Re: [Emc-users] Delta 3D printer with servo drive?

[Gregg Eshelman]

On 2/21/2015 6:44 AM, Viesturs Lācis wrote:
> 2015-02-21 15:16 GMT+02:00 Tobias Gogolin :
>> I am suggesting small geared brushless motors
>
> Gearing will introduce backlash. Linear delta machine may have
> end-effector vs actuator travel ratio up to 2:1, depending on rod
> length vs delta radius proportion, so any backlash in actuator means
> even larger backlash on end-effector. Take all 3 actuators, add
> together their backlash and you might have difficulties to achieve
> desired positioning accuracy for hotend.
> I would be tempted to go the traditional way of mounting belt pulley
> right on motor shaft - tuning feedback loop might be challenging, but
> once that is done, the machine can be very very fast...

Look for ABB Flexpicker on YouTube. It's a delta design with actuator 
arms directly connected to servo shafts. Quite fast and precise, with 
the right type of tool it can pick up and stack delicate items such as 
pancakes at extreme speeds.


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Re: [Emc-users] Delta 3D printer with servo drive?

[Gregg Eshelman]

On 2/21/2015 6:16 AM, Tobias Gogolin wrote:
> So after understanding that a linear driven delta 3D Printer is the most
> attractive tool to have in ones repertoire me and a friend, who has already
> previous cnc mill building experience decided to get serious, and there is
> one disagreement, he thinks he would be fine with inexpensive steppers, I
> am suggesting small geared brushless motors, so I am hoping for an expert
> opion, and also groups, an wikis where maybe lists of the available motion
> controllers are offered?

Have a look at this. 
http://hackaday.com/2015/01/20/closed-loop-control-for-3d-printers/

Proof of concept, now it needs the added functions of stopping the 
extruder and movement when the XY motion of the gantry is blocked.


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Re: [Emc-users] Introduction and a couple questions

[Kirk Wallace]

On 02/21/2015 03:42 PM, Brent Loschen wrote:
> Greetings everyone!  New guy here.  I've been following the group for
> several weeks and feel it's time for an intro and to get some
> suggestions for a small project I'm working on.

Welcome to the world of LinuxCNC.

> First, my motivation for looking into LinuxCNC.  I own an older
> Bridgeport R2E4 CNC mill (Boss 9 with DC servo motors)

My HNC lathe has brushed DC servo motors. If your Bridgeport were in my 
shop, I would probably use the same setup as the HNC. That being keep 
the motors and motor power supply, replace the old drivers with Pico 
System PWM input drivers, add a hardware signal generator such as a Mesa 
5i25 or Pico PWM board, add a Pico or Mesa resolver converter or 
preferably make or buy high resolution quadrature encoders to the ball 
screws. But that's just me.
http://www.wallacecompany.com/cnc_lathe/HNC/

> To start that journey I would like to convert a Shapeoko type desktop
> mill, from TinyG, to a real CNC control in order to become familiar with
> the CNC software.

If the new machine were primarily for learning to convert your 
Bridgeport and you aren't using it more than a couple days a month to 
make money, then I would go ahead and convert the Bridgeport. You can do 
a fair amount work without disabling your mill by building your PC 
controller and swapping cables from your old controller for testing.

For learning, I tend to use old parts that I can get dirt cheap or free. 
Such as, for a small NEMA23 class mill, I have some discarded DC RV 
water pumps that leaked. So far, I have cleaned them up, replaced the 
bearings and I can either rebuild the pump sections or use the motors 
for a mill. For a small mill, I would probably get some US Digital 
sensors and disks to make encoders (although USD parts aren't cheap 
anymore). The motor driver is more of a problem. There may be some DC 
brushed drivers available from robot vendors, but these tend to be lower 
voltage. Either that or build you own. For the spindle, small used VFDs 
and three phase motors can be found on eBay. A parallel port could be 
used for the signal generation, but it would be easier to go with a 5i25 
or similar. This setup would be just like your Bridgeport, just smaller.

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Re: [Emc-users] Delta 3D printer with servo drive?

[Sebastian Kuzminsky]

On 02/21/2015 05:27 PM, andy pugh wrote:
> On 22 February 2015 at 00:17, Tobias Gogolin  wrote:
> 
>> One reply mentions the Ramps1.4 system; I wonder is the translation done
>> between linear delta motion control and Euclidean G-code, or is non
>> Euclidean G-Code used?
> 
>  http://www.linuxcnc.org/docs/html/motion/kinematics.html

Jeff Epler wrote kinematics for a delta robot, but unfortunately it's
not in 2.7 or master, it's in branch called joints_axes6.  It includes a
vismach simulation of the delta robot, which is kind of neat.


