View Full Version : Geckodrives (California USA)

Tue 25 April 2006, 00:30
This is the classic "Gecko":


They live at www.geckodrive.com (http://www.geckodrive.com/). My immediate interest is in the G200 range of Gecko's for driving stepping motors. The Mechmate used G201's. However, adding the capacitors within 1" of the drive was not pretty, and in future I will use G202's. Note added Jul 2008: Now also using G203V drives. (The V is for Vampire. It is not for Vacuum - do not buy G203V with the Vacuum option)

The first impression on meeting a Gecko in real life was that it is very small! Only 2.5" (64mm) square and less than 1" (25mm) high. But you do need one Gecko for each motor and a row of Gecko's starts to look substantial....

Tue 25 April 2006, 00:47
Here are 4 Gecko's lined up on a test board to drive the 4 motors on a PRT Shopbot:


The 75V power supply and fuses occupy the top part of the board. The power supply section has now been tidied up as per this thread. (http://www.mechmate.com/forums/showthread.php?t=350) You can see the capacitor placed on each Gecko 201 - the G202 has the capacitor inside and is therefore a little wider, but the installation will be neater. The G203V is the same size as the G201 - but it is NOT directly replaceable (the supply to the "Common" pin must be changed)

The grey cables are the beginnings of the cables out to each stepper motor plug. (Notice how the screens of those cables are connected to a ground/earth point at one end)

What you see in the photo above is the "Heavy" current sides of the Geckos connected. Each Gecko gets 75V DC on the red & black wires coming from the fuses. And then each Gecko drives out 4 wires to the coils of each stepper motor. So, the left hand, (or upper in the second photo), is all connected. The right hand (lower) six terminals of the Gecko must yet be connected to something that feeds in intelligent information....(will be covered in another thread (http://www.mechmate.com/forums/showthread.php?t=38))

Sun 21 May 2006, 03:31
To get an idea of physical sizes involved......

reza forushani
Thu 15 February 2007, 23:57
How do you slide the cover off the Gecko?

Fri 16 February 2007, 00:04
The cover has two small screws from the bottom that need to be removed first. But, above> (was in another thread) I was talking of the connector blocks, which you just pull vertically up (90 degree to wire direction)

reza forushani
Fri 16 February 2007, 00:18
I tried pushing the connectors up with a lot of force without any success. I don't want to break it. Maybe the 202v is different from 202. Do you have a picture of this?

Fri 16 February 2007, 01:25
http://www.mechmate.com/Forum/messages/16/3404.jpg http://www.mechmate.com/Forum/messages/16/3405.jpg
http://www.mechmate.com/Forum/messages/16/3406.jpg http://www.mechmate.com/Forum/messages/16/3407.jpg

When sliding the cover off, you have to lift it over the LED (light) a little bit.

The photos are of a G201. The other drives are slightly different.

Do not remove the connectors too often - they can wear out. (A batch of connectors was recalled a year ago because of this issue. The supplier has since been changed)

Don't remove the connectors unless the geckos are completely dead (un-powered) with the capacitors fully discharged (g201/202 LED dead for 5 seconds - the 203 has other LEDs). This allows you to insert a screwdriver underneath for leverage without fear of shorting something.

The connectors are split/joined in two halves of 6 pins each. Although it appears that only 3 pins make one connector, they are in fact joined to an adjacent connector.

Gecko supplier part no.'s:
On-Shore Technology the 130-series
BlockMaster. part no. DGPBP111-12-ON

Some RS component stock codes for the connector blocks.

2 way 181-4254
3 way 181-4260
4 way 181-4276
6 way 181-4282

Phoenix Contact
2 way 468-0919
3 way 468-0925
4 way 468-0931

reza forushani
Thu 22 February 2007, 16:10
Gerald as you know I got the G203V. In the manual it says "Term 11 and 12 are for current resistor". Do I need a resistor?

I am calculating a 12k ohm resistor. Is this correct anybody?

Mike Richards
Thu 22 February 2007, 21:24

The Gecko G203 manual says:

The G203V will accommodate motor winding currents from 0 to 7A. Use the following equation to calculate the value, (in kilo-Ohms) of the current set resistor: R (in kilo-ohms) = 47 * I / (7 - I) corrected later

So a 12k resistor would be used with a motor rated at about 1.5-amps

Here are some other values:
1 amp = 8k
2 amp = 19k
3 amp = 35k
4 amp = 63k
5 amp = 118k
6 amp = 282k

(Remember that you can use the closest standard 1/4-Watt resistor value, i.e. 3-amp motor would use a 33k 1/4-watt resistor.)

Thu 22 February 2007, 22:15
Reza, you definitely need a resistor if you don't want to cook the motor.

Before Mike or I can give you a definite size on the resistor, you need to tell us which motor you are using. (I presume you will wire the motor in unipolar (http://www.mechmate.com/forums/showthread.php?t=256) mode)

reza forushani
Thu 22 February 2007, 23:26
I am using the Oriental Motor recommended. I guess I will start with Unipolar and see what happens. Isn't that the way you are using yours? So, my motor should be running at 1.5 A.
For that I need 12K. Please correct me if I am wrong?

Thu 22 February 2007, 23:58
Reza, your resistor calc is solid for the PK296A1A-SG7.2 motor in unipolar configuration. A 12k resistor should be commonly available.

Suggest you also buy a set of 8k resistors in case you want to try the bipolar mode at some time. 8.2k might be more commonly available and they are also okay.

Unfortunately, you need to check the salesguys when they hand you these tiny things. Best way is with an ohmmeter/multimeter.

Fri 23 February 2007, 00:02
While we are talking of setting the geckodrive with a resistor, we might as well remember that the gecko must be "tuned" to your particular motors for resonance. There is a tiny potentiometer to be gently adjusted by a tiny screwdriver. See the instruction sheet. (might not apply to "vampire" model?).

reza forushani
Fri 23 February 2007, 00:16
I am actually using pk292a1a-3.6, I suppose that doesn't change anything. The Vampire controller has a little screw for adjustment also.

Fri 23 February 2007, 00:31
Same logic and value for the PK296A1A-SG3.6 (not pk292...)

Hugo Carradini
Fri 23 February 2007, 14:41
Hello reza. You are making good questions and Gerald is giving very explicit answers. I am going to use the same motors and the same Geckos so know that you are ahead I think the road will be clear out. reza would be nice to see how you install the resistor. Gerald the description of the red, yellow and green buttons is very nice to use.

reza forushani
Fri 23 February 2007, 16:12
Gerald is our God. I have never done anything like this. Remeber I used to be a software programmer for 10 years and been building homes for 15 years. Not too much electrical/electronics or Steel construction background. But, Gerald and other friends are very helpful, patient and nice 9to dumb questions). I think I can figure it out with their help.

I see the capacitor in the pictures on top but not the resistor?

Fri 23 February 2007, 20:57
Look very carefully!

Here is a bigger pic:


If you are following this Forum, you should not be fitting capacitors. They were only needed for the G201 gecko - the G202 and G203 do not need them.

reza forushani
Fri 23 February 2007, 21:12
Thanks. Yes I know for G201 capacitors were needed, but later versions like 202 and 203v don't need. That resistor is pretty small!
I have most of the Control Panel set up except for power supply. It's in the mail somewhere.
As soon as I get the PS and wires I will finish it up. I am still trying to upload pictures.

reza forushani
Sun 25 February 2007, 21:27
Hi Gerald

I ordered another relay.

