Low stepper motor speed

[MagooT]

Hello guys!
I just assembled the electronics for my under construction CNC mill, however i'm having trouble getting any speed out of the motors.

Driver is a simple circuit based on L297 and L298, the motor supply voltage is 46volts.

Motors specifications:
Bipolar 2-phase
Holding torque 1.25 Nm
Nominal current 1.4 A
Coil resistance 4.2 ohms
Coil inductance 15 mH

I have been experimenting with EMC2 (linuxcnc.org), motors are currently set to full step. I can't get them above 250 rpm, they sound fine and run smooth, but when i increase speed over about 250rpm they sound the same but they don't spin.

Am i simply going to have to accept this? It seems a little slow to me but i don't know.

Thanks for answers.

[Tim Tanner]

You should be able to go faster than this but you will have to provide an acceleration ramp rather than clocking at a fixed rate which is what I assume you are doing?

Regards

Tim.

[JRoque]

Hi. Do the motors have any load on them? If not, try dropping the current a bit for faster no-load speed (or change current decay). Once it's mounted and loaded you might be able to get more speed out of them.
The impedance/inductance seem a bit high which may also contribute run performance. For reference, my Bodine steppers are 1.18 ohm and 3.14 mH.

JR

[MagooT]

Hello.
Yes I have played around with acceleration a bit and at this moment 333rpm is the fastest i can get without any tendency to stall.
If I increase it to 350rpm it starts stalling now and then, it accelerates at the beginning but then it stops spinning.

Acceleration is currently at 10mm/sec²

I have focused on tuning in full step mode, should it be wiser to focus on half step? Or which one should be faster?

[MagooT]

JRoque> The motors doesn't have any load currently. They are just sitting on my desk
Yes, the inductance is pretty high too bad I didn't think of that when i bought them.. it's my first time using steppers so i don't have a lot of experience on these things...

Hmm, so lowering the current gives better speed? And putting load on the motors would make them get better speed? Thanks for your tips! I will try it out and post the results.

[MagooT]

Ok now i'm beginning to get something.
Switched to half step and lowered the current to 1Amp = 650rpm and much smoother running.
I can go up to about 700rpm but then i can stop the motor with my fingers if i squeeze hard i guess i will have to see what they are capable of once mounted.

If anoyne has any other tips please let me know, and thanks for your help guys.