Build Thread- 8020 ErectorSet Router...

[jalessi]

Senna,

When you rewire the Hobby CNC steppers using a parallel configuration they will be bipolar compatible and have 425 ounces of torque.

Jeff...

[jalessi]

Senna,

The bipolar parallel amperage rating for the 305-DS8A stepper is 4.2 amps

You may want to increase the current set resistors to 3.48K, that will allow the maximum performance potential from the combination you have.

Jeff...

[jalessi]

Senna,

The stepper phase wiring on your diagram is not correct.

Please see attached picture for correct phase connections.

On your diagram you have the coils shorted out.

Jeff...

[Senna]

Jeff...

The Gecko G251's are rated to a max of 3.5A... I have to run the steppers at the 305 oz/in 3A config. So does your modification of the schematic HobbyCNC provided show the parallel configuration change to bipolar you mentioned or is the provided schematic actually FUBAR'd and won't work as drawn...?

The reason I ask is that these are popular stepper choices from Dave at HobbyCNC and many before me have successfully employed them in their projects... I find it difficult to fathom a shorted circuit diagram was being provided to each customer without this being detected...??? BUT what do I know... clueless.

Steve (aka Senna)

[jalessi]

Steve,

The schematic you posted can't be for the Hobby CNC steppers and G251 drives, the coils are shorted.

If you choose to run the steppers at 3.0 amps bipolar parallel it will work however you are giving away 15% of the torque.

The G251 has a 3.5 amp capacity and the Hobby CNC steppers are rated at 4.2 amps in bipolar parallel configuration.

You may want to consult with Mariss from Gecko before you apply power to the drives.

If you decide to leave the wiring the way it is in the diagram you may need a RMA for stepper drive repair.

Have a most awesome weekend.

Jeff...

[Senna]

Jeff,

I'm confused... and maybe it's due to a wrong impression. Here's where I believe my thinking has gone astray... I drew the controller schematic and placed the colored wires as I did based on my impression that the four things that look like a sideways triple 'U's on the HobbyCNC stepper wiring diagram meant that those particular wires were to be twisted together & paired up... hence pairing the RED & YELLOW, BLUE & BLACK, GREEN & BROWN, and the ORANGE & WHITE in my controller schematic. Your statement that I have the coils shorted out in MY drawing but then providing a revised HobbyCNC diagram led me to believe that the 'as provided' diagram from HobbyCNC was in error. I meant no offense in questioning how a diagram provided by HobbyCNC to so many customers could be wrong. The REAL ERROR here is my mistaking that the stepper diagram was telling me to pair those particular wires. Obviously that's not what those sideways triple 'U's mean... and you're saying that doing so will short the coils. My bad!

Yes... the Gecko G251's are a 3.5A max driver and will not handle the 4.2A of a bipolar parallel configuration. I must go with the 305 oz/in 3A configuration. Does that mean unipolar series wiring then...???

Steve

[Senna]

I made it to town and picked up the Loctite Blue 242. The afternoon was spent assembling the Y carriage and partial assembly of the Z.

Senna

[jalessi]

Originally Posted by Senna Yes... the Gecko G251's are a 3.5A max driver and will not handle the 4.2A of a bipolar parallel configuration. I must go with the 305 oz/in 3A configuration. Does that mean unipolar series wiring then...??? Steve

Steve the answer again is no, you can't use the "305 oz/in 3A configuration"

Wire the steppers bipolar, then use 3.48K resistors.

The steppers will consume the 3.5 amps without having any problem at all and
the Gecko G251's will be happy too.

I will repeat for the final time, the stepper motors are rated at 4.2 amps bipolar.

Running the motors at less than there rated amp capacity will reduce there torque output however will not damage them in any way.

"3.0 amps 305 torque" is the unipolar rating for the steppers, the G251 does not have the ability to be wired in unipolar mode.

I am not offended, I understand you are new and need help.

After wiring and configuring hundreds of machines you do develop a knack for being patient.

Jeff...

[jalessi]

Steve,

Attached is a explanation of the stepper coils and pairs for the motors you have.

I will revise your wiring diagram so the connections are correct.

Jeff...

[jalessi]

Steve,

See attached .jpg for the corrected wiring diagram.

I tried to upload a .pdf however the file may be to large
or the Zone is having upload issues.

I posted the .pdf to Rapidshare if you would like to download it.

http://rapidshare.com/files/27588599...-C10_.pdf.html

Jeff...

[Senna]

Jeff...

Now we're communicatin'...! MY Gecko drivers WON'T do the 305 oz/in 3A config... which is unipolar. I MUST run a bipolar config that the Gecko's can digest BUT I will require a larger current limiting resistor (3.48K) to keep the amps within the max rating of the 251's. I get it now! I was missing the most important part of the deal where 'Gecko's don't do unipolar'... sorry!

I'll go back and correct my schematic per your mods. Your time, efforts and understanding are greatly appreciated!

Oh... would that 3.48K limiting resistor still be 1/4W...?

Steve

[Senna]

Here's something I just ran across regarding the G251's from Gecko..

---IMPORTANT APPLICATION NOTICE FOR G251 GECKODRIVES---

Problem: Eliminating obnoxious hissing, sizzling and squealing sounds. The G251 drives make unpleasant noises in multiple axis applications. This doesn't hurt the drives and they will not have positioning errors but the sounds are very annoying.

The G251 drive is not a chopper. It is a synchronously clocked pulse width modulated (PWM) drive. It is inherently silent by design, it should make no hissing, squealing, grunting or whistling sounds or any sounds at all.

Cause: The G251 drives are not optoisolated. Signal GND (term 12) from each drive must connect to the parallel port GND (pin 25) to complete the step and direction signal path. Each G251 drive's Signal GND has a slightly different voltage potential because of motor phase currents and wiring resistance back to the power supply.

This small but inevitable (<100mV) potential difference between drive grounds causes significant (>100mA) ground-loop currents to flow between the drives. This high frequency (20kHz) AC current is sufficient to disrupt the operation of the of the motor phase current regulators and make them audibly noisy. The drives are still perfectly accurate but now make annoying noises.

Cure: Install a 100 Ohm 1/4W resistor in series with each drive's Signal GND (term 12) to parallel port GND (pin 25) circuit connection. This completely cures the audible noise problem and renders the drives utterly silent while stopped or turning at slow speeds.

The 100 Ohm resistors are too small to have any effect on performance but are large enough to reduce ground-loop currents 1,000 to 10,000-fold (<<100uA). Such small currents are now completely unable to interfere with the normal, silent operation of the G251 drives.

Jeff... what would this look like... I'm now familiar with the Signal GND on the Geckodrives but not with a parallel port GND (pin 25). These 100 Ohm 1/4W resistors would be placed in line between the Geckodrive terminal 12 and this parallel port GND pin...???

Steve