Machsupport Forum
Mach Discussion => Mach4 General Discussion => Topic started by: Will_D on February 01, 2018, 08:58:38 AM
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I had settled on Mach4 and PMDX-416 motiion controller.
However PMDX told me that this combo doesn't support backlask correction "YET"!!
So what USB controllers support backlash compensation with M4?
bit baffling when you consider that Mach3 supported backlash correction all those years ago
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It IS listed in the Features here.....
https://warp9td.com/index.php/products
But, I would definitely verify it before purchasing.
If it IS supported now, it was a loooooonnnnng time coming.
Russ
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Hi,
as Russ has said the ESS has just recently added backlash support and it still has bugs. It cannot really be called mature yet. A new plugin build was due on Monday
but has bee delayed.
Make an enquiry of Vital Systems about their Hicon board, they consistently lead the pack when it comes to feature support. More costly units to be sure but they
enjoy a solid following.
Craig
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The HiCON is ethernet, but the backlash comp works very well on it. Using it on 3 machines at the shop.
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Hi,
when you consider that Mach3 supported backlash correction all those years ago
Backlash compensation is and always has been a feature offered by the motion controller not Mach either
3 or 4.
Craig
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Thanks Russ for the link to warp9 .
Looks like the Ethernet version is Mach 4 only and supports backlash.
Craig thanks for the info! Will check out Hicon and ESS
Lots to research here!
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Thanks Russ for the link to warp9 .
Looks like the Ethernet version is Mach 4 only and supports backlash.
Craig thanks for the info! Will check out Hicon and ESS
Lots to research here!
ESS works on Mach 3 and 4. I ran it on 3 with no problems...
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Hicon looks nice but it should do for the price $595 - EEK!!
Ess looks much more affordable, However: Backlash not fully working. Only controls 4 stepper drivers and it is recommended to buy a BOB as well! So $30 on a C25 BoB. Also no mention of spindle control? Would need another Bob for spindle. Also documentation I have read is VERY unclear as to how you assign and configure the various I/O ports!
Afaik: Mach3 did its own backlash compensation (I have seen videos) because it just sent signals out through a DB-25 connector. Mo motion controllers then.
So it is really looking like as another thread stated "Mach 4 is not really for hobbyists"!
Why do I say this:
1. Lack of money - we are all short of money hence the DiY CNC builds.
2. Home made / old machines NEED backlash compensation.
3. Mach3 was a one stop solution. PC /Mach3/Stepper drivers and limit switches. Mach 4 is anything but one stop shop!
Mach 4 seems to be targeted at high end OEM installs who are happy to spend (and pass on to customer) by specifying high end motion controllers/BoBs/etc etc
Surely Backlash is not that complex:
GetNextCoordinate(Coord, dirChange);
if dirChange
then
ApllyComp(Coord)
fi;
MakeMove(Coord);
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I had settled on Mach4 and PMDX-416 motiion controller.
However PMDX told me that this combo doesn't support backlask correction "YET"!!
Hey Will_D,
During your research, did you get a progress report/timeframe on the implementation of BC from the PMDx folks ?
Just wondering ... before making a direct inquiry.
Thanks for posting your results so far.
Regards,
Russ
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Hi Russ,
This from Steve at PMDX:
The PMDX SmartBOB family does not yet support backlash compensation.
We do intend to do so, but I cannot offer a schedule for it, so plan accordingly.
Regards,
Steve Stallings
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Thank you for sharing the info Will.
Much appreciated,
Russ
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If only it were that simple. Backlash compensation motion cannot happen in zero
time, so you have to figure out what to do with the other axes while the reversing
axis is making the compensation move, and then keep the system happy while
accomplishing this non-zero time event that was not planning for by Mach4.
Even if you can pull it off, this will only work if the only thing moving the machine
is the axis motors. If cutting forces react with the machine to cause motion
across the backlash distance where the axis motor cannot control where the machine
is positioned, then nothing the software can do will fix this. Likewise any pauses
inserted by the correction attempt will allow for the cutter to remove extra
material at that position while the forces stored in the springs of the elements
of the machine that have flexed will get the chance to relax during the pause as
the cutter removes material. This can result in divots or burn marks in the workpiece.
Backlash compensation can help in some cases, but it is no replacement for a properly
designed and built machine.
Surely Backlash is not that complex:
GetNextCoordinate(Coord, dirChange);
if dirChange
then
ApllyComp(Coord)
fi;
MakeMove(Coord);
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Hi Will,
Afaik: Mach3 did its own backlash compensation (I have seen videos) because it just sent signals out through a DB-25 connector. Mo motion controllers then
Incorrect, the motion controller was the parallel port driver. That motion controller is not a separate physical device like an ESS or PMDX SmartBoB but it is none the
less a motion controller, it has code and processing power to take the trajectory planned by Mach and produce pulse streams necessary to drive the motors.