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Re: [Emc-users] Delta 3D printer with servo drive?

[andy pugh]

On 22 February 2015 at 00:17, Tobias Gogolin  wrote:

> I imagine that gear backlash can be measured and if its not captured by an
> encoder on the geared down axis, it should at least in software be
> considered for every change of direction. Is there such an option?
>

There is:  look at BACKLASH or COMP_FILE in the INI config
http://www.linuxcnc.org/docs/html/config/ini_config.html#sub:AXIS-section

I have no idea if it works at all for non-trivial kinematics.

I may on
> my first printer also succumb the temptation to go with steppers maybe
> overdoing torque such as with a fat NEMA34 instead of 17 or 23...
>

As steppers get bigger they get slower. Really quite a lot slower. A
printer does not need a lot of force. I can't imagine any printer needing
NEMA34. Most seem to use NEMA17...

My first 3D Delta shall have a max. build height of  whatever results from
> 1 meter or 1.5m shafts,
>

... But that's a big printer.

One reply mentions the Ramps1.4 system; I wonder is the translation done
> between linear delta motion control and Euclidean G-code, or is non
> Euclidean G-Code used?
>

 http://www.linuxcnc.org/docs/html/motion/kinematics.html

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Re: [Emc-users] Delta 3D printer with servo drive?

[Tobias Gogolin]

Thanks to everybody who replied so far for the rays of light! Maybe I
should admit that I have difficulty to imagine the algorithm to translate
from 3 linear axis of a delta printer to the 'euclidean' 3d space that the
model will be printed in, therefore I also don't really begin to guess what
kind of resolution is required on the linear axis.
I imagine that gear backlash can be measured and if its not captured by an
encoder on the geared down axis, it should at least in software be
considered for every change of direction. Is there such an option? I may on
my first printer also succumb the temptation to go with steppers maybe
overdoing torque such as with a fat NEMA34 instead of 17 or 23...

My first 3D Delta shall have a max. build height of  whatever results from
1 meter or 1.5m shafts, subtracting linear bearing height and linear shaft
mounts, and the min. length required to be able to cause a flat surface on
the build area. I gather that pole length and build diameter are somehow
related probably in a formula that considers the max. deflection angle and
the loss of precision that might result?

One reply mentions the Ramps1.4 system; I wonder is the translation done
between linear delta motion control and Euclidean G-code, or is non
Euclidean G-Code used?

Thanks again for all the participation, and happy weekend!
cheers

Tobias!

On Sat, Feb 21, 2015 at 2:44 PM, Viesturs Lācis 
wrote:

> 2015-02-21 15:16 GMT+02:00 Tobias Gogolin :
> > I am suggesting small geared brushless motors
>
> Gearing will introduce backlash. Linear delta machine may have
> end-effector vs actuator travel ratio up to 2:1, depending on rod
> length vs delta radius proportion, so any backlash in actuator means
> even larger backlash on end-effector. Take all 3 actuators, add
> together their backlash and you might have difficulties to achieve
> desired positioning accuracy for hotend.
> I would be tempted to go the traditional way of mounting belt pulley
> right on motor shaft - tuning feedback loop might be challenging, but
> once that is done, the machine can be very very fast...
>
> Viesturs
>
>
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-- 
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Tel. D1 (49) 0151 5187 5210
Tel. D2 (49) 0152 0839 5060
skype: moontogo
messenger: usert...@hotmail.com

You develop Sustainable Ranch Technology at
http://tech.groups.yahoo.com/group/SURA-TECH
an Open Source Electric Motor/Alternator at
http://groups.yahoo.com/group/Performance_Axial_Flux
and an Open Source Motor Controller at http://groups.yahoo.com/group/GoBox
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Re: [Emc-users] Introduction and a couple questions

[andy pugh]

On 21 February 2015 at 23:42, Brent Loschen  wrote:

> My question for the group is, what hardware would you
> all recommend for this task?  I've looked at some of the ~$150 Chinese,
> 3 axis, PLC/control/stepper drive combos available on Ebay,
>

I think that those are a good choice for a "practice" machine. A cheap way
to get started and find out what  you really want.

I probably wouldn't convert a Bridgeport with steppers anyway, as they are
right on the edge of where steppers are usable.
(Yes, I know that the original control is stepper)



>  One final consideration is whether to use a
> parallel port solution, or if there are USB or network controls
> available in a wallet friendly price range?
>

USB is right out, the USB spec allows latency of milliseconds, it can never
be used for real-time control, so the solutions that do use USB run the
motion-controller in the box at the end of the USB cable.
There are a couple of Ethernet controlled boards available for LinuxCNC,
but they are not properly mainstream yet.
There are several options for PCI cards, and a couple of alternatives that
use the p-port as a data bus to an FPGA which is hugely more powerful than
bit-banging the parport.

