PathPilot: VFD selection

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25 Apr 2016 03:18 #73831 by tomdchi
I'm researching VFDs (the drives themselves) and while it's a big, complex field, the range of readily available drives for 1 to 1.5hp (750w to 1.1kw) motors seems to have some consistent characteristics. If I understand correctly, many use a 10v range control signal for spindle speed. Do Tormach systems use this approach to communicate with the VFD, and do they use -5v full reverse/0v stop/+5v full forward?

I'm planning on using a Mesa 5i25+7i76 setup.

Are there issues to look out for when selecting a VFD to be used with a PathPilot-based system to make setup as simple as possible?

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25 Apr 2016 08:50 - 25 Apr 2016 08:51 #73834 by cncbasher
Replied by cncbasher on topic PathPilot: VFD selection
the mesa 7i76 has a analog 0-15v capable isolated output for driving spindles including direction and enable , this is just about every vfd on the market . the actual voltage can range up to 15v , this is usually supplied by the vfd .
10v is industrial standard , they allow up to 15v to allow for voltage drop , if using long cables etc
Last edit: 25 Apr 2016 08:51 by cncbasher.

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26 Apr 2016 17:21 #73923 by tomdchi
Replied by tomdchi on topic PathPilot: VFD selection
I realize I should clarify that I'm focusing on mills, but I realize that other readers would be interested in the same info for their lathe setup.

My overall question is: Is this analog signal the default means that PathPilot expects to use to control spindle speed and direction?

Following on: If yes, is it low end of voltage range is full speed reverse, mid point of range is 0 rpm and high end of range is full speed forward?

And related: PathPilot both has to interpret G code spindle speed/direction commands and (IIRC) displays spindle speed. On Tormach mills, what is the default means that this is handled, including how does PathPilot know which level the belt is on? I was looking at Tormach's schematic and I don't see an indication of an encoder or similar - but I may have missed it.

So, to the point: when using PathPilot on a non-Tormach setup, how do you get spindle RPM accurately back to PathPilot for display and G code interpretation?

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27 Apr 2016 20:21 #73963 by tomdchi
Replied by tomdchi on topic PathPilot: VFD selection
I found this thread:

forum.linuxcnc.org/forum/49-basic-config...encoder-setup-in-hal

That discusses and example of setting up spindle encoding with LinuxCNC, but part of my question is wether PathPilot can use additional information like this by default or can be configured to do so.

I guess a different way of asking about how PathPilot controls the VFD is: what would I look for in the configuration and HAL files to see how PathPilot is interfacing with the VFD?

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28 Apr 2016 09:46 #73993 by andypugh
Replied by andypugh on topic PathPilot: VFD selection
Spindle rpm and positionfeedback does not normally come from the VFD, it comes from the spindle encoder.

I would expect this to be exactly the same between PathPilot and standard LinuxCNC.

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28 Apr 2016 10:02 #73997 by cncbasher
Replied by cncbasher on topic PathPilot: VFD selection
Pathpilot is no more than a GUI Front end to Linuxcnc abeit an old version , by todays .
treat it no differently to Linuxcnc version 2.6.3 ( ubuntu 10_04 ) vintage.
their are a few dissimilar naming used , but no more , this is only to connections to the GUI and not the underlying linuxcnc codebase .

Pathpilot again interfaces to VFD'S exactly as Linuxcnc does .
connections and of course your bit file will be different thats all .
( see the pathpilot tutorials to get round the mesa / bitfile issues
if your stuck connecting / configuring , let me know ,

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01 May 2016 01:45 #74092 by tomdchi
Replied by tomdchi on topic PathPilot: VFD selection
I definitely understand that PathPilot is (mostly) just a user interface overlaid on top of LinuxCNC "under the hood." I'm trying to figure this stuff out to set things up so that I've got as few "variables" as possible when getting the system up and running, and to avoid any major incompatibilities.

I found some of the answers to my earlier questions. Part of the PathPilot interface is a "button" to select the high or low range/belting, and that's the only way the controller knows how the machine's belts are set up.

I also found a discussion thread online where users were talking about how to better calibrate the spindle speed of their Tormach mills because they were seeing enough difference between what the controller thought the spindle's RPM was versus what they were measuring that they expected to have problems tapping. Section 9.5.8 of the Tormach 1100 manual describes the process for calibrating the spindle based on issuing an M spindle speed command when the belt is in the low range, checking the spindle RPM and adjusting a setting.

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01 May 2016 08:54 #74098 by andypugh
Replied by andypugh on topic PathPilot: VFD selection

I also found a discussion thread online where users were talking about how to better calibrate the spindle speed of their Tormach mills because they were seeing enough difference between what the controller thought the spindle's RPM was versus what they were measuring that they expected to have problems tapping.


This must be based on a misunderstanding of how tapping works. Tapping (and threading) are slaved to spindle position as measured by the encoder, not related at all to the displayed or commanded speed.

To be honest, the absolute spindle rpm isn't that important as long as it is consistent.

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01 May 2016 12:14 #74103 by cncbasher
Replied by cncbasher on topic PathPilot: VFD selection
tomdchi:
you appear to be trying to hard ! , are you using a tormach machine ? , are you using geared belts on your spindle
if not then you dont need to use it , remember this has been designed by tormach for Tormach machines , anything else
is simply Linuxcnc , for Tapping you need to have a resonable spindle Encoder . or opto's etc ,
Reading whats needed for a tormach machine or associated problems are only going to confuse you , even more .
if it works with linuxcnc then it works with PathPilot the same way .
the only difference is a few hal links to the GUI that you need to hook up for the display .

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01 May 2016 14:19 #74104 by tomdchi
Replied by tomdchi on topic PathPilot: VFD selection
Yes, I guess I am trying hard! :lol: Thank you for your patience! I hope that my very basic questions and your answers are helpful to other people beginning to look into this.

I'm not using a Tormach but the PathPilot interface appears to be easy to work with "out of the box" rather than making all sorts of tweaks and additions to Axis. My situation is that I don't have an in-depth understanding of LinuxCNC or working familiarity with how to tweak it to make it work with a specific setup. (Or Tormach systems, which is why I'm asking basic questions about the interface!)

The discussion I found about spindle RPM was about using Tormach's "tension/compression" head - I'm not sure why these people were so concerned about specific RPMs in that case. I have to guess that this system has a very limited RPM range that will work consistently. I understand that PathPilot/Tormach mills can't do rigid tapping and that requires standard LinuxCNC and an encoder. Thank you for pointing out these details, but at least on these points I'm not confused (I think!)

I understand that LinuxCNC is very flexible and can be made to work with a huge range of CNC systems. But I have some experience configuring other open-source systems. Powerful... Very flexible... and not too difficult to configure and make work if you understand them deeply, but difficult if you don't have an extensive, detailed, deep understanding of the software. When you don't have a good understanding of a system, "just check the wiki" usually isn't clear enough!

I'm asking these questions so that I can minimize the range and extent of configuration issues. Also, I hope that when I do need to make "a few HAL link" adjustments, I better understand what I'm doing. Again: thank you!

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