Re: [Emc-users] BeagleBone and LinuxCNC for a lathe.
So I've done a little more investigation all without spending any money yet. The Probotix web site links to the wiki which points to the MachineKit LinuxCNC for the BBB. I downloaded the 8GB image and installed it on a MicroSD card. Stuck it in a Rev B (2GB FLASH) BBB and booted. It shows up as 192.168.0.124 on my network and after a few hours struggling to get Xming working I now have the following up and running. http://www.autoartisans.com/cnc/PBX_BB_Xming.jpg Clearly it's been configured for the Probotix BB Cape. And there's no input set up for a spindle sensor. This is really a Mill or Rapid Prototyper configuration. The previous MachineKit I installed wasn't that much different. Forgetting for the moment a controllable speed spindle and just going for a single pulse per rev spindle sensor where would I begin to set up this system to run a lathe? I have to use X and Z for the cross slide and lead screw respectively. That leaves the pins for Y and A. There are limit inputs for ESTOP, XYZ A for limits. I almost wonder if there should be a book called Beagle Board MachineKit Linux CNC for Dummies with Windows 7. John Dammeyer -- ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
Re: [Emc-users] BeagleBone and LinuxCNC for a lathe.
I did exactly that with a BBB and Xylotex cape, using one of the unused limit inputs for a single pulse per rev sensor. You might want to follow the discussion on https://groups.google.com/forum/#!topic/machinekit/RW_bnXdXzyE (you'll have to read up to the end). You need a little familiarity with redirecting the input pins of the BBB to the hardware encoder (eqep) on the BBB processor, and in case of the Xylotex cape, I had to remove the large capacitor of the input RC-circuit because it smears out the pulses too much. The eqep encoders are fully supported in the present machinekit images for BBB. I did successfully manage to do threading on a small lathe with that contraption. Cheers, Karl Am 13.08.2015 um 10:07 schrieb John Dammeyer: Forgetting for the moment a controllable speed spindle and just going for a single pulse per rev spindle sensor where would I begin to set up this system to run a lathe? I have to use X and Z for the cross slide and lead screw respectively. That leaves the pins for Y and A. There are limit inputs for ESTOP, XYZ A for limits. -- ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
Re: [Emc-users] BeagleBone and LinuxCNC for a lathe.
Hi John; I've a small Unimat SL that I've CNC'd (and talked about it at the last CNCWorkShop back in June, and in my blog) Some random thoughts: 1) Beaglebone is fine. Sure, graphics is slow, but so what? Change Axis to the DRO display and you are fine. That's what I thought too 2) My OLD Unimat has a not so great spindle, which is a bit of a problem. And an old motor, which is very weak. 3) Currently, I have no spindle feedback for threading. It's unlikely you can thread with a weak spindle. I found with the ELS that the best place to put money into a lathe for doing that wasn't on a multi-line encoder but instead on a stable spindle motor.That's why the idea of using the stepper. A DC Servo is also an option and brings in a multi-line encoder for much better tracking. 4) Others have used stepper motors for spindle control on Unimats; one chap in Germany, and, maybe Cecil on this list? Be interested to see that. 5) I've a larger, stronger lathe (a big brother to the Unimat - an Emco Compact-8) that is my target lathe for CNC; not sure if I'm going to develop the Unimat further. I have a Gingery and a South Bend. The Gingery has full Z,X and Spindle control and can thread using the ELS. AS yet I've not added a cross slide motor to the taper fixture end of the X axis. I have the Xylotex cape, with the Beaglebone direct from them, pushing a Gecko G540. OK. I'll look at the Xylotex cape. Look at cnc-for-model-engineers.bogspot.com and top left corner is a search box, put Unimat in there. Maybe it'll give you some ideas. Thanks. That's a great suggestion and it turned up this below. http://cnc-for-model-engineers.blogspot.ca/search?q=unimat John John. -- ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
Re: [Emc-users] BeagleBone and LinuxCNC for a lathe.