So, for your "practice" conversion I would say to go with an eBay TB6560
board and the parport. You might want to see the board as a "sunk cost"
that will be replaced later when you are in a better position to specify
hardware.
That was the approach I took, and I don't regret it. I am still using some
of the motors from the eBay kit, but the controller board was replaced by
separate Leadshine-style black-box drives and the parport bit-banging was
replaced by a parport communicating with a Mesa 7i43.

Then the next machine was all 750W brushless servos with resolvers and a
lot more money spent.

-- 
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[Emc-users] Introduction and a couple questions

[Brent Loschen]

Greetings everyone!  New guy here.  I've been following the group for 
several weeks and feel it's time for an intro and to get some 
suggestions for a small project I'm working on.

First, my motivation for looking into LinuxCNC.  I own an older 
Bridgeport R2E4 CNC mill (Boss 9 with DC servo motors) that works 
flawlessly at the moment. However, every time I open the cabinets and 
look at the mass of wires and circuit boards I know at some point, 
something inside is going to fail.  Even though I have the schematics 
and am comfortable doing basic electronic troubleshooting, I know that 
sooner or later I will be faced with replacing that rats nest with a 
modern servo control and software. In anticipation of that event, I 
would like to experiment with different control software to see which I 
like best.  I generally prefer Linux over Windows and am currently 
favoring LinuxCNC.  To that end, I plan to start on a small project and 
go big if/when the BP fails.

To start that journey I would like to convert a Shapeoko type desktop 
mill, from TinyG, to a real CNC control in order to become familiar with 
the CNC software.  My question for the group is, what hardware would you 
all recommend for this task?  I've looked at some of the ~$150 Chinese, 
3 axis, PLC/control/stepper drive combos available on Ebay, but I get 
concerned when I read articles regarding the poor quality and wide 
variation in the actual driver chips used in many of those stepper 
drives.  I'm not sure if those problems are actually related to junky 
hardware, or possibly just operator error, so I'm left wondering if 
anyone has found anything in that realm that actually works?  (I only 
need to drive NEMA 23's)  If not, I would appreciate hearing what some 
of you may be using for motion control/drive hardware for an inexpensive 
mill like the Shapeoko.  One final consideration is whether to use a 
parallel port solution, or if there are USB or network controls 
available in a wallet friendly price range?   I've read that USB 
controls tend to be susceptible to induced electrical noise, but I have 
no idea how widespread the problem is or if a good quality, short, 
shielded USB cable plus shielded stepper cables can resolve noise 
issues?  My preference would be to consider an alternative to the 
parallel interface, but the price of other options may be overkill for 
this small application.  From what I've read, LinuxCNC seems to have 
good support for parallel, but I'm unclear if/how it supports network or 
USB controls and would like to hear your thoughts on that aspect. Down 
the road (hopefully WAY down the road!)  I may poll the group again for 
Bridgeport servo control recommendations, but for now, any suggestions 
on the most appropriate hardware (ie low cost, reliable, LinuxCNC ready) 
for this small 3 axis mill would be greatly appreciated.

Looking forward to hearing feedback from the experts!

Thanks in advance,
Brent

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Re: [Emc-users] Call a Python file from Axis

[Kirk Wallace]

On 02/21/2015 10:17 AM, John Thornton wrote:
> Just exploring the GladeVCP angle and I can not find a way yet to send
> output to Axis like I do with my G code Generators.

The UI I worked on has the conversational g-code appended to a string 
variable. The conversational process concludes with a Post which saves 
the g-code variable to a file. Then loads the file to the code and plot 
views. I haven't done anything on the file handling side so I don't know 
any details.

We also use g-code files as probing routines. In this case one or a few 
numbered parameters are calculated, then passed with an MDI call for an 
o-word file.

self.command.mdi('o' + 'call [%f]' % (feedrate))

http://www.linuxcnc.org/docs/html/gcode/o-code.html#_calling_files

-- 
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[Emc-users] LinuxCNC 2.7.0~pre4 bugfix release

[Sebastian Kuzminsky]

This is just a quick bugfix release for a silly bug that made it into
the Axis GUI in 2.7.0~pre3.

This release fixes a bug in the Axis GUI when transitioning to
world-mode, on non-trivial kinematics machines.


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[Emc-users] LinuxCNC 2.6.7 is out

[Sebastian Kuzminsky]

This is just a quick bugfix release for a silly bug that made it into
the Axis GUI in 2.6.6.

This release fixes a bug in the Axis GUI when transitioning to
world-mode, on non-trivial kinematics machines.  All 2.6 users are
encouraged to upgrade.


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Re: [Emc-users] Delta 3D printer with servo drive?

