If the output from the breakout board can't source enough current for two driver inputs, then you can buffer it with just one transistor and two resistors and that's guaranteed to work.
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If the output from the breakout board can't source enough current for two driver inputs, then you can buffer it with just one transistor and two resistors and that's guaranteed to work.
Ok but why would you need marks on rotating nuts to aid correction if it never loses a step or position.?? Should be nothing to correct.!!Quote:
Originally Posted by Jonathan
But what was you cutting and at what feeds.? . . Aluminium I presume.! . . . Try cutting wood with inertia of rotating screws not rotating nuts around 7-8mtr/min for 47hrs and check it.!!Quote:
Originally Posted by Jonathan
Also your machine is setup correctly and presumably with plenty of torque left, I'm talking higher feeds and motors tuned close to edge which often happens causing lost steps and much sooner than 47hrs.!!
Again I'll say it " Tune the motors properly with plenty of safety margin and there's no problem with slaved motors" but still it can happen and that's not good and healthy for screws or machine if one motor stalls racking gantry at rapid speeds.!!!!. . . . With belts running out of sync is not even in the frame and stays set just like the day it was set regardless of crashing or motor tuning.!! . . . .And trust me I've crashed hard and plenty so it's well tested. . .Lol
The marks are there so I can check that it's square when I switch the motors on, as clearly they can move when turned off. I could do the same with switches, but a permanent marker is cheaper!Quote:
Originally Posted by JAZZCNC
Not aluminium. The feedrates were low and the acceleration set quite high. The result would be the same if I ran my machine for that amount of time with the maximum feedrates, because the motors are tuned properly. Yes, I could set the rapid feedrate slightly higher and loose the odd step here and there, but there's no reason to as I chose the correct size motors for the machine, so the safe feedrates are adequate.Quote:
Originally Posted by JAZZCNC
If that's the case then they should buy the right motors and set up the machine correctly in the first place, instead of linking the screws with a belt so it doesn't matter if there's a missed step.Quote:
Originally Posted by JAZZCNC
How do you accurately set the machine square when a belt is linking the screws?
Yep agreed but that's not always the case and some don't have knowledge to setup correctly from beginning and damage can be done before they learn.!! Plus there's the other added benefits using belts give like piece of mind a stall isn't going to turn gantry into a Twizzler.!! . . . Anyway it's bit Linux vs Mach thing we are obviously going to have to agrees to disagree.!Quote:
Originally Posted by Jonathan
Loosen bolts on gantry etc and pulleys then turn ball screws . . . . Simplizz.!! . . . Bit fiddly and time consuming at first but one time deal so no problem.Quote:
Originally Posted by Jonathan
Well it's been a busy day for the credit card. The drivers, steppers, ballscrews and nuts, bearings and mounts, spindle and vfd have all been bought mostly from China. I think I might have accidentally bought a collet set as well - I asked for a spindle with a ER20 collet and I think he's read that as "collet set". Not a problem though as I was going to buy a set anyway, I hadn't realized Chai had started sell them. If anyone needs drag chain he seems to be doing some nice looking stuff at a reasonable price.
I've also been tempted over to the dark side, I installed LinuxCNC on one of the old machines I have kicking about last night and I have to say I like what I see. There were a couple of minor complications but over all it seems to be a nicely put together system. I ran the latency tests for a couple of hours with a fully stressed machine and achieved ~7,000ns max jitter so I think it should work quite well. The parallel port supports SPP, EPP, ECP and ECP + EPP modes. I've seen someone mention that one of EPP or ECP is better but I can't find the thread again.
I was looking closely at the electronics in Jonathans "sufficiently strong" build and I can't see a BOB anywhere in the control box. In fact it looks like the drivers are connected directly to the parallel port with the cable being wrapped in a bit of foil. Is that correct? I've not been able to find all that much mention of people running steppers direct from the parallel port, just the odd post here and there but I wouldn't mind giving it a go. As has been mentioned elsewhere I can always move onto using an ESS + BOB if necessary but I might as well give it a shot.
I ordered my ballscrews off Chai last week, I also bought a set of collets off him but got 2.5m of energy chain off fleabay...going to be like Christmas soon with all this equipment arriving. Best order some steel Monday and get welding...
7000ns is exceptionally good latency, what motherboard etc are you using?
I left Sasha to wire up the control box and he had problems with the breakoutboard, so for now the stepper drivers are indeed connected directly to the port. The output voltage of the port is sufficient so switch the driver inputs reliably and the driver inputs are opto-isolated, so there's no chance of damaging the port. To get isolated inputs it's easiest to just get a breakout board. In short, it works... but that doesn't mean it the best idea. So by all means give it a shot, but I wouldn't advise using this setup permanently.Quote:
Originally Posted by Wobblycogs
Not sure why the foil is there, maybe he ran out of shielded cable but I thought I lent him a 100m reel!