There was a time when Mach3s PP couldn't do backlash compensation. Even when external motion controllers came along not all manufacturers had support for
backlash compensation. The situation is similar today with Mach4 manufacturers adding backlash compensation 'when they get around to it' rather than as a fundamental
function. As Steve points out adding backlash compensation is by no means trivial and there will always be shortcomings with it that no software can solve. He is not
unique in saying 'fix the backlash in your machine, software can't fix your sloppiness'.
Ess looks much more affordable, However: Backlash not fully working. Only controls 4 stepper drivers and it is recommended to buy a BOB as well! So $30 on a C25 BoB. Also no mention of spindle control? Would need another Bob for spindle. Also documentation I have read is VERY unclear as to how you assign and configure the various I/O ports!
1) Backlash compensation is not working perfectly at the moment, backlash compensation will never be perfect, a beta test version is being trialled at the moment
2) The ESS can control six coordinated axes and another six out-of-band axes WITHOUT counting slave axes
3) Yes you need a BoB, you can hook direct to the ESS but if your hamfisted you'll blow the FPGA and then have to buy another ESS. DON'T DO IT!! A BoB protects your ESS
4) The ESS plugin allows you to ascribe an alias to any pin and then assign that pin by name to a Mach signal. The ESS plugin will update Machs plugin to keep them
consistent.
5) Any output pin can be made to produce PWM. All that is required is an amplifier and filter circuit....if you make your own...one opamp, a couple of resistors and capacitors,
OR you can buy a BoB to do it for you.
Once you start adding a couple of BoBs and a power supply for the ESS it is the same or even more than a PMDX-424 which has its own supply and no BoB required
except for the spindle. PMDX have taken considerable effort to make their devices as easy as possible to use.
If backlash compensation is absolutely vital to you either wait a bit for the ESS or stump up the extra for a Hicon.
Craig
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Hicon looks nice but it should do for the price $595 - EEK!!
While it is not very prominent on their site they offer the Hiconn in a hobby version for ~$450 IIRC.
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Hi,
just had a look at the Vital Systems site and found:
Note: We now offer 7541 version only. 7544 version is now obselete bacause of lack of demand
So the slightly cheaper version is no longer available.
Craig
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So the slightly cheaper version is no longer available.
Because it was still to expensive for most hobbyists. :)
If you want a really good breakout board for the ESS, that includes VFD control, look at the MB2 from CNC Room.
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Thanks Ger, never saw them before.
Actually, the ESS/MB2 combo looks like a pretty good deal. Shipping from Thailand doesn't look so bad either.
I like that type of terminal, if they are of good quality.
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Hi,
just had a look at the Vital Systems site and found:
Note: We now offer 7541 version only. 7544 version is now obselete bacause of lack of demand
So the slightly cheaper version is no longer available.
Craig
Hi Craig,
Can you send me the link to that. I just went to http://www.vitalsystem.com/portal/store.php and added one to my shopping cart for $435.00 so as far as I can see they have not been dropped but it could be I am doing something wrong.
Mike
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Hi,
I found the quote on the MONTENC Lite page. I see the price for the cheaper device is still there at $495 but just above the price list was the note
about the availability of it.
http://www.vitalsystem.com/portal/motion/motenc/motenc_lite.php (http://www.vitalsystem.com/portal/motion/motenc/motenc_lite.php)
Craig
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Thanks Ger, never saw them before.
Actually, the ESS/MB2 combo looks like a pretty good deal. Shipping from Thailand doesn't look so bad either.
I like that type of terminal, if they are of good quality.
CNC Room breakout boards are very high quality. I was using an MB2 with my UC300ETH, until they made a dedicated board for the UC300ETH, the UB1.
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Hi,
I found the quote on the MONTENC Lite page. I see the price for the cheaper device is still there at $495 but just above the price list was the note
about the availability of it.
http://www.vitalsystem.com/portal/motion/motenc/motenc_lite.php (http://www.vitalsystem.com/portal/motion/motenc/motenc_lite.php)
Craig
I think you might be a little confused. The 7544 MOTENC-Lite PCI 4-Axis Board (8DAC, 4ENC, 0ADC, 48 I/O) is being dropped but that is a LinuxCNC compatible board that goes into a PCI slot.
The Integra-Hobby Motion Controller 4-Axis 125KHz is #7754 Whic is an Ethernet controller.
Mike
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Wow, thanks for saving me the expense and disappointment by creating this thread, this should be a sticky! I'm really glad I checked/clicked here as I was just about to order the same exact board with a Mach4 license.
When I saw the vendors/manufacturers listed on the Mach4 page I understandably assumed that they were the recommended boards that were fully compatible (and tested) with Mach4's features. In fact, the ONLY reason I was going the Mach4 route over the GRBL setup was because I wanted the backlash compensation. The search continues...