On 8/12/2015 4:25 PM, Gene Heskett wrote: On Wednesday 12 August 2015 12:35:18 Dave Caroline wrote: Why stepper ? gearing up the speed with a pulley even less sense, they lose so much torque at a sensible lathe spindle speed that I cannot understand the reasoning for going down the wrong rabbit hole. Just think what would happen if your chatter frequency was anywhere near the stepper resonance too. I do use small lathes (watch (DC) and clockmaker (AC induction motor) sizes) and need to get the RPM up a lot for small stuff. Dave Caroline In re gearing up a stepper to get the desired rpms, I am 110% with Dave here. If you do not need the spindle to function as an angle lock at arbitrary angle, then IMO the servo approach beats the stepper by a wide margin. Very wide. Cheers, Gene Heskett For a small lathe I'd consider using a sewing machine motor. Google servo sewing machine motor If you can tie into the speed control, it might work fine. And the price can likely not be beat. Dave --- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus -- ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
Re: [Emc-users] BeagleBone and LinuxCNC for a lathe.
On 8/12/2015 6:22 AM, John Alexander Stewart wrote: 5) I've a larger, stronger lathe (a big brother to the Unimat - an Emco Compact-8) that is my target lathe for CNC; not sure if I'm going to develop the Unimat further. That's what the Denford ORAC was based on. Somewhere there's a forum thread with a full teardown of an ORAC. You *can* mill out the existing channel in the saddle for a ball screw, but it has to be a quite small one. That's why I decided to CNC my $50 JET 9x20 rather than try to get an ORAC - especially because I don't care for the way Denford did the cross slide. They cut about the back 1/3 off it and its stroke is limited, no way to mount rear tooling and a gang tooling plate would also be limited. I'm going to mount mine in tension to make it a bit stiffer. --- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus -- ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
Re: [Emc-users] BeagleBone and LinuxCNC for a lathe.
On Wednesday 12 August 2015 12:35:18 Dave Caroline wrote: Why stepper ? gearing up the speed with a pulley even less sense, they lose so much torque at a sensible lathe spindle speed that I cannot understand the reasoning for going down the wrong rabbit hole. Just think what would happen if your chatter frequency was anywhere near the stepper resonance too. I do use small lathes (watch (DC) and clockmaker (AC induction motor) sizes) and need to get the RPM up a lot for small stuff. Dave Caroline In re gearing up a stepper to get the desired rpms, I am 110% with Dave here. If you do not need the spindle to function as an angle lock at arbitrary angle, then IMO the servo approach beats the stepper by a wide margin. Very wide. Cheers, Gene Heskett -- There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order. -Ed Howdershelt (Author) Genes Web page http://geneslinuxbox.net:6309/gene -- ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
Re: [Emc-users] BeagleBone and LinuxCNC for a lathe.
John, If you are using a stepper at any significant revs, will there not be a problem as the torque drops off as the rpm increase (unlike a servo)? Marcus Thanks Marcus, Yes. I realize that. The lack of a spindle input or PWM output on the Probotix cape and the higher price of the PMDX cape rules out the Beagle for any sort of Linux CNC at the moment. That and what appears to be a lack of continuing support for the Beagle and LinuxCNC. John -- ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
Re: [Emc-users] BeagleBone and LinuxCNC for a lathe.
From: jmkasun...@fastmail.fm To: emc-users@lists.sourceforge.net Date: Wed, 12 Aug 2015 01:58:57 -0400 Subject: Re: [Emc-users] BeagleBone and LinuxCNC for a lathe. On Wed, Aug 12, 2015, at 01:31 AM, John Dammeyer wrote: In this case I'm considering installing it on a Unimat Lathe. The 650 oz-in size 34 motor appears to be large enough compared to the small DC brush motor currently attached. I'd have to step up the RPM in order to get the turning speed currently available. In either case, the question is whether or not LinuxCNC can even create stepping pulses for a spindle or if only PWM is available. John LinuxCNC can create any mixture of step pulses, PWM, and other ways of controlling motors. The motor interface is modular and you can set it up to do just about anything. jmkasun...@fastmail.fm Linuxcnc doesn't actually support the beaglebone. It was supported for a while on a branch that was not and will not be merged. It may be that you are using that old branch of linuxcnc or you may in fact be using machinekit (a fork of linuxcnc) that does support the beaglebone. That said if the beaglebone driver supports velocity step mode then it would be easy to add a stepper as a spindle drive. Let us know what fork of linuxcnc you are using and we can direct you to the best info. Chris M -- ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
Re: [Emc-users] BeagleBone and LinuxCNC for a lathe.
