ShapeOko + RAMBo Electronics?

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wisof
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Joined: Sun Apr 21, 2013 6:38 pm

ShapeOko + RAMBo Electronics?

Post by wisof » Sun Apr 21, 2013 7:47 pm

Has anyone tried this combination: ShapeOko + RAMBo electronics?

I have been doing some looking around and trying to find a form factor for my next 3D printing project. My main concern was to have bed be free of movement, meaning not involved in the x, y, or z movement. Sitting in our lab, looking at our routers, and seeing how some friends around here every once in a while add an extrusion head, I thought that this was the form factor I was looking for.

There are many choices, but when you look for ATMega based versions, those choices become a handful.
ShapeOko seems like the perfect size for what I wanted to build, I just need to match it with the appropriate electronics.

I am wondering, has anyone used the RAMBo electronics (https://github.com/ultimachine/RAMBo http://reprap.org/wiki/Rambo) to run the ShapeOko? I can't see why it would not work, just wanted to see if there were some experiences that could help me put this together.

The extrusion I will be doing does not necessarily need another stepper driver, but I will need to run other accessories off the board.

Thanks!

cvoinescu
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Re: ShapeOko + RAMBo Electronics?

Post by cvoinescu » Sun Apr 21, 2013 8:05 pm

I see no reason the RAMBo would not work. I drive my eShapeOko with an Arduino Mega 2560 and a RAMPS-inspired design, which should be pretty much exactly what the RAMBo is. The only minor catch is that they provide two connectors for the Z and you'll need two for the Y (see below), but that's nitpicking. You can even swap the Y and Z ports in the firmware configuration.

I'm saying you need two motors on the Y for dual-drive. Do not attempt this without some form of dual-Y, positioning won't be precise enough for 3D printing. However, a shaft-type dual-drive upgrade works too, and needs only one motor. If you go for the dual-motor solution, it's OK to run two Y motors off one driver, but it's even better to use one driver for each.

Marlin has the ability to duplicate the Z output on E1; with some minor tweaking, I added the same ability for the Y axis, so you can run two separate drivers for the two Y motors, if you don't need that second extruder.
Proud owner of ShapeOko #709, eShapeOko #0, and of store.amberspyglass.co.uk

wisof
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Re: ShapeOko + RAMBo Electronics?

Post by wisof » Sun Apr 21, 2013 8:32 pm

Thanks for the reply! I was thinking I would need dual y, but the shaft approach would interfere with having a free bed area. I think I will go with the dual y, two motors, two drivers as you mention. Might be good to get the ACME Z upgrade for the ShapeOko.

I guess I am getting a bit caught up in the electronics choices. I've been reading this: http://www.reprap.org/wiki/List_of_electronics in order to get a better idea of what is active and what is in stale development. It seems TinyG and RAMPs / derivatives are pretty active, and I like the form factor of RAMBo. My main concern is how I can develop ways to drive other accessories from the electronics through GCode. For example, I see in many of the Github repos that there are M codes for Coolant / Mist etc. Can I hijack these and run something else on those ports? I can easily write a script to fix the gcode, just not sure how much those can drive. Is it possible to switch on or off accessories that need 12 or 24v?

cvoinescu
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Re: ShapeOko + RAMBo Electronics?

Post by cvoinescu » Sun Apr 21, 2013 9:31 pm

The 12/24 V question I can't answer without reading more about the RAMBo; same about how much they can drive. I know the RUMBA (another RAMPS derivative) has a few MOSFETs that are on Vmot (typically 24 V) and some that are switchable between Vmot and 12 V (useful for fans). In any case, pretty much all pins can be controlled with G-code: if not with a command specific to the function of that pin, then with the M42 command, which can change the status of any pin that's not "protected", i.e. explicitly allocated to a function.
Proud owner of ShapeOko #709, eShapeOko #0, and of store.amberspyglass.co.uk

Guile2912
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Joined: Tue Mar 26, 2013 8:59 pm

Re: ShapeOko + RAMBo Electronics?

