Mechaduino

[T. Joseph Nkansah-Mahaney]

https://hackaday.io/project/11224-mechaduino

Thought this might be of some interest to the group. Maybe we could set up a group parts buy and have a major build session. Thoughts?

Joseph

[John England]

Yeah, Ken and I were looking at that a few weeks back. Very interesting, indeed. Looking forward to more information on the higher powered 2A versions, and the cost for one without the steppers.

I for one would be interested in either a group buy of pre-built ones, or of the parts and PCB's.

John

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[Mike Wirth]

Hmm... very interesting.  I think I've been scooped -- sort of.  I've been working on a controller design for BLDC motors for the same goal.

BTW, hope to attend the meeting this week and will bring a small BLDC motor with me, high torque, 0-60 RPM (with a planetary gear case), all for $5 from "China, Inc.".

Mike

[T. Joseph Nkansah-Mahaney]

Hi John,

Indeed. The GitHub repo has a pic stating Mechaduino 1.0 but I will have to dig a little deeper to see if BOM and PCB files are recent. I had not heard of a 2A version. Could there be a major difference between the current Mechaduino design and a 2A version be a different H-Bridge? I noticed the version on the NEMA23 stepper had a heatsink and an additional component.

Would be great to have a drop in replacement for a number of applications, 3D printers not withstanding.

I could definitely go for a group buy of parts and PCBs.

Joseph

[John England]

Didn't even realize that the Mechaduino Kickstarter was already in full swing, and only has 8 days to go! The price break is sort of abysmal for multiple, fully-assembled PCB's (1 PCB is $45, and 10 PCB's is $425?? Hmm). I'd go in for 3, though.

https://www.kickstarter.com/projects/tropicallabs/mechaduino-powerful-open-source-industrial-servo-m

I'm also still game for rolling our own from the design files, but I wonder if we'd save much once we ordered custom boards from OSH Park or the like. I also don't personally have any experience soldering fine-pitch SMT parts... The benefit to doing it this way, though, is I'd really like to have 7-8 of them, not 3, so that I can trick out my 3D printer and upcoming CNC router.

Thoughts, anyone?

-J

[Ken Snyder]

I'd be up for a group effort to source our own.  I'd be in for 10 fully populated boards.  The difference between their PCBs and full servos is only $15, so the components can't be very much.  I'm no expert, but I think $45 for the PCB is pretty steep.  Bill S., how much did it cost you to get your printer LCD controller boards made?

Using one of these on the extruder motor would be a great way to detect when you have a filament jam.  Does anyone know if it has an output signal when it senses a misstep?

[Bill Seiler]

I do boards at pcbway.com A 3 x 4 two sided board is about $3 a board.  Pcbway also assembles board too.  I have yet to use this service.

[Ken Snyder]

Wow, big difference!  I see pcbway.com is in China.  Personally I wouldn't mind paying a few extra dollars each to have them sourced in the US.  But at least we know we can get the boards cheap.  

Anybody want to take this on as a project to get some built?

[Mike Wirth]

Try http://bayareacircuits.com, a US vendor (local even, in Fremont).  Good price, good service.  Usual disclaimers, just a satisfied customer.

Mike

[John England]

Bay Area Circuits looks cool. What about populating the boards? I imagine we can buy the chips and all that for next to nothing, but we need someone who can teach fine-pitch soldering kung fu. I know I for one would like to learn.

[John England]

The BOM: https://github.com/jcchurch13/Mechaduino-Hardware/blob/master/BOM/Mechaduino01_BOM.csv

[Mike Wirth]

Several points:

1. Count me in for one unit of a group buy of parts, including PCB.
2. I design and build wearable, wireless sensors that communicate with Bluetooth LE to smartphones for my day job, i.e., challenging SMD assemblies.  There are a number of PCB layout tricks that make hand assembly of such devices easier and more reliable.  I would be happy to review and adjust the Mecharduino PCB layout to accomplish this.  I can also help shepherd the PCB design through electrical and DFM checks and manufacturing process.
3. I'll be happy to run an SMD assembly class at a Reprap meeting in SJ.
4. It might be that screening solder paste through a SS stencil, followed by hand pick-and-place and controlled oven reflow would be easier than straight hand soldering.  I can help everyone work through that process, too.

HTH,

Mike

On Tue, Jul 12, 2016 at 4:16 PM, Mike Wirth <mwi...@gmail.com> wrote:

[John England]

Great! Thanks, Mike!

As a side note, I'm seeing $4.43 a piece just for the Atmel chips if we buy 25 of them from Mouser. I wonder if we can do any better than that.

[Mike Wirth]

Remember that in any assembly process, there are "infant mortalities" or other lossage, especially on complicated to assemble parts.  The can be handled in one of two ways: 

1. Orders some extras as spares in the group order, and share the cost.
2. Order the exact amount and reorder as necessary (often at higher cost).

Usually with PCBs, ordering a few extra is very low cost (and the PCB house will often toss in extras since they follow the same practice :-)

Mike

[John England]

Good to keep in mind. I guess we need a participant/unit count to start figuring out price breaks, etc.

[Ken Snyder]

So looks like Bay Area Circuits only does the boards?  Are there local places that will populate the boards for us?

These boards look like they're the same footprint as a NEMA 17, 42mm x 42mm.  Ordering 25 individual boards is $586!  How do you get the cost down?  Do you design a larger board with 20 or more on one large break-away board?  If we can do that, the price drops down dramatically.

[Mike Wirth]

Ken,

Yes, you always panelize small boards together if you can. (Some vendors allow it, others don't.  Some make it convenient by allowing internal routing, board scoring, etc., others don't.  All in the details.) In fact, for small boards, some assembly houses prefer a larger, panelized group.

A well-regarded local assembly house is AQS (http://aqs-inc.com, which also does boards). Check with David Laranjeira (dlara...@aqs-inc.com) there.  Usual disclaimers, I'm not even a customer, but have a friend who is a satisfied one.

Mike

[Tim Driedger]

David is no longer with AQS.

I use UMAI http://www.umai.com/ in Fremont. Great service!

Tim

[Ken Snyder]

Hey Guys,

Any progress on the Mechaduino?

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[T. Joseph Nkansah-Mahaney]

I ordered 12 boards via OSH Park. I have yet to tackle the component order however.

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[Ken Snyder]

Hi Joseph,

Any progress on the component list?

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[T. Joseph Nkansah-Mahaney]

Probably not until November. October delivered a bunch of paid projects for me to work on.

I did just found a Google Group with the same name. 

https://groups.google.com/forum/#!forum/mechaduino

[Trampas Stern]

I have made a stepper controller like the mechaduino but with some additional features [misfittech.net]. 

First off there is a error pin. If an motor skips a step then the error pin is asserted until the NZS fixes the problem. This could be used by Marlin to stop the other motors until the error has been fixed. For example if the extruder binds and misses a step then error pin is set and Marlin could stop the X, Y, and Z motors until the error is fixed. This is not implemented in Marlin firmware that I know of but the NZS has the capability. 

Second there is an LCD such that you can calibrate without requiring you to recompile and reprogram firmware. The LCD also allows for feedback and DRO capabilities. 

Third the driver's heat sink is soldered to PCB for better heat and higher currents on motors.

Fourth the firmware is complete rewrite with numerous bug fixes and modular design

Details about the development and testing can be found on the blog at misfittech.net, additionally a limited number of hardware boards is in stock and ready for shipment. 

Of course the firmware and design is open source.

Thanks
Trampas