Now I installed Mach3 and connected one stepper motor and Gecko. Now, I ran a g-code (I don't know anything about g-code or mach yet) program called cut-a-circle and it started to turn the motor in both directions. The motor is heating up very quickly and also makes a lot of noise. I know you said it needs to be tuned, I also know the dial on the Gecko is used to tune it. How do I go about doing this. Do I need to run a program in Mach and while it's running tune it or how? Thanks

reza forushani
Sun 25 February 2007, 21:40
BTW, I used the black wire of the motor for phase a, yellow for phase a-, red for phase b, yelloow for phase b-. Are these the right wires to be used for Unipolar? The resistor is 1/4 w and 12k.

Sun 25 February 2007, 22:07
Did you check the resistor with an ohmmeter?

reza forushani
Sun 25 February 2007, 22:08
yes and ut's ok. is my wiring right

Sun 25 February 2007, 22:09
Did you separately insulate the motor wires that are not used?

I will go and check the wire colours now......

Sun 25 February 2007, 22:16
In your description, you used the yellow twice??? The last time you mention yellow, it should be white instead.

A: Black/yellow
B: Red/White

(green & blue not touching anything, not connected to each other.)

You already got movement!!!! That is a good surprise!

First we will have some coffee, and then talk about the tuning. It is not critical for you now.

reza forushani
Sun 25 February 2007, 22:21
I have black.yellow, red.white.
Green and Blue are free and not touching.

Yes we have movement.

Coffee is on me. Let me pour you a cup?!

Sun 25 February 2007, 22:45
Are you absolutely sure the resistor is 12k and not 120k? That motor should only be slightly warmer than room temperature after about 30 minutes to an hour. If you left it on all day then you should still be able to hold your hand on it very comfortably for a loooong time.

You are making it sound like you can brew coffee on your motor? Well, a stepper is allowed to get that hot, but in this case there is something very wrong. It can only be the resistor choice, a faulty gecko (unlikely), a faulty motor (very unlikely), or a bad connection between the resistor and the gecko (possible?).

I suggest you cure the heat problem while the PMDX is not connected - take it one step at a time......

Thanks for the first coffee, pour me another please? (while your motor is still hot)

reza forushani
Sun 25 February 2007, 22:58
Hi Gerald: COFFEE WAS THE CULPRIT OR the lack of enough of it.

Yes you were right. There was a loose connection. Everything works now perfectly. Things are quiet and cold.

You win another round. This is a temporary set up as I havn't got my permanent cables yet. Hopefully next of days, I will the cables and complete the control panel. Tommorrow I am suppose to get the laser parts and other steel and get started on the table.

Thanks again for everything and being such a wonderfull mentor.

Sun 25 February 2007, 23:15
This is a perfect illustration of why this must be done on the kitchen (http://www.mechmate.com/forums/showthread.php?t=279) table! Imagine building the full-size beast and then walking around it to learn these lessons....

Hugo Carradini
Mon 26 February 2007, 17:46
Reza, you really nohow to keep us in tension. It is a good way to keep our attention on this nice tread.
We will need some extra coffee.

reza forushani
Tue 27 February 2007, 01:55
How do you know when a Gecko has a fault. I was running the system and something happened the Gecko is displaying a green and red LED. Mach continues to run as if everything is Ok but the motor is not running and Gecko has faulted.
1. How do you get to know if that's happened. Geck is inside the control box and you don't see when it has faults
2. Does Mach not know about this to stop the program. If this Gecko is on one X-axis, that motor stops but everything else is running.

Tue 27 February 2007, 02:17
You make an extremely important point. The whole MACH/Gecko approach is very much open-loop with one axis not knowing about a problem on another axis. The guys have been talking of closing the loop, but nothing is available yet.

This a very good reason to use the highest quality workmanship and materials when building your own system. And to make sure the Gecko (and other components) are installed in accordance with the manufacturers information. You don't get second chances.

Thu 01 March 2007, 06:55
The closed loop / encoder discussion continued here (http://www.mechmate.com/forums/showthread.php?t=257)

Jon Conner
Fri 02 March 2007, 07:01
Hi I am about to update my G202's with some new steppers that are 4.2 amps. I was going to change the resistor to 75k, and "tune" the motors with the pot on the back of the drive. Any suggestions or am I missing anything? Thanks

christipher saint denis
Sat 31 March 2007, 11:27
I have the hardest time formulating my questions. There are so many aspects to wiring this project and the fact that I am very new to this sort of thing does not help. I have collected the motors and most of the electrical components.

I am having trouble understanding how to correctly wire my AnTeck PS-8N70Rxx power supply to my Gecko G203 driver.

Info from the Gecko G203 manual says:


(TERM. 1) POWER GROUND Connect the power supply ground to term.1

(TERM. 2) +15 TO 80 VDC Connect the power supply ?+? to this terminal

My 110v line has black(hot), white(neutral), and Green(ground).

My Antect power supply has 2 red wires and 2 black wires. AnTect states that in connecting my 110v line both the Anteck reds are connected to neutral(white) and both Anteck blacks are connected to hot(black). That I understand well enough(hopefully)? What I don't understand is where is this "POWER GROUND" wire to be connect to the Gecko g203 term.1. Are they asking for the ground(green) wire for my 110v supply line. This "Power Ground" is throwing me off.

The Anteck 70Vdc 11A unregulated output block has three terminals and from the Antect info sheet the out side two are + and - and the inside term is unlabeled.

Thanks for you time. Really, I appreciate it!

Sat 31 March 2007, 11:52
Christipher, the power ground for the Gecko is the terminal marked "-" (reference (http://toroid-transformer.com/PS-6N56R.pdf)) The middle terminal should be "dead". They use a 3-position terminal to get some space between the + and - connections because these can make very good sparks when they touch.

They are NOT asking you to connect the Gecko's terminal directly to ground wire of the 110V incoming.

Can you post some photos of your power supply?

christipher saint denis
Sat 31 March 2007, 13:27
Thanks so much for the information. I would be glad to post some photos of my supply.

Christipher did post photos and I moved them to the power supply section here (http://www.mechmate.com/forums/showthread.php?t=54)

von hous
Thu 09 August 2007, 08:16
Hi Gerald_D and to the others into this group.:)
I am going to use steppers motors and I want to ask you what i must do to connect those steppers motors (look attachment) to geckodrive G320v.
I am not wise in the electonics and i want to understand the maths to do it.
Also in 4'axis controller system what size of power suplies i must use. Please keep it simple, with some "exaples" to understand.
thank you.:)


Thu 09 August 2007, 09:01
The Gecko G320 is for SERVO motors. You will need to use the G201, G202 or G203 modules with STEPPER motors.

(I have a G320 with a servo motor on my test bench and it works very well, but without a lot of gear reduction, the servo motor would not work on a rack and pinion driven CNC router.)

Gerald D
Thu 09 August 2007, 10:50
Welcome von hous!

The Slo-Syn motor 103-807 is a stepper motor, but it is not good for the MechMate if you want to put the pinion gear direct on the motor shaft. The shaft is too thin.

Also, the GeckoDrives work much better (60%?) with motors that have a square body shape. That Slo-Syn is round. The square body motor contains more iron.