Post by Guile2912 » Wed Apr 24, 2013 3:14 pm

An other board to watch for CNC / 3d printing : http://smoothieware.org/smoothieboard

wisof
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Joined: Sun Apr 21, 2013 6:38 pm

Re: ShapeOko + RAMBo Electronics?

Post by wisof » Wed Apr 24, 2013 3:31 pm

Yes! I am intrigued by the ARM offerings in this field:
Smoothie: http://smoothieware.org/smoothieboard
4pi: https://0xfb.com/shop.html
R2C2: http://www.3dprinting-r2c2.com/?q=conte ... umentation

But this does deviate from the original discussion. I suppose the conclusion of that is, yes, a RAMBo board should work with some proper configuration. Whether is has MOSFETS I can drive through GCODE is another question. RAMPS has em, MIGHTY BOARD has them, G4 electronics has em, etc.

akhlut
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Joined: Wed Mar 27, 2013 1:16 am

Re: ShapeOko + RAMBo Electronics?

Post by akhlut » Wed Apr 24, 2013 8:20 pm

Have you seen the Reprap wiki entry?

I really like the RAMB0 as you can set the Vref for the driver chips in the firmware via a digital potentiometer.

It has 6 MOSFETS: 3 fan, 2 extruder, 1 heated bed

The only downside is that you can't drive it with more than 26V. Depending on the parts you solder up RAMPS is only limited to the voltage the drivers can handle (45V for DRV8825), so long as you don't push too much current through it. :)

And +1 for everything that cvoinescu said.

You're definitely going to want each Y-axis stepper to have its own driver - don't just swap Y and Z and edit the firmware.

Also. Do yourself a favor and stick with the M8 threaded rod on Z. Going to imperial creates issues with layer heights that cause serious surface finish issues. Try to stick with metric if at all possible. I invite you to check out Josef Prusa's new reprap calculator. Play with the third calculator down for layer heights, and remember that slic3r and most other programs will only take a layer height to 3 decimal places. Anything else results in errors. Trust me, I encountered this exact issue when I moved away from M8 to 1/4" -16 ACME screws. My prints went from pretty good to terrible really quickly. Major tweaking and reading led me to the conclusion that my layer heights were wrong due to the pitch of the rods. M8 is 1.25mm, 1/4" - 16 is 1.5875mm. Also, moving to full-step layer heights and full-stepping on Z helps remove micro-stepping error as well.

For example, using a 1.8 degree motor the full step layer height for an M8 rod is 0.00625mm. Lets say you want a layer height of 0.2mm - that's 32 steps. Easy

But let's look at the ACME screw with a 1.8 degree motor. The full step layer height is 0.0079375. Getting a 0.2mm layer height is impossible. :( the best you can do is a 25 (0.1984mm) or 26 (0.2064mm) steps, which results in an error of 0.007875496094242115mm per layer, which may not seem like much. But this error is cumulative, which is really bad. It'll make your prints look like they're mushrooming as they grow - all that plastic has to go somewhere.

Another tip - your steps per mm on Z should be a whole number in Marlin. Anything more than 2 digits of precision will throw print defects as well.

Just trying to save you some sanity.

tl;dr - RAMB0 should work fine, stick with an M8 rod for Z.

Sorry to ramble on...

wisof
Posts: 9
Joined: Sun Apr 21, 2013 6:38 pm

Re: ShapeOko + RAMBo Electronics?

Post by wisof » Wed Apr 24, 2013 9:11 pm

@akhlut This is the kind of response that makes a person want to be part of a community! Excellent points. For the mosfets, I will not be needing more than 24v...probably can even get away with 12v...need to check the current, but thus far, other seemingly similar electronics have been able to drive what I need without any issues.

Good point on the Z axis...very important cumulative errors, and something that I would not have intuitively understood right away! I hope to be able to purchase all of this within the month.

[On another note, I saw a very nice piece of kit today on my visit to Festo, an XY kit of linear actuators. Actually pretty reasonable price when you add the Z axis, dimension it up a bit, and add the controller.]
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