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  #1  
Old Sat 05 January 2008, 15:02
J.R. Hatcher
Just call me: J.R. #4
 
Wilmington, North Carolina
United States of America
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Slaving a motor - put its drive in parallel to another drive on the same BOB output

This thread assembled from various posts:

How many gecko 203Vs will the PMDX-122 breakout board run?
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  #2  
Old Sat 05 January 2008, 19:20
smreish
Just call me: Sean - #5, 28, 58 and others
 
Orlando, Florida
United States of America
JR,
I am controlling 5 gecko's with my PMDX-122 by sharing the X1 and X2 geckos with one output. The other outputs are solo. x1 / x2 shared, y solo, z solo, a solo (indexer)
SO, 5 on one unit is possible with the MM.
So far, so good.
Sean
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  #3  
Old Mon 07 January 2008, 14:49
smreish
Just call me: Sean - #5, 28, 58 and others
 
Orlando, Florida
United States of America
Mike and others,
I want to make clear that I used 1 output to drive 2 individual gecko's. I checked with Mariss and Steve Stallings at PMDX and both assured me that this logic and the electrical separation was adequate. Although, Steve at PMDX tried hard as heck to sell me an additional PMDX-122
So far, I have run the test bench for about 7 hours without any issues. I had Mach3 endlessly cycle the "roadrunner" program for the length of a shop day to "burn" in the controller.

Let me know if I should be looking or doing something different.

Sean
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  #4  
Old Mon 07 January 2008, 15:20
J.R. Hatcher
Just call me: J.R. #4
 
Wilmington, North Carolina
United States of America
Send a message via Skype™ to J.R. Hatcher
Sean, you made it nice and clear in post #2 (now that I have gone back and read it again). I don't quite understand why I didn't get it the first time. I can't even think up a good lie right now that might make me look smarter .
But I got it now, 1 step and direction output running 2 Gecko drivers, right? Who says I aint smart. Still
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  #5  
Old Tue 08 January 2008, 06:29
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
The 74ALS245 devices, such as those found on the PMDX-122, can sink about 24mA and source about 15mA. The Gecko G203v draws about 2.5mA, so the PMDX-122 should have no problem driving two G203v stepper drivers per circuit. The Gecko G202 draws about 15mA, so only one G202 should be connected to each circuit on the PMDX-122; however, if necessary, your could build an auxilary board with a 74ALS245 to split one incoming signal into two outgoing signals.

(J.R., Don't worry about misreading a post. I've done it many times. You'll find proof of that in this forum, on the Shopbot forum, on CNCZone's forum, in the Letter's to the Editor section of the two local newspapers, and in a bunch of other places. If you only have one goof, you're doing really well. I have dozens.)
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  #6  
Old Tue 08 January 2008, 16:08
smreish
Just call me: Sean - #5, 28, 58 and others
 
Orlando, Florida
United States of America
Mike,
You hit the point nicely.
I didn't have the data on hand to verify what the sink/source current of both devices. Thus, my phone calls to PMDX and Gecko. I was told on very finite terms to only do this with the G203 series drives. You have disclosed the data behind the use.
Thanks again for having a really great "test bench and the right gear to use with it".
Sean
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  #7  
Old Tue 08 January 2008, 20:41
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
To summarise: One "channel" of a PMDX-122 can drive 2 Motors only if one also uses 2 Gecko G203V drives. Cannot use 2 G202 drives. Cannot use only one drive for the 2 motors.
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  #8  
Old Mon 02 June 2008, 09:11
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
Be sure to jumper the PMDX-122 correctly for the G203v. You MUST connect terminal #10 on the G203v (Common) to Ground on the PMDX-122. The PMDX-122 must pull the step and the direction signals High when it sends step pulses to the motor.

(My PMDX-122 came jumpered from the factory ready for use with the G201 and the G202 stepper drivers, not for the G203V stepper driver. JP1 is the jumper to check.)

When wired half-coil (Black/Yellow, Red/White), the maximum voltage for the PK296A2A-SGxx motor is about 38V. If you're using a 58V power supply, you will need to wire the motors using the Black/Green, Red/Blue wires, otherwise the motors will get too hot.
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  #9  
Old Fri 10 October 2008, 13:41
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
You could theoretically drive a pair of G203V's, for your x-axis, off one "channel" of the PMDX-122. (The PMDX-122 user manual says it can sink or source 16mA, each G203V needs about 2.5mA). The only downside is that you would not be able to auto-square the gantry.
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  #10  
Old Fri 10 October 2008, 14:40
domino11
Just call me: Heath
 
Cornwall, Ontario
Canada
Gerald,
How usefull is the autosquare function? Is it something you find usefull or needed in your experience?
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  #11  
Old Fri 10 October 2008, 15:20
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Have not needed it, or even considered it for our machines. Our squaring is done once mechanically (with shim washers behind the v-rollers) and the machine happily maintains that square from day to day. If in doubt, then we run it to the stops to check.
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  #12  
Old Fri 10 October 2008, 19:27
smreish
Just call me: Sean - #5, 28, 58 and others
 
Orlando, Florida
United States of America
I am happily driving 2 x axis motors off a "shared" dir/step channel so the 4th axis on the PMDX can be used to drive the 4th axis. ALL works very well and no issues to date. Almost 10 months of hard work out of my machine thus far - perfect.

