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Stepper Motors
  • Vote Up0Vote Down
    April 2011
    The CNC Torch Table and another CNC devices in the GVCS will all need stepper motors. The current plans call for using off-the-shelf motors, but eventually we will want to fabricate our how. I have started to collect information in, but more work is needed. I have no experience with lathing or milling - which will be needed to fabricate a motor from scratch. I'd like to invite anyone reading this to contribute to the effort in terms of information gathered, personal experience, or other sources of knowledge (books, videos, etc.).

    There are several kinds of stepper motors. It is not clear to me which type would be the best trade-off between fabrication simplicity and useful characteristics. What kind of stepper motor would you recommend for our first prototype?

    - Mark J Norton
  • 21 Comments sorted by
  • Forgive my ignorance, but I thought that DC servo motors were the correct choice in positioning applications where serious actuation force might be needed. Not true?
  • Mark, are you still working on this? Do we have a plan for a motor controller yet? I think the motor controller is the first thing we need to get nailed down. From what I understand it will consist of a microcontroller and some power electronics. The microcontroller will need to implement a motor control program which can receive commands from a PC, I'm assuming. I'm also assuming it will be based off G code.

    Is anyone else working on the controller currently?
  • i sorta assume the reprap team has designed a microcontroller for their 3d printer but im not sure.

    for the motor itself, maybe we need someone to crack one open to get us started? i dont have any idea whats different between it and a regular motor.
  • I'll see if I can't disassemble and document a stepper motor. How do we submit invoices for this sort of thing?
  • unfortunately services performed for non profits are not tax deductible
  • I wasn't saying for tax deduction, the OSE isn't without funding, so they should be able to reimburse me for the purchase of assets for the exclusive use of the OSE.
  • oh i thought you were joking lol so i was joking too

    you're right though, seems like they could distribute a little cash for satellite projects

    or order it and have it delivered at your house
  • That raises the question... As a donor I would like to see the financial records of the OSE to see exactly where the 2000+ dollars a month us true fans pour into the organization. They can't expect the volunteers to absorb all of the expenses for all of the work being done. I do think there needs to be a process whereby project expenses need to be approved and not just throw money at all the projects without accountability. But if I am doing work as a member of a project for the OSE I should get a budget to work with.
  • We need program managers who get funding for a program, then those managers distribute it to their team as needed.
  • @ Jason - Yes exactly, there is no way Marcin can handle all this by himself. Time to delegate.

    The Dawg
  • for those curious about fund allocation, the way to audit at the moment is to apply for an onsite visit and come see what your funding is doing for yourselves, though that is impractical for many i understand. the next way is to look at the results and planned builds reported on the blog, and estimate costs to do this from the wiki and one's own intuition. but we're working on org development to better address accounting and like issues. 

    a project that marcin will be funding is the solar fire one, in the sense that he'll develop an automated version and build a prototype of it. that takes money, time and labor, like all the other prototypes. there is also discussion of hiring area experts for design work. so those are two informal paths to receive funding for offsite development.

    a discussion of marcin's core values would currently likely best be held by those who have developed relationships with him, likely by coming here to FeF to do so. of course, each of us is able to freely associate and work with those whose values best match our own. some may have different views than him. his priority right now seems not to organize a community, virtual or real (that comes later), but to get the technical work of building the prototypes done. this requires trust from his supporters, true. but as one of his (many) true fans, after coming here and seeing what is happening, he certainly has mine.

  • This is Marcin speaking for himself to some of these issues:
  • @vann

    Great blogpost, I recommend everyone read it. It sets both the organizational structure and current technical status and needs.
  • I have traded emails on the subject of servos vs. stepper motors with Marcin in the (distant past), and I think that even though there are existing (& Open Source) projects that are mature enough to be adaptable for or directly usable for this, there wasn't enough volunteer time (on my part?) to lead that charge.

    Open Source Servo project would be good for the electronics, and can be scaled up with some effort by one familiar with electronics at - this is focused on small hobby servos for mainly RC-controlled devices, but the electronics can be re-purposed for any motor that you can obtain a suitable controller for.  No matter the size!

    Also, the Open Source Motor Controller project has a mature enough product that it can probably be directly used with DC motors, as is.  They are most active in their Yahoo Group at but there is also a website located at that has more information on the project too.

    I still don't have the time to pull this out, but when I get to a point where I'd be making any CNC machines, this is the route that I expect to take, for better accuracy than what is possible with stepper motors.

    Perhaps someone else here will be better able to capitalize on this information now, rather than later, as I feel that eventually, all of the serious CNC work on the GVCS50 will have to be moved to servos to be market competitive.
  • On another note, if we were to ever scale up to serious industrial CNC, most of them are actually running AC servos, but by the time we are close to that, We'll probably be building our own motors from scratch to spec.
  • Vote Up0Vote Down
    August 2011
    The servo motor controller project, like many OSE projects, started strong and kinda fade.  My part in it got shifted over to the Steam Engine project, which also may be stalling or seriously changing at this point.  I think an open source servo motor (AC or DC) would be very useful on several other projects.  The robot comes to mind, since it seems to be nearing the end of it's design/spec phase.

    If the project appeals to you, jump in and start pushing it.

    - Mark
  • That would be the crux of the matter...  Robotics is/was my hobby interest, which is how I discovered  both of those, long before I ever heard of OSE.  I've since become bogged down with the dreary realities of running my own business, and haven't had the time to pursue my hobbies since.

    I've seen the term "Wage Slave" used around these parts, but you don't really know slavery until you become self-employed in a retail consumer market!!!

    I already know how to do the DC servo part, it is commonplace in robotics, and that would probably suffice for anything OSE would likely be needing for a good long while, but I have not the personal bandwidth to push that platform without risking going out of business by neglecting my current customers.  One day, I shall abandon this job for a simpler life, and I will love doing it when it happens.

    Until then, I fear I won't be any more than a casual contributor on the forums.
  • Vote Up0Vote Down
    August 2011
    LOL, I sympathize with you.  I also have my own business, but it is a consultancy rather than retail.  Perhaps the trick is to find a product with a very high margin that allows you to have a comfortable work schedule that leaves time for other activities.

    - Mark
  • I have been active with the LinuxCNC group for a number of years and have formed opinions on steppers, brushed servos and  brushless servos. I'm still trying to get up to speed on what the OSE/GVCS context is, but in my view, steppers are easyier to understand, implement and cheaper, but if an axis motor needs to cater to lower tech and local manufacture, brushless motors have my vote, especially out runners. Magnets and silicon steel might be an issue, but would be for any motor. LinuxCNC has a driver for software commutation control of various brushless configurations, so all that is needed is a three channel h-bridge and some sort of motor encoder system.

    Actually a little more is needed than a simple h-bridge, such as current control and protection, and high voltage FET drivers if using high voltage motors.

    I have steppers on my mill and brushed servos on my lathe. I like the brushed servos because the driver is more basic, a single h-bridge, but I think brushed motors would be harder to make from scratch. Decent steppers, in my view, would be nearly impossible to make from scratch.
    Kirk Wallace
    California, USA

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