another first time cnc builder

[dansal]

Yes i'm another newbie and i've come with little knowledge and therefore many questions!

I want to build a cnc wood router. But before I get into the mechanical side of things I want to get my facts straight on stepper motors and drivers.

How does it work? If the motors are rated at 3 Amps per phase (bipolar, series connection, 6 leads), does this mean in bipolar operation i need to have 6A (3A phase x 2) continuosly available for each motor? (18A total)?
So do I need a 6A driver or a 3A driver (each axis)

Also my machine will require my motors to hold their position while under force from a load.
The motor will be connected to a driver that is on, but the stepper is not stepping, it is
just holding the weight of the load (Z axis). Will this use/dissipate more power than when it is stepping
under the same load? How is this usually done?

thanx

[ger21]

If it's bipolar only 4 leads are connected to the driver. If the driver is a chopper (Xylotex or Gecko), then the total current needed is 2/3 of 1 phase x # of motors which is about 6 amps total. If not a chopper driver than you might need the 18a. Look at the White papers at http://www.geckodrive.com for an explanation.

Drivers are rated per phase. 3a/phase motors wouls need a 3a driver.

Not entirely sure on the last one.

[dansal]

thanks i'll check that out.

[balsaman]

If the motors are 3 amps per phase they will draw 3 amps when stalled, and also 3 amps when running normally and slightly less than 3 amps when running quite quickly.

Eric

[dansal]

I can't seem to find anywhere that supplies proper bipolar stepper motor drives in Australia, can anyone suggest where to start?

[dansal]

anybody?

[IJ.]

Give the lads at CNCTeknix at a try they should be able to point you in the right direction.

[dansal]

thanx IJ.

[dansal]

for my first machine i'm only aiming for .1mm accuracy. Could somebody look over the following cacluations and correct me if i am wrong.

If i am using threaded rod and ball nuts for my driving system and the threaded rod is 10 turns per inch,
is the following correct?

1 revolution will move the nut 2.54mm linearly (horizontally). so therefore 1 step from a 200 step motor
will move the nut 12.7 micro metres back or fowards?

To me it looks like i don't need micro stepping? or do I?

Could someone explain why micro stepping is used and if i should be taking anything else into consideration when designing the drive system.

Thanx

[balsaman]

No...you don't. BUT, microstepping makes the motors run smoother. I personally didn't bother with microsteps (IMHO microstepping is over rated) and the stepper noise was like music to my ears anyways, and it worked fine and was very accurate.

Eric

[dansal]

thanx Eric

[dansal]

Is it ok to run my stepper motors at less than the specified phase current? Obviously power out will decrease, but by how much? Is there anything else that can happen? Is it electrically wrong or unsafe to do this?

I am asking because my motors are rated at 3A per phase but, I am finding it hard to find an affordable driver board rated at 3A per phase, that is a chopper and does microstepping.

I think the Xylotex 3 axis board would suit my appliation and budget perfectly, but it is only rated at + or - 2.5A. Can i use this board? What does + or - 3A mean anyway? Please explain?

The info on the board is here: http://www.xylotex.com/

thanx