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  1. #1
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    inexpensive nema 17 "closed loop" stepper driver

    https://www.cnczone.com/forums/attac...d=446992&stc=1




    Anyone here have experience with these "mechaduino" type closed loop drivers?
    https://github.com/jcchurch13/Mechaduino-Firmware

    It was a kickstarter thing that delivered and then finished. It's now open sourced. You can either build it yourself from the github files or you can buy clones for $15 on aliexpress. I have 3 of them on order from Aliexpress (I opted for "servo42a") and was wondering if anyone else has tried them also.

    I'm using CNC to etch PCB's on a modest 2418 CNC router, and with the low torque that comes with microstepping, I just want to ensure I'm not missing any z-axis steps and/or lateral steps on fine pitch etches.

    There's also Ustepper, made in Denmark and of a similar design, and it looks to be nice because it uses Trinamic TMC5160's and can handle a bit more current. It's newer though, so I wasn't sure as to whether it's still in the de-bug phase.
    Attached Thumbnails Attached Thumbnails mechaduino.jpg  

  2. #2
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    Re: inexpensive nema 17 "closed loop" stepper driver

    Quote Originally Posted by WhiteHare View Post
    with the low torque that comes with microstepping,
    There was an article that was published by someone many years ago that is circulating the internet, that is commonly misinterpreted. It was actually about accuracy at higher microsteps, not torque loss due to microstepping. It gets regurgitated just about everywhere.

    I'm not really smart with all of the electronics that drive stepper motors, but what I've come to understand is that with a good driver, you won't loose much (if any) torque while microstepping. But you shouldn't expect that using a really high number of microsteps will increase your accuracy proportionately.

    Quote Originally Posted by WhiteHare View Post
    Anyone here have experience with these "mechaduino" type closed loop drivers?
    I don't think many people on these forums use Nema 17's. Are these available for Nema 23's or 34's?

    Really interesting.

    So the dev's of this are saying that these aren't closed loop steppers.....that instead they've converted a stepper motor into a true servo motor.

    So it's a closed loop system that has no rotary encoder. It still uses a stepper driver, the A4954 as a component on the board...they should have used a trinamic driver.

    How is this a servo and not a closed loop stepper? It would be interesting to see a before and after torque chart for a motor with one of these on it!

    The encoder without adding any additional rotating parts is really cool.

    https://www.kickstarter.com/projects...strial-servo-m

    https://tropical-labs.com/mechaduino/

    Quote Originally Posted by Tropic Labs
    Mechaduino is an affordable open-source servo motor for DIY and professional mechatronics under development at Tropical Labs. Mechaduino is Arduino-compatible for ease of use.

    About:

    Engineers use servo motors to achieve the precision motion required in applications such as robotics, automation, and CNC manufacturing. Like RC servos, industrial servos actively correct for external disturbances. Unlike RC servos, industrial servos can provide very accurate motion, and often support advanced motion control modes. Unfortunately the cost of industrial servos is prohibitive to the individual maker.

    Tropical Labs engineers have been developing an affordable open-source servo motor, opening the door to sophisticated mechatronics applications. Our design leverages the low cost of mass produced stepper motors. We are able to achieve very high resolution via 14b encoder feedback (after calibration routine!).
    Is this this the same thing? It still has the salmon skin on 3d prints common with the Allegro drivers.

    https://www.youtube.com/watch?v=R1TghZmE6Gs

  3. #3
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    Re: inexpensive nema 17 "closed loop" stepper driver

    Quote Originally Posted by NIC 77 View Post
    Is this this the same thing? It still has the salmon skin on 3d prints common with the Allegro drivers.

    https://www.youtube.com/watch?v=R1TghZmE6Gs
    Yes, that's the model that I have on order. They did their own board spin. The end of the user manuals says "much of the work is based on Mechaduino project by J. Church." At a glance, it looks substantially the same, and I'm hoping that it is, because the Mechaduino seems to have reasonably good documentation.

    Teaching Tech reviewed a variant of it (called the SERVO42B), based on an STM32, where he several times whacks a 3D printer hard with a mallet while it's doing a print, and--unlike an open loop stepper-- it doesn't shift any layers:
    https://www.youtube.com/watch?v=eM8zSG8fEkk&t=756s
    It's a pretty cool demo.

