Motors too big for Geko?

[smithgi]

Hi, this is my fist post so appologies if I have posted in the wrong place.

I'm attempting to CNC an oly Miestergram Embroidery machine, which I bought at auction. I'm planning on adding a Z axis to the machine to make a 3 axis wood router.

The machines electronics were removed, and I was left with 2 fairly chunky stepper motors with the following info on them

Vexta PH200-01-04

3v
4A

1.8 degree step
2 - Phase

I have a Geko G540 interface, and wondered if this will be ok to drive these 2 motors, and another different one for the Z axis (smaller Nema 23)

I read somewhere that the Geko is only rated at 3.5 amps, so would I risking damaging the interface or would the right current set resistors allow me to use them?

Many thanks

Gavin

[Crevice Reamer]

These are 60-70V motors and, if they are bipolar (Not 5 or 6 wire motors) should work very nicely within G540 3.5A/50V envelope.

Use 3.48K CS resistors and the motors will detune in torque slightly. IE: Torque will drop by 13%, so 300oz motor will drop to 261 oz.

http://search.digikey.com/scripts/Dk...K-ND&x=15&y=19

CR.

[smithgi]

Hi, thanks for the reply.

They have 6 wires each, so does thsi mean they are unipolar?

I did manage to get them running with a cheap controller from ebay, using 4 wires on each motor. However, the torqe was very poor with the 12v power supply i was using for the test, and when I upped the voltage to the 36v CNC power suppply I have now, I fried one of the controllers. Doh! I had mounted heatsinks on them, but later found they had been incorrectly advertised as 36v and other people had the same issue.

Anyway, I'm keen not to fry my nice new geko so want to be sure everything is in order before I turn them on this time ;-)

thanks again

Gav

These are 60-70V motors and, if they are bipolar (Not 5 or 6 wire motors) should work very nicely within G540 3.5A/50V envelope.

Use 3.48K CS resistors and the motors will detune in torque slightly. IE: Torque will drop by 13%, so 300oz motor will drop to 261 oz.

http://search.digikey.com/scripts/Dk...K-ND&x=15&y=19

CR.

[Crevice Reamer]

Hi, thanks for the reply.

They have 6 wires each, so does thsi mean they are unipolar?

I did manage to get them running with a cheap controller from ebay, using 4 wires on each motor. However, the torqe was very poor with the 12v power supply i was using for the test, and when I upped the voltage to the 36v CNC power suppply I have now, I fried one of the controllers. Doh! I had mounted heatsinks on them, but later found they had been incorrectly advertised as 36v and other people had the same issue.

Anyway, I'm keen not to fry my nice new geko so want to be sure everything is in order before I turn them on this time ;-)

thanks again

Gav

You can still use the 6 wire motors with G540. You can either wire them Bipolar Series or half coil. I recommend half coil wiring, which is probably the way you HAVE been wiring them.

http://geckodrive.com/upload/Step%20...cs%20Guide.pdf

CR.

[smithgi]

Right, that doc makes ita lot clearer. Should I still, use a 3.48k resistor when wired full coil using 4 wires?

Cheers

Gav

You can still use the 6 wire motors with G540. You can either wire them Bipolar Series or half coil. I recommend half coil wiring, which is probably the way you HAVE been wiring them.

http://geckodrive.com/upload/Step%20...cs%20Guide.pdf

CR.

[Crevice Reamer]

Right, that doc makes ita lot clearer. Should I still, use a 3.48k resistor when wired full coil using 4 wires?

If by full coil you mean Series, then NO, you will want to use a 2K resistor.
http://kelinginc.net/KL23H276_30_6A.pdf

I do not recommend series wiring though, as it will be slow. I recommend Half-coil wiring, which involves using only a single coil from each phase, (by wiring one of the outside wires to the center tap of each phase) for best performance. If you wire it half-coil, then YES, you will still use a 3.48K resistor.

CR.

[smithgi]

thanks for your advice, I have wired up the first of the DB9 connectors, with a 1/4 w 2.5k resisor (which was about the size of a grain of rice? seems much smaller than I'd imagined).

Will try instaiiling mach 3 now and see if I can get the first motor to move before doing the next one ;-)

If by full coil you mean Series, then NO, you will want to use a 2K resistor.
http://kelinginc.net/KL23H276_30_6A.pdf

I do not recommend series wiring though, as it will be slow. I recommend Half-coil wiring, which involves using only a single coil from each phase, (by wiring one of the outside wires to the center tap of each phase) for best performance. If you wire it half-coil, then YES, you will still use a 3.48K resistor.

CR.

[Crevice Reamer]

If you are wiring the motor in Series, the Voltage required for best operation doubles, to about 120V. This will severely lower the max speed. The Amperage halves to 2A. Running the drive with a 2.5K resistor will overAmp the motor, cause excessive heat, and probably fry the motor.

If you are wiring half-coil, then the 2.5K resistor is too small and will cause a 63% drop in torque. (A 300 oz motor detunes to 189oz.) Either use a 2K resistor for series, or a 3.48K resistor for half-coil.

CR.

[smithgi]

Sorry, that was my typo, I meant to say I have wired them half coil ( 1 wire from outside and 1 to central position for each side)

The resistor i used was a 3.5k 0.25 w (not 2.5 as I previsouly stated)

I bought some bigger 3.5k 5w restistors but in the doco I've read, it suggests mounting the resistor inside the Db9 blug, and it the 5w resistor would be too big so I assumed them meant a small .25w resistor.

So, do you reckon I'm good to go with this setup?

thanks for you patience!

If you are wiring the motor in Series, the Voltage required for best operation doubles, to about 120V. This will severely lower the max speed. The Amperage halves to 2A. Running the drive with a 2.5K resistor will overAmp the motor, cause excessive heat, and probably fry the motor.

If you are wiring half-coil, then the 2.5K resistor is too small and will cause a 63% drop in torque. (A 300 oz motor detunes to 189oz.) Either use a 2K resistor for series, or a 3.48K resistor for half-coil.

CR.

[Crevice Reamer]

So, do you reckon I'm good to go with this setup?

Yep! sounds good.

CR.

[smithgi]

Hey, it worked! but not perfectly.

My motors are not running smoothly , even if I remove the drive belts, they will turn, but occationally judder and miss step. If I try running them with the belts on, the machine shakes about and makes a terrible noise.

I am running mach 3 on a laptop just now, till I get an old PC, could this cause problems?

Cheers

Gav

[Crevice Reamer]

Hi Gav. That is not the way it should be with a G540. Check all of your DB-9 connections for cold solder joints, loose or stray wiring contacting other pins etc.

What power supply are you using? Are those motors square or round?

CR.