Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: sn96 on August 29, 2017, 02:33:05 PM
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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.
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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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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.
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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.
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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/ (https://warp9td.com/)
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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?
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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
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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
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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.
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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.
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the advantages of AC servos with my thinking is speed, not cut speed, but speed regarding approach, plunge, and transfer all with improved resolution.
You probably already have all the resolution your Sherline can handle.
And you can get plenty of speed out of steppers, with the right steppers, drives and power supply voltage.
Get some Leadshine AM882's from Ebay, and some low inductance, high current steppers, and you'll get all the speed and power you need. And they'll run smoother, cooler and quieter than what you have.
I also want to say more torque is not what I am after.
You can't get more speed without more torque. Generally, acceleration requires more torque than cutting does.
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.
You can't push a closed loop stepper any faster than an open loop stepper. When an open loop stepper runs out of torque, it stalls. When a closed loop stepper runs out of torque, the drive will fault. There's no magical power reserve to kick in when it loses position.
And I think you are confusing drives and motion controllers.
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Hi Mike,
you have some very good advice from some seriously experienced CNCers. It would appear that they all agree your machine could be maximised
by the right steppers/supply and drivers without the expense of either servos or hybrid closed loop steppers. My own modest experience with open loop
steppers is consistent with what they are saying also.
One thing you did comment on in an earlier post was that the old PCs you have been using for a parallel port controlled machine have been unreliable
and you wish to do better.
If you were to use an external motion controller then your choice of PC is much much broader and new and reliable PCs come into their own.
Because your existing control unit is integrated to use a separate controller will require that you use separate drives for your steppers, but you had
already come to that conclusion and were not phased about making the investment. If you were to buy three good quality drivers, say 80V and 7-8A
capable you could, in the first instance, continue to use your existing power supply and steppers. It maybe that just by improving the drivers that your existing
steppers now behave acceptably. If not you can upgrade the power supply and/or the individual steppers until you have achieved the level of performance
you are after. The advantage of this approach is that its progressive. You will have to stump up for an external controller, probably a breakout board or two
and three stepper drivers initially. Thereafter you can spread your purchases to suit.
I'm not familiar with the AM882 that ger21 recommended but guess they are similar to Gecko drivers, that is to say 80V 7A capable and quality/reliable build.
They can be had for about $150 each. There are a few choices of motion controller in the 'cost effective' end of the market, the ESS among them at $180.
Add a breakout board for $50 say...a total initial investment of $680.
Craig
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Actually, AM882's typically run about $75 each on Ebay, and I've got them for as low as $58 each.
The downside is they are unsupported, as they are I believe intended to be sold to the chinese market only. But yes, they are comparable to Gecko G201's, and some would argue that they are better.
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Hi ger21,
at $75 makes them very attractive, would save OP $225 on my scratch budget.
For whatever reason the Leadshine website times out when I try to browse.
Craig
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The AM882 is excellent. I have 5 running from an ESS, flawlessly. hey have an auto setup for getting a baseline, and a free software tuner for the finer stuff.
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I have Leadshine as well, no problems at all.
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I was looking at Clear Path servos and I'm impressed with the technology. They are very expensive servos but you get what you pay for. I don't think I would buy these for a Sherline mill, but I have discovered you can use these in-place of Sherline steppers. The SD series servos will accept step and direction signals with ease.
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Hi Mike,
very nice albeit expensive solution.
Most if not all modern servo drives accept step/dir inputs. If you really want a servo solution there are lots to chose from
ranging from expensive upwards!
Have you seriously questioned whether a stepper motor solution can achieve what you want?
Craig
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The biggest benefit the Clearpaths have, is that they are drop in replacements for steppers.
AC servos tend to be more powerful, and in many cases less expensive. But the frame sizes don't match steppers, so they are not quite as easy to implement on a stepper machine.
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Hi Mike,
very nice albeit expensive solution.
Most if not all modern servo drives accept step/dir inputs. If you really want a servo solution there are lots to chose from
ranging from expensive upwards!
Have you seriously questioned whether a stepper motor solution can achieve what you want?