  4. #4
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    Re: inexpensive nema 17 "closed loop" stepper driver

    These 3d printers can push the Nema 17's too far. Also, sometimes the inexpensive electronics are not the best. These factors can lead to missed steps and layer shifts. Also, running at 12V is not ideal. Better printers will have a Nema 23 moving the bed.

    Some of the electronics can be really good though, things like the Duet boards.

    For the kinds of routers and such usually discussed here, using the larger stepper motors, Nema 23 or 34 with good quality drivers, missed steps aren't normally an issue unless there is a design flaw, mismatched components, or unrealistic expectations on speed and acceleration in relation to the motor torque.

    I read that these claim a resolution of 0.1 degree, but it wasn't on the official website that I could find....if that's true, for a 1.8 degree stepper, it's the equivalent of 18X microstepping with a closed loop guaranteed resolution, and if that's true it's pretty darn good!

    Teaching Tech has one video I like about nonplanar 3d printing.

    I'd like to see a version of this for some larger motors. It's too bad the salmon skin artifacting is still present.

  5. #5
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    Re: inexpensive nema 17 "closed loop" stepper driver

    Quote Originally Posted by NIC 77 View Post

    I'd like to see a version of this for some larger motors.
    Wish granted. Makerbase has a similar driver for nema23's called servo57A and servo57B:
    https://www.aliexpress.com/item/3296...778b1b968s1qZU
    and its priced the same as the nema17 closed loop driver.

    What seems like the biggest barrier to nema23 adoption is the greater current requirements exceed the typical inexpensive driver modules.. However, with an inexpensive closed loop driver such as this to power a nema23, I suppose that barrier goes away.

    The MKS user manual hints that it might (?) be wired into a duet board through the duet board test pins. It didn't sound terribly definitive though.

  6. #6
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    Re: inexpensive nema 17 "closed loop" stepper driver

    [QUOTE=WhiteHare;2395338]Wish granted. Makerbase has a similar driver for nema23's called servo57A and servo57B:
    https://www.aliexpress.com/item/3296...778b1b968s1qZU

    That one is limited to 3 Amps Peak and 24V. Still an improvement. What driver is on the board? I couldn't tell.

    I have recently become interested in these:

    Home

    Trinamic driver based, 4.33A up to 60V. Put that on the makerbase board!

    I think the new Duet 3 board's onboard drivers are good for up to 6A, but limited to 24V in practice.

    Quote Originally Posted by WhiteHare View Post
    What seems like the biggest barrier to nema23 adoption is the greater current requirements exceed the typical inexpensive driver modules.. However, with an inexpensive closed loop driver such as this to power a nema23, I suppose that barrier goes away.
    A good higher current Gecko or Leadshine open loop stepper driver might cost $50 to $100 per driver, so compared to a $10 Allegro driver, yes it's a different kind of thing.

    But the newer trinamic based drivers like the one I posted a link to could be a game changer in this area.

    The Makerbase board is totally cool, but it still needs a stepper driver on it to run.

    Quote Originally Posted by WhiteHare View Post
    The MKS user manual hints that it might (?) be wired into a duet board through the duet board test pins. It didn't sound terribly definitive though.
    An expansion board should give the pinouts to run this as an external driver from a Duet board. I'm working on an industrial 3d printer project at the moment. I wonder if I should use some of these makerbase boards for the extruders. Eventually I want to try doing pellet extrusion, but first I need to get the basics running.

  7. #7
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    Re: inexpensive nema 17 "closed loop" stepper driver

    Quote Originally Posted by NIC 77 View Post

    I read that these claim a resolution of 0.1 degree, but it wasn't on the official website that I could find....if that's true, for a 1.8 degree stepper, it's the equivalent of 18X microstepping with a closed loop guaranteed resolution, and if that's true it's pretty darn good!
    Yup. The acme screw on my cnc advances 2mm per revolution. So, that would be 2/3600=0.00056mm per step, guaranteed. Provided that it has enough holding power, that should be plenty good enough for milling a PCB, including carefully grinding off solder mask above the pads (without grinding off the pads). Well, at least there's reason to hope it might be good enough.

    According to package tracking, the package is now in my country. So, I expect I'll receive it sometime next week, or maybe earlier.

    If holding power turns out to be an issue, then I'll switch tactics by maybe getting ample precision from using planetary gears, which will surely provide ample holding power as well. With a 100:1 gear reduction, I probably wouldn't need to microstep at all. The only question then would be whether or not I could run the stepper at 100x the speed so that the whole operation doesn't crawl. Seems unlikely, doesn't it? Maybe this is the reason why a 5x gear reduction is the most popular.