LinuxCNC can create any mixture of step pulses, PWM, and other ways of controlling motors. The motor interface is modular and you can set it up to do just about anything. jmkasun...@fastmail.fm Linuxcnc doesn't actually support the beaglebone. It was supported for a while on a branch that was not and will not be merged. It may be that you are using that old branch of linuxcnc or you may in fact be using machinekit (a fork of linuxcnc) that does support the beaglebone. That said if the beaglebone driver supports velocity step mode then it would be easy to add a stepper as a spindle drive. Let us know what fork of linuxcnc you are using and we can direct you to the best info. Chris M Machinekit is the port I was looking at. http://blog.machinekit.io/p/machinekit_16.html https://groups.google.com/forum/#!forum/machinekit Further research appears to show that the Probotix Beagle Cape doesn't support any sort of index pulse so it's pretty well out for a lathe. Their schematic shows three PWM pins from the Beagle but they don't go anywhere. As in not routed to a connector. PMDX also makes a cape for $129. From PMDX: The lack of support for hardware acceleration for OpenGL on the BeagleBoneBlack continues to be a significant deterrent to using the BBB as the console device running a GUI for a CNC controller. Toolpath display using the on-board graphics of the BBB is barely usable, so plan on remote access with the GUI running on another computer if you need toolpath graphics. I had hopes for LinuxCNC running on the Beagle and being supported for the next decade or longer. I guess not. Thanks John -- ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
Re: [Emc-users] BeagleBone and LinuxCNC for a lathe.
On Wed, Aug 12, 2015, at 01:31 AM, John Dammeyer wrote: In this case I'm considering installing it on a Unimat Lathe. The 650 oz-in size 34 motor appears to be large enough compared to the small DC brush motor currently attached. I'd have to step up the RPM in order to get the turning speed currently available. In either case, the question is whether or not LinuxCNC can even create stepping pulses for a spindle or if only PWM is available. John LinuxCNC can create any mixture of step pulses, PWM, and other ways of controlling motors. The motor interface is modular and you can set it up to do just about anything. jmkasun...@fastmail.fm -- ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
Re: [Emc-users] BeagleBone and LinuxCNC for a lathe.
John, If you are using a stepper at any significant revs, will there not be a problem as the torque drops off as the rpm increase (unlike a servo)? Marcus On 12 Aug 2015, at 08:28, John Dammeyer wrote: LinuxCNC can create any mixture of step pulses, PWM, and other ways of controlling motors. The motor interface is modular and you can set it up to do just about anything. jmkasun...@fastmail.fm Linuxcnc doesn't actually support the beaglebone. It was supported for a while on a branch that was not and will not be merged. It may be that you are using that old branch of linuxcnc or you may in fact be using machinekit (a fork of linuxcnc) that does support the beaglebone. That said if the beaglebone driver supports velocity step mode then it would be easy to add a stepper as a spindle drive. Let us know what fork of linuxcnc you are using and we can direct you to the best info. Chris M Machinekit is the port I was looking at. http://blog.machinekit.io/p/machinekit_16.html https://groups.google.com/forum/#!forum/machinekit Further research appears to show that the Probotix Beagle Cape doesn't support any sort of index pulse so it's pretty well out for a lathe. Their schematic shows three PWM pins from the Beagle but they don't go anywhere. As in not routed to a connector. PMDX also makes a cape for $129. From PMDX: The lack of support for hardware acceleration for OpenGL on the BeagleBoneBlack continues to be a significant deterrent to using the BBB as the console device running a GUI for a CNC controller. Toolpath display using the on-board graphics of the BBB is barely usable, so plan on remote access with the GUI running on another computer if you need toolpath graphics. I had hopes for LinuxCNC running on the Beagle and being supported for the next decade or longer. I guess not. Thanks John -- ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users -- ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
Re: [Emc-users] BeagleBone and LinuxCNC for a lathe.