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In fact, the ONLY reason I was going the Mach4 route over the GRBL setup was because I wanted the backlash compensation.
This has been debated to death and in some cases backlash comp. can work. The problem is the 99.9% of the cases it wont work in. Backlash compensation on a control truly is an oxymoron. And in those cases it wont work in, this is not just my opinion it's a simple fact. Until someone finds a bit of software that can rewrite the laws of physics the only fix for backlash is removing the mechanical backlash.
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Absolutely right. Thinking you're going to take a Bridgeport with .015" backlash in the acme screws and comp it out with software is a fallacy. If that worked machine tools wouldn't need ground ways with scrapped Turcite, ball screws, pressure fed oiling systems. Just whack the machine together out of cold rolled, put a bunch of sensors on it, and comp the whole thing in software as it teeters along.
Take circular interpolation, the X is slowing down as it gets to the right or left side at which point the Y is going full tilt, when X hits the turn around point, what does the X do, jerk the .015 out? Even if some algorithm "eases" it out over time, you still don't have a circle!! And even if it jerks it out, it can't jerk it all out in 0 time while the Y is going full feed rate. 015" is just an exaggeration to make the point, but the same thing happens trying to comp .0015" out. It DOES sound good in the literature, tho'.
All these motion controller sellers spending all this time on Backlash Compensation when they could be spending time on real stuff.
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Thanks for the responses, however, I guess as a programmer and a novice machinist I'm not following the reasoning, and the fact that Mach3/4 has backlash compensation (as well as LinuxCNC and others) means it's something that can be adjusted to work. I've also seen folks who've upgraded from grbl to linuxcnc for this reason and were able to dial it in. Thinking through this for the very first movement you can drive the motor in the opposite direction by the compensation amount, then move it in the correct direction (again in the backlash compensation amount) at this point that axis is good to move until it changes direction (so it does the compensation routine again), no?
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Wish I had time to explain it all but I don't. It has been explained very well many, many times already. Here (on this forum) and other places.
But I can save you some time. Just reread my previous reply. It's been my job for 25 years to make machines produce good parts. thosj gave a real good real world example. If you have code that rewrites the laws of physics then please ignore my input. Otherwise backlash comp is a selling point most software and hardware manufacturers are pressured into implementing by customers that are certain it is an acceptable solution.
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Hi stoic,
have you tried 'conventional milling verses climb milling' in a machine with significant backlash?
The old Bridgeport copy at work has 0.2 inch backlash in X. If you try climb milling you will break something....I've done it myself and watched and tried to warn
a workmate from the same trap to no avail...he broke a new 16mm High Speed Steel tool, and that takes quite a bit of doing!
The only software that is going to help with backlash is the stuff that starts: 'Dear God'.... and ends in 'Amen'
Craig
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Hi stoic,
have you tried 'conventional milling verses climb milling' in a machine with significant backlash?
The old Bridgeport copy at work has 0.2 inch backlash in X. If you try climb milling you will break something....I've done it myself and watched and tried to warn
a workmate from the same trap to no avail...he broke a new 16mm High Speed Steel tool, and that takes quite a bit of doing!
The only software that is going to help with backlash is the stuff that starts: 'Dear God'.... and ends in 'Amen'
Craig
Nice one, Craig.
.2" of backlash, INCHES? Tell me that's a typo! :o Now THAT would be some software to comp THAT out, that's a full turn of the screw!!
Tom
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Exactly Craig. Programming strategy (when it can be used) is a far better approach to easing the pains of backlash than backlash compensation.
Lol, we had a bed mill once that the table had so much backlash in it you could see it wobble when changing directions (wish I had a video). We would tweak the program as necessary to comp for it and ran it several months till the new machine could get there. It made a lot of good parts in that time but what a pain it was to pull it off.
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So basically what you guys are saying is that Mach 3/4's as well as the few controller that have implemented backlash compensation is all smoke and mirrors to get the customers to buy into their hype? Glad I learned something new.
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Backlash compensation can be useful for work where the forces from the cutting tool will
not cause the machine to move across the backlash zone, and where pauses of one
axis while another is compensating will not leave divots or burn marks.
Drilling a pattern of holes is an example where backlash compensation usually works
out OK. Pick and place operations for a robot is another that can benefit.
General purpose milling gets into trouble because climb cutting may cause the table
to move due to cutting forces and there is nothing the control software can due to
prevent that.
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Hi,
Steve has made a very nice summary of those situations where backlash compensation can be benefical.
For a mill with high cutting forces its not going to help.
.2" of backlash, INCHES? Tell me that's a typo!
No its no typo....and yes at 0.25 inch per turn, its almost a complete turn. The brass yoke is that worn the remaining threads must be so thin they break out some day soon.