Sean
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  #13  
Old Tue 23 December 2008, 05:46
zetacnc
Just call me: Fabio
 
Atibaia
Brazil
Wayne,

I know there are a lot of people using Geckos and Machxx controlling them, and specially the "X" axis that uses two motor, one is the "master" and another is the "slave".

I had problems with these setup because time to time Mach3 loosed config (direction signal pin changed with no intervention) and the result is the same you experienced.

I solved just sharing the same direction and step signals to both drivers - in Mach there is only one "X" axis (no slave)...
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  #14  
Old Tue 23 December 2008, 06:02
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Excellent tip Fabio, thanks!

I don't know if the G201 drives can easily be put in "parallel" with Wayne's controller. (The G203's are easy to parallel). Mike Richards, if you are reading this, comment please . . . . Wayne's Ascension has the Bob Campbell controller.

Wayne, you could ask Bob Campbell if it is okay to do it.
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  #15  
Old Tue 23 December 2008, 14:25
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
The problem with running two stepper drivers from one signal is the amount of current that each stepper-driver signal requires. The Gecko G201 and G202 require about 15mA per signal. The Gecko G203v only requires about 2.5mA at 2.5V to 5V.

Most TTL signals (regular integrated circuit chips) can barely handle 15mA when sinking a signal (for the G201 and G202). They only handle about 0.4mA when sourcing a signal (G203v).

So, it depends on the break-out-board that you use. If the break-out-board uses high-current driver chips (30mA per signal or more), then you could safely run two stepper drivers from the same signal.

If your break-out-board can not handle the additional current, you can add a single buffer TTL chip to the controller and then use two outputs from the buffer chip to drive the two stepper drivers.

This is an example of a buffered circuit:


(Sorry about the image quality, but my schematic editor only exports bitmapped.
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  #16  
Old Wed 24 December 2008, 04:18
zetacnc
Just call me: Fabio
 
Atibaia
Brazil
Mike, - good point!

If I rememeber, when I was setting up one installation with two drivers sharing the same signals, fist I tryed to use two wires derived directly from LPT port, and sonn I discovered that there is no current to drive both drivers together.

Then I made a simple surgery under the BOB - and in my case that BOB is a buffered type - and the drivers ran well...(unfortunatedly I don't have any photo)
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  #17  
Old Wed 24 December 2008, 09:57
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
(Gerald, thanks for fixing the image. Yesterday, I stopped at the shop for ten minutes to pick up a part for a customer when I noticed your request. It only took a few minutes to write my reply, but that didn't leave enough time to play with the image.)

This morning I checked the data sheets for the 74HC245 and the 74AHC245 chips. It looks like both the HC and the AHC can SINK or SOURCE 35mA per pin. That means that one output pin on the 74AHC245 or the 74HC245 could drive two step or direction signals when connected to either the Gecko G202 or the Gecko G203v stepper drivers.

----

The PMDX-122 uses a 74HCT244 buffer/driver chip. I don't have the schematics for that board, but the traces on the board go from the 74HCT244 chip to the step/direction connectors (J1 - J4).

I'm running a test right now with the PMDX-122 board and Gecko G202 steppers drivers. I connected two G202 stepper drivers to the PMDX-122's J1 connector. Both stepper motors are running perfectly with the Mach 3 G-code file that I use to test basic stepper motor functions.

Unfortunately, I don't have the PMDX-122 card currently connected to the G203v stepper drivers, so I can't verify that the PMDX-122 can handle two G203v drivers, but the data sheet shows that one pin on the 74HCT244 can SINK or SOURCE 35mA and the G203v only requires 2.5mA for the step/dir inputs.

It looks like those who use the PMDX-122 can directly connect the input of two Gecko G20x steppers drivers to one PMDX-122 J1-J4 step/dir output.

Of course anyone who drives two X-axes motors from one signal source will have to change the wiring to ONE motor so that one motor runs CW and the other motor runs CCW. On the test bench, I wired the motors this way to have the master X-motor turn CW and the slave X-motor turn CCW (my Oriental Motor PKB2A-SG3.6 motors are wired half-coil):

Master X-motor
Term 3 = Black (coil A)
Term 4 = Yellow (coil /A)
Term 5 = Red (coil B)
Term 6 = White (coil /B)

Slave X-motor
Term 3 = Yellow (coil A)
Term 4 = Black (coil /A)
Term 5 = Red (coil B)
Term 6 = White (coil /B)

(Because the motors are wired half-coil, the Slave X's wiring had to be completely changed.)
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  #18  
Old Wed 24 December 2008, 20:26
smreish
Just call me: Sean - #5, 28, 58 and others
 
Orlando, Florida
United States of America
Mike,
I have been running (2) g203V drives from a shared step/dir output on the pmdx for a year now without fail. Nils too, is now sharing the x output for the gantry motors.
Both Mariss and Steve? at PMDX both concurred that this was acceptable.
I don't have the test gear to actually check the sink/source current. But, everything is still working.
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  #19  
Old Thu 05 March 2009, 13:50
SteveE
Just call me: Steve
 
Louisville, KY
United States of America
Can this be done?