  8. #8
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    Re: inexpensive nema 17 "closed loop" stepper driver

    Quote Originally Posted by WhiteHare View Post
    Yup. The acme screw on my cnc advances 2mm per revolution. So, that would be 2/3600=0.00056mm per step, guaranteed. Provided that it has enough holding power, that should be plenty good enough for milling a PCB, including carefully grinding off solder mask above the pads (without grinding off the pads). Well, at least there's reason to hope it might be good enough.

    According to package tracking, the package is now in my country. So, I expect I'll receive it sometime next week, or maybe earlier.

    If holding power turns out to be an issue, then I'll switch tactics by maybe getting ample precision from using planetary gears, which will surely provide ample holding power as well. With a 100:1 gear reduction, I probably wouldn't need to microstep at all. The only question then would be whether or not I could run the stepper at 100x the speed so that the whole operation doesn't crawl. Seems unlikely, doesn't it? Maybe this is the reason why a 5x gear reduction is the most popular.
    With a 2mm lead, it will be slow anyway.

    With 100:1 gear reduction, it would be unuseable. You are stuck thinking that you will loose torque by microstepping. Like I mentioned, that article that has been misinterpreted, it's about accuracy. You need microstepping to smooth out the motor. That's for a regular stepper motor.

    Whatever the next increment at 18x or above is for microstepping would be my guess for these drivers. Do you even have the option to adjust it? They've changed up how it works and claim it's a servo now. You just use it as intended. Trying to change it to lower microstepping will not get you more torque.

    There are a few things to consider when using gear reduction...low backlash planetaries are expensive, alot more than a larger stepper... inexpensive ones will have backlash.

    The rotary inertia of the gear is important when considering the acceleration of the system, and for a 5:1 planetary, the output acceleration of the planetary will be 5 times less than the acceleration of the motor. For what you're doing with a 2mm lead, I can't see this being a good choice. It would be very slow.

    You might find that your motors can not keep up when you try to go too fast, and this has a few factors, speed, acceleration, and the motor torque graph. You might be better off to go with an 8mm lead screw, the opposite of using gear reduction.

    Not knowing anything about your design or what you hope to achieve for performance, top speed and acceleration, I can't really say more.

    With the closed loop motor, the accuracy you will achieve will be limited by your other components, such as your end support bearings, your leadscrew and leadnut, and your spindle. Also your linear bearings and machine design. So in practice if you can get to 0.05mm or 0.002" accuracy then you've done very well.

  9. #9
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    Re: inexpensive nema 17 "closed loop" stepper driver

    I'm surprised to still see the usage of NEMA as a power reference for steppers/motors, NEMA is a mounting frame size and has not alot to do with power.
    For e.g. I have catalogues for a couple of the very large Stepper manufacturers, they have certain NEMA size motors with different core (body) length, each one has a different Nm torque value, but have exactly the same (NEMA#) mounting .
    Al.
    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.

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    Re: inexpensive nema 17 "closed loop" stepper driver

    Quote Originally Posted by Al_The_Man View Post
    I'm surprised to still see the usage of NEMA as a power reference for steppers/motors, NEMA is a mounting frame size and has not alot to do with power.
    For e.g. I have catalogues for a couple of the very large Stepper manufacturers, they have certain NEMA size motors with different core (body) length, each one has a different Nm torque value, but have exactly the same (NEMA#) mounting .
    Al.
    That's true Al. Good point.

    Typically the Nema 17 motors used on 3d printers are pretty wimpy and on better printers, the bed will be moved with a Nema 23 that has more torque. But it's just a generalization, and you need to look at the specs of each motor to make a valid comparison. I thought that was an obvious thing, sorry if I mislead anyone.

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    Re: inexpensive nema 17 "closed loop" stepper driver

    Quote Originally Posted by NIC 77 View Post

    Not knowing anything about your design or what you hope to achieve for performance, top speed and acceleration, I can't really say more.
    I'd be happy if I could remove the solder mask that's above the solder pads without also removing the solder pads in the process. Like this:
    https://www.youtube.com/watch?v=vaqOFH0Te5Q

    Bantam Tools can do it, and so can Wegstr, so those are my existence proofs that it's possible.