[Gene Heskett]

On Saturday, February 21, 2015 11:11:36 AM Kirk Wallace wrote:
> On 02/21/2015 07:29 AM, Peter C. Wallace wrote:
> > On Sun, 22 Feb 2015, Erik Christiansen wrote:
> > 
> > snip
> > 
> >> On a 3D printer, free of cutting forces, I figure microstepping
> >> would be OK at constant velocity, but rubbery under strong
> >> acceleration. At least it's only full steps that you can
> >> permanently lose.
> > 
> > Actually step motors lose steps in multiples of 4 full steps
> > (a full pole slip = 360 electrical degrees, a full step is 90
> > electrical degrees)
> 
> In case it might be handy, considering stepper design reminded me of a
> link I sometimes go back to to refresh my understanding:
> http://homepage.cs.uiowa.edu/~jones/step/physics.html
> http://homepage.cs.uiowa.edu/~jones/step/#abstract

A bible like pair of documents.. Pretty well covers it IMO.

We should  all bookmark that page FFR.

Thanks Kirk.

Cheers, Gene Heskett
-- 
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Genes Web page 

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Re: [Emc-users] Delta 3D printer with servo drive?

[Gene Heskett]

On Saturday, February 21, 2015 10:29:56 AM Peter C. Wallace wrote:
> On Sun, 22 Feb 2015, Erik Christiansen wrote:
> 
> snip
> 
> > On a 3D printer, free of cutting forces, I figure microstepping would
> > be OK at constant velocity, but rubbery under strong acceleration.
> > At least it's only full steps that you can permanently lose.
> 
> Actually step motors lose steps in multiples of 4 full steps
> (a full pole slip = 360 electrical degrees, a full step is 90
> electrical degrees)
> 
> 
> Peter Wallace
> Mesa Electronics

Thanks for pointing that out Peter, and keeping me honest. It's one of the 
details that slipped my mind in my earlier expounding on it. On the usual 
200 steps/rev motor, thats 7.2 degrees, and a part wrecking error, even on 
a 20 tpi acme leadscrew in one of the toy tabletoppers.

Most such slippage is at or near the top speed, which results in an 
outright stall, so the machine has to be recalibrated to its home switches 
anyway.  I could see it happening at motion startup, but that would likely 
be such a nuisance the user would soon find the missing decimal point in 
his 4, or 5 digit accel setting in the .ini files accel settings.

Cheers, Gene Heskett
-- 
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-Ed Howdershelt (Author)
Genes Web page 

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Re: [Emc-users] Delta 3D printer with servo drive?

[Gene Heskett]

On Saturday, February 21, 2015 10:22:15 AM Erik Christiansen wrote:
> On 21.02.15 09:27, Gene Heskett wrote:
> > The disadvantages are that they will continuously burn from 25% to
> > 50% of their running power even if being driven by smart controllers
> > that can reduce the drive when they have stopped.  And the discrete
> > steps they make, which with smart controlers can be subdivided by
> > microstepping, look like a prob lem but in the world of flying
> > swarf, not terribly important.
> 
> And even burning that power, the torque to hold a 1/16th microstep is
> only 10% of the full step holding torque, if I caught all of what was
> said in a LinuxCNC youtube clip I looked at last night. (It was in
> German, and it's a while since I used mine.)

True, so when I want to really calculate, I use an error that is at least 
1/3 rd of a full step as the worst case.  But I've not calculated that 
recently, since I put ball screws in the mills xy table drives.  They, 
being faster will make that a sloppier tolerance.
 
> > But unless the current mapping in the controller is exactly matched
> > so that a 1/8th step is exactly 1/8th step, there will be a cyclic
> > positioning error. Miniscule, its less than .001" at any point when
> > direct coupled to a 5mm per rev ball screw.  Best match I would
> > guess is when the motor is being run at exactly its nameplate
> > amperage.  With commonly available stepper drivers having a dip
> > switch current setting that typically changes in 10 to 15%
> > increments, this isn't as easy to as it should be.
> 
> On a 3D printer, free of cutting forces, I figure microstepping would
> be OK at constant velocity, but rubbery under strong acceleration. At
> least it's only full steps that you can permanently lose.

One of the reasons I, as a general rule, do not set accels to more than 
50% of what it tests that it can do.  So I can definitely hear it doing 
its "whee" as it starts up for a G0 move. 

