GRBLshield add 2nd Y axis

LineKernel
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GRBLshield add 2nd Y axis

Post by LineKernel » Fri Oct 19, 2012 9:03 am

hi
i am ordering everything for 2nd Y axis

the only big problem i am confronted with is i am running my shapeoko with the GRBL shield

so i wonder if i can use any driver ?
knowing that i ll order the exact same motor https://www.sparkfun.com/products/10846, and my driver (big easy driver : https://www.sparkfun.com/products/10735) has a 1/8 micro-stepping option , so it ll be the same option as the original Y axis .

i dont know how to measure the load on my power supply
it is rated for 24V 5A but i don t know if i can directly add another motor and its driver or if i have to add a new power supply ?

LineKernel
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Re: GRBLshield add 2nd Y axis

Post by LineKernel » Fri Oct 19, 2012 10:22 am

i just read this thread http://www.shapeoko.com/forum/viewtopic ... 6&start=10
and it seems that you can cable the 2 Y axis motor together
torque is halved but i might give it a try

did any body try on a grblshield ?

T4b
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Re: GRBLshield add 2nd Y axis

Post by T4b » Fri Oct 26, 2012 5:11 pm

I think I've read of some people who succesfully do that with a grblshield.
The cables to both steppers running on the same driver should have about the same length because of something the driver does to microstep, I think.
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edwardrford
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Re: GRBLshield add 2nd Y axis

Post by edwardrford » Mon Oct 29, 2012 12:24 pm

I've done it with my grblShield. I know that synthetos doesn't officially support that configuration, but I haven't had a problem with it. I read somewhere else on the forum that the cables should be the same length to stay in sync. That is a fact that I wasn't aware of when I teamed mine together, subsequently one cable is roughly 3' longer than the other. I have seen no ill side effects. YMMV.

-Edward
Shapeoko 1 #0 - a couple of upgrades.
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cvoinescu
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Re: GRBLshield add 2nd Y axis

Post by cvoinescu » Tue Oct 30, 2012 12:37 am

edwardrford wrote:I read somewhere else on the forum that the cables should be the same length to stay in sync.
It's not to stay in sync, it's to split the torque equally. It doesn't really matter unless the cables are thin and the difference is large.
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aldenhart
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Re: GRBLshield add 2nd Y axis

Post by aldenhart » Wed Oct 31, 2012 11:13 am

A number of people have added a second motor to the grblShield Y axis w/o issues using NEMA17 motors, although I'm not sure I'd do this with NEMA23 motors. At least not without some really good cooling. Please let us know if you do have any problems but this should be relatively straightforward.

--Alden

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Re: GRBLshield add 2nd Y axis

Post by cvoinescu » Wed Oct 31, 2012 12:56 pm

One way to avoid heating issues would be to wire the two motors in series. Then, the driver still supplies the same current, so you get the rated torque at low speeds, but some acceleration and speed is sacrificed (as if running the setup from 12 V instead of 24 V; the rated current can still be achieved, albeit more slowly). This is not a problem at all with the current GRBL and the ShapeOko, because the speed is limited to what the Z axis can do, so you never hit any speed limitations on X and Y. Also not a serious problem with milling, where very high speed isn't usually needed.

For reference, here's one possible wiring diagram (many other combinations work, too):

Code: Select all

Driver   Motor 1   Motor 2
  A1 ----- red
           blue ---- black
  A2 --------------- green

  B1 ----- green
           black --- blue
  B2 --------------- red
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phlamingo
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Re: GRBLshield add 2nd Y axis

Post by phlamingo » Wed Oct 31, 2012 2:12 pm

Concerning whether wire length would affect the timing of pulses in a parallell dual-motor configuration, the rule of thumb for electrical signals is 1 foot = 1 nanosecond.

.3 m / (3 * 10^8 m/second) = 10^-9 second

I doubt that a 3-foot = 3 ns difference in pulse arrival time would be detectable in a pulse measured in milliseconds.

Of course, if you are working with RF signals, everything becomes either an antenna or a transmission line, or both, and things get weird quickly.
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ShapeOko Batch 2, Number 571, dual-Y motors, Y belts outside, odd anchors. Not operational at the moment: needs rewiring.

T4b
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Re: GRBLshield add 2nd Y axis

Post by T4b » Wed Oct 31, 2012 2:47 pm

phlamingo wrote:Concerning whether wire length would affect the timing of pulses in a parallell dual-motor configuration, the rule of thumb for electrical signals is 1 foot = 1 nanosecond.

.3 m / (3 * 10^8 m/second) = 10^-9 second

I doubt that a 3-foot = 3 ns difference in pulse arrival time would be detectable in a pulse measured in milliseconds.

Of course, if you are working with RF signals, everything becomes either an antenna or a transmission line, or both, and things get weird quickly.
Makes sense, should have done that calculation before mindlessly repeating what someone else has written. :oops:
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cvoinescu
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Re: GRBLshield add 2nd Y axis

Post by cvoinescu » Wed Oct 31, 2012 9:11 pm

You could run the wires of one motor around the block and solder the other one directly to the driver, and it still wouldn't make a difference as far as timing went. :)
Proud owner of ShapeOko #709, eShapeOko #0, and of store.amberspyglass.co.uk

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