stepper motor problem

[domonic_cnc_guy]

hi all,

hope somone can help with this problem

i have three of these stepper motors and i'm powering it with an atx powersupply, with 4 power mosfet and a pic18f4550 to provide the correct sequence which i've managed to get the stepper moving, however when i've got it bolted to my milling machine, which is a hm-30 from hare and forbes in australia link i've got a 2 tooth timing gear on the stepper and a 60 tooth timing gear on the leadscrew so a 3:1 ratio the stepper is currently running on the rated 12v and the powersupply is capable of up to 20 amps, even with 500ms between sequence changes there is only enough torque to take up the backlash in the leadscrew but not enough to actaully go any further,

the question is what are my options, should i gear it up even further to a higher gear ratio, or start turning up the supply voltage, if so how high can thses motors take, as they are only rated for 12v?

[JLClinehens]

Sounds like you need to turn up the amps to me. I have a 5volt/ 3.5 amp motors running at 40volts / 3.5 amps. You turn up the volts to run faster/ Amps for torque. BUT don't go over the max AMPS on the motor
Hope this helps.
JIM

[domonic_cnc_guy]

so would jacking up the voltage and current limiting it have any effect on torque at all?

what if i were to change the configuration from unipolar to bipolar, would i get more torque out it that way?

acording to my multimeter at 12v it well and truely sinks the rated 400ma

[JLClinehens]

Guy,
What size motors are they? What is there Max AMPS?

[domonic_cnc_guy]

size: 23
rated voltage: 12
rated current: 0.4 Amps
resistance: 40 ohms
inductance: 5.7mH
detent torque: 14.8 mNm
holding torque: 260
step angle :1.8

it doesn't actaully say anything in the datasheet about max Amps

[JLClinehens]

Guy
If you are at 400ma that's all it can take. It's only rated at .4 amps and I don't know what 260mNm is in good old U.S.A oz/in. Went to the web sight and I have the same Mill at my shop, and I used Nema 34 400 oz/in 5volt/3.5amp motors. I realy think your going to need bigger motors. Or go 30 to 1 on your timing belts.

[domonic_cnc_guy]

ok 260mNm = 36.8 oz/inch
my steppers are gears 3:1 so effectively i've got 108 oz/inch worth of torque,
so it's quite a way short,

what i'll do for now is gear it up further and run it at 12v, i'll get a much higher resolution, but i'll take longer to move the table, thankfully i've got patience, somtime down the track i'll get some much bigger steppers and get some ballscrews,

at the moment i just want it moving,

thanks for your help!

[H500]

Unfortunately, the setup you have is not usable on the mill you have in the link. Bigger motors alone is not enough. You need a high voltage drive that limits the current using some sort of pwm technique.

Try these:

motors: http://www.kelinginc.net/KL23H276-30-8B.pdf
drives: http://geckodrive.com/product.aspx?c=3&i=14471

[domonic_cnc_guy]

i've actaully built my own controller that i've been using with an atx powersupply , i'm putting together a 24v powersupply, plus i've rewritten the firmware on the controller, instead of just going up or down the steppers sequence it's now pulsed with a variable pulse length, which i'm still playing with,..