> > Thanks for reading this far, stay warm guys. We're collecting more
> > white stuff this morning.
> 
> There's been an awful lot of it in some states, we hear. Once it's deep
> enough, mebbe just tunnel through it to the workshop. (I spent an
> afternoon skiddooing at Whistler, years ago, on 7 meters of snow.)
> We don't have that stuff here. We just need a way to stop dumb parents
> from broiling their infants in cars. (see sig)

We have that same level of idiocy here. Unfortunately for the children so 
trapped.  I am in West Virginia, and have nominally 10" on the ground. But 
I learned to drive in a bad Iowa winter 65 + years ago, so 10" isn't a big 
problem for me.  I might have to put my "West Virginia Cadillac" (a 99 GMC 
3 door pickup with 4wd) in 4wd for 6 feet to get out of the drive.

We're about out of milk & some onion buns + Dee needs her daily crossword 
fix from the paper, so I will be out in it in another half hour.
 
> Erik

Cheers, Gene Heskett
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Re: [Emc-users] Call a Python file from Axis

[John Thornton]

Just exploring the GladeVCP angle and I can not find a way yet to send 
output to Axis like I do with my G code Generators.

I tried:

sys.stdout.write('this is a test')

but the output goes to the terminal where as when I ran that from my G 
code Generator the output went to Axis

http://wiki.linuxcnc.org/uploads/arcgenl18.py

Thanks
JT

On 2/21/2015 9:02 AM, andy pugh wrote:
> On 21 February 2015 at 13:38, John Thornton  wrote:
>
>> Is it possible to add a menu item to Axis with .axisrc to open a python
>> program?
>>
> I never figured out ,axisrc.
>
>
>> Or is it possible to call a python program via a PyVCP button?
>>
> Via MDI_COMMAND and an M-code you can, but it's a bit  unwieldy
>
> Or is it possible with GladeVCP
> Yes, you can have any code you want in the handler for the button press
> event. Many buttons in the examples use the provided MDI-action but it is
> easy to link the button to a handler you have written yourself.
>


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Re: [Emc-users] Delta 3D printer with servo drive?

[Jon Elson]

On 02/21/2015 07:16 AM, Tobias Gogolin wrote:
> So after understanding that a linear driven delta 3D Printer is the most
> attractive tool to have in ones repertoire me and a friend, who has already
> previous cnc mill building experience decided to get serious, and there is
> one disagreement, he thinks he would be fine with inexpensive steppers, I
> am suggesting small geared brushless motors,
Gears have backlash.  Belt reduction would be better if you 
even need the
reduction.  Anyway, before making a choice, you need to know 
how much
the backlash is on those gearheads, and how much that 
translates to on
the complete machine.  (I'm normally a servo bigot, but if 
servos require
adding backlash, that may turn them into a minus.)

Jon

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Re: [Emc-users] LinuxCNC 2.6.6

[Jon Elson]

> From: chris [mailto:ch...@builderofstuff.com]
>
> I agree wholeheartedly. If it weren't for you folks out there who bring us
> Linuxcnc I wouldn't have cnc. Huge thank you to everyone involved.
>
>
And, I WOULD still have CNC.  But, it would be AWFUL CNC!  
I'd still be using my
Allen-Bradley 7320, which had a bunch of disadvantages, not 
to mention breaking
down every couple months.

THANK G*D for LinuxCNC, I was able to retire that heap and 
move to PCs.
More reliable, more flexible, better motion control, no 
CRAZY moves if
you mis-coded the G-code.  (I once had something wrong with 
a G02
endpoint, and it made a 12-revolution spiral to get to the 
endpoint!
Lucky me, I did a test cut with a ballpoint pen and paper.)

Even though I'm considered a "developer" I still stand in 
awe of the
guys who can dig DEEP into the motion planning, etc. and 
come out
alive!  I also want to thank the guys who plug away at 
documentation
and making sure commits build reliably, and getting new 
releases all
squared away.

Jon

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Re: [Emc-users] Linuxcnc 2.6.6 gantry error

[Sebastian Kuzminsky]

On 02/21/2015 07:45 AM, Horváth Csaba wrote:
> Hello Sebastian,
> 
> I try  v2.6.6-1-g8679f71 and work fine!

Ok good.  Thanks for the quick turn-around on the bug report and the fix
report.  2.6.7 is on its way...


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Re: [Emc-users] Call a Python file from Axis

[Kirk Wallace]

On 02/21/2015 05:38 AM, John Thornton wrote:
> Is it possible to add a menu item to Axis with .axisrc to open a python
> program?
>
> Or is it possible to call a python program via a PyVCP button?

Sorry, I haven't a clue.

> Or is it possible with GladeVCP?

I suppose one could import the other Python file and call it in your 
on_my_button_click callback function. I found this link which indicates 
there may be problems with that approach:
http://stackoverflow.com/questions/3781851/run-a-python-script-from-another-python-script-passing-in-args

-- 
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http://www.wallacecompany.com/machine_shop/
http://www.wallacecompany.com/E45/

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Re: [Emc-users] Delta 3D printer with servo drive?