Yes, I was quite pleased with the latency. Looking at the machine spec I'd forgotten quite how good it was, massive overkill for a control box I know but it was sitting around not doing anything. In fact it's been switched off for so long the BIOS battery needs replacing. I'll replace that and re-run the latency test to confirm the result.
The machine is:
Motherboard: GA-K8NXP-SLI
Processor: Athlon 64 3000+ (not sure which revision, I think it's a 130nm ClawHammer as I bought it quite soon after they were released)
Memory: 3GB DDR400
Video Card: some old nVidia card, can look it up if you're interested.
Initially I was getting a latency of about 50,000ns but I noticed that was caused by a spike when I first played sound through the on-board sound card. Disabling the on-board sound in the BIOS gave me a 7000ns. After performing all the package updates the system required I re-ran the tests and got around 6500ns. I also tried the nVidia binary drivers to see if that would improve video performance - bad idea, whenever anything using OpenGL started it caused a 250,000ns spike in jitter!
I hear what you are saying regarding running direct from the parallel port. Would you also recommend the PMDX-126 as a nice BOB?
I've been a bit busy with work for the last couple of months hence the lack of posts but the build has moved forward a bit. I've now got the steppers, drivers, screws, nuts, bob, nut brackets, spindle, VFD and a few other bits and bobs as well.
I met up with Neil the other night to swap parts from a joint buy and he kindly gave me a bit of 10mm plate to have a practice with. When I first saw it my heart sank - it looked distinctly too thin to build a machine from. I thought I'd give it a crack anyway and build one of the 8 brackets that I plan on using to support the X-axis and here's the results:
Attachment 10571Attachment 10572Attachment 10573
The angle from the base to the back is 89.7 deg which I'm fairly pleased with considering this is my first attempt at metal work. It's surprisingly strong but is it strong enough? The the parts we first roughly jigsawed (or hand sawn once the jigsaw blade gave up) and then cut to exact size on the mitre saw. The accuracy is ok but not exactly the perfection I had envisioned. I'll have to decide now whether to get some kind soul to mill the parts for me or to press on with trying to cut the pieces myself.
After my bracket making endeavours the other week I've been thinking that it's probably better if I just get the majority of the pieces cut professionally. I think I probably could just about cut the pieces myself and end up with a working machine but I'd be old and grey by the time I finished (or I'd end up buying a milling machine).
A benefit of getting the parts made is I don't have to worry about cuts that would be difficult for me to make. With that in mind I've changed the design slightly. The parts in eye watering green have been upgraded from 10 to 15mm. The brace for the gantry is gone in favour of a single stronger side plate (there will be M5 bolts through the side plate into the front and back gantry plates and the base plate).
Attachment 10774Attachment 10775
I was thinking about maybe getting the parts water jet cut by a local company that could also supply the aluminium for the job. Unfortunately I have no idea how much water jet cutting costs, I'm guessing it's not cheap though. The other option would be to find some kind soul around these parts that would cut them for me.
Only do this for non critical parts has water jetting can leave slight angle on the edges so any plates the mate to each other can end up at and angle.Quote:
Originally Posted by Wobblycogs
I've been reading up on the system electronics recently and I'm a bit confused about the current settings for the drivers. I'm using AM882 drivers and 60BYG301B steppers from CNC4YOU. The steppers will be wired in parallel and the stepper data sheet lists the current for that configuration as 4.2 Amps - all well and good so far.
The problem is that the manual (I have) for the AM882 under "Connections to 8-lead motors > Parallel Connections" it says:
...Multiply the per phase (or unipolar) current rating by 1.96, or the bipolar current rating but 1.4, to determine the peak output current.
That seems to imply that I should set the driver to 4.2 * 1.4 = 5.8A (dip switch settings SW1 = On, SW2 = On, SW3 = Off gives 5.5A or set exactly using ProTuner). That feels wrong to me though. I think the AM882 manual is assuming that the stepper data sheet will give the RMS current but it's not clear from the data sheet if that is the case.
What I think I should do is use ProTuner to set the peak current to 4.2A as the nearest dip switch setting is SW1 = On, SW2 = Off, SW3 = On which only gives 3.6A. Sound right?
From your data sheet the unipolar current is 3A so 1.96*3=5.88
the bipolar current is 4A so 1.4*4.2=5.88
the nearest setting is 5.5A with switches 1,2,3 set to ON,ON,OFF, this setting also supplies 3.93A RMS according to the AM882 manual.