Craig
Yes I have thought about using different steppers but the speed and quietness of ac servos is very enticing to me. At my work I run an electronics probing machine that uses ac servos and it is never boring to watch it zip around stopping with in +/- 3 microns at each x/y location.
for under 2k you can have an awesome servo configuration. I paid 1k for a basic Sherline stepper system so as far as cost goes in comparison, its rather insignificant considering the performance gain.
I found drop in replacements for $270 each they are nema 23's with a 1/4" shaft the same as sherline steppers. A controller card would be needed And I found one for 159.90 os for approx $970 you can have a 3 axis ac servo system that connects via any pc using an Ethernet port.
Here's the links:
Motion card:
http://www.ebay.com/itm/like/172287858504?chn=ps&dispItem=1
Servos:
https://www.teknic.com/model-info/CPM-SDSK-2311S-RQN/
Video:
https://youtu.be/-gigcf7ZzAQ
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Do NOT buy a chinese motion controller, unless you want partial functionality, and no support.
I paid 1k for a basic Sherline stepper system so as far as cost goes in comparison, its rather insignificant considering the performance gain.
You can probably put together a stepper system for half that, that performs twice as well.
A $2K upgrade on a sherline that does little more than reducing noise is crazy, but that's just my opinion. ;)
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In this image, just one piece takes 8 hrs to complete. Much of the time is wasted in position transfers. I'm ok if you call me crazy, nuts, whack-o... for wanting to not buy, but to look into and research the possibilities outside conventional steppers. I've been using steppers for 3 years, and if I'm ready to upgrade I have many options to choose from. If speed, quietness and step accuracy are important factors to me, then the value relates to what is important to the end user. No? ???
Point taken about Chinese products. We agree there.
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Hi,
if you want to spend that sort of gold on servos but the save $10 buying a Chinese motion controller?
Some research on the forum will reveal hundreds if not thousands of posts about Chinese controllers and the battle people have had trying to
get them to work. Even if they succeed features we regard as standard fare like probing often don't work. China might as well be a different planet
when it comes manufacturers support.
In the 'value' end of the market
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Hi,
to continue...the value end of the market..
https://warp9td.com/ (https://warp9td.com/) the ESS recommended
https://www.pmdx.com/ (https://www.pmdx.com/) the 411 for simplicity and price the 424 for increased functionality
https://www.poscope.com/products/pokeys-devices/ (https://www.poscope.com/products/pokeys-devices/) the 57CNCd25 for simplicity and price the E57 or E57CNC for functionality
http://www.cncdrive.com/ (http://www.cncdrive.com/) have useful product, the simple and cheap UC100 is Mach4 capable, the larger and more functional products are Mach3 capable only
http://www.vitalsystem.com/portal/index.php (http://www.vitalsystem.com/portal/index.php) have a superb reputation but useful solution start at $600.
You may note that all of the recommendations I've made are Mach4 capable which is also my recommendation. The list might be somewhat longer for good Mach3 only
products like
http://en.cs-lab.eu/ (http://en.cs-lab.eu/)
http://dynomotion.com/KFLOP.html (http://dynomotion.com/KFLOP.html)
Craig
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Hi,
to continue...the value end of the market..
https://warp9td.com/ (https://warp9td.com/) the ESS recommended
https://www.pmdx.com/ (https://www.pmdx.com/) the 411 for simplicity and price the 424 for increased functionality
https://www.poscope.com/products/pokeys-devices/ (https://www.poscope.com/products/pokeys-devices/) the 57CNCd25 for simplicity and price the E57 or E57CNC for functionality
http://www.cncdrive.com/ (http://www.cncdrive.com/) have useful product, the simple and cheap UC100 is Mach4 capable, the larger and more functional products are Mach3 capable only
http://www.vitalsystem.com/portal/index.php (http://www.vitalsystem.com/portal/index.php) have a superb reputation but useful solution start at $600.
You may note that all of the recommendations I've made are Mach4 capable which is also my recommendation. The list might be somewhat longer for good Mach3 only
products like
http://en.cs-lab.eu/ (http://en.cs-lab.eu/)
http://dynomotion.com/KFLOP.html (http://dynomotion.com/KFLOP.html)
Craig
Thanks for those links. I like the Model PMDX-340 that was in the second link you provided.
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Hi,
the 340 is NOT a motion controller it is a boxed parallel input breakout board.