[Kirk Wallace]

On 02/21/2015 07:29 AM, Peter C. Wallace wrote:
> On Sun, 22 Feb 2015, Erik Christiansen wrote:
>
> snip
>>
>> On a 3D printer, free of cutting forces, I figure microstepping would be
>> OK at constant velocity, but rubbery under strong acceleration. At least
>> it's only full steps that you can permanently lose.
>>
>
>
> Actually step motors lose steps in multiples of 4 full steps
> (a full pole slip = 360 electrical degrees, a full step is 90
> electrical degrees)

In case it might be handy, considering stepper design reminded me of a 
link I sometimes go back to to refresh my understanding:
http://homepage.cs.uiowa.edu/~jones/step/physics.html
http://homepage.cs.uiowa.edu/~jones/step/#abstract


-- 
Kirk Wallace
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Re: [Emc-users] LinuxCNC 2.6.6

[rick]

I definitely have to agree with that,

Thank you to all of the developers, and all of the testers.  


 Original Message 
Subject: Re: [Emc-users] LinuxCNC 2.6.6
From: "Belli Button" 
Date: Sat, February 21, 2015 3:19 am
To: "'chris'" ,"'Enhanced Machine Controller (EMC)'" 


"Never in the field of CNC was so much owed by so many to so few"




-Original Message-
From: chris [mailto:ch...@builderofstuff.com] 
Sent: 21 February 2015 02:37
To: Marius Liebenberg; Enhanced Machine Controller (EMC)
Subject: Re: [Emc-users] LinuxCNC 2.6.6

I agree wholeheartedly. If it weren't for you folks out there who bring us
Linuxcnc I wouldn't have cnc. Huge thank you to everyone involved.

Chris




> On February 20, 2015 at 12:09 AM Marius Liebenberg 
> 
> wrote:
>
>
> A big thank you to all they guys working on improving the software. 
> And all without remuneration.



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Re: [Emc-users] Delta 3D printer with servo drive?

[Peter C. Wallace]

On Sun, 22 Feb 2015, Erik Christiansen wrote:

snip
>
> On a 3D printer, free of cutting forces, I figure microstepping would be
> OK at constant velocity, but rubbery under strong acceleration. At least
> it's only full steps that you can permanently lose.
>


Actually step motors lose steps in multiples of 4 full steps
(a full pole slip = 360 electrical degrees, a full step is 90 
electrical degrees)


Peter Wallace
Mesa Electronics

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Re: [Emc-users] Delta 3D printer with servo drive?

[Erik Christiansen]

On 21.02.15 09:27, Gene Heskett wrote:
> The disadvantages are that they will continuously burn from 25% to 50% of 
> their running power even if being driven by smart controllers that can 
> reduce the drive when they have stopped.  And the discrete steps they 
> make, which with smart controlers can be subdivided by microstepping, look 
> like a prob lem but in the world of flying swarf, not terribly important.

And even burning that power, the torque to hold a 1/16th microstep is
only 10% of the full step holding torque, if I caught all of what was
said in a LinuxCNC youtube clip I looked at last night. (It was in
German, and it's a while since I used mine.)

> But unless the current mapping in the controller is exactly matched so 
> that a 1/8th step is exactly 1/8th step, there will be a cyclic 
> positioning error. Miniscule, its less than .001" at any point when direct 
> coupled to a 5mm per rev ball screw.  Best match I would guess is when the 
> motor is being run at exactly its nameplate amperage.  With commonly 
> available stepper drivers having a dip switch current setting that 
> typically changes in 10 to 15% increments, this isn't as easy to as it 
> should be.

On a 3D printer, free of cutting forces, I figure microstepping would be
OK at constant velocity, but rubbery under strong acceleration. At least
it's only full steps that you can permanently lose.

...

> Thanks for reading this far, stay warm guys. We're collecting more white 
> stuff this morning.

There's been an awful lot of it in some states, we hear. Once it's deep
enough, mebbe just tunnel through it to the workshop. (I spent an
afternoon skiddooing at Whistler, years ago, on 7 meters of snow.)
We don't have that stuff here. We just need a way to stop dumb parents
from broiling their infants in cars. (see sig)

Erik

-- 
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cars in the first five weeks of 2015. Last year more than 1,100 children were
rescued from inside locked cars.
- 
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Re: [Emc-users] Call a Python file from Axis

[andy pugh]

On 21 February 2015 at 13:38, John Thornton  wrote:

> Is it possible to add a menu item to Axis with .axisrc to open a python
> program?
>

I never figured out ,axisrc.


