- August 29, 2016 at 2:11 pm #16823
So this article, http://hackaday.com/2016/08/29/how-accurate-is-microstepping-really/, made me think about our drivers.
I need to start this saying I have never had an x or y axis power issue. This is just a cool test/explanation.
I have the means to easily test our drivers in series vs the tried and true parallel. The problem we have, and the reason I made the wiring harnesses in parallel is speed. The power advantage goes to series wiring until about 4000 steps /second, and then parallel starts to pull ahead. For us at 32nd stepping this means 20mm/s, above that and parallel is (should be) stronger.
We can very easily up this to 40mm/s by dropping down to 16th stepping. I know all the data says 16th should be stronger anyway, I can not tell a difference and opted to supply the directions and kits at 32nd stepping.
Here’s where some of you are going to not like my little experiment, the rub. To do the test I should have turned up the drivers to 1.4V for the parallel tests, but the drivers at that high of current output get way to hot to ship. So I did the tests like I would want to ship the boards, no active cooling required.
Now that that is out of the way. I chopped up a wiring harness and checked out series. I did it very scientific, almost as much as the article linked above. I put a pulley on the steppers and tried to fight the steppers with my Hercules like Kung Fu grip. Same steppers from the kit, Drv8825 driver set to .7V. I just swapped my doctored up wiring harness for the stock one. At 15mm/s series in very noticeably stronger. I tried it at 60mm/s, they still felt a little stronger. When active and idle they are still much stronger in series. explained by the .7v and not using 1.4V on the drivers.
So now what…Change everyone to 16th stepping and order new wiring harness? Leave it as is, because I have never had an issue? I didn’t expect this to be a very noticeable difference, wrong. Kinda cool that this thing just keeps getting better for no added money though right?
Easy to try yourself. Make sure you disconnect all power before unplugging a stepper, you’ve been warned. See the attached picture.
Attachments:August 29, 2016 at 3:00 pm #16829
Good timing, just tore my machine apart yesterday to install my longer rails and have to modify my wiring to reach now.
Thinking I may have to give series a try since I have to re-wire it all anyway….
One thing I found when I switched my printer to DRV’s and 32nd stepping is that apparently some RAMPS boards have traces under the step selection headers so it doesn’t matter what your jumper settings are it’s always as if you have them all installed. Not sure if you’ve checked that on the RAMPS you provide or not but might explain why you didn’t see a difference between 16 and 32 – if those boards have the hidden traces you may not have actually been changing to 16. Just something to check.August 29, 2016 at 3:27 pm #16832
These definitely have all the jumper options, Easy to tell by how far they move.August 30, 2016 at 4:35 am #16859
When I first setup my machine it was in parallel. I had to crank my drivers up to 1 or 1.1 to get the whole gantry to move properly without strange binding. Then after looking around talking to some people I switched it to series. It definitely made a difference I was able to turn my drivers down to around 0.7. I could no longer cook eggs on my drivers. The motors did warm up slightly to the touch but nothing to be concerned about. I would recommend series for the large builds like mine (5’x5′)
Attachments:August 30, 2016 at 7:05 am #16865
Honestly I didn’t expect much, but man, huge difference. I need to get one set up as a printer and do some long term tests before I order a different harness or anything crazy. I have seen a few reports of missed steps on one side, but I don’t see how that can happen. From an electrical stand point series seems like it should be less susceptible to that sort of thing. But we we all know those armchair forum engineers are always right…hahahaahAugust 30, 2016 at 7:08 am #16866
Theory and reality are some times very different beasts. But from my POV switching was worth it.August 31, 2016 at 7:58 am #16934
So last night I wired my machine back up following my notes on how it was before I took it apart…and apparently I messed up my notes because after re-wiring all I get now is steppers juddering so something is miswired. So much for my notes, must have got something mixed up and am going to have to figure it all out manually again.
So figure I may as well give serial a go.
But I want to confirm as it’s not entirely clear from your initial post…did you switch to 16th stepping when you switched to serial? It sounds like you did but I’m not entirely sure even after re-reading that post a few times 😀August 31, 2016 at 8:06 am #16938
I had messed up to the first time… It was one coil wired wrong.August 31, 2016 at 8:13 am #16944
I tried serial, but didn’t change the stepping. Just got stuttering. Wired in parallel, and it’s working, so I’ll wait until better destructions are available.August 31, 2016 at 8:27 am #16947
I left it in 32nd stepping, I use the cnc pretty slow, except printing.
@Barry, make sure your drivers weren’t up too high, which can be done in series. It is very noticeably stronger. Sounds like you had a reversed connection. All the pics out there are for a printer z axis, both moving the same way, which would cause your symptoms. We still need to reverse one.
