I googled SPI motor controllers and found a few, but the SPI is used for communications and you still need PWM pins, etc. Is this the type you are talking about or is there ones out there that does everything over SPI?
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This encoder only provides angle (0-360) and doesnāt count rotations, correct? Is the idea that since this is on the pinch roller (not turning all that fast), that you continually poll it to get position and, in software, you log transitions between 360/0-degrees to calculate chain length? Something like
chain_length = (transitions_counter + encoder.read()/360) * pi * D?
I think Iāve skipped a cog here somewhere, so apologies if I just missed itā¦ but what is the question that is trying to be answered?
If we go back to the idea of the top 3 things, it sounds like @bar has set the priority at
- Keeping the next revision of the design as close as possible to the $500 entry point. So thatās really good to have nailed down since that informs virtually all other hardware decisions.
While the constraint is clear, the focus of the revisions isnāt quite clear to me. To @dlangās point, it seems like itās a bit difficult to zero in on accuracy and repeatability changes at this point. There is a lot of data out there about different experiences, but I think it was @WoodCutter4 who pointed out that he had pretty darn good accuracy with a 10ā frame, while the common suggestion is to go to 12ā. Is the goal of the next revision to substantially improve accuracy and repeatability?
Other potential goals might be cost-shrink, improved reliability, reduced complexity for new users, improved safety, etc. Excited to see the active discussion, just trying to wrap my (product management guy) head around what the objective is.
-Jeff
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@JWoody18 - I LOVE this.
If I may, I think the topic title is in reference to possibly going away from the Arduino.
Bar can weight in, but I didnāt see $500 specifically referenced, although, even cheaper would be better, right (regarding keeping the price as low as possible)?
Also, in case you missed it (I did), here Barās topic āMusings on a new designā that lays out some goals going forward.
Right now, the community is in the ideation stage. Lots of options. The giants in the room, whoās shoulders newbies like me stand on, are thinking about the options and possibilities. Iām very excited and hope to someday be able to contribute more on their level.
Also, I regret to say, this was not me. I started with 12ā top bar.
Best
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Found this earlier today and thought, especially since it is open source, that it was worth sharing to review for potential ideas: https://buildbotics.com/
-Jeff
That is cool! Looks like a very capable controller. Their site shows it is $450, so after adding a sled, motors and other necessary hardware, we would be well above $500. Of course, router and frame materials need added to that for the users total cost.
Oh I wasnāt suggesting that we go with the controller, merely pointing out that I think a lot of thought and effort has gone in to it and since it is open source the design files are available in great detail. May save treading some ground that others have previously. It also appears to be based around a RaspberryPi so I figured there may be some breadcrumbs laying around to help answer questions around the edges. 
-Jeff
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even if the bolt pattern isnāt the same, as long as the motor can be mounted it
could be used. It also removes some of the concerns about backlash if we measure
on the output shaft rather than the input shaft of the gearbox
David Lang
as long as you are polling at least a couple of times per revolution, you know
what direction you are turning, so if the count crosses the boundry, you know
what direction it crossed and can account for it.
David Lang
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it does not handle DC motors and encoders, only steppers, so it would need as
much surgery as linuxCNC or grbl for us to use itās software. I think we are
better off aiming at linuxCNC and grbl than this system.
but itās worth looking at their parts list, what H-bridge chips do they use? how
expensive are they?
David Lang
Docs for the Buildbotics controller are in Github here: https://github.com/buildbotics/
@Metalmaslow excellent idea. Do you plan on further breaking out your offering? For example, sled, metal linkage, z-axis all as separate items?
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We may want to split this thread in two - one for āStrategy and Roadmapā and the other for executing on the next controller iteration.
Most any entity engaged in large-scale consumer product development such as automotive, electronics, pharma, cpg all have a product range with (using Honda here) HondaJet, F-1 Racing, to the Civic, Fit, and your lawnmower. New ideas start out on a small scale where āwin at any costā is the attitude, and innovations here make their way downmarket overtime. Concept cars have a role here as well, but more for the aesthetic / experience vs engineering.