While from time to time I do give this machine some hard work mostly it sits a month between jobs. I work repairing welding equipment and we might use it for facing
or otherwise shaping some insulation or shaping copper electrodes for a spotwelder for instance.
Despite the backlash you can still do some pretty good and accurate work with it but it takes patience and practice. Software cant do it, I can, and I prefer
to call myself 'squishyware'.
Craig
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So basically what you guys are saying is that Mach 3/4's as well as the few controller that have implemented backlash compensation is all smoke and mirrors to get the customers to buy into their hype? Glad I learned something new.
If that is what you pulled out of it you need to pay more attention. Quit listening for what you want to hear and listen to what your being told.
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If that is what you pulled out of it you need to pay more attention. Quit listening for what you want to hear and listen to what your being told.
Or perhaps you need to get your message across in a way you mean it, which seems the below isn't:
The problem is the 99.9% of the cases it wont work in. Backlash compensation on a control truly is an oxymoron. And in those cases it wont work in, this is not just my opinion it's a simple fact. Until someone finds a bit of software that can rewrite the laws of physics the only fix for backlash is removing the mechanical backlash.
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Or perhaps you need to get your message across in a way you mean it, which seems the below isn't:
Well after saying the same thing over, and over, and over, and over, all these years, we sometimes try to change the way we reply so folks who can't get it get it. If at first we don't succeed we try, try again is our motto! ;)
RICH
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What does the quote button do on a post? Not a lot by the look of it. How do I quote a message?
Anyway BOT:
Quote Steve: "General purpose milling gets into trouble because climb cutting may cause the table
to move due to cutting forces and there is nothing the control software can due to
prevent that."
Agreed there is no way backlash compensation can compensate when climb milling.
Answer: Don't climb mill on a hobby machine with backlash. This is standard newbee instruction.
However conventional milling should be more like lathe work where BLC is an every day "do it by hand" operation.
Sure BLC in a cnc controller would work very well on a lathe.
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Hi Will,
you are correct....climb milling on ANY machine with significant backlash is a disaster waiting to happen.
What you are expecting of backlash compensation software is to replicate the same techniques that every competent machinist uses to achieve accurate
work in face of backlash. My experience is that computer software falls well behind an intelligent human operator....see my previous quip about 'squishyware'.
I think the way to proceed is to get a controller that has BLC and try it. I would caution you however that it MAY not be as good as you'd hoped and if that
proves to be the case you'll have to weather the 'I told you so'.
The quote button places two editing characters on your text input screen. Between these two characters you may paste a quote
previously saved to your clipboard.
Craig
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The quote button places two editing characters on your text input screen. Between these two characters you may paste a quote
previously saved to your clipboard.
Cheers Craig,
It didn't do that the other day though!!
Now it just quoted your whole message as I would expect - ah well at least something is working!
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Sure BLC in a cnc controller would work very well on a lathe
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Not really. If you want to do accurate work the heart of the machine, ball screws / bearings ,etc. must be as good as one can provide. Just as Brett has replied. I used BC on mills and lathes and it helped, BUT, the accuracy will never be consistant.Note that every machine has some non-movement it's just a matter of degree. No one will ever convince me that BC will work just as good a mechanicaly correct machine.
I do think that BC has a place to improve the preformance of many hobby machines. Many users are not going to spend the money for quality components or machines. That is fine, BUT, they need to keep use of BC in perspective.
RICH
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The quote button places two editing characters on your text input screen. Between these two characters you may paste a quote
previously saved to your clipboard.
The quote button places two editing characters on your text input screen. Between these two characters you may paste a quote
previously saved to your clipboard.
Cheers Craig,
It didn't do that the other day though!!
Now it just quoted your whole message as I would expect - ah well at least something is working!
There are a couple of ways to insert quotes into post. They both work now and were the other day as well. Just below the search box there is a help button. It may help. Just because you don't know how something works doesn't mean it's broke. ;)
Very true Rich.
No one will ever convince me that BC will work just as good a mechanically correct machine.
No and no one should waste their time trying to convince you or anyone else. It's simple physics and it doesn't take a rocket surgeon to understand it. They just need a little common sense and understanding of what backlash is.
Lots of controls backlash compensation works as good as is physically possible. But most often it will not be an acceptable solution. In the very few cases it will give acceptable results it could also be fixed with programming strategy.
So, in a nut shell, if you can write your programs to overcome the backlash of the machine and produce acceptable parts backlash comp. may be a feature you want to consider. Otherwise the only fix is to fix the backlash. It really is that simple. Anything else is a waste of your time and everyone's time that tries to help you.
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I agree - it is always best to remove backlash. That being said - bc does work decently well.
this is 2 circles - one with bc off and one with bc on. can you see the difference?