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Offline sn96

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Motion controllers - Take me to school
« on: August 29, 2017, 02:33:05 PM »
Hello Guys,

I have been doing a lot of research on closed loop steppers / hybrid servos and I am confused as to how all this interfaces with Mach3. It looks to me that each stepper servo has an encoder and a separate motion controller card example: 3 motors, 3 cards. Now does there need to be a separate driver board to interface the 3 cards to to a pc where as the driver board is the middle man? Does a parallel port still need to be used? USB? If you are using external controllers/drivers, are you now free to use any 64 bit operating system?

I am currently using a Sherline mill, Sherline steppers, Sherline 3-Axis stepper controller using the LPT printer port. I have been considering upgrading to the closed loop system.
________________
Mike

Sherline 5400 with Sherline steppers
Visual Mill 6.0 Standard
Mach3
Windows XP
Re: Motion controllers - Take me to school
« Reply #1 on: August 29, 2017, 03:04:05 PM »
Hi,
I'm guessing that your existing arrangement is one large board with three stepper drivers  and a LPT interface?

To run separate drivers as you are proposing would require a breakout board. It job is to interface with the computer and provide some protection
for it so that whatever you hook up to it can't wreck your PC. Then two wires (signals) from the breakout board would go to each of your drivers.
In this situation the PC is still the 'motion controller' normally called a parallel port. You could use a separate motion controller if you wish but you
don't have to.

Is there a reason you wish to go for closed loop steppers?. When all said and done they are still steppers, they can't go any faster or magically get more
grunt by running with a closed loop drive irrespective of the advertising hype. If your existing steppers are prone to losing steps then closed loop drivers
can correct that by inserting extra steps to make up for the ones the stepper couldn't quite make. You are paying a premium when for just a little bit
more you could have genuine AC servos with all the speed advantages they bring. If your existing steppers don't lose steps then why bother with closed loop?

Craig
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Offline ger21

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Re: Motion controllers - Take me to school
« Reply #2 on: August 29, 2017, 08:58:13 PM »
The stepper drives are separate from the motion controller.

Steppers are powered and controlled by the stepper drives, whether open or closed loop. The difference with closed loop is that the encoder signals go back to the drive.

Both types accept step and direction commands from Mach3, and as far as Mach3 is concerned, there is no difference.

Mach3 normally generates the step and direction pulses in software, and sends them out through the parallel port. For a variety of reasons, you can opt to use an external motion controller and not use the parallel port. In that case, Mach3 sends signals to the motion controller, and the motion controller generates and sends the step/direction pulses to the drives. Motion controllers can be either USB or ethernet, but ethernet is usually preferred.
Gerry

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Offline sn96

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Re: Motion controllers - Take me to school
« Reply #3 on: August 29, 2017, 09:05:58 PM »
Thanks for the information. I misunderstood what closed loop was then. I thought by adding an encoder you are creating stepper/servo with resolution dependent on the encoder used. My interest is to upgrade to servos perhaps ac servos. I woukd like to use servos and have mach3 communicate to a servo driver board that sends signals to the servo controller cards. I really dont know what Im doing. I just would like to use more modern computers because the old stuff is just not reliable. I bought an old dell desktop tp replace and old compaq deaktop and the new/old dell is starting to act up. Im kind of tired of the old junk and I dont want to buy yet another OLD desktop to run my mill.

Id like to run AC Servos using windows 7 or higher but dont know what I need to learn.
________________
Mike

Sherline 5400 with Sherline steppers
Visual Mill 6.0 Standard
Mach3
Windows XP
Re: Motion controllers - Take me to school
« Reply #4 on: August 29, 2017, 09:21:00 PM »
Hi,
in broad terms you are correct but the finest resolution that can be achieved by a stepper remains the same.
The closed loop part means it correct its own errors.

AC servos on the other hand can offer greater resolution and speed but at a price. If you wish to get best resolution
at max speed then the humble parallel port may not be fast enuf for your purposes. In that case an external motion
controller is indicated, for instance and incidentally my perference is the Ethernet Smoothstepper by Warp9.

Whether you run Win7,XP or Win8 or 10 32 or 64 bit is immaterial to Mach if you are using an external controller.
I run a dual core Atom single board computer for my machine controller, hardly enuf computing power to get out of its
own way, but it works fine and is of course new. With an external controller using new PCs is well in order.