As Mike said, you need either the G201, G202 or G203V drives from Gecko for stepper motors.

Let us first find out your final motor choice before we talk about the drive.

von hous
Thu 09 August 2007, 14:46
Hi Gerald D,
It was my fault, I mean 203V, but in a rush I write the wrong geckodriver.
I am going to build a small version of your machine.
Dimesion is about 1m X 0,6m. I think that is ok also those steppers motors. What do you think. Any advise?:confused:

Also by yours opinion which stepper motors is going to work best with the gecko. I mean which is the best for my machine.
(In the future I maybe use the same controller+steppers motors with a much larger machine), but for now -for the space that I have in my home- that is the best I can do. :mad:

Gerald D
Thu 09 August 2007, 23:29
Von hous, if you make the MechMate smaller, you still have to keep to the same motor size. The recommended motors are fully discussed in this thread: Selecting motors for the MechMate (http://www.mechmate.com/forums/showthread.php?t=254) Read the first post very carefully.

Gerald D
Fri 10 August 2007, 12:23
A discussion on the geckodrive yahoo group in the last day:

Q: Does anyone know if it is possible to set the current limit of a G203 (and other Gecko Stepper drive) with a voltage in place of the current set

A: Yes, it's easy. The voltage on the G203V terminal 11 is proportional
to motor current. The relationship is 2.12 Amps per volt, 3.3V
maximum. The source impedance should be less than 500 Ohms to
swamp-out the effect of the internal 47.5K pull-up resistor to 3.3V.

Q's: Three questions if I may:

1) Terminal 12 is commoned to terminals 1, 10, both, none(floating)?

2) If terminal 11 of multiple drives are supplied by one voltage
controller, are there risks of a single drive fault impacting on others?

3) Does a voltage control apply to G201 and G202?

1) Terminal 12 is common with terminal 1. The difference is terminal
12 is a "quiet" ground. The top inner layer of the printed circuit
board is a ground plane. It is divided into two sections, power ground
and logic ground. Power ground carries the large motor currents, logic
ground carries only small currents. The two connect at a single point
only (at the ground end of the current sense resistors).

Terminal 10 goes to the cathodes of the DISABLE, STEP and DIRECTION
optoisolator LEDS only. It is electrically isolated from the rest of
the drive circuit.

2) Terminal 11 has a 47.5K resistor pull-up to 3.3V and a 100K / 100nF
low-pass filter going to an op-amp input. The op-amp input is diode
clamped to GND and 3.3V with a pair of Schottky diodes. A worst-case
failure in the drive results in terminal 11 still having at least a
33K input impedance.

3) All of our other step motor drives have a 0.39 Amps per Volt scale.
An 18V input gives a 7 Amp current output while a 2.5V input (minimum)
gives a 1A output current. The 0V to 2.5V input range is not recommended.

The G203V input range is 0V to 3.3V which results in a 0A to 7A
current output range. The scale is 2.12 Amps per Volt.

Marc Shlaes
Fri 10 August 2007, 13:05
I'll go ahead and say what probably many others are thinking.

"I wish I had a clue what this said!"

Gerald D
Fri 10 August 2007, 13:16
Marc, this is stuff you might want to know when you build the third MechMate. Don't worry about it! :)

Marc Shlaes
Fri 10 August 2007, 14:01
Thanks, I needed that! Now I can go from this :eek: to this :D.

Greg J
Sat 11 August 2007, 14:06
I found some 12K resistors :D (actually the 12K read low at 11.75 so I added an .82K in series).

Anyways, when power is applied to the drivers, 3 operate normal, but one does not. It has the momentary red led and then nothing. There is 70VDC to terminals 1 and 2. If I had a blown fuse, would the red led show at all?

Any suggestions?


Greg J
Sat 11 August 2007, 14:07
Ooops, I'm using the 203V Gecko drivers.


Sat 11 August 2007, 17:47

Here's some info from the G203 manual:

ERROR LED: The RED ERROR indicator is lit when:
1) During power-on reset for 1 second when power is first applied to the G203V.
2) While the DISABLE input is active.
3) When there is a short-circuit on any motor output. Momentarily activate the DISABLE input to reset.
4) During over-temperature shutdown. The LED automatically resets when the drive temperature drops.

I'm guessing that somehow one of the motor's leads is shorted.

Greg J
Sat 11 August 2007, 19:33

I did a continuity check between phase A and phase B coils and everything looked OK (I'm configured Uniphase), no short between coils.

Just a reminder, that when I first (the very first time) powered up, I did not have the 12K resistors on the current set "ports" of the Gecko drives. During that first time, this same drive showed yellow LED while I was cooking the motors. The other 3 drives, showed green LED's.

I wonder if its advantageous to change drives. Switch number 3 with number 4. I'll wait to see what you think.

Sat 11 August 2007, 19:58

The yellow L.E.D., which is available on the newest G203 drives has a special function. According to the manual:

FULL POWER LED: The YELLOW FULL POWER indicator is lit when the motor is turning fast enough to generate
maximum possible mechanical power. Power is torque times RPM and power output reaches its maximum value
when this indicator is lit. Use this indicator to verify your motor is optimally geared to the load.

I would try switching two of the stepper motors to see if the problem follows the motor or if it remains with the stepper driver. In case the stepper driver has been damaged, Mariss has a special 'opps' policy where he will replace a stepper driver as long as you explain exactly what happened. (He uses the 'opps' data to design even better drives.)

I can't imagine that running the motors for a very short time without current limiting resistors would have 'cooked' either the stepper driver or the stepper motor, especially if the table covering was not hurt. I've run a PK299A2B-SG3.6 drive with 70V, when 25X the drives rated voltage was 35V. That drive got really hot. In fact, I smelled it before I burned a fingertip when I touched it. Other than getting really hot, both the stepper and the stepper driver still work perfectly fine.

Greg J
Sat 11 August 2007, 20:24

I switched out motors (changed motors with drivers) and no change. From this test, its not the motors. I'd rather have a driver go, than a motor.

I think I'll switch driver also. You never know if I have a bad BOB.

Give me a little time and I'll report results.


Greg J
Sat 11 August 2007, 20:40

Nope, I switch the DIR, STEP, and COMMON, leads on the BOB and no change.

I'll see what the boys at Gecko have to say.

Thanks for your help on a Saturday night.

We're a strange lot who enjoy our play on a fine evening.

"Piloting on the Mississippi River was not work to me; it was play--delightful play, vigorous play, adventurous play--and I loved it . . ."
- Mark Twain in Eruption

Have an enjoyable time,

Gerald D
Sat 11 August 2007, 22:21
Greg, you can use the Gecko forum as well:

Gerald D
Sun 12 August 2007, 01:41
I would not rush to call the one drive suspect until I had done a lot of swapping and checking. Leave the suspicious drive to one side for now and focus on getting some motors to turn on command. Once you have control (understanding) of the whole process from keyboard to motor motion you are then better equipped to diagnose faults.

Greg J
Sun 12 August 2007, 08:58
Thanks Gerald,

Will do. I'll try to get some motors turning today.


Greg J
Thu 23 August 2007, 21:10

That yahoo/gecko drive forum is addicting. The way Mariauss (Not spelled correctly) solves problems is worth reading.