That's how I would set them anyway but seeing as my setup is very similar AM882 + 60BYGH401 I'll be interested to see other replies.
Thanks Eddy, last thing I want to do is fry a stepper as soon as I switch it on.
The AM882 drivers can be connected to a PC for set up. This lets you set an exact current limit (0.1A resolution it looks like from the screenshots) amongst other things.
The correct current is the current at which the motors don't get too hot, i.e. above 80°C. Generally the easy way to find this, as you've done, is to use the datasheet, but if you're not sure then you can just start with a lower current and work up.
There's also this to set first.
"Auto configuration by SW4
Change SW4 two times in one second to identify the motor parameter after
power-up if it is the first time installation. Please note that the rotation
switch position must be 0 when using this function. "
Also to set the microstep resolution and current using Pro Tuner then switches 1,2,3,5,6,7 all need to be set to ON and switch 4 OFF
Thanks Jonathan, that was basically the approach I was going to take if necessary.
Eddy, I don't know why but I was under the impression that the auto-detect would only work for Leadshine steppers. I suppose if it's measuring the steppers response to given input signals though it could work for any make of stepper. I'll give it a go to see what it comes up with, I think the auto-detect can be triggered from software as well which is probably the way I'd go.
I had some time off over Christmas so got cracking with putting together the electrical cabinet. I've literally just achieved "first rotation" as it shall forever be known in our house.
Attachment 11183
My main inspiration was Eddy's recent build but there are some of my own ideas in there too. The case is a 600x600 and I've left space for an additional driver if / when I add one. The power supply was proving difficult to fit in until I had the burst of inspiration to go vertical. The clear perspex cover (I call it the idiot guard) was a secondary addition after I got a first hand experience of quite how much power the capacitor bank holds:
Attachment 11184
The capacitors were almost completely discharged when I probed the top to see what voltage they still held. One slip with the positive probe and a bright flash and bang later and I need a new probe.
The builds not quite finished yet but as you can see I've got a stepper attached and had it rotating using the test mode of the PMDX. Some how, despite measuring everything ten times I've still managed to make it a bit tight around the BOB. I must have been having an off day or something but fortunately I've got just enough space.
I'm going to look at building a soft start for the transformer. As I mentioned in another thread I'm getting some nuisance trips off a 6A Type D breaker. I might give a slow blow fuse a go if I remember to buy one next time I need some parts but I can't imagine it's good for the transformer to be getting whacked with 100A+ at start up. What I can't decide is whether to build a timer circuit to disconnect the soft start thermistor or to just leave it in all the time. The power supply is delivering a steady 71V, many thanks for the help with that so far guys :D.
Anyway, the one thing that surprised me about the set up was that the stepper wasn't silent when it was stationary. It makes a sort of kettle just going off the boil sound if that makes any sense. Is this normal? When it's turning it's quite quiet although I've only had it turning at one speed. I should probably say I've not fine tuned the current for the steppers yet, I just quickly selected a setting that was well below the maximum the steppers can handle.
"First Rotation", sounds like a maiden flight.
Looking great, 600x600 seems a good size as there's plenty of room in there. Perspex cover is a good idea, it's always best to aim for IP2X with a panel.
I also found stepper a bit noise upon first fire up, used Pro Tuner to set the current and now very quite indeed.
I don't know what the requirement are for that inverter but mine specified 75mm free space both top and bottom for cooling, must be installed upright, no requirement for free space at the sides.
Eddy Is that to stop the electric from falling out.:beer:Quote:
I don't know what the requirement are for that inverter but mine specified 75mm free space both top and bottom for cooling, must be installed upright, no requirement for free space at the sides.
Cheers Eddy. Once the case is finished it will be dust tight (I think your case is the same design). I figure anyone inside the case should have a pretty damn good idea of what they are doing or they shouldn't be in there! The cover over the power supply is stop stupid accidents, it wouldn't stop a concerted effort to electrocute yourself.
I don't remember seeing any spec's for space around the rectifier although I'm guessing there will have been some. There's a good bit of space around it though and the aluminium it's bolted too will act as a great heat sink. I'll keep an eye on it but I don't envisage a problem. I don't like the way the bleed resistors are connected at the moment, it feels like a bodge although it works fine. I was asking about the power supply over on another forum and someone pointed me in the direction of active rectifiers, apparently they dissipate almost no power - I bet they cost a fortune though.