On 12 August 2015 at 09:37, John Dammeyer jo...@autoartisans.com wrote: The lack of a spindle input or PWM output on the Probotix cape and the higher price of the PMDX cape rules out the Beagle for any sort of Linux CNC at the moment. That and what appears to be a lack of continuing support for the Beagle and LinuxCNC. I think you may be misinterpreting the situation. Machinekit seems to be committed to the Beaglebone, and the Machinekit flavour of LinuxCNC will work just as well as old-school LinuxCNC with a lathe. All you need to do is set up one of the step generators in the PRU in velocity mode and connect then net spindle-speed motion.spindle-speed-out-rps = .stepgen.02.velocity-cmd (*** because I don't know the BBB PRU Hallname). That gives you a working lathe, though it doesn't give you an index, so threading won't work initially. However, this does not mean that threading can't work. It should be possible to configure a synthetic index in HAL. But I suggest you talk to the Machinekit folks about that. ( www.machinekit.io ) As for the Probotix cape not having a PWM output, you can use a step-dir output. PWM is just another aspect of the PRU driver. If you want to convert that PWM to analogue voltage then some external components might be needed, but this can be as simple as a resistor and capacitor. Or, off the shelf, http://store.mesanet.com/index.php?route=product/productpath=74_78product_id=205 -- atp If you can't fix it, you don't own it. http://www.ifixit.com/Manifesto -- ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
Re: [Emc-users] BeagleBone and LinuxCNC for a lathe.
On 08/12/2015 07:43 AM, andy pugh wrote: On 12 August 2015 at 13:36, Gene Heskett ghesk...@wdtv.com wrote: This is a case where a hardware stepgen might be needed as software only has a limit in output step frequency on the x86 driven pc of 40Khz that is largely removed by the use of something like a mesa 5i25 card. The Beaglebone has a PRU (and a Machinekit driver) that can achieve similar step rates to the FPGA cards. Well, no, not quite true, as a blanket statement. However, the PRU can definitely achieve step rates that are needed by most practical microstepping systems. If you use a drive with insane (1000X) microstepping, or a servo drive that is commanded by step pulses, then the PRU may not be able to provide fast enough steps to reach the top speed. But, for Gecko drives and similar, yes, the PRU is plenty fast enough. Jon -- ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
Re: [Emc-users] BeagleBone and LinuxCNC for a lathe.
Why stepper ? gearing up the speed with a pulley even less sense, they lose so much torque at a sensible lathe spindle speed that I cannot understand the reasoning for going down the wrong rabbit hole. Just think what would happen if your chatter frequency was anywhere near the stepper resonance too. I do use small lathes (watch (DC) and clockmaker (AC induction motor) sizes) and need to get the RPM up a lot for small stuff. Dave Caroline -- ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
Re: [Emc-users] BeagleBone and LinuxCNC for a lathe.
On Wednesday 12 August 2015 08:43:33 andy pugh wrote: On 12 August 2015 at 13:36, Gene Heskett ghesk...@wdtv.com wrote: This is a case where a hardware stepgen might be needed as software only has a limit in output step frequency on the x86 driven pc of 40Khz that is largely removed by the use of something like a mesa 5i25 card. The Beaglebone has a PRU (and a Machinekit driver) that can achieve similar step rates to the FPGA cards. I am aware of that Andy but have no experience, which is why I mentioned the x86 platform specifically. I have thought of trying the BBB, but the comments in this thread so far are quite off-putting, No indexing and poor GFX speed would turn me off. Its gfx is slow enough on the X86 stuff, so What You See Is Not WHat You Are Getting. WYSINWYAG would be the applicable acronym. :) Cheers, Gene Heskett -- I'll report more on that once I decide on a cape (or build my own). John -- ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
Re: [Emc-users] BeagleBone and LinuxCNC for a lathe.
Hi Gene, Thanks, Warning, Ramblings have been edited for size. GRIN Warning, generalized ramblings of an old fart follow. .SNIP Usable torque was pretty much gone by 2000 rpm. I agree. Since the resolution for the spindle isn't nearly as a big a deal for a spindle I thought I'd use pulleys to step up the speed. Unless I'm using the spindle as an indexing head a minimum RPM of 30 is more than reasonable for any large diameter threading that fits on that small a lathe. I've found steppers don't do much better after about 700RPM. So if I want 5600 RPM I'd have to go 1:8. A stepper excels at a smooth 3.75 RPM and has the torque so that a smooth 8x=30 RPM wouldn't be an issue. Or just change belts and pulleys for the different speed. Software step generation suffers from latency which causes less than a steady frequency, and this detracts from the usable torque because the motors speed is being asked to vary as much as 20% in a single revolution. On the x86 platform, the next slower software step frequency is nominally 20 Khz, but thats such a huge percentage change that neither is likely to be a usable step frequency for software generation. Because of that, the practical limit is lower, probably under 5Khz for stall free operation. Thats about 600 Hz as you hear it from the motor when using a /8 diviser. Hardware (FPGA) generation raises that bar quite a ways. /16 to as much as /64 is usable then. But a /64 explores the speed limits of the opto's in the drivers, limiting the top speeds. I run the ELS at 20kHz. I've also found about 700RPM as the limit with the on board 8x micro-stepper. I only have one nema 34 motor, on the Z axis of my GO704 mill. Using a 5i25 card, and /16 as the microstep divisor, it has a huge resonance at one relatively low speed, but can happily run at 3x that speed while lifting the head of the machine. How much of that resonance is the rather filligree mounting of this particular conversion kit I haven't determined. I would love to have been able to install some dampers, but the motors supplied are single ended shaft. That's one of the questions I'd not yet posed about using a stepper for the spindle. On my JGRO CNC at some speeds they do growl. I wonder if that would translate to surface finish even with a belt drive. The spindle and chuck tend to be a pretty good damper though. SNIP Cheers, Gene Heskett -- -- ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
Re: [Emc-users] BeagleBone and LinuxCNC for a lathe.