Craig

https://warp9td.com/
My wife left with my best friend...
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Re: Motion controllers - Take me to school
« Reply #5 on: August 30, 2017, 01:02:52 AM »
What do you expect AC servos to do that you can't do with steppers? My homebuilt with THK linear rails and ball screws will rapid or cut at 300 ipm and never misses a step. I have a USB motion board, 906 oz/in motors, 68 volt power supply and 80 volt digital stepper drives. Do you need higher performance than that? Is you machine stiff enough to handle higher speeds?
Re: Motion controllers - Take me to school
« Reply #6 on: August 30, 2017, 04:03:12 AM »
Hi,
garyhlucas  poses a very good question.

My own machine is probably even smaller than your Sherline, the X,Y,Z is 200mm/200mm/200mm. I use 5 phase Vexta steppers with low backlash
(less than 3 arc min)  10:1 planetary gearboxs. The gear reduction means they have heaps of thrust and great resolution (1um) but are slow,
G0s are 1200mm/min (60in/min). Given the size of the machine I don't really consider the slow rapids to be too much of a disadvantage.
Like garyhlucas my steppers never miss a beat either. If I replaced them with something faster I might be able to use some of the High Speed Machining
tooplaths talked up by all the major CAM manufacturers but that's about it. That's a lot of money to spend to achieve so little. Might make more sense
if this were a production machine but it isn't and will never be a production machine.

I have started to buy up components to speed up my machine... 34 size 5 phase steppers from Vexta at 900 oz.in. If I were to use half steps, entirely adequate
with the smoothness of 5 phase steppers and drive the ballscrews directly without the gear reduction I would have a resolution of 5um, still adequate and
based on published performance curves G0s between 7500mm/min and 12500mm/min. Vexta steppers and drivers are expensive and don't come up that often,
given that the benefits are fairly limited I've become quite tepid about shelling out all those bucks when they do come up!

I did however need a decent high torque spindle for machining steels and did get around to spending $1500 or so on the parts to make one, it does get
used and represents a better use of my budget than faster steppers/servos. Yes garyhlucuas raises a very interesting question, do you really need to improve
on what you already have?.

Craig
My wife left with my best friend...
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Offline RICH

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Re: Motion controllers - Take me to school
« Reply #7 on: August 30, 2017, 06:59:16 AM »
Use the Sherline machines in the capacity of what they were meant to do.

I have both a Sherline mill and lathe. I did change the lathe steppers to get more torque.
They both work fine for small stuff. Also use the pp here.

I would not put more money into them.


RICH
« Last Edit: August 30, 2017, 07:02:47 AM by RICH »

Offline sn96

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Re: Motion controllers - Take me to school
« Reply #8 on: August 30, 2017, 02:03:13 PM »
All great points. It may not be worth the cost and certainly the Sherline platform is limited as to how hard you can push it. the advantages of AC servos with my thinking is speed, not cut speed, but speed regarding approach, plunge, and transfer all with improved resolution. This can dramatically improve run times. If I push steppers to fast they loose steps and sometimes not move at all... the dreaded ZZZZZ sound. Another advantage is to use the external hardware drivers which I know steppers have as well but steppers are just noisy and don't like to be pushed very fast, at least open loop anyway. Using driver boards seems to be the way to go for more modern computer options.

I also want to say more torque is not what I am after. All you need is enough torque to handle the maximum cut you would ever make anything more is overkill. More torque means more broken tools. There has been a few times my steppers stalled when taking to aggressive of a cut saving my endmill from breaking. Not so much the smaller endmills though.

I appreciate all the information and shared opinions. I will need to think about all this and see what is the best option for me personally.
________________
Mike

Sherline 5400 with Sherline steppers
Visual Mill 6.0 Standard
Mach3
Windows XP
Re: Motion controllers - Take me to school
« Reply #9 on: August 30, 2017, 03:16:00 PM »
Hi Mike,
yes you have some decisions to make.

Be aware that while steppers aren't great at speed they are very grunty when slow, in fact they beat the hell out of servos for torque of the same size.
You may find that to even come close to matching a steppers torque you have to buy a larger servo than you imagined. While you may be happy
enuf with lower thrust as a result of low torque you will absolutely miss the acceleration. Acceleration is way more important to cycle times than
high max speeds.

Given that this is a hobby sometimes you have to consider the fun/learning/satisfaction of doing a certain thing rather than its economic justification.
Having said that spending a big chunk of your budget on a certain project may well prevent you from taking on anther project that may have greater
value or applicability.
My wife left with my best friend...
     and I miss him!