While I was initially attracted to the Maslow project by sheet size x cost, I am now excited by the community support and the pace of innovation. I will avoid adding up what I have spent on my Maslow at this point. And I have yet to make a cut towards something other than a better Maslow. But Iām hooked, and will be spending more. BUT - the price got me to start.
All of this is background to reiterate the idea behind my Accuracy Rankings post, which is to create a vehicle to:
- Clearly communicate the state of quality of the machine
- Set clear expectations for what you get for a given level of investment
- Drive development progress forward
The āunlimitedā class could spur new thinking from unexpected places (like @Mike_Thomas Death Star sled, the Metal Maslow, etc). The middle class ($1000? $2500) could show what you could do for the same as an entry-level x-y CNC. These classes may also be in a position where they have more money than time and could help to support a commercial ecosystem.
And of course the original $500 price point. I would hope that innovations that occur because of the no-limits thinking at the top level would filter down to the lower levels over time. Meticulous designs originally conceived at higher levels may be replicated (often with an investment of time) at lower price points by those with the time to noodle on them. And constraints at this level can drive innovations for all.
I propose a simple 3-tier system that helps us all to focus on what we are building towards. As a new design comes into focus, it can be āslottedā in to where it fits. For example, the Meticulous-Z would seem to be a reasonable upgrade for a budget minded Base Maslow. It is getting to where there that thread has a solid BoM and enough experience to say "You can spend another $50, 6 hours, and improve the Base Maslow accuracy by 20% on average - with reference measurement on file for review.
For the mid-priced user, or the user that may not have 6 non-cutting hours to spare, then $150 and 1 hour will get you 25% better accuracy. It helps understand the best choices available for your situation.
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Exactly some of the things Iāve been thinkingā¦
The DIY nature of the project means everyone has a different frame, which effects the accuracy. I think kit providers have done some work, and could do more, to prep or even assemble critical components to eliminate potential sources of error.
Exact conversations Iāve been having lately. If new users had more options and the info to make the decision on the options, it would move the user base forward at a different pace.
This is difficult, since we are all strapped for time. I, for one, intend on doing more technical learning and contribution in fw and gc development and bug squashing.
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Agreed. This is why I was thinking more of a āclassā, with machine documentation guidelines (like a Airtable survey into a base) that would help document all the factors. Maybe Iāll play with this idea and bring it back here.
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I meant development of the project overall, not necessarily the software. My observation is that mechanical issues far outrank software driven ones, but I admittedly donāt grasp the details of current calibration efforts. I would think getting to a max-accurate (for a given class) machine would be a baseline.
Please check out:
The Maslow Machine Census (alpha)
Agree wholeheartedly. It is not at all clear to me what frame should be chosen (let alone at a given time commitment/complexity or price point) in order to yield the most accurate Maslow. If I had more time and was willing to spend more money can I be relatively assured of a better cut than with Beeās cheap and cheerful (wonderfully documented) frame? I still donāt have a clear answer. 
Iām intrigued by the laser cut top beam emerging from the MetalMaslow iteration of the design. Lots of conversations suggest the direction of finely tuning the motor spacing and vertical position -should- lead to optimal results and greater consistency (makes logical sense) but I havenāt yet seen a more formalized and repeatable test that confirms this. If itās true, it leads one to ask if there is a shipping/mail friendly way to perhaps make something like laser cut motormount templates that slide over imperial or metric sized square tube that can be bought at local home centers around the globeā¦ Afterall, we donāt need the whole bar shipped, only templates that register to the ends and provide mounting holes (at least if I understand correctlyā¦) to achieve this.
Building on what @cmullins70 said, even without stratifying in to various āsmall/medium/largeā budget tiers, Iād be happy if there was a 3 or 5 item āif you do X youāll get Y benefitā that properly documented the āupgradeā or change and talked about reasonable expected improvement in accuracy or repeatability (or even reliability if applicable). There is a great sense of urgency and engineering ingenuity in the air here, which is something I think we all enjoy partaking in, but it does sometimes feel like we skip a cog every now and then and the best we can do is point someone to a dense and rolling 400+ entry post that ākind of has the answer, youāll get the ideaā¦ā but doesnāt quite answer the question completely.
