View Full Version : "Gecko 540" vs. "PMDX-122 & Geckos 203V"

Mon 16 February 2009, 14:06
Seems like this thread will be interesting :D, I dont want ot start a WAR :p but I think the dicsussion is quite positive and will dissipate lots of doubts that will sure arrise to all those new guys as me in this dilema...So post your comments...

Mon 16 February 2009, 15:12
Actually, I think most everything on this topic has been covered elsewhere, but centralizing it might help. Here are some aspects to consider when making your personal choice here:

1) Will your motors run to their full capacity on a G540?
2) Is replacement an issue in your location?
3) Do you need access to every I/O pin from your parallel port?
4) Are you comfortable with the connectors / heatsinking of the G540?

1) If you're using the geared OM motors, there is no capacity issue, because the limiting factor is the torque rating of the gearbox. If you intend to attempt direct drive motors, the G540 isn't the device for you.

2) If you are within easy shipping range of Gecko, there isn't as much of an issue with the integrated design of the G540. If you are weeks away, then you may want to consider the PMDX solution, as it may be easier to obtain or stock repair parts with a less integrated environment.

3) The G540 uses the usual pins from 2,3; 4,5; 6,7; and 8,9 to drive it's four axis (X,Y,Z,A). In a Mechmate, we use two of these ("joints") to drive our X axis. With a PMDX you can potentially recover two of these pins by driving both X 203Vs with the pins 2,3 (and a little circuitry). The G540 provides 4 input pins that map (after optoisolation) to pins 10,11,12, and 13 on the parallel port. The G540 provides two output pins that map from pin 17 and pin 1 on the parallel port. The G540 uses pin 16 as a charge pump (failsafe shutdown if the computer hangs up), pin 14 as a PWM output to generate 0-10V for a VFD speed control, and pin 15 as an input back to the PC if the Gecko has a fault. All of this means that you lose choices in how pins 8,9,14,15 and 16 are used, which could have been as anything between 1 input/4 outputs, and 3 inputs/2 outputs. It depends on how well your needs fit the design assumptions Gecko has made.

4) There exists some skepticism about the long term reliability of DB-9 connectors for the motor connectors. You'll just have to make up your own mind, or else wait a year or two for evidence to emerge.

For me, (1) I'm using the OM motors, no issue there. (2) I'm in the US, and cheap shipping from Gecko gets here in three days; emergency shipping could be here overnight. Given the cost differential, though, if I were really concerned, I'd buy a spare G540. (3) For the proxies at each end of my gantry and on the car, plus my Z-Zero plate, I use the 4 optoisolated inputs. I use the charge pump for it's designed purpose; if EMC2 stops running on my PC, the Gecko goes into shutdown. I use the fault input for it's designed purpose - to halt the G-code interpreter if the Gecko faults. I use one of the outputs to flip the SSR that controls my router. The other output is a spare. I hope to someday use the PWM output on the spindle that Santa will bring me next year - too late for this year, I've already been bad! (4) I've been soldering DB-9s and DB-25s for several decades now, and I'm comfortable with how to build and maintain them.

Mon 16 February 2009, 15:16
Since I have both the G540 and the PMDX-122/G203v on my test bench, perhaps I can help.

The G540 is a great little unit - if you can live within its limitations. It has TWO general purpose outputs, FOUR general purpose inputs, a VFD output for a spindle and a E-stop/disable input to disable the motors. It allows the use of a power supply up to 50VDC and 3.5A per motor. Those are hard limits that can't be extended. Fortunately, many CNC routers will work just fine within those limitations. The very popular PK296A2A-SG7.2 motors, if wired bipolar half-coil, require less than 50VDC (35VDC in my case) and the motors are rated at 3A. I'm running four PK296B2A-SG3.6 motors on my test bench with my G540 and the combination works great.

If the limitations listed keep you from doing what you need to do, then you can go the PMDX-122 / G203v route. With that combination, you can use a power supply up to 80VDC. You can use motors that draw up to 7A per motor. You have more options with I/O on the PMDX-122 board than you have with the G540 (but not too many more options).

My only worry about the G540 is the use of DB-9M connectors. Time will tell whether they are reliable. So far they have worked perfectly.

The first step anyone needs to take, before deciding on the components for his control box is to make a list of everything that the control box needs to 'control'. Then, he can see whether the G540 could handle his needs or whether he needs more options.

Tue 17 February 2009, 13:44
My final goal after building the mechmate and making some upgrades to it after gathering some extra money...Is a Mechate, with proximity sensors, VFD and spindle and vacuum table...

Right now im thinking if I can go with direct drive...the idea is save some money for now and get some keling motors I can reuse later on a X3 mill retrofit.
If the 540 serves the job for know the idea is that it can stay in the mechmate when I get the Oriental Geared Motors. And get other 540 for the X3 mill retrofit. Other way is getting later the pdmx-122 with the Oriental Geared Motors, but I think this will be a mayor upgrade.
Any ideas to save some money for now and be ready for the future?

Tue 17 February 2009, 21:22

If you are going for direct drive motors then you will need to do your own deep analysis of the suitability of the G540. My analysis showed it would not work well, and so I spent $$$ on the OM motors. I think I saved over the cost of 203Vs.

There are other concerns with direct drive motors, including both torque and accuracy on curved cuts. Again you need to do your own analysis and see what works for you.

Tue 17 February 2009, 21:34
What drive you into the conclusion that the G540 did not work well for your case?

Ive seen that inexpesive motors suplemented with a reduction belt (timing belts work great (other plus is no backslash)) and a thought is that if I have to replace a motor in the future it will not be a 250 dlls motor, maybe just 90dlls for one. besides having a setup like that is open to experimenting with reduction ratios...this is just one thought going around my head right now.

Tue 17 February 2009, 22:19
Now I see a great problem with the G540...it has a maximum of 3.5A...havent found one nema34 that is that rating except the oritentals...:o Is there a workaround this issue?

Wed 18 February 2009, 05:38
Somewhere Mariss stated that the G540 was designed to work with all size 17 motors, most size 23 motors and some size 34 motors. The G540 works very well with the PK296A2A-SG7.2 motor w/gearbox. If you want to use motors that are rated at more than 3.5A, you would be better advised to use the G203v stepper drivers.

The G540 is not a universal solution. Although its price makes it very attractive, it has some very definite limitations. If your design falls within those limitations, then the G540 might be your best choice; however, if your design requires more than the G540 offers, then the G540 is not well suited to your application.

Wed 18 February 2009, 07:08
Hector, as you've picked up, the G540 will only work with small, "single stack" NEMA34 motors. I'm sure you could find a combination of motors and belt reductions that would work with the G540, but I'm not sure you'll save money doing so. See this thread (http://www.mechmate.com/forums/showthread.php?t=1114) and particularly the linked threads under post #1 and post #79 for lots of background.

Thu 19 February 2009, 07:29
Well, although the G540 is capable of running the oriental geared motors, yesturday i decided to go with the 203vīs, and made my order, $600 dlls for 4 of them, auch!!! :(,I did also order the pmdx-122, that one didnt hurt, Im breading heavy and taking more air for the oriental motor purchase :eek: (Im saying goodbye to my akrapovic 4-2-1 exhaust for my Suzuki Hayabusa 2008 :( )---for now:)

Thu 19 February 2009, 08:19
Hector. The upside to your purchase is the MM will make you money, the bike will take it away from you! Wise choice in these economic times. :D