You need either the 411 as a single port output controller or the 424 which has two effective ports worth of IO.
Craig
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http://www.cncdrive.com/ have useful product, the simple and cheap UC100 is Mach4 capable, the larger and more functional products are Mach3 capable only
They now also have a Mach4 plug for the UC300ETH. The UC400ETH plugin will probably follow.
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Hi ger21,
kool, that's good to know. I think we are well served by our long term suppliers with Mach4 ready products.
Craig
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Hi Mike,
I notice the servo you are looking at has rated torque of 58 oz.in. Seems very wimpy to me...don't under do it...you'll regret it each time the servo
faults. When a stepper gets pushed it gets hot, starts making noises, push a bit more its starts losing steps and then stalls. An under specified servo
gets hot, starts making noises, push a bit harder and the drive faults 'following error'. If a servo can't keep up and lags behind where its supposed to
be by 20 (programmable) encoder counts it faults out and usually E-stops the machine.
While cutting forces can prevent a servo from keeping up it much more likely because it can't accelerate fast enuf to follow the trajectory you have set it.
Torque= J(moment of inertia) x dW/dt (angular acceleration).... that is without torque there is little or no acceleration and so it will take forever to get to
any speed.
May I suggest an experiment. You say that the Gcode job to machine the item pictured takes several hours to run. Have you tried the 'Simulate Program
Run' button on the toolpath tab? I use it a bit and find it accurate enuf for most purposes. Here's the experiment....edit your motor tuning as if your steppers
can go twice as fast but leaving everything else the same and <Simulate Program Run>, how much did your cycle time improve? Now go back and edit
your motor tuning with your regular speed but double the acceleration setting on all the steppers and <Simulate Program Run>, how much did your cycle
time improve.
There have been a number of posts that talk about the relative merits of speed verses acceleration and most of us vastly underestimate the acceleration
required to achieve fast cycle times.
While my mill is homemade it is cast iron and steel probably not dissimilar to your machine in terms of weight. With the gearboxes on the steppers I have
rated torque of 705 oz.in. I have settled for 0.3g for acceleration, the steppers can handle better than 1g but the whole machine rocks around and has to be
bolted down. I can't help but think 58 oz.in sounds too low.
Craig
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If speed, quietness and step accuracy are important factors to me, then the value relates to what is important to the end user. No?
It's your money so do as you wish with it,BUT, when asking for advice realy consider what is being said.
Step Accuracy - testing we did with steppers counting steps / pulses ( ie;simutaneous recording of 6 inputs for comaprison with a measurement accuracy of 29 ppm ) showed that actual steps / pulses sent at various points along the system could for all practical purposes be spot on through the system if the system is capable of it.
Heck my engraving machines smallest actual move is 0.000040 but is limited to 7 ipm!
Yes step accuracy is important as it relates to theoretical resolution but actual accuracy
of the system comes from the mechanical components.
In 2.5 / 3d machining acceleration is very important (more so than velocity) and even if the actual material removal is small, fast acceleration ( which requires torque ) provides for reliable movement of small axis moves.
Hmm......, spend your money so you feel good, let us know how all goes! ;D
RICH
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Hmm......, spend your money so you feel good, let us know how all goes! ;D RICH
LOL you so silly. I get it... I get it. You hate the idea of servos put on a small machine where steppers would work just fine. Still doesn't change my fascination about the crazy speed and performance of AC servos.
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Hi Mike,
I notice the servo you are looking at has rated torque of 58 oz.in. Seems very wimpy to me...don't under do it...you'll regret it each time the servo
faults. Craig
I saw the max torque was 200+ oz.in. but I see that it's short burst acceleration, and that the 50+ oz.in is continuous. There are other models that have the max/continuous torqe in a more usable range.
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There are not many options in the nema 23 form factor with a high torque much more than 90oz in in a 1/4" shaft configuration. There are two ratings: one is peak torque that the motor can deliver for a short period of time, say like overcoming sticky ways as an example, and the continuous rating is how much torque it can provide continuously if you try to grip it with your hands. Steppers would just go into a "ZZZzzzzZZ" after max stall was applied, were as the ac servo would constantly try to turn the shaft with 90oz in of force even if the motor is fully stalled. This is how I understand it anyway.