Something else I meant to ask, how are you connecting the various bits inside your cabinet to the various bits on the outside e.g. steppers, e-stop / limits etc. I'd like to be able to just unplug everything and take the case away but I'm concerned plugs and sockets will introduce noise.
No that's what insulation is for :nevreness: also when I first read it was an 'inverter' I mounted it upside down :stupid:Quote:
Originally Posted by Clive S
You can't use that as an excuse though.Quote:
Originally Posted by Wobblycogs
I meant the VFD, sorry I never usually call them VFD'sQuote:
Originally Posted by Wobblycogs
I'm going straight into terminals via compression glands in the bottom gland-plate, I can't see me wanting to move it much but I'm prepared to disconnect if I do. From my experience, albeit on much larger VFD's, the plugs & sockets did not like the high frequencies coupled with the current, although they were sized for the job the insulation used to break down over time.Quote:
Originally Posted by Wobblycogs
That's a very nice box setup/layout.
Can I ask where you get your Din rail and connectors etc. from - I may have to look at something similar for my control box and also I have a 1970's horror of a lighting circuit junction box in my loft that needs replacing with something more elegant.
Regarding the VFD, the mounting orientation advice in the manual is likely because of the cooling fan, so its not blowing hot air over something else that might be susceptible to over heating (the number of times front to back and side to side cooling for servers and networking kit has been overlooked when buying kit for some data centres I have had to look into is scary).
Almost all the DIN mounted stuff comes from Chalon Components. Their prices are about as good as I found anywhere. The enclosure is particularly nice. I think the only major item I didn't get from them was the main door locking switch.
Now that I realise Eddy meant the VFD I can see why he's mentioned it. There's not 70mm below but there's not much air restriction. There will be a hole above to let hot air out and it's at the top of the case specifically so it doesn't heat anything else.
I've been working on the control case on and off for the last couple of months, I got a good few hours in today so I thought I'd share an update and a couple of pictures.
I got the soft start parts ordered, built and fitted. I'm really pleased with the out come. There's certainly no more tripping breakers / blowing fuses. I don't know if it's psychological but it actually sounds quieter when the main power is engaged. I've set the timer to two seconds to give the capacitors a chance to fully charge while the system is still being current limited. I also re-jigged the bleed resistors so that they dissipate a lot less power.
After that I set about making the top and bottom panel. My plan was to have all the connections coming out the bottom of the control case with just a couple of vents at the top. The whole case can then be mounted on a wall somewhere up out of the way. I spent an inordinate amount of time researching connectors and eventually settled on some from ebay (and AliExpress). I have to admit they weren't the cheapest connectors but they are a pleasure to work with and well over spec'ed.
As I (currently) have the VFD in the case I've gone for a 16A connection. I'm sure the total draw could be met by a 13A connector but the 16A stuff is just better suited to this sort of situation.
With all my focusing on the main connectors I completely forgot to leave space for the parallel port. Fortunately there was just enough space up the right hand side next to the fan. I actually think I would probably have put the connector there if I had planned it so all in all that's worked out well. The only slight bodge is that it's actually glued into place. The PMDX manual states that the metal outer case for the socket shouldn't be connected to the case (earth loop issues). I didn't have space for a plastic mounting plate so it was hot melt glue to the rescue.
Attachment 11852Attachment 11853Attachment 11854
That looks really neat and professional. Well done. G.
Thanks Geoffrey.
In answer to your question on Neils thread yes it was Lincoln with an l (I found the missing l on the floor). I was surprised how much I liked the place actually and I agree everyone was very friendly. We were up at the top of the hill just by the castle, the walk up and down the hill each day to get into town certainly helped burn off any excess calories!
Glad you liked Lincoln, there are some great places in the UK, but I am off to sunny Tenerife for a week tomorrow (won't be burning off any calories though. I bet that there will be a week of wall to wall sunshine here and that it will probably end on the 24th when we return!!! G.
4 seems a bit excessive to me. You can maybe justify two for the slaved axis, but I doubt you'll see much benefit using them compared to DQ860MA on the other axes.
BOB/Spindle control/ESS/Mach3... well if you must.
hi Jonathan, when you say 4 seems excessive to you what exactly are you referring to? if it's the drivers then i'm at a loss because i was under the impression that each motor needed a dedicated driver, or have i the wrong end of the stick? (again !!!)
I was referring to stepper drivers. You do need one per motor, but my point was you don't have to use the same driver for every motor. There are arguments for getting different drivers for slaved motors which don't apply to the other motors.Quote:
Originally Posted by PAULRO
Paulro Have you posted in the correct place as this post is 9 months old!!! >Clive
edit Obviously not !!