I've been trying to find this in the forum, but no luck. As I've stated, my electronic knowledge is next to nothing. Is there a reason the 2 x axis motors cannot be driven from one gecko drive. Could you set one motor to run CCW to the other?

Sorry in advance if the answer makes me look foolish, but as I said, electronics are not my selling point....

Steve
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  #20  
Old Thu 05 March 2009, 18:57
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
The rule is one stepper motor for each Gecko stepper driver. Even though some motors require much less than maximum current, there are subtle differences between each motor, even motors from the same manufacturer. Those differences can destroy the stepper driver.

Marris Friemannis, who designed the Gecko products posted the exact reasons why you CAN'T use two motors with one stepper driver, but I can't find that post at the moment.
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  #21  
Old Thu 05 March 2009, 21:08
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Mariss did say there are certain sizes and speeds where it could work, but I checked them against our MM needs and there is no luck.
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  #22  
Old Fri 15 May 2009, 13:11
smreish
Just call me: Sean - #5, 28, 58 and others
 
Orlando, Florida
United States of America
Copied from elsewhere:

Heath,
To recap from another thread I wrote a while ago....

As long as you have a PMDX-122 and the Gecko 203 series drive, you can.
Other sink/source current combination's may not work.

This will disable your ability to use the self squaring feature in Mach 3.

I have a great deal of success sharing the steps for the x'-x axis on mine and Nils machine. No issues.....just careful planning is needed on machine set-up to make sure the hard stops on the machine are truly adjusted for a square gantry.

Sean
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  #23  
Old Fri 15 May 2009, 14:13
domino11
Just call me: Heath
 
Cornwall, Ontario
Canada
Thanks Sean,
I knew it was on here before, and Greg from Smith Falls set his up this way as well. Seemed to be easier to do it this way than have a slaved axis.
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  #24  
Old Fri 15 May 2009, 14:17
smreish
Just call me: Sean - #5, 28, 58 and others
 
Orlando, Florida
United States of America
The only tough part was making up a Y-cable since those blocks on the PMDX are so darn small and only accept a single ferrule!
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  #25  
Old Sat 16 May 2009, 03:22
sailfl
Just call me: Nils #12
 
Winter Park, FL
United States of America
It is a tight fit but you can get two wires in there. Using the ferrules keeps it clean. I shortened them by cutting off part of the tips.
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  #26  
Old Sat 16 May 2009, 05:39
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
The type of ferrules I use will accept 2 wires into the ferrule.
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  #27  
Old Sat 16 May 2009, 09:38
lumberjack_jeff
Just call me: Jeff #31
 
Montesano, WA
United States of America
Quote:
Originally Posted by smreish View Post
Heath,
To recap from another thread I wrote a while ago....

As long as you have a PMDX-122 and the Gecko 203 series drive, you can.
Other sink/source current combination's may not work.
What about the 201 Gecko? Can you drive both x motors from one channel?
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  #28  
Old Sat 16 May 2009, 10:09
domino11
Just call me: Heath
 
Cornwall, Ontario
Canada
Jeff,
This is from memory so check the facts, but I remember Mike R saying that driving 2 gecko 201s with the pmdx was too much current draw. He suggested a buffer circuit to allow you to do this. I am not sure if this is in your field of expertise. If it is then it should be able to be done with a buffer. The 203s inputs draw only a fraction of the current the 201s do so that is why it is possible with the 203s and no buffer circuit.
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  #29  
Old Sat 16 May 2009, 11:36
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
The G201 and G202 stepper drivers Sink 15ma, which requires a high-current driver. The PMDX-122 is built with high-current drivers which allow it to drive ONE 15ma signal line. You will need to add a buffer chip or other external circuitry to drive more than one G201 per signal line. If you try to drive two signal lines with the buffer/driver chips on the PMDX-122, you may find that it works; however, on a hot day your steppers might suddenly stop working. It is never a good idea to assume that any device can drive beyond its specifications.

The G203v requires a driver to Source about 2.5ma. Most TTL type chips can Sink from 4ma to 10ma. Special driver chips can sink 15ma to 25ma. HOWEVER a TTL chip can normally Sink 10X as much current as it can Source. So, unless you have a driver chip that can Sink or Source 15ma, even the G203v will draw more current than a standard TTL chip can produce. (The PMDX-122 can easily Source or Sink about 25ma per signal line.)
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  #30  
Old Sat 16 May 2009, 11:55
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
As I understand it, the Gecko 201 and 203 are being "upgraded" to 201X and 203VX versions soon one of the things being changed is to simplify their input signal requirements. Their current draw will probably be reduced. (Common can be connected to either ground or 5V - both will work)
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