXIS_0] MAX_VELOCITYwww.linuxcnc.org/docs/html/config/ini_co...b_custom_variables_a
Also note that once the configuration is made by Pncconf it is done and does not come into play when running a configuration.
JT
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04 Oct 2013 08:53 #39522
by cmorley
Replied by cmorley on topic Post PnCConf velocity & acceleration tweaking
Big John:
If fact the line of code you show above is not right.
Stepgens should not be set to max_velocity. They need to be 20% or so higher.
Chris M
If fact the line of code you show above is not right.
Stepgens should not be set to max_velocity. They need to be 20% or so higher.
Chris M
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04 Oct 2013 14:43 #39527
by cncbasher
Replied by cncbasher on topic Post PnCConf velocity & acceleration tweaking
could this be changed so that it's named say stepgen.00.step_max_vel and the value is then calculated to add the 20% internaly
thus removing one common error
thus removing one common error
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04 Oct 2013 18:14 #39533
by BigJohnT
Bad example... I was trying to show the syntax of variable substitution.
JT
Replied by BigJohnT on topic Post PnCConf velocity & acceleration tweaking
Big John:
If fact the line of code you show above is not right.
Stepgens should not be set to max_velocity. They need to be 20% or so higher.
Chris M
Bad example... I was trying to show the syntax of variable substitution.
JT
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04 Oct 2013 21:53 #39550
by andypugh
What I don't understand is why stepgen thinks it _needs_ to limit acceleration and velocity (I can see why it should be able to, to control non-axis steppers)
git.linuxcnc.org/gitweb?p=linuxcnc.git;a...01d5f6f;hb=HEAD#l114
Seems to suggest that the driver writer considered 0 to be a valid maxaccel.
And maxvel is used purely as a clip (not in any calculations) and is allowed to be 0.
git.linuxcnc.org/gitweb?p=linuxcnc.git;a...01d5f6f;hb=HEAD#l238
I do recall some discussion that concluded that zero maxvel and maxaccel were bad, but I can't recall why.
Replied by andypugh on topic Post PnCConf velocity & acceleration tweaking
I don't think that makes any sense. The whole point of the pin is that that is the limit you wish to apply to the stepgen velocity. (and similarly for the accelleration).could this be changed so that it's named say stepgen.00.step_max_vel and the value is then calculated to add the 20% internaly
What I don't understand is why stepgen thinks it _needs_ to limit acceleration and velocity (I can see why it should be able to, to control non-axis steppers)
git.linuxcnc.org/gitweb?p=linuxcnc.git;a...01d5f6f;hb=HEAD#l114
Seems to suggest that the driver writer considered 0 to be a valid maxaccel.
And maxvel is used purely as a clip (not in any calculations) and is allowed to be 0.
git.linuxcnc.org/gitweb?p=linuxcnc.git;a...01d5f6f;hb=HEAD#l238
I do recall some discussion that concluded that zero maxvel and maxaccel were bad, but I can't recall why.
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04 Oct 2013 22:00 #39551
by cncbasher
Replied by cncbasher on topic Post PnCConf velocity & acceleration tweaking
Andy,
it was more a point of removing the ambguity of the problem , i dont see why that that particular problem with increasing the value for mesacards could not be internaly set , in some way or another
and remove some of the setup problems in the process , making setup simpler in the long term
it was more a point of removing the ambguity of the problem , i dont see why that that particular problem with increasing the value for mesacards could not be internaly set , in some way or another
and remove some of the setup problems in the process , making setup simpler in the long term
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04 Oct 2013 22:03 #39552
by andypugh
You think it is _less_ ambiguous to have a pin not do what it says it does?
Replied by andypugh on topic Post PnCConf velocity & acceleration tweaking
it was more a point of removing the ambguity of the problem
You think it is _less_ ambiguous to have a pin not do what it says it does?
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04 Oct 2013 22:25 #39554
by cncbasher
Replied by cncbasher on topic Post PnCConf velocity & acceleration tweaking
no more a question of hiding the requirement for it to be 20% higher for use with mesacards , or where this requirement is needed , by whatever means
so hopefully removing some setting up errors . and interactions between them ..
so hopefully removing some setting up errors . and interactions between them ..
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04 Oct 2013 22:28 #39555
by andypugh
Replied by andypugh on topic Post PnCConf velocity & acceleration tweaking
The driver is clearly written with the expectation that you would use a value of zero if you don't want the driver to apply a limit.
We don't want the driver to apply a limit (that is the job of the motion planner).
So it seems to me that the thing to fix is the requirement that the stepgen module has to have limits even when you don't want it to apply limits.
We don't want the driver to apply a limit (that is the job of the motion planner).
So it seems to me that the thing to fix is the requirement that the stepgen module has to have limits even when you don't want it to apply limits.
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