So now, I have tried 16th stepping many times and never noticed a difference. I might just have to by a force gauge and do some better tests. Seriously might have to find smaller steppers if it gets much stronger.August 31, 2016 at 10:03 am #16952
I was using this wiring diagram. Could have been the power though, didn’t mess with that.
http://www.shapeoko.com/forum/viewtopic.php?p=14566#p14566August 31, 2016 at 10:05 am #16955
I was using this wiring diagram.
Hopefully I didn’t break anything with the site. I posted the above link without the code tags and it linked to a post on this forum! When I first added the code tags the post disappeared completely.
August 31, 2016 at 10:13 am #16958
- This reply was modified 3 weeks, 2 days ago by vicious1.
That is the worst pic, it always comes up. The colors are all switched. I actually can’t tell if it is correct. For example the parallel the easiest one, why are all 4 colors switched and going to different coils? if red went to red and blue to blue of the same coil and you just switch the other motor it illustrates the point easier. I have a few diagrams on here but really the real picture shows how easy it is. My take on parallel, one opposite, http://www.vicious1.com/assembly/wiring-the-steppers/.
Way too easy to screw up. Did you see my picture of the actual harness?August 31, 2016 at 10:16 am #16959
The one without all the wires connected?
I thought you had to wire both pairs reversed?
This is how my parallel steppers are wired right now.
Works just fine.August 31, 2016 at 10:42 am #16962
If you reverse both pairs it would be going the same direction. That’s why that picture is confusing. In my wiring page you can see that only one coil gets reverse for parallel. What you have is opposite coils wired together, and one reversed (fine, it really is no different) it is just too confusing when all steppers have different color wires for their coils.
Attachments:August 31, 2016 at 12:09 pm #16968
Ahh! Okay, I think I got it.September 4, 2016 at 5:32 am #17150
Stepper drivers are so cheap (about $1 per driver now) that if milling is your use and you don’t have it set up as a printer I would suggest just adding two more drivers and setting them all to .75V. You do have to edit the firmware you choose to run, Repetier makes it very easy with a web interface to do it all before you even download the firmware, but Marlin wasn’t too bad once I found the right part of the stepper code I just told it everytime you set direction or pulse for X/Y do it for E0/E1 pins too.
I have the kit motors and I believe they are rated for 1.5A right? They don’t seem to be overheating at that.
If I add printing functions later I could also just add some TB6600 drivers for $8. The Diamond hotend in particular has caught my eye and adding it to MPCNC would actually be easier than with any of my other printers.September 4, 2016 at 1:11 pm #17165
That is a possibility but totally not necessary, especially when wired in series. So much power, I really might sorce newer lower powered steppers so people don’t rip their machines apart, like people where doing when trying to put nema 23’s on here.
The problem for me is these are sold for all kinds of different reasons. I am pretty stuck/happy with ramps/marlin. I don’t see any deficiencies, it’s inexpensive and works for every use. Tons of users are very intimidated by flashing firmware. I have had two boards shipped back just so I could flash firmware for them, at their cost. I have to stick to well documented and versatile. I want to start sending the kits off configured a little different but really can’t until the mods have stood the test of time (at least a few months).
I am going to try and start adding a “how to” section, for different boards/settings, firmware, ect.September 4, 2016 at 3:37 pm #17193
One of the things I love about MPCNC is just how comfortable I have started to become with mods. Before the MPCNC I actually hadn’t editted firmware at all – much less considered doing things like external steppers, or even switching to a Due with all external steppers just to run a different firmware (TinyG G2Core) just for different acceleration management. It has made me a lot more capable of everything from terminating cables, firmware, Arduino, laser, the technology used in most 3D printers, and before MPCNC when I heard ‘router’ it meant something entirely different. I have even started doing more modeling – recently made and printed some new legs that eliminate three connection points for just one solid printed leg (ABS at a very high infill). Even got a Filastruder so I could make things at just $2 a pound.September 4, 2016 at 3:56 pm #17196
So your saying The MPCNC is a gateway tool? Haha awesome!September 4, 2016 at 7:04 pm #17207
Yeah, the accessibility is amazing when you think of it – CNC, laser, 3D Printer, vinyl cutter – so many things people can do; so many things you can learn.
Even when things didn’t go to plan – looking back now – it was good for me. When my Dewalt brushes were getting low it started putting out massive EMF that caused my Arduino to keep restarting. I obviously didn’t know it at the time, so I tried so many different things (learned how to modify/flash firmware, replaced my Arduino then replaced my RAMPS, then my drivers – all of which I learned a great deal about). Eventually the Dewalt just wouldn’t turn on which finally showed me what was really the problem (wasn’t the electronics at all). Now, at the time it wasn’t good, but again, looking back now – there’s no doubt that even when things weren’t working for me – I was learning new things that would come in handy later.