Greg, you can use the Gecko forum as well:

Greg J
Mon 27 August 2007, 20:44
Gerald / Mike / anyone,

Received G203V back today. "No problem found. Drive working properly" was Gecko's notes.

It has to be in the Mach 3 config. somewhere. I did notice on the PDMX-122 BOB, that pin 4 of J2 is not lit. Pins 2 & 3 of J1 are lit, Pin 5 of J2 is lit, Pins 6 & 7 of J3 are lit and Pins 8 & 9 of J4 are lit.

The suspect G203V is connected to J3.

Any help is appreciated. Just for the record, I've never operated a CNC machine, wrote any G code, let alone, built a CNC router. This is all from the ground up for me.


Gerald D
Tue 28 August 2007, 00:20
If you swopped drives without doing anything else, and the fault swopped as well, then it is a faulty drive.

Tue 28 August 2007, 06:26
Here's the way that I have Mach 3 configured for my G203 stepper drivers:

X-axis enabled (GREEN Check Mark), Step = pin 3, Direction = pin 2, Step Active Low = RED X, Dir Active Low = RED X

Y-axis enabled (GREEN Check Mark), Step = pin 5, Direction = pin 4, Step Active Low = RED X, Dir Active Low = RED X

Z-axis enabled (GREEN Check Mark), Step = pin 7, Direction = pin 6, Step Active Low = RED X, Dir Active Low = RED X
A-axis enabled (GREEN Check Mark), Step = pin 9, Direction = pin 8, Step Active Low = RED X, Dir Active Low = RED X

Slave Axis: A is slaved to X

On the PMDX-122:

JP1 is set with the jumper on the bottom (between GND and the center pin)
JP2, JP4, JP5 are all jumpered with the jumper on the top two pins (closest to the cable connector)
JP3 is jumpered with the jumper on the top two pins (away from the green connector)

A 12V power supply is plugged into J11

NOTE: The L.E.D.s for pins 2, 4, 6, 8 will be ON when the steppers are turning one directions and OFF when the steppers are turning the other direction. The L.E.D.s for pins 3,5,7,9 may be ON or OFF depending on the status of the step pulse, but those L.E.D.s should flicker ON/OFF when the motors are turning.

With a multi-meter, check your wiring between the problem G203's Step, Direction, and Common pins and the PMDX-122's Step, Direction, and Common pins to verify that resistance readings between connection pins shows zero resistance (with the power off!).

If that doesn't work, email me your telephone number and the best time to call and I'll try to help you troubleshoot the circuit. (miker@xmission.com)


Greg J
Tue 28 August 2007, 10:37

I'm going to swap out the drivers one more time to make sure. I believe Gecko when they say the driver is good (maybe a fault on my part). I will exhaust all causes ( and document) on my end before I resend the driver to Gecko.


My Mach3 Config is the same. I will check resistance. Thanks for the offer of help. Gerald and yourself have been a great help and its my responsibility to use all my troubleshooting abilities before I waste your time. If I run into a brick wall by ... oh ... Thurs/Fri, I'll call for help.

Thanks again guys,

Gerald D
Tue 28 August 2007, 11:35
Greg, with 4 positions on the BOB, 4 drives, 4 sets of drive connectors, 4 sets of wires, 4 motors loose on a bench, and 3 of everything works okay, then you swap, swap, swap till you find the culprit. Just remember to switch off till the Gecko LED's die completely before doing any swopping.

Sun 18 November 2007, 19:27
With my indexer I was having problems with the A (rotation) axis moving. Fix was to disable automatic voltage reduction. Automatic voltage reduction occurs 1 second after the last motor movement and reduces the power to the stepper by 30% to 50%. Problem was apparently fixed with the automatic voltage reduction disabled on the Gecko 202. However about 30 days later another problem emerged. After few minutes or a few hours the Gecko dropped ALL power to the motor. I will skip all the trials and tribulations and give you the short story. In 3 days on the Gecko news group there were 4 others who reported the same problem and all were with larger steppers and Gecko refuses to even discuss the problem. The 203 is not a solution because the automatic voltage reduction cannot be disabled. I have installed a Chinese drive and I will update when I am sure of the results. The thing about this whole epasode is Gecko's apparent refusal to acknowledge/resolve the problem with one of it's products. Doesen't give me a comfortable feeling using their other products.

Gerald D
Sun 18 November 2007, 22:36
Art, I have been watching those reports, and with all due respects, they are poor reports being light on facts regarding the cooling of the Geckodrives. Can you give us a photo of how your drives are mounted, details of the heatsink, thermal grease, the control box volume, the fan and the filter (if applicable)?

Gerald D
Sun 18 November 2007, 22:41
Mariss did reply this morning:

The biggest drawback of a G202 is the lack of a short-circuit
indicator LED. What you call "a well known problem" is actually the
drive tripping its short-circuit protection latch. This happens with
old, partially demagnetized motors whose inductance has dropped and
some Chinese motors whose windings arc internally at elevated
temperatures when driven at high supply voltages.

Since you are dissatisfied with the G202s, you are kindly encouraged
to return them for a full refund. I'm not trying to change your mind
and I wish you the best with your new drives but I'd like to correct a
few things:

1) The G202 doesn't have temperature protection, only short-circuit
protection. Drives and motors warm up at the same time. As motors warm
up, they expand. If the motor wire insulation is compromised, internal
arcing happens while it's warm, not cold.

2) No drive has "voltage reduction". Some drives have "current
reduction". The G202 and G203 have current reduction.

Mon 19 November 2007, 10:55
I haven't gotten into the details of wiring the panel yet. I just ordered 4 Gecko G203V drives :eek: and I guess I'm trying to get my head around what exactly your saying about these drives. Both the enclosure and the drives should arrive today or tomorrow. Does this all mean that I shouldn't have bought these drives :confused: or am I OK:D. I'm planning on finishing the kitchen table project this winter and the metal fabrication and paint this spring. I expect to be done by late spring or in the summer with the MechMate Mamba project.


Gerald D
Mon 19 November 2007, 10:59
Herb, what motors are you planning to drive? If you stick with the Oriental Motors suggested here, you will be 100%.

Mon 19 November 2007, 11:59

Yes, I plan to stick with the Oriental Motors. Thanks for the info. I'm going to get nervous about all my purchases until I see this thing start throwing chips.


Mon 19 November 2007, 12:26
I've logged thousands of hours with Gecko G202 stepper drivers and Oriental Motor stepper motors. I've also logged well over 1,000 hours with Gecko G203v stepper drivers and Oriental Motor stepper motors. So far, there has been NO problem of any kind. And, may I also add, my test bench time with the motors and drivers would have to be considered harsh time. Usually, I'm on a quest to see just how fast I can spin the motors, or how high I can run the Voltage of how long I can slowly toggle steps back and forth to get maximum heat out of a motor and driver.

Recently, I bought back four Oriental Motor PK268-02AA drives that I installed years and years ago when that model motor first came to the market. Those motoors were in use five days a week, eight hours a day, cycling once every second for well over a decade. During their service life none of the drives failed (or even failed to perform as expected). On the test bench, they perform exactly like four brand-new, just out-of-the-box motors. They have the same torque and the same speed.

As far as Gecko products go, I've never had any kind of problem or concern with anything. Mariss and I have talked on the telephone twice. Both times I called to get some very simple assistance. Both times Mariss personally answered the telephone and spent as much time as I needed to teach me how to better use his product (and while doing that, to teach me more about stepper motors than I thought any one person could know).