The largest nema 23 servo in a 1/4" shaft with the largest torque is this one:
https://www.teknic.com/model-info/CPM-SDSK-2321S-RQN/
Also what is neat about these servos are the built in driver boards. All you need is a pc with a BOB USB or Ethernet, and wire step and direction outputs directly to the servos.
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were as the ac servo would constantly try to turn the shaft with 90oz in of force even if the motor is fully stalled.
No, the drive will fault once it gets a certain amount out of position.
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Hi Mike,
the most powerful 23 size from Clearpath is in the HP series CPM-SDHP-2341S-ELN, 165 oz.in but to get it they
had to drop the rpm back to 1680 rpm and up the price to $631.00
At slow speeds steppers produce a lot of torque, better, considerably better than a servo of the same size. At high speeds
the servo comes into its own but that won't matter a damn if the servo can't accelerate fast enuf to stay within its
following window and it fault out.
If you're really keen on servos you will probably need to go up to 34 size units.
The cheaper alternative is low inductance, high torque steppers with a decent high voltage drive, 68V or better.
On the basis of my previous post I would recommend a continuous torque of at least half my steppers/gearbox,ie
350 oz.in
Keep looking, keep talking, keep comparing, all of these are free, its too bloody late when you've just dropped a grand on the
wrong thing!
Craig
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Hi Mike,
ger21 is right. My servo is set with a following error of 20 encoder counts. It is an 8000 ppr encoder so 20 counts equates to 0.9 degrees, a half-step
of a two phase stepper.
I can set the following error window to be smaller, 4 counts I think is minimum, but then I have to slow everything down otherwise the drive faults out
all the time. I can likewise increase the following error but then there could be a noticeable inaccuracy between where I wanted the part cut and where it
actually gets cut, on the other hand you can push the speed up without running foul of following errors.
Craig
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I get it. You hate the idea of servos put on a small machine where steppers would work just fine
Not realy....do / buy whatever you want.
Our thinking is different.
Your learning and many replies are servo / stepper application.
So continue learning and take into consideration posted replies.
I would suggest that you just take a moment and define what you want out of the Sherline.
1. Max axis velocity for rapids
2. Max feed rate which will be required to accomplish the machining for whatever tooling and
material you will use.
3. Required acceleration
4. Accuracy and repeatability of the axes.
5. Then review the machine and answer this question:
Is the current machine ( basic and all components) acceptable to do 1. to 4. above as is, with
with steppers, with servos?
Have fun in school,
RICH
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I appreciate all shared information from all of you. I am learning there is definetly more than what meets the eye. Ill reply more later. Im at work.
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Hi Mike,
just been scanning around some of the other servo manufacturers and commonly a 400W servo has a rated torque of 1.27Nm which is equivalent to
160 oz.in. A 400W servo seems ridiculously large on Sherline mill.
My mill having gearboxes and so on is unusual and so my recommendation may likewise be way off as well. Do you have a specification for the torque of
the existing Sherline steppers? You know they work so you might say just double the torque and say 'now it'll work better'.
Craig
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I have a new 400w servo at home. It's slightly larger than a 570oz nema 23 motor. And probably 10x more powerful, if used properly. The servo has 160oz continuos torque at up to 3000 rpm, and still about 100oz in at over 4000 rpm.
The 570oz stepper is down to about 160oz of torque at about 800-1000 rpm. If you use a 4:1 gear reduction, the servo has 4x the torque of the stepper. But the servo's peak torque rating is almost 3x higher, so when acceleration up to speed, you then have over 10x the torque of the stepper, in a similar size package.
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Hi Ger21,
sounds like OP is talking about direct connection between the servo and lead screw.
Do you think that 160 oz.in is adequate in absence of that reduction?.
The reducing gearboxes on my steppers have spoiled me, I have 705 oz.in at low speed, more than sufficient.
The torque curve published by Vexta suggest that the torque has dropped to about 175 oz.in at rapids speed,
the Vexta drivers have 150V open circuit!
My suggestion to OP was 350 oz.in ...do you think that's over the top?
Craig
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I would think that a 400w servo is overkill for his machine, even direct drive. Remember, peak torque is near 500oz. And I think those machines have 20tpi screws, so you have a large mechanical advantage.