I’ve done so much cutting that my replacement router, the DWP611, also needed brush replacements. Interesting thing though – the DW660 when the brushes got low it put out so much electrical noise that you noticed something was wrong weeks ahead of time, but the DWP611 – no electrical interference, no prewarning problems – it works, you turn it off, go to turn it back on, and it won’t start. Even that though has been a positive because now I know motors have brushes (yeah, I didn’t really know how motors worked before the MPCNC – didn’t know how incredibly easy it was to open them up and replace brushes, I would just replace the motor needlessly).September 8, 2016 at 1:05 pm #17410
So now I started second guessing all the things I checked in the very beginning of this machine. So I just checked out full step vs 32nd steppin on the z axis (looking for more free power). Since these all articles quote micromo’s paper (now behind a registration wall) they say at 32nd stepping we should have 9.8% max holding torque, so you’d think if I put the z axis into full step mode I could notice a difference….nope. Full step does sound kinda nasty, but I didn’t notice any different in power while in motion or just holding position. Again I got super scientifical about it and used my finely calibrated fingers. But for me if it isn’t obvious it isn’t worth the update confusion.
Anybody else played with this?September 9, 2016 at 7:11 am #17448
Full step doesn’t make much sense with the stepper drivers we use because the DRV8825 limits the current in full step mode to just 70% of what you have set. Half stepping at a minimum makes sense when you consider that.September 9, 2016 at 9:11 am #17457
I tried it at each setting, 1/32, 1/16, 1/8, 1/4, 1/2, and full. You could hear how nasty full stepping is, would vibrate/oscillate badly if used. Either way series to my surprise is a huge difference, step rate is minimal to zero difference as far as I can tell. MicroMo posted that paper that everyone quotes but there are others showing that Microstepping down to 1/64 show no difference. One was an actual test on the steppers and showed zero difference in torque when using microstepping. Makes me think Maybe the micromo Paper was about a specific type of stepper or something but When I went to read it again, it is behind a registration wall now.September 13, 2016 at 10:48 am #17658
Now set up mine in series, did not change microsteps, still 1/32, lowered voltage to .7v (even my steppers are rated to 2A), could not run my mpcnc too fast cause i switched to Estlcam / Arduino uno and it can not handle 195mm/s, but who cares, i got plenty of time. But i am thinking of going down to 1/16 for Z axis to lower the overall stepload for the small Uno… Dunno if this is really required, will test if it makes any difference.September 22, 2016 at 6:06 am #18130
I had read before that torque drops with speed, but never really comprehended the magnitude of it. Look at this chart I was sent: http://blog.misumiusa.com/wp-content/uploads/2015/02/Stepper_Server_Comparison.jpg
At idle it is just about 300oz-in, but at just 5 revolutions a second (at 8mm a revolution that would be 40mm/s) at 12V instead of 300oz-in it is just 100oz-in, but at 24V it is still 250oz-in. If you need more torque or want to go faster wouldn’t it make a lot more sense to modify your electronics to accept 24V rather than bumping up current?
I would think series wiring would just amplify the whole torque over speed at 12V drop because of the additional resistance of the extra wiring to the other stepper.September 22, 2016 at 9:01 am #18138
Just to make sure no one takes this thread the wrong way, I’m going to keep this here. I have never, ever, not once, had a power issue on the x and y axis, even when running steppers half the size that we use now.
Yes 24V is beneficial, but not by very much. Most of my cuts are run at 15-20mm/s. I like that speed so if I need to I vary the depth of cut more than the speed of travel. There are lots of ways to squeeze out a little more, but series has been by far the most dramatic, it surprised the hell out of me.September 22, 2016 at 9:44 am #18142
I tried series because of this tread and yes, with my magical fingers I feel the difference of torque.
(Moreover, just to thanks Ryan: I have now a 75cm*75cm*6-8cm MPCNC 525, with a 500W Chinese spindle and classic steel pipes 25mm. With a single flute 1/8, I can mill MDF with 2-3mm DOC, feedrate 15-20mm/s, plunge 3-6mm/s with a final tolerance of 0.2mm maximum. That’s a huge improvment of my first MPCNC (more than just an improvment in fact). To sum up: it works well! I still have to try other materials like plastic or aluminium now. Thanks again).September 22, 2016 at 10:03 am #18146
For me personally doing 3D carvings, the Z axis is where I would really like to boost things if at all possible. Every line of gcode for the 3D carvings is at a different Z height, so I’m limited to the speed of Z for all cutting. The bit’s tip is 0.5mm and 1mm with stepovers of 20% and under so even at 30mm/s Z speed I have some stuff that takes over 16 hours. What do you think has more bang for the buck – going from 12V to 24V or going up to a larger Z motor – to improve Z speed above 30mm/s?September 22, 2016 at 10:14 am #18148
You can improve you z speed by decreasing your step rate, it works great all the way down to quarter or even half stepping. Full steps are kinda rough. No problem, but 30mm/s not gunna happen. Too much inertia on large moves. You just want faster accelerations for small moves.
Go to half stepping and torture test your zaxis to increase the z max speed to maybe 12-16mm/s and accel as high as you can go before loosing steps. I have some torture test scripts on here.
You must be logged in to reply to this topic.