I haven’t yet seen one, but the beast might exist. I still go back to the idea that if you are going to build a custom motor controller, go ahead and add a simple, low cost microprocessor to the board whose function is to just perform motor controls and read the encoders and let it talk to the “master” device (RPi, whatever) through SPI, serial, etc. You could use a PIC controller (multiple PWM outputs and quadrature encoder interfaces) but I don’t know how easy they are to program or update in the event there’s a need to.
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Would it make sense for organized efforts to focus on Epics (themes) to move work forward in a particular area? For example, a theme might be ‘Eliminate Bad Experiences’. (A $500 CNC busts its target price if I have to reorder a controller or a motor - not that I’m speaking from personal experience or anything 
). Your #6, 7 address this. I also see “Better Accuracy”, “Faster Cutting”, and “Broader Software Support”. I think.
Another Epic I would like to see is “reduce or eliminate recalibration”.
we need to fix the ‘manually set chain length’ in the stock GC. This is one
thing webcontrol does much better.
in webcontrol you have the motor controls to set the sprockets to 12 o’clock in
the manually set chain length screen. So the process is, go to that screen,
tweak the sprockets to 12 o’clock, set the marked links on the sprocket, hit the
button, return to cutting
in Ground Control you have to go to automatic calibration, tweak the sprockets,
quit, answer the scary warning telling you that things may not work if you quit,
go to an advanced tab to then find the ‘manually set chain lengths’ button and
then go back to cutting.
if you don’t mark your chains, or you change something else on the machine, you
are going to have to re-calibrate.
David Lang
better accuacy is a software/hardware issue, not a controller issue.
faster cutting requires different motors (plus acceleration planning in the
firmware)
what are you thinking of when you say “Broader Software Support”?
David Lang
So does this bring us back around to the importance of unsticking the holey-calibration branch and web control updates and getting those merges approved and new builds out so this can become mainline? I was very pleased to hear from @WoodCutter4 that there is some movement in that direction but it still sounds like it’s not quite clear yet how to get it all over the finish line. Are there any blocking items? Certainly having better usability around ensuring you stay calibrated will go a long way to accurate cutting. 
-Jeff
not enough people with time/expertise in firmware and GC programming
I’m afraid that isn’t my area of expertise but I guess this is a good opportunity to put out the call. Maybe we should sticky a “job opening” at the top of the relevant forum and catch a few casual eyeballs who don’t know there is a need?
-Jeff
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So does this bring us back around to the importance of unsticking the holey-calibration branch and web control updates
no, this is a fix to GC independed of holey-calibration
Are there any blocking items?
testing, we need people to test the git master branch, both with the holey
calibration, but (in some ways more imporantly) also with the tradional
calibration to make sure it didn’t break anything.
David Lang
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Maybe someone can create a new post asking for testers (this thread has digressed a bit ). I can’t test it because I don’t even have a functional Maslow at this point (all my motors are used in the four-motor test rig).
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If someone was going to hypothetically design a controller for testing but include a stepper motor controller for z-axis, is there any ‘preferred’ stepper motor module? I see them readily available all over the internet.
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To clarify further, my thought was perhaps a controller with components for five DC motors and headers installed if someone wants to install an optional stepper motor module and use it for the Z-axis.
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I would use the standard plugable module
see the wide variety in the first list at
These are all pin compatible [1] and most new driver chips get packaged into
this format so that they can be used with a bunch of 3d printer boards.
David Lang
[1] some of them have options for serial or SPI interfaces to the boards for
enhanced features, such as detecting when it has hit it’s limit without switches
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I am leaning in the stepper for the zaxis direction too, especially since linear slides can be had cheaply with a stepper motor already attached. I don’t have any recommendations, but I am excited to see the results.
One possibility is that the same chip could be used to power a DC motor option if needed. A stepper motor is basically two DC motors in one.
Can someone briefly explain the advantage of a stepper motor?
main advantage is availability, one can buy them almost everywhere. supposedly they are cheaper, but we are talking about maybe saving $5 when bought in bulk.
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You can get a linear slide with a stepper motor mounted to it cheaply. People have mounted DC motors to them, but it doesn’t bolt right up… I think @MeticulousMaynard’s zaxis uses a belt or something between the motor and the linear slide… as an example.
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That would be possible if we use a chaip that’s a pair of H-bridges, but if we
use one of the off-the-shelf stepper drivers, they don’t support that mode of
operation. And the small stepper drivers are so cheap (<$1 in quantity from
china) that it’s hard to justify the cost and complexity (both in software and
hardware) to support this.
David Lang
steppers are used on almost all 3d printers, so if you can use the particular
size steppers that they use, they are really cheap (I got 5 for $25),
Also, because of the 3D printer and desktop CNC markets, there are a lot of Z
axis setups ready made that have the screw holes to mount a stepper (if they
don’t include the stepper as well) an example being $37 (free shipping) for
David Lang
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Late…
Video streams aren’t interactive and don’t require precise response to events like encoder inputs or carefully timed motor control (would have said steps but these are dc motors with encoders). Real-time is a whole different world than video streaming
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