One last point: I have never been a fan of using stepper drives or stepper motors of unknown or unproven quality. The stepper motors and stepper drives are the very heart of a CNC machine. Does it make any sense to carefully follow Gerald's plans to build a robust and elegant machine - and then slap on bargain basement stepper motors? You only pay for quality once. Junk is a continual drain on the wallet.

Edited: Mariss has continually cautioned us against using extra large motors. In some of his literature, he recommends that the size 34 motor as being the best size partly because it has enough mass to radiate heat away from the motor. (Smaller motors like the size 23 PK268 motors get hot and stay hot because of their small size.) I've found that the PK29x size motor from Oriental Motor works very well. Models are available handling torque ranges from 300 oz*in to 880 oz*in. The PK299-F4.5 motor, at 880 oz*in Bipolar Parallel, is the largest motor that I will use. Other, larger motors are available, but I just can't see the need of using larger and slower motors on a CNC machine when a smaller motor can be geared to outperform the larger motors.

J.R. Hatcher
Fri 04 January 2008, 04:55
Quote by Mike; "You only pay for quality once. Junk is a continual drain on the wallet".

Quote by unknown; "The bitterness of poor quality lingers long after the sweetness of cheap price has gone"

Oh... while we are on the subject if anyone would like to buy some cheap drivers I have a rather large collections (26):o I obtained before I decided to go with Geckos. Ditto the motors too before I bought the PK296 & PK299 series.

Where were you Mike Richards 2 years ago when I needed your expert advice???;)

All joking aside thanks for your willingness to share that knowledge base now!!!!!!!

Fri 04 January 2008, 04:58

EBay and CNCZone. There are plenty of people on CNCZone looking for drives and motors. Many use motors out of Photocopy machines. I think you will find lots of buyers there.

J.R. Hatcher
Fri 04 January 2008, 05:11
Thanks Nils, however I was joking about selling them to you guys. But now that you mention it maybe I should sell them on ebay, trust me I got plenty of other stuff that will catch the dust.:D:D

J.R. Hatcher
Fri 18 January 2008, 05:39
Mike my motors PK299-01AA are pulling 2 amps. You said the resistor for the gecko 203 drives needed to be 18k to 20k. I have a bunch of 22k I think this would give 2.2 amps, will this be ok?

Fri 18 January 2008, 08:02
22K should work okay. That allows about 11% more current to be pulled through the motors, which should not be a problem. If the motors run hotter than you would like, then try a lower value resistor. (The resistors only cost about 15 cents each.)

Excessive heat can also be caused by high voltage, but that should not be a problem with PK299-01AA motors because even at 80VDC (Gecko maximum voltage) with the motors connected half-coil, you would only be using 70% of the voltage that the motors could handle.

Gerald D
Fri 18 January 2008, 08:03
JR, if you put 100k to 220k in parallel over 22k, you end up with 18k to 20k. Food for thought. (Personally I would use the 22k's, check for heat, find none, and forget to get the "correct" one :))

Gerald D
Fri 18 January 2008, 08:04

Fri 18 January 2008, 08:51
If you need an assortment of resistors let me know and I will mail you a kit of what you need. I have tons of them. :) And I send mail to the US all the time. No trouble.

Wed 23 January 2008, 11:42
When I cut air (the router is turned off), the motors sound like they are playing a musical tune. It isn't loud and doesn't bother me but I'm wondering if that's normal. Do you think I need to tune them? The instructions for tuning the motors are somewhat imprecise so I thought I would ask the question.

Gerald D
Wed 23 January 2008, 12:14
Playing tunes is normal - those are the step frequencies making those "notes". Some people have even written air-cut programs that play recognisable tunes.

Tuning the drives is important, and easy. The instruction says:
"Set the motor speed to about 1/2 revolution per second and then turn the trimpot until a distinct null is noted in the motorís vibration" . . . .

Drop motor away from rack, set a move speed where the MOTOR takes 2 seconds to make a full turn. With a 7.2 gearbox, it must take 14 seconds for the pinon gear to make a full turn. (This need not be precise - it just indicates very low speed)

While holding one hand on the motor, tune the drive until the motor feels at its smoothest. There is a distinct smooth spot and it is easy to feel it.

Wed 23 January 2008, 16:59
Thanks Gerald!

Sun 20 April 2008, 17:32
What is the difference between carbon film and metal film resistors and which would be the choice for the geckos?

Sun 20 April 2008, 17:39
Carbon film resistors are really old technology. These days metal film resistors are the way to go. Early in the day, carbon comp resistors were cheaper to make and therefore for non critical applications they made sense. These days metal film resistors offer better performance in tolerance, temperature and drift and they are affordable. Use them if you can.

Greg J
Wed 04 June 2008, 16:29
Everything on my MM seems to be operating just fine.

But, one of the Gecko V203's has no green light. When power is first applied to the control box, I get a red and yellow light on the drive. The three other drives have a green light.

This happened during the kitchen project, so I sent the drive off for inspection. Gecko said everything was fine.

Just thought I'd mention this. Maybe just a failed light bulb.

Thu 05 June 2008, 02:26

If you only got a Red light, then I would agree that the Green side of the L.E.D. was not working; however, to get the Yellow light, both the Red side and the Green side of the L.E.D. have to be on at the same time.]

According to the spec sheet, the G203v should have the Red L.E.D. on when the G203v is first turned on (1 sec), when the G203v overheats, when the Disable input is active, or when there is a short circuit present. The Yellow L.E.D. turns on when the drive is running at full power. Otherwise the Green L.E.D. should be on at all times.

However, if the G203v is driving the stepper motor properly, then having the Green L.E.D. on or off really doesn't matter.

By the way, does the Green L.E.D. come on when you ONLY have power supplied to the G203v? (No motor connections. No step/direction/common connections. No resistor connections.)

Greg J
Thu 05 June 2008, 21:14

First, thanks for the help.

I re-checked it this evening. I was in error before. I get a red LED on all four drives when first powered up. No yellow LED is ever present. I was working from memory in the previous post (I should know better :o)

After the red LED, 3 of the 4 drivers go green, and the fourth, shows nothing.

Just to re-iterate, everything seems to be operating fine. I have not cut anything yet, so the motors/drives have not been under much of a load.

Gerald D
Thu 05 June 2008, 23:14
I have not cut anything yet, so the motors/drives have not been under much of a load.

The weird thing with stepper motors is that their heaviest load (electrically speaking) is when they are idle. Get them to do some real work and then they get cooler!

Greg J
Fri 06 June 2008, 06:05
The weird thing with stepper motors is that their heaviest load (electrically speaking) is when they are idle. Get them to do some real work and then they get cooler!


Back to the Gecko documentation on "basics of stepper motors".

Fri 06 June 2008, 08:20
Another site to check for info on stepper motors and drivers is
www.pminmo.com. There is a lot of good reading there. :)
Actually, he references geckodrives article as well! :eek:

Greg J
Fri 06 June 2008, 08:21
thanks Heath.

Mon 09 June 2008, 19:12
The L.E.D.s for pins 3,5,7,9 may be ON or OFF depending on the status of the step pulse, but those L.E.D.s should flicker ON/OFF when the motors are turning.