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Hi ger21,
yeah, 20tpi is mighty fine, should have any amount of thrust/accel.
I don't want to make a recommendation to him that would see him spend untold bucks without cause.
Craig
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Hi,
does anyone know what diameter the lead screws are. I know THK recommend no more than 2500 rpm for my 20mm
ground ballscrews with 300mm unsupported. All the manufacturers seem to have a similiar spec depending on diameter
and unsupported length.
I'm thinking if the Sherline lead screws are smallish in diameter Mike may not be able to spin them really fast anyway.
Craig
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Hey guys,
The "threaded" lead screws are 1/4-20.........
Check out how expensive good small accurate ball screws are!
So I echo #5 from my post:
Is the current machine ( basic and all components) acceptable to do 1. to 4. above as is, with with steppers, with servos?
But #5 is useless without defining the first four steps. ;)
RICH
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Hi,
bloody hell, try to spin those things at speed and they'll whip themselves to shreds. Much more than 1 ft.lb
or 200 oz.in is likely to see them twist up like a carrot.
I think the OP may be on a hiding to nothing trying to get this machine to go fast.
Craig
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Hi Mike,
just been scanning around some of the other servo manufacturers and commonly a 400W servo has a rated torque of 1.27Nm which is equivalent to
160 oz.in. A 400W servo seems ridiculously large on Sherline mill.
My mill having gearboxes and so on is unusual and so my recommendation may likewise be way off as well. Do you have a specification for the torque of
the existing Sherline steppers? You know they work so you might say just double the torque and say 'now it'll work better'.
Craig
I believe these are the current specs. of my Sherline steppers:
Frame size: NEMA #23
Shaft: 1/4″ diameter, dual
shafts
Torque: 100+ oz. in.
Voltage: 3.2 V.
Current: 2 A
Step Angle: 1.8° (200
steps/rev)
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Hi,
bloody hell, try to spin those things at speed and they'll whip themselves to shreds. Much more than 1 ft.lb
or 200 oz.in is likely to see them twist up like a carrot.
I think the OP may be on a hiding to nothing trying to get this machine to go fast.
Craig
No... just looking at different systems and yes more speed/performance for my machine is always welcome in my opinion. Is it practical or economical for a small beginner machine such as the Sherline? probably not, but if all I am ever going to make are small parts and if I want to spend any kind of money to improve my existing machine, why not look at other options? I don't understand the harm in that. I haven't spent a penny yet, and wont until I look at whats required, cost, and benefits (Things that are important to me). If a comprehensive servo solution is a few hundred dollars more than conventional steppers, then there may be something to consider... plausible.
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Hey guys,
The "threaded" lead screws are 1/4-20.........
Check out how expensive good small accurate ball screws are!
So I echo #5 from my post:
Is the current machine ( basic and all components) acceptable to do 1. to 4. above as is, with with steppers, with servos?
But #5 is useless without defining the first four steps. ;)
RICH
Ding Ding! Schools in! I'm at my desk teacher Richy!
Shoots hand up in the air:
"Whats your opinion on closed loop steppers?" :D
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Hi Mike,
whether you use ordinary steppers, closed loop steppers or servos is not that important, any of these devices can do the job.
If ger21 is correct that your lead screws are 1/4 diameter then the speed at which you can rotate them before resonance is limited,
additionally they will flex torsionally for a loss of accuracy and if you up the torque the problem gets worse.
Look at your machine and see if you cant replace those lead screws with, ideally ground ball screws (really really expensive),or
rolled screws. Ebay has zillions of them, go for 16mm ones if you can get them to fit. They typically have a pitch of 4,5 or 6mm
so to spin them at 1000 rpm means rapids of 4m, 5m or 6m per minute, very useful.
If it proves impossible to replace your existing lead screws then significantly increasing the speed of your machine will be limited.
Under those circumstances better specified but otherwise standard steppers with decent drivers and a 68V+ power supply would easily
provide an increase in speed up to the resonance limit of the machine whilst conserving you budget. You could certainly achieve similar
results with servos say, they would cost a lot more and you will still only be able to turn up the wick to the limit imposed by the
mechanics of your machine not the capability of the servos.