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    Re: inexpensive nema 17 "closed loop" stepper driver

    Quote Originally Posted by NIC 77 View Post

    I read that these claim a resolution of 0.1 degree, but it wasn't on the official website that I could find....if that's true, for a 1.8 degree stepper, it's the equivalent of 18X microstepping with a closed loop guaranteed resolution, and if that's true it's pretty darn good!
    It's a wonder that it has taken so long for stepper products to surface in this area. A full 10 years ago magnetic encoders were allowing for 0.08 degree accuracy and repeatability in RC servos in a similar "all-in-one" design:
    https://www.youtube.com/watch?v=8jajnIBX2cU

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    Re: inexpensive nema 17 "closed loop" stepper driver

    What is it that you're building? What's your design? What Nema 17 motors do you have, have you bought them yet?

    I had a look at the Bantam tools machine. I was curious what components they used as far as bearing supports for the leadscrews and also the lead of the leadscrews they use. Couldn't find any nitty gritty details. All hype videos. What have you found in your design research?

    IMO, if you're making a machine, consider a minimum max speed of 100 IPM. With a 2mm lead, I'm not sure you'll get there at any decent acceleration.

    https://www.bantamtools.com/machines...illing-machine

    $3600 USD, not inexpensive. IMO, you are better of with an Omio CNC that has square rails...some of them have round...avoid those.

    https://www.omiocnc.com/

    https://www.omiocnc.com/products/x4-...-800l-usb.html

    In general, the unsupported round rails are the worst for CNC. You're doing some very light work for pcb milling, so you can get away with quite alot. It doesn't need to be perfect or expensive. The frame can be made of wood. Do you have a budget for this?

    Another option would be 3 of these and a short travel Z axis

    https://www.ebay.ca/itm/Linear-actua.../202373227731?

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    Re: inexpensive nema 17 "closed loop" stepper driver

    Yes, if I were to start over from scratch I would probably get three of those. Or maybe three of these:
    https://www.aliexpress.com/item/4000...c00SRt2ze&mp=1

    or maybe just one of these:
    https://www.aliexpress.com/item/3301...c00SRt2ze&mp=1

    but at the moment, what I have isn't any of those but rather just a very modest 2418:
    https://www.cnczone.com/forums/attac...d=447158&stc=1
    that I use to mill PCB's, and I'm at a point where I'm trying to make some improvements to it so that it's better able to etch finer pitched PCB's.

  15. #15
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    Re: inexpensive nema 17 "closed loop" stepper driver

    Oh, cool, you're just doing some upgrades to the motors.

    I'm really interested in hearing how the upgrades with the mechaduino work out for you after you have used them for a bit.

    Please let us know.

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    Re: inexpensive nema 17 "closed loop" stepper driver

    Sure, will do, although looking back I think you're original reaction was right: no benefit for CNC over simply using adequately powered stepper motors in the first place other than maybe as an alarm that an exception has occurred. I can see how it would be helpful when setting up the initial calibration though.

    Is there a standard suite of tests that everyone can run on their CNC to break down just exactly what each source of a CNC's inaccuracies is and what the magnitude of each is? It would be especially useful in comparing different machines. Most of what I read on forums is almost at the level of alchemy because it's lacking an analytical framework that such a diagnostic suite might provide.

  17. #17
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    Re: inexpensive nema 17 "closed loop" stepper driver

    Quote Originally Posted by WhiteHare View Post
    Sure, will do, although looking back I think you're original reaction was right: no benefit for CNC over simply using adequately powered stepper motors in the first place other than maybe as an alarm that an exception has occurred. I can see how it would be helpful when setting up the initial calibration though.
    I'm not sure about that. These drivers may allow for more torque to be used before missing steps or faulting out than the same stepper with a different driver. So from a cost perspective for fixing things like 3d printers, and eliminating layer shifts, that's an advantage. Too bad about the salmon skin! Also, from what I've read, I'm not an expert on this subject, I'm not sure that microstepping above 10x does anything to increase the accuracy of the stepper, even though it might run smoother. So the 0.1 degree accuracy, if that's what this can do, is better.

    The problem there is that the other factors affecting accuracy in the machine design will dominate the accuracy anyway. With larger lead linear components (like 25mm per rev or even much more) and using better quality linear components, then the increased accuracy from the stepper starts to become more relevant to the overall system accuracy.

