Dual Drive Setup (Dual Motor)

discussion of design changes / improvements / suggestions
calica
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Re: Dual Drive Setup (Dual Motor)

Post by calica » Sun Apr 29, 2012 10:42 pm

Ok. I should have specified max speed earlier.

ejs
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Re: Dual Drive Setup (Dual Motor)

Post by ejs » Fri Jun 01, 2012 6:33 pm

Going back to the OP, a note on the electronics rather than the components:

While Edward's example was taking the power from one driver and splitting it to two motors, the revision 3.0 Buildlog.net Arduino shield has a configurable fourth axis. The extra axis can be set up independently to work, in theory, an extruder head or a spindle on/off relay. Moving from theory into reality, it can be configured to act as a second Y-axis controller.

Basically this works by taking the signal from the microcontroller and sending it to two separate driver chips; each driver chip is dedicated to one motor.

I'm still playing with set up, but considering that the test span of 33" (http://j.mp/LTjgZy is driven by splitting one driver chip over two motors, the possibilities for using two drivers over two motors would seem to suggest a really serious span could be achieved given the right structural considerations.
Build it better than it was built for you. And give permission for the next guy to do the same. That's how Open Source works.
ShapeOko # 497: http://bit.ly/reactshop producing the Buildlog CNC Stepper Shield

aldenhart
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Re: Dual Drive Setup (Dual Motor)

Post by aldenhart » Sat Jun 02, 2012 6:02 pm

Your logic on 2 motors makes sense, but there are some further considerations. It's fine to send the same stepper signals to 2 drivers, then run 2 motors "in parallel". You can do this in hardware with grbl. TinyG does this in software - the motors are mapped to axes (not the other way around - once you think about it). The complication come in when the dual axes are not completely aligned. The system will start to bind and ultimately it can lock up due to "racking". So you have to be really careful about manually aligning things first, then not dropping any steps. This is why I like Edward's idea of a drive shaft instead of 2 motors. They can't get out of alignment. This assumes you have enough power to drive both sides, which should not be a problem.

In order to solve the alignment issue on TinyG the system treats each motor separately. I have written a general purpose homing function and have stubbed in a dual axis alignment function but have not completed it.

--Alden

Enraged
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Dual Drive Setup (Dual Motor)

Post by Enraged » Sat Jun 02, 2012 7:26 pm

Why not use a driveshaft to connect 2 motors? :)

Tom Smith
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Re: Dual Drive Setup (Dual Motor)

Post by Tom Smith » Sat Jun 02, 2012 7:41 pm

Enraged wrote:Why not use a driveshaft to connect 2 motors? :)
http://shapeoko.com/forum/viewtopic.php?f=11&t=6

There has been some discussion on that very thing - a hot topic, it would seem :)
_______________
ShapeOko1 191

alpha
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Re: Dual Drive Setup (Dual Motor)

Post by alpha » Fri Jun 22, 2012 1:52 pm

Using the assembly step pages from the wiki I think these are all the parts that one needs to do a dual motor setup:
Item/ Qty./ Part Num./ Title
1/ 2/ SM-H04/ M5 Hex Nut
2/ 2/ SM-H01/ 1/4" Nylon Spacer
3/ 2/ SM-H08/ M5 x 30mm SHCS
4/ 2/ MSK01-06A/ Smooth Idler Assembly*
5/ 1/ MSK01-09/ 18 Tooth Timing Pulley
6/ 1/ SM-E01/ Nema17 Stepper Motor
7/ 8/ SM-H03/ M5 Flat Washer
8/ 4/ SM-H14/ M3 x 8mm SHCS
10/ 4/ SM-H15/ M3 Flat Washer

*Smooth Idler Assembly
1/ 2/ MSK01-07/ 5mm x 16mm x 5mm bearing
2/ 1/ MSK01-08/ Precision Washer (1mm thick)
3/ 1/ MSK01-06/ Smooth Idler Drum

Belt Anchor and belt.
Did I miss anything?

edwardrford
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Re: Dual Drive Setup (Dual Motor)

Post by edwardrford » Fri Jun 22, 2012 2:57 pm

That looks right to me. You are only missing:
- qty:475mm - MXL belting
- qty:2 - Belt Anchors
- qty:2 - M5 x 10mm bolt
- qty:2 - Insertion Nut


-Edward
Shapeoko 1 #0 - a couple of upgrades.
Shapeoko 2 #0 - a couple of upgrades.
Shapeoko 3 #2 - Stock

alpha
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Re: Dual Drive Setup (Dual Motor)

Post by alpha » Fri Jun 22, 2012 4:01 pm

I just ordered most of the parts, thank you Edward! Maybe in the future Inventables could create a Y axis upgrade kit...

Maker
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Re: Dual Drive Setup (Dual Motor)

Post by Maker » Wed Jun 27, 2012 4:16 am

hi everybody,
I have done some numbers relating to the displacement of the drive shaft. using either an 8mm solid steel rod or 12 mm aluminium hollow tube would give a differential displacement of around 1/20 of a millimeter which is fine for our purposes I think. That also ignores stiffness in the frame and assumes using the ShapeOko 400 step motors at full torque (stalled motor) 69oz.in (480N.mm). I think that the aluminum tube would be best as it has less inertia. I have no idea how to connect it to the motor though, I don't think that i will have enough shaft on my stepper after the pulley is on there. I could get a stepper with a longer shaft but then i might as well have a motor on each side. I tried to attach the calculations for any one interested but i cant attach a pdf.

alpha
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Re: Dual Drive Setup (Dual Motor)

Post by alpha » Wed Jun 27, 2012 2:01 pm

Maker wrote:I don't think that i will have enough shaft on my stepper after the pulley is on there. I could get a stepper with a longer shaft but then i might as well have a motor on each side.
This was my thought too, I do like the shaft idea a whole lot, but the dual drive looked easier to implement...

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