I'm having some issues with my setup as well. I have one PK296A1A-SG7.2 (half-coil), two compumotor LN series motors (full coil), three g203v drivers, and one pmdx-122. I got everything powered up and was even able to get some motor movement, but the thing is, all my motors are real darn slow. I definately do not see pins 3,5,7 flickering. They are always on. Pins 2,4,6 do turn on and off depending on the direction. The gecko green lights are on as well, which is expected.
I think I might know why everything is slow but I'm looking for a little confirmation here. I am temporarily using a variable DC power supply that supplies 20V and up to 20A. I checked while the motors were turning at max jog rate and I'm getting from 0.3A -0.36A on the PK motor, and about the same on the other two.
I have tuned the motors but still they are slow. Is the power supply my problem here?


Mon 09 June 2008, 20:59
The PK296A1A-SG7.2 motor wired half-coil needs a power supply voltage around 45VDC for optimum performance. I don't have data sheets on the Compumotors.

Pins 3,5,7 should flicker on/off with every step pulse. Pins 2,4,6 should either be steady on or steady off, depending on the direction signal.

Things to check:

1. PMDX-122 JP1 connector must be in the bottom position with G203v stepper drivers.

2. Mach3 setup configuration - verify the pins and the polarity of the step and direction signals.

3. Wiring - verify that you have continuity between the PMDX-122 and the G203v stepper drivers.

4. Current limiting resistor - verify that you have the correct value resistor (+/- 10%) for the motor that your using.

5. Mach3 - verify that the feed rate, ramping are set properly.

I have run stepper motors at less than 50% of the optimal voltage with excellent speed, so I don't think your power supply is the main problem. It's hard to know what voltage is actually going to a stepper motor without using an oscilloscope. A digital meter responds too slowly to get accurate readings.

If you still have problems after re-checking everything, please post your Mach3 pin-outs and speed settings so that we can cross-check things with you.

Greg J
Mon 09 June 2008, 21:12
I would also check

Mach 3 motor tuning configuration - Check the velocity on all motors.

Tue 10 June 2008, 06:04
1. PMDX-122 JP1 connector must be in the bottom position with G203v stepper drivers.
JP1, JP2, JP3 are all in the bottom position; JP4, LP5, JP6 are all in the top position. "Outputs Enabled" is lit, and "pin17" is lit. Direction led is lit when moving in one direction and off when moving in the opposite direction

2. Mach3 setup configuration - verify the pins and the polarity of the step and direction signals.
Step/Dir pins are all wired correctly (checked 3 times)
X Axis: Enabled, StepPin#3, DirPin#2 DirLowActive Disabled (red X mark), Step LowActive Disabled (red X mark)
Y Axis: Enabled, StepPin#5, DirPin#4 DirLowActive Disabled (red X mark), Step LowActive Disabled (red X mark)
Z Axis: Enabled, StepPin#7, DirPin#6 DirLowActive Disabled (red X mark), Step LowActive Disabled (red X mark)

3. Wiring - verify that you have continuity between the PMDX-122 and the G203v stepper drivers.
I have checked continuity and all is well here

4. Current limiting resistor - verify that you have the correct value resistor (+/- 10%) for the motor that your using.
Resistors are correct, PK296 motor (unipolar) is 33k, the compumotors (2.2A/phase) are 22k

5. Mach3 - verify that the feed rate, ramping are set properly.
The compumotor motors are driving direct ballscrew, so disregarding them for now, and focusing on the X Axis with the PK296:
I have 20/20 pinion and I'm working in Inches:
1 revolution of the motor gearbox output shaft makes 3.1416" of travel .
or 1 x pi = 3.1416"
2000 pulses from computer will turn the motor one turn. Motor must turn 7.2times for one revolution of gearbox output shaft.
7.2 gearbox would make 14,400 pulses for one turn of the output shaft.

divide the pulses from computer by inch travel:

14400/3.1416= 4583.66 Steps/Per

With these settings, I'm only able to get about 21 IPM's of Velocity while tuning in Mach3 before skipping occurs.

Gerald D
Tue 10 June 2008, 06:31
Have you verified the current limit resistors with an ohm-meter - I have made mistakes with colour bands before.

Tue 10 June 2008, 06:47
DOH! I checked again and I grabbed the 3300 and 2200 ohm resistors instead of the 33000 and 22000 ohm resistors. That did it for the motor velocity issue as they are getting up to speed nicely now. But I still do not see the LED's on the Step pins of the pmdx-122 flickering.

Gerald D
Tue 10 June 2008, 07:06
Evan, welcome to the club of the wrong resistors! :)

You won't see a kilohertz flicker - realise that you don't even see a 60Hz flicker from a lightbulb. Remember, us club-members don't have the best of eyes. ;)

Tue 10 June 2008, 07:12
If you use metal film resistors, then some type have numbers on them for easier identification. Also more stable than other resistor types. :)

Gerald D
Tue 10 June 2008, 07:57
I would still check them with an ohm-meter for this application ;)

Tue 10 June 2008, 08:22
Thanks Gerald. Next time I check with an ohmmeter I'll try and actually read the display. Thanks for the quick replies.


Mon 28 July 2008, 08:11

Today I mounted Geckos (G203V) on Alu plate, two of them (pin1) does not show continity with Alu plate or back plate, it means there me be ground voltage difference with another two which are showing continity.
I even scratched back plate and checked continity with pin 1 but no continuity.
I am providing seperate power for each Gecko and shilding of each power cable is grounded to Alu plate.
Should I go with it or if there is any issue?

Gerald D
Mon 28 July 2008, 09:17
Bob, do not worry if there is continuity between the Gecko's case and the alu plate. The power ground for the gecko runs from pin 1 straight to your power supply negative pole, and from that negative pole there should be a wire to the alu plate.

The gecko case is hard anodised, which makes a pretty good insulator, except where your mounting screws might manage to break the insulation/anodising. Gecko needs the insulating property on the inside of the base plate, because there they have some semiconductor devices pressed against the plate as a heatsing.

The power wires feeding pins 1 and 2 need not be shielded. They are commonly unshielded.

Gerald D
Mon 28 July 2008, 09:29
You can read more about the Gecko grounding here:

and here:

Mon 28 July 2008, 11:27
Oops, I mean to say two drives (pin 1) show continuity with Alu plate but other two does not show continuity. That continuity comes through back plate of Gecko. Should I also provide path for ground via back plate to Alu plate?

Alternatively should I screw power -ve to Alu plate then star connect to Gecko's pin 1 ? (Like attatched file - borrowd from unknown cnczone link)

As in first link at #10413 para 1, Mariss said This current must be shorted back to ground, otherwise the drive
mounting plate would radiate a tremendous amount of RFI. This RFI
would even interfere with the operation of the drive because the drive
board is coplanar with the mounting plate.

Sorry for my mistake, my Gecko power cables are unshilded, I unthoughfully recalled step/dir/common cable as shilded power cable while posting.

Thanks for the links. And hope that I am not causing any confusion here.

Gerald D
Mon 28 July 2008, 11:58
I have caused confusion by giving those links! :(

This picture should answer your questions. +ve wire is all red, -ve wire has black stripe on red. Capacitor -ve is the star point for all the wires going to all the pin 1's. Capacitor -ve also connected to alu plate:


After connecting like this you can measure Gecko pin 1 to alu plate - it will be a good connection. You need do nothing more to ground the geckos.