Hi John; I've a small Unimat SL that I've CNC'd (and talked about it at the last CNCWorkShop back in June, and in my blog) Some random thoughts: 1) Beaglebone is fine. Sure, graphics is slow, but so what? Change Axis to the DRO display and you are fine. 2) My OLD Unimat has a not so great spindle, which is a bit of a problem. And an old motor, which is very weak. 3) Currently, I have no spindle feedback for threading. 4) Others have used stepper motors for spindle control on Unimats; one chap in Germany, and, maybe Cecil on this list? 5) I've a larger, stronger lathe (a big brother to the Unimat - an Emco Compact-8) that is my target lathe for CNC; not sure if I'm going to develop the Unimat further. I have the Xylotex cape, with the Beaglebone direct from them, pushing a Gecko G540. Look at cnc-for-model-engineers.bogspot.com and top left corner is a search box, put Unimat in there. Maybe it'll give you some ideas. John. On Wed, Aug 12, 2015 at 5:45 AM, andy pugh bodge...@gmail.com wrote: On 12 August 2015 at 09:37, John Dammeyer jo...@autoartisans.com wrote: The lack of a spindle input or PWM output on the Probotix cape and the higher price of the PMDX cape rules out the Beagle for any sort of Linux CNC at the moment. That and what appears to be a lack of continuing support for the Beagle and LinuxCNC. I think you may be misinterpreting the situation. Machinekit seems to be committed to the Beaglebone, and the Machinekit flavour of LinuxCNC will work just as well as old-school LinuxCNC with a lathe. All you need to do is set up one of the step generators in the PRU in velocity mode and connect then net spindle-speed motion.spindle-speed-out-rps = .stepgen.02.velocity-cmd (*** because I don't know the BBB PRU Hallname). That gives you a working lathe, though it doesn't give you an index, so threading won't work initially. However, this does not mean that threading can't work. It should be possible to configure a synthetic index in HAL. But I suggest you talk to the Machinekit folks about that. ( www.machinekit.io ) As for the Probotix cape not having a PWM output, you can use a step-dir output. PWM is just another aspect of the PRU driver. If you want to convert that PWM to analogue voltage then some external components might be needed, but this can be as simple as a resistor and capacitor. Or, off the shelf, http://store.mesanet.com/index.php?route=product/productpath=74_78product_id=205 -- atp If you can't fix it, you don't own it. http://www.ifixit.com/Manifesto -- ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users -- ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
Re: [Emc-users] BeagleBone and LinuxCNC for a lathe.
On 12 August 2015 at 13:36, Gene Heskett ghesk...@wdtv.com wrote: This is a case where a hardware stepgen might be needed as software only has a limit in output step frequency on the x86 driven pc of 40Khz that is largely removed by the use of something like a mesa 5i25 card. The Beaglebone has a PRU (and a Machinekit driver) that can achieve similar step rates to the FPGA cards. -- atp If you can't fix it, you don't own it. http://www.ifixit.com/Manifesto -- ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
Re: [Emc-users] BeagleBone and LinuxCNC for a lathe.