Craig
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"Whats your opinion on closed loop steppers?" :)
Teacher responds:
That is a very good question Grasshopper, but, since you didn't do the homework ( reply #36) like all the other students did, go sit in the corner of the cave with your candle and envision $400 + for one ball screw, the whipping of the existing screw at 30 ipm, not being able to hold tolerances because the existing wimpy screw may have antibacklash nuts that need constant adjustment.
Now go sit in the corner and think about it all....and remember Grasshopper:
You can have anything off the shelf your heart desires but once you choose it
you must pay for it. Some times that which one envisioins may not be a complete truth. ::)
;D
RICH
-
"Whats your opinion on closed loop steppers?" :)
Teacher responds:
That is a very good question Grasshopper, but, since you didn't do the homework ( reply #36) like all the other students did, go sit in the corner of the cave with your candle and envision $400 + for one ball screw, the whipping of the existing screw at 30 ipm, not being able to hold tolerances because the existing wimpy screw may have antibacklash nuts that need constant adjustment.
Now go sit in the corner and think about it all....and remember Grasshopper:
You can have anything off the shelf your heart desires but once you choose it
you must pay for it. Some times that which one envisioins may not be a complete truth. ::)
;D
RICH
But but but.... Ok, ill go sit in the corner. :D
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Hi Mike,
whether you use ordinary steppers, closed loop steppers or servos is not that important, any of these devices can do the job.
If ger21 is correct that your lead screws are 1/4 diameter then the speed at which you can rotate them before resonance is limited,
additionally they will flex torsionally for a loss of accuracy and if you up the torque the problem gets worse.
Look at your machine and see if you cant replace those lead screws with, ideally ground ball screws (really really expensive),or
rolled screws. Ebay has zillions of them, go for 16mm ones if you can get them to fit. They typically have a pitch of 4,5 or 6mm
so to spin them at 1000 rpm means rapids of 4m, 5m or 6m per minute, very useful.
If it proves impossible to replace your existing lead screws then significantly increasing the speed of your machine will be limited.
Under those circumstances better specified but otherwise standard steppers with decent drivers and a 68V+ power supply would easily
provide an increase in speed up to the resonance limit of the machine whilst conserving you budget. You could certainly achieve similar
results with servos say, they would cost a lot more and you will still only be able to turn up the wick to the limit imposed by the
mechanics of your machine not the capability of the servos.
Craig
Thanks very much for the information. Yes, I never intended to go full bore with the servos because of the limitations of the machine. I only wanted to be able to have quiet motors that can swiftly do rapids (within limitations of the machine of course) without loosing steps. I think after all the input from everyone, steppers are going to be the best option in this case. I guess I will just have to endure the "wrrreeeeerrrr" noise and settle for steppers. I really don't want to go so far as to replace ball screws. Id would then consider a different machine in that case which already has ball screws like the X2 or something like that. it was my thinking that if I am going to spend close to a grand in new steppers, driver boards, and a BOB, it was worth looking into servos for a bit more money and take advantage of more speed and quiet operation. Apparently the design of my machine simply will not allow any justifiable benefit from using servos. So I have decided to do nothing and just keep my mill the way it is. For everyone who was patient enough to put up with me, I really appreciate the knowledge that was shared.
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Hi Mike,
seems like you've concluded that the mechanical limitations of your machine make it impractical to markedly increase its performance.
Without replacing the lead screws I tend to agree.
At the end of last year I started using an external controller, an ESS. Amongst the things I have noted is that my steppers are not as noisy,
or rather that the noise is very much less harsh. Also its possible to push them somewhat harder to accelerations and speeds which would
have caused a stall with the parallel port. These are consistent with improved pulse stream timing available from a dedicated controller
rather than your PCs CPU which has hundreds of tasks on the go at any one time.
An external controller may be a worthwhile improvement to your machine, in your case it means a controller, a BoB and either a combo
or individual drivers, not an insignificant investment. If they are chosen wisely however you will certainly be able to reuse them in your next
machine, and your post suggests you are thinking about it,... have you told your wife? I suspect with decent high voltage drivers and supply
your existing steppers will surprise you.
Craig
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I've found that my motors running on an AM882 drive at 1/16 microstepping are pretty quiet, when they are not spinning at full speed.