> Or is it possible to call a python program via a PyVCP button?
>

Via MDI_COMMAND and an M-code you can, but it's a bit  unwieldy

Or is it possible with GladeVCP
>

Yes, you can have any code you want in the handler for the button press
event. Many buttons in the examples use the provided MDI-action but it is
easy to link the button to a handler you have written yourself.

-- 
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Re: [Emc-users] Linuxcnc 2.6.6 gantry error

[Horváth Csaba]

Hello Sebastian,

I try  v2.6.6-1-g8679f71 and work fine!

Thanks!




2015.02.21. 2:58 keltezéssel, Sebastian Kuzminsky írta:
> I just pushed fixed this in the 2.6 branch, i think.  Can you try
> v2.6.6-1-g8679f71 from git or from the buildbot?
>


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Re: [Emc-users] Delta 3D printer with servo drive?

[Gene Heskett]

On Saturday, February 21, 2015 08:16:07 AM Tobias Gogolin wrote:
> So after understanding that a linear driven delta 3D Printer is the
> most attractive tool to have in ones repertoire me and a friend, who
> has already previous cnc mill building experience decided to get
> serious, and there is one disagreement, he thinks he would be fine
> with inexpensive steppers, I am suggesting small geared brushless
> motors, so I am hoping for an expert opion, and also groups, an wikis
> where maybe lists of the available motion controllers are offered?
> 
> Thanks!
> 
> Tobias Gogolin

The basic design might look similar, but for smaller stuff (under 10,000 
lbs sitting on the floor) steppers are the economic winner hands down.

The disadvantages are that they will continuously burn from 25% to 50% of 
their running power even if being driven by smart controllers that can 
reduce the drive when they have stopped.  And the discrete steps they 
make, which with smart controlers can be subdivided by microstepping, look 
like a prob lem but in the world of flying swarf, not terribly important.

But unless the current mapping in the controller is exactly matched so 
that a 1/8th step is exactly 1/8th step, there will be a cyclic 
positioning error. Miniscule, its less than .001" at any point when direct 
coupled to a 5mm per rev ball screw.  Best match I would guess is when the 
motor is being run at exactly its nameplate amperage.  With commonly 
available stepper drivers having a dip switch current setting that 
typically changes in 10 to 15% increments, this isn't as easy to as it 
should be.

OTOH, who among the likes of me, has the gauges to actually meaure this 
non-linearity in the real world.  I have one dial that reads in .0001" 
increments, and when I put it on the table and start looking for those 
errors, they are completely buried in the stiction and the machines frame 
flexibility.  So while its a theoretical error, its effectively masked by 
the other sources of noise between the motor shaft and the tables motion.  
That hasn't kept me from making something with a tolerance of a thousandth 
or better as long as I have both eyes open.

Step into the servo world, and you immediately have to add the expenses of 
adding a precision position readout, and interfacing that back to the axis 
driver in order to obtain a desired position vs actual position error that 
is then used to drive the motor to reduce the error, which can never be 
zero because there is no error to drive the motor then.

Servo's can probably be made to maintain a higher accuracy but the 
difference in a well geared stepper system and an equally well balanced 
servo system are for the most part buried in other measurment noise.  
Either can be made to move from point AB to point CD at an arbitrary angle 
that stays well within .0005" of a straight line.

Depending on driver and psu for the servo, it can move faster than the 
stepper can, this because the steppers own inductance prevents the 
available torque from being maintained as the driving frequency is raised.

OTOH, a few weeks ago, I tested a new 48 volt psu for my mill, and 
successfully drove a 425 oz triple stack nema 23 motor at over 3400 rpm.  
That top speed limit I got the impression, was set more by the speed of 
the opto's in the 2M542 driver than anything else as the function 
generator was then running at nearly 375 kilohertz.  Even 2000 rpm will 
move my tables at 100+ ipm. And to even get that speed will take a 5i25, 
my parport is all done at 30 ipm.  At a base thread of 30 u-secs, thats 33 
kiolhertz, 1250 rpms and 10% of what the function generator was doing.  If 
my math is correct, 33k/8/200*60 where the 8 is microstep, 200 is a rev, 
and 60 is the rps to rpm multiplier.  If I didn't blow the math...

If I was to make a bid and win that K&T thats on ebay with a starting bid 
of $1k, and figure out where to put its 12,500 lbs when it got here, I 
would probably put some geared down nema 42's on it.  With a carton of 
tailgate hatch struts under the knee.  But then I would have to find some 
work for it to do just to pay the electric bill to run its spindle, 50 
horse IIRC. :(  Work, that's a 4 letter word at my age. :)

Thanks for reading this far, stay warm guys. We're collecting more white 
stuff this morning.

Cheers, Gene Heskett
-- 
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Re: [Emc-users] Delta 3D printer with servo drive?