Mon 28 July 2008, 18:47
Thanks Gerald,
Everything about grounding is crystal clear right now.
I should have checked pics more thoroughly.

Gerald D
Mon 28 July 2008, 23:37
No problem Frank.

You can also omit the resistor across the capacitor. A single gecko across the capacitor does a good enough job of draining the capacitor when you switch off. Four geckos across the capacitor does an extremely good job of draining the capacitor. In this circuit, the resistor is a waste of time and space.

Gerald D
Mon 28 July 2008, 23:42
Frank, your fan wiring is unusual, unless you have a non-standard fan that runs off the transformer's secondary voltage.

Also, there is a serious error in my photo above. The ground wire from the PMDX to the alu plate should not be there. The PMDX-122 must NOT be grounded inside the control box. The reason is that the parallel cable from the PC grounds the PMDX to the PC's ground.

Tue 29 July 2008, 03:46

I ground my computer's case to the common ground on the frame of my CNC. The power supply inside the computer is grounded to the case via the power supply's mounting screws, so all things (computer, control box and CNC router) have a common ground point.

As you mentioned, because the PMDX-122 is grounded via the computer's parallel port, a secondary ground wire is not needed and may actually cause a ground loop.

Gerald D
Tue 29 July 2008, 04:38
Mike, is your computer case also grounded to your computer's incoming mains power? For us that would be normal (that our computer cases are "mains" grounded), and that is why I wouldn't connect the computer case to the CNC control box case.

Tue 29 July 2008, 05:01
I am taking the supply to my computer through the control box (off the main isolator) so it would share the same ground/earth as the control panel, much like Richard above, anybody see any problem with that?

Gerald D
Tue 29 July 2008, 06:20
We had ours like that for a while, then an inteference problem crept in. Moving it to completely different supply breaker improved the interference issue. We resolved the interfence by taking our mains E-stop circuit out of the screened cable that was doing all the other signals. But we havn't moved the PC supply back to the control box isolator. I am fairly sure that the PC running from the control box isolator would be fine.

Tue 29 July 2008, 07:15
I have dirct power line fan.
My PMDX is completely isolated from grounding. Even parallel cable does not have shielding (I wonder if it should be there). Signal cable shieldings bolted to Alu Plate.

Gerald D
Tue 29 July 2008, 07:41
I have dirct power line fan.

Then your left diagram above is incorrect.

Tue 29 July 2008, 07:51
Oops again.
This is borrowed photo for reference. See #103.

Sat 21 February 2009, 11:05
Can someone tell me what function a Gecko GRex-100 Controller have in a simple way, and what is the advantage of having this?

Sat 21 February 2009, 11:44
It is a USB supported 6 axis controller that is at end of cycle for production and will no longer be supported. It was addressable and could be networked, but for the MM use, no advantage.

Sat 21 February 2009, 12:21
Thanks :)

Tue 20 October 2009, 14:30

The Gecko G203 manual says:

The G203V will accommodate motor winding currents from 0 to 7A. Use the following equation to calculate the value, (in kilo-Ohms) of the current set resistor: R (in kilo-ohms) = 47 * I / (7 ? I)

So a 12k resistor would be used with a motor rated at about 1.5-amps

Here are some other values:
1 amp = 8k
2 amp = 19k
3 amp = 35k
4 amp = 63k
5 amp = 118k
6 amp = 282k

(Remember that you can use the closest standard 1/4-Watt resistor value, i.e. 3-amp motor would use a 33k 1/4-watt resistor.)

Mike, I'm starring at the gecko manual here and not sure what there looking for for the Resistor equation. I'm using PK296A2A-SG7.2 motors, so my amps per phase are 2.1 amps wired Bipolar?

What is "I" stand for and what is "?" in the equation.

R (in kilo-ohms) = 47 * I / (7 ? I) [/i]

I'm just trying to figure out this simple equation...I must be missing something simple here.


Tue 20 October 2009, 18:44
Travis, I is the current in amps. The equation as stated had an error.
From the gecko manual
R (in kilo-ohms) = 47 * I / (7 – I)

Gerald D
Tue 20 October 2009, 23:06
So, for 2.1 amps:

47 times 2.1, divided by, 7 minus 2.1

= 98.7 divided by 4.9

= 20 kiloOhm

Wed 21 October 2009, 07:55
If you wire those motors half-coil you will get better performance and still have all the torque that the gearbox is rated to handle. Wiring a motor half-coil gives about 70% of the torque as the same motor wired bipolar series. (1 / SQRT(2) = 0.7071)

Those motors, when wired half-coil, can draw up to 3A, so 47 X 3 / (7 - 3) = 35K. A standard 33K resistor works fine.

When you look at the torque charts, you'll see that a motor wired bipolar series is meant to be used at low speeds. That motor drops to about 100 oz*in at 250 RPM when wired bipolar series, but doesn't drop to 100 oz*in until it is spinning at 900 RPM when wired half-coil.

Thu 22 October 2009, 06:24
Thanks Mike and Gerald. I appreciated the guidence. 20 kohm is what I got to, so good to see it confirmed. I just couldn't find out what the Silly "I" standed for in the equation in the gecko manual. I've decided to go full coil for now, as I'll be doing plenty of 3d and and advanced pocket routines, so I hope to see the motors perform nicely. I'm enjoying this learning experience.

Gerald D
Thu 22 October 2009, 06:41
The I stands for current Intensity. They couldn't use C for current because C is the speed of light. No, I don't know why C is for the speed of light! :)

Thu 22 October 2009, 06:44
Mike something that I noticed on my motors is that when I wired them half coil it ended up getting hot verry quickly.I then changed to full coil and it seems to be fine but the moment I pump up the speed it gets quite hot.Before I had the heat thing the motors used 202 steppers then 1 packed up and I stuffed the other one up.I got some 203 `s to replace them .These are the two ones for the x-axis.Yesterday I surface planed the table and halfway I actualy stoped it for the motors to cool down.I am running 202 on the z-axis and the y-axis.I run 3:1 gearboxes Maybe i am pushing them to hard.

Thu 22 October 2009, 06:49
Hennie, What is your power supply voltage? If your voltage was picked for full coil, switching to half coil would be driving the motor with too high a voltage I would think. Give us the specs for the motor and power supply. Maybe your voltage is too high for full coil too?

Thu 22 October 2009, 08:06
Heath I think that it gives me 57 volts dc with the motors rated at 3.5 amps.I will check it tomorrow when I am back at the shop had hospital food since yesterday afternoon.

Thu 22 October 2009, 17:51

When wired half-coil the voltage should be 40VDC or less. (I use 35VDC). Also, be sure to change the current limit resistors to something around 33K so that the motors can pull 3A through the stepper drivers.

(The motors are rated at 6mH inductance when wired bipolar series, but only 1.5mH inductance when wired half-coil. So, the forumla for MAX VOLTAGE = 32 X (SQRT(Inductance)).

Gerald D
Thu 22 October 2009, 22:51
I'm using PK296A2A-SG7.2 motors, so my amps per phase are 2.1 amps wired Bipolar?

To which Mike replied:

Those motors, when wired half-coil, can draw up to 3A, so 47 X 3 / (7 - 3) = 35K. A standard 33K resistor works fine.