On Wednesday 12 August 2015 01:31:07 John Dammeyer wrote: I am one who is running a small lathe with LinuxCNC, which it does far better than I can. This subject has come up in the past, and I don't recall anyone saying no it can't be done. Given a big enough motor, I see no huge show stopper in substituting a stepgen for the pwmgen module. But the high speed performance as a spindle motor might not be universally usable. Cheers, Gene Heskett Thanks Gene, In this case I'm considering installing it on a Unimat Lathe. The 650 oz-in size 34 motor appears to be large enough compared to the small DC brush motor currently attached. I'd have to step up the RPM in order to get the turning speed currently available. In either case, the question is whether or not LinuxCNC can even create stepping pulses for a spindle or if only PWM is available. John Warning, generalized ramblings of an old fart follow. This is a case where a hardware stepgen might be needed as software only has a limit in output step frequency on the x86 driven pc of 40Khz that is largely removed by the use of something like a mesa 5i25 card. Software has, when near its limits, rather large steps in speed cause by the speed limit of the base-thread that drives it on the X86 platform. I did some fooling around with a 425 oz nem 23 a few months back, driving a 2M542 driver with a function generator. The results were basically a speed limit detector of the opto-isolation used in that particular driver, but by playing with the microstep divisor settings I was able to get above 3000 rpms but no usable torque. The speed limit of the opto's seemed to have been something just above 350 kilohertz as long as the duty cycle was near 50%. I was also using a 48 volt power supply, so that was more voltage than is normally used with a 2M542 driver as its rated at 50 volts 4.2 amp max. Usable torque was pretty much gone by 2000 rpm. Software step generation suffers from latency which causes less than a steady frequency, and this detracts from the usable torque because the motors speed is being asked to vary as much as 20% in a single revolution. On the x86 platform, the next slower software step frequency is nominally 20 Khz, but thats such a huge percentage change that neither is likely to be a usable step frequency for software generation. Because of that, the practical limit is lower, probably under 5Khz for stall free operation. Thats about 600 Hz as you hear it from the motor when using a /8 diviser. Hardware (FPGA) generation raises that bar quite a ways. /16 to as much as /64 is usable then. But a /64 explores the speed limits of the opto's in the drivers, limiting the top speeds. Generally speaking about steppers, the top speed of a given motor will go up as a function of the applied voltage as its limited by the inductance of the motors windings. You get less current flow because of the inductance, and the only way to alleviate that is more voltage, or find a motor with lower inductance windings. Since even here, the operative word is TANSTAAFL, that also implies it will need more current to achieve the same torque. I only have one nema 34 motor, on the Z axis of my GO704 mill. Using a 5i25 card, and /16 as the microstep divisor, it has a huge resonance at one relatively low speed, but can happily run at 3x that speed while lifting the head of the machine. How much of that resonance is the rather filligree mounting of this particular conversion kit I haven't determined. I would love to have been able to install some dampers, but the motors supplied are single ended shaft. The damper can be a huge help, absorbing much of the resonance between the mass of the armature and the magnetic springs of its operation, and adding some home-made dampers to my micro-mill rather easily took the rapids moves from 7 or 8 ipm (on the 20 TPI OEM screws) to as high as 34 ipm, however that mills head sled onfit the post is so poor that in everyday usage its rapid limit is more like 14. But that was still a very real improvement. That mill now has ball screws in its XY table, but the Z drive is still the 10 tpi acme screw in front of the post, a modification I made within months of its purchase when I found that no amount of torque applied to the Z handwheel could generate more than 5 lbs of downforce on a drill bit because it was all used up in binding the short wheelbase head on the post. With an extended wheelbase by adding 1/2 thick alu bars carrying some roller skate bearings riding the post, and a 425 oz driving the nut, I can now put just a hair over 150 lbs on the tip of a drill bit. That _will_ drill the hole. And that Z drives accuracy is spotty but can for a jobs duration, be adjusted for less than 0.002 effective backlash. The rotateing acme nut is actually 2 nuts that allow the backlash to be adjusted out. I'd probably put a 16mmx5 screw in there, if I
Re: [Emc-users] BeagleBone and LinuxCNC for a lathe.
On Wednesday 12 August 2015 08:43:33 andy pugh wrote: On 12 August 2015 at 13:36, Gene Heskett ghesk...@wdtv.com wrote: This is a case where a hardware stepgen might be needed as software only has a limit in output step frequency on the x86 driven pc of 40Khz that is largely removed by the use of something like a mesa 5i25 card. The Beaglebone has a PRU (and a Machinekit driver) that can achieve similar step rates to the FPGA cards. I am aware of that Andy but have no experience, which is why I mentioned the x86 platform specifically. I have thought of trying the BBB, but the comments in this thread so far are quite off-putting, No indexing and poor GFX speed would turn me off. Its gfx is slow enough on the X86 stuff, so What You See Is Not WHat You Are Getting. WYSINWYAG would be the applicable acronym. :) Cheers, Gene Heskett -- There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order. -Ed Howdershelt (Author) Genes Web page http://geneslinuxbox.net:6309/gene -- ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
[Emc-users] BeagleBone and LinuxCNC for a lathe.