He was referring to post #64 ... had to Google search the forum to find out!Quote:
Originally Posted by Clive S
i'm still getting to grips with the forum!!!:stupid: i'll have to get one of my young fellas to bring me up to date with all the new forms of communicating:shame: just when i think , yeah, that's makes sense ! that's the way to go ... i read on and find one of you bright sparks has another alternative and that really gets the hamsters running in different directions
Hello again :calm:. Seems a bit quite around these parts, where's everyone gone?
Anyway, it's been a while (cough, 10 years) but I've finally got around to starting to build this CNC. I started by building a sturdy bench for it to sit on. I was on safe ground here. The cross members are 2x9's and it's covered with a sheet of 18mm ply.
Attachment 32021
Attachment 32022
I made my first mistake while making one of the support brackets for the x-axis box section. I was rushing and I managed to break a drill bit. In the replacement hole I then managed to break a tap. :applouse:
Attachment 32023
Moving swiftly on... Here's a shot of all the parts I've put together so far carefully arranged to make it look like I've done more than I have. I was going to mount the linear rail to the box section when it occurred to me that might not be a good idea. Obviously, I've got to get the x-axis exactly perpendicular to the y-axis. I feels like I should build the y-axis and mount it before drilling the mounting holes for the x-axis. Does that sound about right or should I mount the x-axis rails now and then try to adjust them square to the y-axis later? To adjustment them I'll have a tiny bit of play in the rail mounting screws or I can get more by opening up the holes that mount the x-axis rail assembly to the frame. It feels like I'll only get one shot at this so I don't want to screw it up.
Attachment 32024
Not quite sure what the problem is about squaring - it might not be as bad as you think!
On my own machine, I bolted down one rail to the frame as straight as I could. I then used the gantry to align the second rail to it, to guarantee parallelism - just enough slack in the mounting holes using M5 (from memory) bolts to allow the second rail to move slightly, then slide the gantry back and forth to get it parallel and tighten bolts. I built the gantry as accurately square as I could, and once the machine was almost finished I could take test cuts and then adjust the gantry to be as square as I could measure from the test pieces. How to square it? Again, in my case, I was driving the gantry at both ends so I could adjust the home position at each end of the gantry so that each time it homed, it automatically re-squared itself. I had arranged the gantry itself to be bolted to "feet" at each end which carried the ball slides and during the initial squaring, I could slacken the bolts slightly to allow the gantry to swivel slightly, then tightening once I was happy. The process does rely, obviously, on having a master and slave drive to the gantry, one at each side, and the motion controller needs to support separate homing of master and slave axes.
There is an underlying design principle in all this. For a home-built machine, where you do not have the machining and assembly facilities to build accuracy immediately into the machine, you need to build in wiggle room so that once built, you can adjust everything. "Adjust on assembly" is an expensive nightmare in a commercial setting so you pay a fortune for manufacturing capability to build in accuracy. As amateurs we don't have that luxury but our time costs a lot less so we do it the hard way! But it works - witness the number of successful machines described on this forum. Good luck!
Thanks, Neale. I'll have another think about it. What you describe is pretty much what I'd planned on doing and then I was standing there yesterday looking at the parts and I started wondering if it was going to work. My concern in terrible ascii art is something like this:
Ah, now I've drawn it out I can see the method you describe will work. You just use the second x-axis stepper to pull the gantry into alignment.Code:y axis (in home position)
V
________
/ /
/ / <-- The x rails are parallel but not perpendicular to the y axis
/ /
Thanks again. I'm sure I'll have plenty of other stupid questions :-)
I had a quick look back through the thread after I wrote my last post (thread started a long time ago!) and it seems that you are driving both gantry ballscrews by belt from a single stepper. In this case you could adjust gantry squaring by tweaking the belt position on one or other of the ballscrew pulleys a tooth or two at a time - I guess that that is what you were planning? I was able to just move a home switch trigger point slightly but at the cost of doubling up on steppers, drivers, switches and wiring, and general configuration complication!
Cheers, I've just looked through the thread and noticed there's no good images of the back of the machine. There are two steppers on the x-axis, they are set down a little and then connected by short belts to the screws. It allowed the machine to be a little more compact.
This build has, indeed, taken a really long time for a variety of reasons, just over ten years at this point I think. I'll get there eventually.
I don't suppose you know a good source for ball screws do you? The ones I bought originally have seized. Somehow condensation must have formwed in the ball nut and they have rusted solid to the screw. I thought my workshop was dry and warm enough for that to not be a problem.
No personal experience of buying ballscrews from anyone still in business, I'm afraid. BST Automation via Aliexpress is often recommended in this forum but I have never dealt with them myself.