Mike, are you sure about that? Our half-coil wired PK296A2A-SG7.2 motors have a 42VDC supply and 20k resistors for current limiting. It sounds like you go for 35VDC & 33k for current limiting?

Fri 23 October 2009, 06:01

Page C231 of the older Oriental Motor catalog shows:


- Bipolar Series
2.1 A current
6 mH Inductance

- Unipolar (half-coil)
3 A current
1.5 mH Inductance

I'm using the formula 47 * A / ( 7 - A ), which gives 35K for the PK296A2A-SG7.2 motor when wired half-coil. That page also gives 1.5mH for the motor when wired half-coil, so 32 * SQRT( 1.5 ) = 39.19 V. I use 33K for the resistor and 35VDC for the power supply.

If you reduce the current going through the motor to 2.1A then 47 * 2.1 / (7 - 2.1) = ~ 20K. That would also allow you to increase the voltage a little before the motor runs too hot.

I just checked the watts that the motor would produce . At 2.1A and 42VDC, it would produce ~ 88.2W, using the formula ( Amps * Volts ) = Watts. At 3A and 35VDC, it would produce ~ 105W. Using the Gecko formula of 32 * SQRT( Inductance ), Mariss gives 117W as maximum before the motor gets too hot. With 35VDC, my motors run between 65C and 75C, when I run them at 39V, they reach 80C to 88C. Mariss believes that a cool motor is not being worked hard enough. I would rather run a little cooler in exchange for longer life.

Gerald D
Fri 23 October 2009, 10:06
I must be loosing my marbles? I was quite sure that I always spoke of 2.1 Amps when there was a question on the current setting for PK296A2A-SG7.2 motor when wired half-coil. Maybe that is why we have cool motors and transformers at 42VDC and 300VA? Right now I not sure what resistors are in our system anymore . . .

Mike is of course right; the current limit for a PK296A2A-SG7.2 motor when wired half-coil is 3 Amp (not the 2.1 Amp I have in my head today).

Fri 23 October 2009, 10:35
I decided to run a spreadsheet on some Oriental Motor steppers against the formulas that Mariss published to see what how many watts each motor would produce. I expected to see a close match for each motor size, instead, I found quite a large variation.

(You'll notice that the PK296A2A-SG7.2 motor produces less heat when wired half-coil than it would if it were wired series, but that assumes that you're using the maximum voltage with each type of wiring.)

Series, 112.0 watts
Half Coil, 60.0 watts

Series, 168.0 watts
Half Coil, 179.6 watts

Series, 250.8 watts
Half Coil, 176.4 watts

Series, 164.6 watts
Half Coil, 117.6 watts

Series, 168.0 watts
Half Coil, 235.2 watts

Series, 254.4 watts
Half Coil, 227.7 watts

Series, 254.4 watts
Half Coil, 227.7 watts
Parallel, 318.8 watts

Mon 26 October 2009, 13:51
Any thoughts on using a Gecko G540 or four G250s instead of four G203Vs? The price difference is substantial and to my (untrained) eye, they seem to be equivalent.


G540 Spec Page here: http://www.geckodrive.com/product.aspx?c=3&i=14469

G250 Spec Page Here: http://www.geckodrive.com/product.aspx?c=3&i=14472

Mon 26 October 2009, 14:21
Joe, this has been discussed quite a bit. If you search on "g540" you should find at least five threads. Hint: I use one on my build, successfully.

Mon 26 October 2009, 14:43
Brad: Thanks, I guess I missed them. Are you happy with the G540? Joe

Mon 26 October 2009, 17:22
Yes, I'm quite happy with it. The only issue I had was that the PWM output for spindle speed control turned out to be bad. I discovered it a full year after I'd purchased the G540 when I upgraded, and one quick email to Gecko later, they replaced it. Good people there. Just make sure your motors match the G540 specs (the OM PK296A2A-SG7.2 does).

Tue 27 October 2009, 07:15
and have a good heat sink for it too.

Tue 27 October 2009, 07:28
The G540 does not require a heatsink. Mariss ran some heat tests showing that if you simply have a computer CPU fan or case fan blowing against the G540's case, that the fan will keep the G540 well within the recommended temperature range.

Tue 27 October 2009, 09:18
I think I have read somewhere on the CNCzone of the 540 behaving better with a heat sink - what ever the way - its not bad to have a heatsink afterall (along with the CPu fan)

Tue 27 October 2009, 12:13
Those posts on the CNCzone forum led to Mariss's running those heat tests. Inside the G540, each of the stepper driver cards is using the G540's case as a heat-sink. Adding an additional heat-sink was not necessary as long as a fan was used to circulate air past the G540's case.

A similar condition exists when you use an aluminum or steel controller case. Circulating the air around the inside of the case allows the entire case to help dissipate the heat. Blowing air onto the outside of the case helps with the heat transfer. That's the method that I use to cool my Shopbot's controller on those wonderfully hot days where the temperature is over 100 F (unlike today where it's snowing outside).

Tue 27 October 2009, 15:08
Ok Mike - I (we) take your word for it :)

Mon 15 March 2010, 23:55
I searched the forum for a pic of a G540 mounted in the control box and couldn't find one. So after reading the info from gecko about heat sinks for the G540 I decided that I will mount the drive on stand-offs (like Gerald shows his drives on a alu plate) without the plate and in front of the fan. Does anyone see any problem with this?

Tue 16 March 2010, 04:33

That is the recommended procedure. The G540's case is the heat sink for the boards inside the case. Blowing air against the case will dissipate the heat. The newer model G250x runs cooler than the original G250 modules that I have, but in either situation, keeping air moving past the G540 will greatly reduce any 'hot spots'. Make sure that the fan has free space front and back so that it has unrestricted air flow.

Wed 17 March 2010, 10:16
...I will mount the drive on stand-offswithout the plate and in front of the fan. Does anyone see any problem with this?

Steve, I mounted my 540 on two delrin blocks (just scrap from around the shop, wood would work as well.) No fan, no heatsink. I have not had any heating problems whatsoever. (Of course I live in a place that doesn't get above 70 degrees - ever!) :D

Wed 17 March 2010, 11:36
I think I would stay away from wood in an electronic enclosure. It is another source of fuel. Delrin is a better choice.

Thu 18 March 2010, 17:57
Steve, I mounted my G540 in the side of my box. Cut the rectangle, drill pilot holes, self-tapping sheet metal screw it in place; the entire box becomes an extension of the heatsink.

The screw strip that you need to wire to your BOB and power supply will be inside the box; the DB9 connectors for the motors will be outside where they are ready to attach cables.

If you decide things are running too warm, add a fan across the back. It seems to me that this is consistent with how the G540 is designed.

Fri 19 March 2010, 21:50
Thanks for the info!

Fri 09 July 2010, 01:56
Hi Mike i need of a your personal suggestion : i have nema 34 - 5.6A - 4.4 NM
gecko drive G203V what resistor power is correct? 180K ? Thanks

Fri 09 July 2010, 10:56
For the G201, G203, or the G203v stepper drivers, the formula is:

47 X Amps / ( 7 - Amps) = Resistor.

So, for your motor:

47 X 5.6A / ( 7 - 5.6A) = 188K resistor.

A 180K or a 200K 1/4 Watt resistor would work fine ( or any other resistor that is +/- 5% of 188K).

Fri 09 July 2010, 12:20
Thanks Richards