I'm thinking of ordering one of the Probotix Breakout Boards for my Beagle Bone Black. Probotix has a downloadable image of LinuxCNC so getting it up and running shouldn't be an issue. http://www.probotix.com/CNC-CONTROL-SYSTEMS/BREAKOUT-BOARDS/PBX-BB-BeagleBon e-Breakout-Board I've not looked at LinuxCNC for some time but I'm wondering how it does with lathes nowadays. For example if I mount a stepper motor to drive the spindle does LinuxCNC support standard step/dir signals to drive the spindle motor? Thanks John Dammeyer ELS! Nothing else works as well for your Lathe Automation Artisans Inc. http://www.autoartisans.com/ELS/ http://www.autoartisans.com/ELS/ Ph. 1 250 544 4950 -- ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
Re: [Emc-users] BeagleBone and LinuxCNC for a lathe.
On Tue, 2015-08-11 at 23:53 -0400, Gene Heskett wrote: On Tuesday 11 August 2015 21:43:46 John Dammeyer wrote: I'm thinking of ordering one of the Probotix Breakout Boards for my Beagle Bone Black. Probotix has a downloadable image of LinuxCNC so getting it up and running shouldn't be an issue. http://www.probotix.com/CNC-CONTROL-SYSTEMS/BREAKOUT-BOARDS/PBX-BB-Bea gleBon e-Breakout-Board I've not looked at LinuxCNC for some time but I'm wondering how it does with lathes nowadays. For example if I mount a stepper motor to drive the spindle does LinuxCNC support standard step/dir signals to drive the spindle motor? Thanks John Dammeyer I am one who is running a small lathe with LinuxCNC, which it does far better than I can. This subject has come up in the past, and I don't recall anyone saying no it can't be done. Given a big enough motor, I see no huge show stopper in substituting a stepgen for the pwmgen module. But the high speed performance as a spindle motor might not be universally usable. One might have to get creative for a motor/controller source. I have seen pix of someone using the huge stepper motor out of a modern washing machine, which would seem to have the torque, and since its also doing the spin cycle, might have the high speed performance too. But in terms of positional accuracy, those do not have the pole count of a moderm stepper. Someone who has actually done it should pipe up and testify. Searching ebay, the largest motor I can come up with is a nema 42, rated at 4120 oz/in. I believe that I have seen nema 56 motors on ebay in the past, but not tonight. Here is one candidate possibility, but its 3 of them for $900 USD: http://www.ebay.com/itm/big-force-3-nema-42-stepper-motors-4120oz-in-8A-3-drivers-DM2722A-9-8A-12-months-/261930438088?hash=item3cfc454dc8 I note that the driver remembers what microstep it was at in the sequence, even if power cycled, provided it has been stopped for at least 5 seconds. That is not something the smaller drivers like the DM860 does, but I can see where that could be handier than bottled beer. No loss of machine positioning from power cycling the whole machine. Cheers, Gene Heskett hmm, I had some problem with microstepping my hybrid motors, they where changing direction at random and had a small force, so I have set them at full step and the problem went away. I have read that it has something to do with the way the motor is driven in microstepping mode. -- ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
Re: [Emc-users] BeagleBone and LinuxCNC for a lathe.
I am one who is running a small lathe with LinuxCNC, which it does far better than I can. This subject has come up in the past, and I don't recall anyone saying no it can't be done. Given a big enough motor, I see no huge show stopper in substituting a stepgen for the pwmgen module. But the high speed performance as a spindle motor might not be universally usable. Cheers, Gene Heskett Thanks Gene, In this case I'm considering installing it on a Unimat Lathe. The 650 oz-in size 34 motor appears to be large enough compared to the small DC brush motor currently attached. I'd have to step up the RPM in order to get the turning speed currently available. In either case, the question is whether or not LinuxCNC can even create stepping pulses for a spindle or if only PWM is available. John -- ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