Iām not sure what the answer is, but it does seem like marshalling all the resources and getting a vetted, updated and comprehensive set of baseline docs and specs and accuracy readings in place is necessary to determine if all the other work is materially moving things forward in ways that can be easily measured. How to do that, well I donāt have any big thoughts on that one yet.
I will say that the one problem with opensource designs and āeveryone can do it their own way, huzzah, itās open sourceā is that you can end up losing the very constraints and challenges that make engineering both more enjoyable but also more useful. 
Constraints are actually fun and helpful and make it easier for newcomers to engageā¦
-Jeff
PS - Said a different way, Iām still hoping for a clear 1-2-3 for the what/why of the new controller design. Super stoked reading Barās musings in the thread @WoodCutter4 linked but even for a sub component it shouldnāt be too hard to clearly state the key objectives. Brainstorming is all well and good, especially for clean sheet ideas, but when youāre trying to improve an existing one it helps to know if weāre shooting for pure innovation or improving and rounding off sharp edges of the existing oneā¦
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Iām leaning towards the Texas Instruments DRV8873. When I first glanced at the datasheet I assumed that āSPI or Hardware Interface Optionsā meant that I could interface fully through SPI to command something like āset power 50%ā and it would stay there until a new command was sent. On reading the data sheet more closely I believe that you are correct that it requires a regular PWM interface and then SPI can be used to set error flags and read the current draw. I still think itās a nice chip, but you are right that more pins will be needed than just the SPI bus I was hoping for.
Has anyone seen a cheap motor driver chip which can be controlled over just SPI?
Afterall, we donāt need the whole bar shipped, only templates that
register to the ends and provide mounting holes (at least if I understand
correctlyā¦) to achieve this.
see New motor mount suggestion
this mount registers to the end, designed to fit unistrut or wood
Building on what @cmullins70 said, even without stratifying in to various
āsmall/medium/largeā budget tiers, Iād be happy if there was a 3 or 5 item āif
you do X youāll get Y benefitā that properly documented the āupgradeā or
change and talked about reasonable expected improvement in accuracy or
repeatability (or even reliability if applicable). There is a great sense of
urgency and engineering ingenuity in the air here, which is something I think
we all enjoy partaking in, but it does sometimes feel like we skip a cog every
now and then and the best we can do is point someone to a dense and rolling
400+ entry post that ākind of has the answer, youāll get the ideaā¦ā but
doesnāt quite answer the question completely.
part of the problem we have is that some people are getting good accuracy,
others, are not, and we donāt know why.
My current working theory is that there are three main reasons for this
-
frame (mostly top beam) is too flexible
-
the calibration routine is not working well enough and is resulting in
calculated measurements that are obviously wrong (I am thinking that holey
triangulation will help this a lot, but Iām struggling to run it) -
the tape measure being used is inaccurate enough to cause grief. We recently
had an interesting discussion on class 1, class 2, and unclassified tape
measures. see
In search of accurate measurements
we also donāt have anyone who has gotten a good accurate machine go through and
test other configs to see what effect the other configs have.
PS - Said a different way, Iām still hoping for a clear 1-2-3 for the what/why
of the new controller design.
We currently have three controllers
arduino mega and stock maslow controller
arduino due and modified maslow controller
arduino mega and TLE controller
Pairing one of these with a Raspberry Pi and using WebControl seems like it is a
huge win (Iāll say that being able to use my phone to bump things to get a
sprocket to 12 oāclock is a HUGE win compared to having to get to the computer
to move things and the machine to see if itās in the right position yet)
So one goal of the new controller is to see if we can combine this, make the
controller run WebControl (or equivalent)
Additional features that we want to see if we can support (not in any order)
- support a stepper for a Z axis
- support other encoder types (SPI and RS422/RS485 communications)
- support 4 motor designs
- support higher current for the motors
- support higher voltages for the motors
- eliminate the ability to plug the power supply into the wrong plug
- current limiting on the motors to avoid frying chips
- current measurements on the motor drive
- wifi connectivity
- faster processor to handle the calculations a little better
- double precision floating point math for more accurate calculations
David Lang