[John Thornton]

Are you thinking servos because your building a giant delta?

There are thousands of users that build Kossel deltas with a Ramps 1.4 
Power and Nema 17 steppers. In fact that is what I'm planning on 
building as soon as the Chinese New Year is over.

http://gnipsel.com/images/3-D%20Printing/

JT

On 2/21/2015 7:16 AM, Tobias Gogolin wrote:
> So after understanding that a linear driven delta 3D Printer is the most
> attractive tool to have in ones repertoire me and a friend, who has already
> previous cnc mill building experience decided to get serious, and there is
> one disagreement, he thinks he would be fine with inexpensive steppers, I
> am suggesting small geared brushless motors, so I am hoping for an expert
> opion, and also groups, an wikis where maybe lists of the available motion
> controllers are offered?
>
> Thanks!
>
> Tobias Gogolin
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Re: [Emc-users] Delta 3D printer with servo drive?

[andy pugh]

On 21 February 2015 at 13:16, Tobias Gogolin  wrote:

> he thinks he would be fine with inexpensive steppers, I
> am suggesting small geared brushless motors, so I am hoping for an expert
> opinion
>

The internet is full of opinions, but it is hard to decide how expert they
are :-)

There are thousands of printers out there that have steppers and that work.
There is no reason to think that steppers are not a perfectly adequate
solution. There are so many that the motors have also become very cheap, as
have the drivers for the motors.

A brushless motor solution will be more expensive, both for the motors and
the drivers. You may end up with a "better" solution, but you have to think
about what problems you are trying to solve, given that the stepper-driven
machines all seem to work.

There is a halfway house, Leadshine, Vexta and others are now offering
closed-loop stepper motors. A stepper motor and a brushless motor are
largely identical, a stepper is just a very high pole-count 2-phase
brushless motor. Some manufacturers are capitalising on this by adding an
encoder and a smart motion controller that uses the encoder.
This is an example of the type. http://www.ebay.co.uk/itm/161481647080 I am
not recommending that one, you still need to decide on your requirements.

All that being said, I can't see myself building any more stepper-driven
machines.

-- 
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Re: [Emc-users] Delta 3D printer with servo drive?

[Viesturs Lācis]

2015-02-21 15:16 GMT+02:00 Tobias Gogolin :
> I am suggesting small geared brushless motors

Gearing will introduce backlash. Linear delta machine may have
end-effector vs actuator travel ratio up to 2:1, depending on rod
length vs delta radius proportion, so any backlash in actuator means
even larger backlash on end-effector. Take all 3 actuators, add
together their backlash and you might have difficulties to achieve
desired positioning accuracy for hotend.
I would be tempted to go the traditional way of mounting belt pulley
right on motor shaft - tuning feedback loop might be challenging, but
once that is done, the machine can be very very fast...

Viesturs

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[Emc-users] Call a Python file from Axis

[John Thornton]

Is it possible to add a menu item to Axis with .axisrc to open a python 
program?

Or is it possible to call a python program via a PyVCP button?

Or is it possible with GladeVCP?

Thanks
JT

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[Emc-users] Delta 3D printer with servo drive?

[Tobias Gogolin]

So after understanding that a linear driven delta 3D Printer is the most
attractive tool to have in ones repertoire me and a friend, who has already
previous cnc mill building experience decided to get serious, and there is
one disagreement, he thinks he would be fine with inexpensive steppers, I
am suggesting small geared brushless motors, so I am hoping for an expert
opion, and also groups, an wikis where maybe lists of the available motion
controllers are offered?

Thanks!

Tobias Gogolin
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Re: [Emc-users] LinuxCNC 2.6.6

[Stuart Stevenson]

On Sat, Feb 21, 2015 at 2:19 AM, Belli Button  wrote:

> "Never in the field of CNC was so much owed by so many to so few"
>
> Heh - I must agree here.
There is a LOT of LinuxCNC out there as a result of a relative few
contributors.
I certainly appreciate the effort and sacrifice.
Stuart

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Re: [Emc-users] LinuxCNC 2.6.6

[Belli Button]

"Never in the field of CNC was so much owed by so many to so few"




-Original Message-
From: chris [mailto:ch...@builderofstuff.com] 
Sent: 21 February 2015 02:37
To: Marius Liebenberg; Enhanced Machine Controller (EMC)
Subject: Re: [Emc-users] LinuxCNC 2.6.6

I agree wholeheartedly. If it weren't for you folks out there who bring us
Linuxcnc I wouldn't have cnc. Huge thank you to everyone involved.

Chris




> On February 20, 2015 at 12:09 AM Marius Liebenberg 
> 
> wrote:
>
>
> A big thank you to all they guys working on improving the software. 
> And all without remuneration.



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