    Quote Originally Posted by WhiteHare View Post
    Is there a standard suite of tests that everyone can run on their CNC to break down just exactly what each source of a CNC's inaccuracies is and what the magnitude of each is? It would be especially useful in comparing different machines. Most of what I read on forums is almost at the level of alchemy because it's lacking an analytical framework that such a diagnostic suite might provide.
    How do you know if you have backlash in your leadscrew or a problem with your end bearing supports? I don't know it's hard to tell without tearing into it and taking things apart.

    Things like spindle runout can be measured by putting a long straight bit into the spindle, putting a block next to the tip of the bit, and manually rotating it, If it's pronounced enough, you will be able to visually see the wobble and even measure it with some shims. If you have a dial indicator it would be easier but there's alot you can check without one.

    Also things like using an electric touch plate. Zero your machine to the plate, move it around, bring it back to the plate and see if you're off any.

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    Re: inexpensive nema 17 "closed loop" stepper driver

    Time to upgrade the motion controller. The woodpecker is hopeless because it takes 12v-36v input voltage and downconverts it to 12v:
    https://www.cnczone.com/forums/attac...d=447202&stc=1


    This means you can't actually drive your stepper stick at more than 12v, even though the A4988 can use up to 36v and the DRV8825 up to 45v. The TMC5160 allows up to 60v. I'm guessing the grbl board designers did this to avoid any possibility of going over the allowed voltage, which would mean fewer warrantee returns. All well and good for them, but if I'm not mistaken, it deprives the user of snappier accelerations.


    So, I ordered just a primitive arduino shield, and hopefully it is lacking this "feature":
    https://www.cnczone.com/forums/attac...d=447204&stc=1
    The board markings do indicate the same 12-36v range, though, but I'm guessing that's there purely either as a cautionary warning for A4988 users or because that's the highest voltage that the capacitors are rated for. Given the cramped board, perhaps trace widths are a factor as well.


    The mechaduino driver can handle voltages up to 40v, but the mechaduino board itself was designed with 36v capacitors. The MKS-servo42a has a 30v maximum according to the design they borrowed from.


    All this does make me interested in trying a TMC5160 at 60v just to see how much snappier it might be.

    Unfortunately, the uStepper (http://ustepper.com/product_sheet_revB.pdf), despite using the TMC5160, doesn't take advantage of the 60v possibility. It recommends 24v input voltage, with a 30v maximum.

    Good grief! Why, oh why, did they do that? Was it just to save a few pennies on component cost? Will I have to design my own board if I want high performance?

    I was originally hoping for this to be a drop-in upgrade. Maybe it still is, but I'm starting to have doubts about just how much of a performance upgrade I can expect from it.

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    Re: inexpensive nema 17 "closed loop" stepper driver

    Reporting back: I received the el cheapo GRBL boards (below). The good news is that they don't have a buck converter getting in the way, the way the woodpecker does. The bad news is that the caps are rated at only 40v. So, I may replace them with ones rated for higher voltage. Also, there's a mysterious glass fuse soldered in the midst of it all. Not sure at what current it's rated to blow but, meh, probably high enough if the designer did his homework.


    So, overall, I expect this will be an improvement over woodpecker for running GRBL at higher voltage :-)

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    Re: inexpensive nema 17 "closed loop" stepper driver

    If you're using external drivers you don't need to run your board at the same voltage as the drivers.

    I don't know how the mechaduino drivers work, do they typically plug into the board in place of the regular drivers? Can you not power them separately from the main board supply?

    If you look at this picture from this link:

    Home

    Attachment 447208

    You can see that the signals to the driver need to be at 5V. The up to 60V to run the main power for the driver is from a separate supply than the main board. You can see where it gets connected in the pic I attached.

    You need to check what voltage your motors can handle. I've never heard of running a Nema17 at 60V but it's something you'd need to check for the motors you want to use.

    I would personally never run any machine on 12V. But I would consider 24V as a minimum. The increased voltage typically give better torque performance on steppers with higher inductance at higher RPM. The gains in performance you might achieve are dependent on the motors you are using and the max RPM you are going to.

    Below is a graph for one of the Leadshine Nema 23 stepper motors. You can see how the increased voltage doesn't change the available torque that much for this particular motor.

    Attachment 447212

    There may be some additional benefits of higher voltages like better acceleration of the motor, etc, but for the kind of machine you have and what you are doing, I don't see this as being relevant. Please remember that I am not an expert on electronics, and you should always get more than one opinion.

    Sorry if I misinterpreted what you were saying, it's entirely possible.

    Was that helpful?

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