[kooroshi60]

Hello guys

I have made a 3 axis cnc controller based on TOSHIBA TA8435H ICs.
It works perfectly at low speeds. for example when I set Mach3 like below settings, there is no problem and the motors spin without losing steps (but slowly!).

Steps per mm : 1800
Velocity: 100
Acceleration 20
Slow jog rate : 25

It's so slow and takes minutes to move the machine for 20cm.

But as I set a higher speed, the motors make a high pitch noise, jerk with high frequency ( like they want to spin fast but they can't) and they don't spin.

Here is the complete specifications of the stepper motors I'm using:

Model: 42BYGH023 (Bipolar , 4 wires)
Step angle: 1.8
Voltage: 12v
Current: 0.4A
Holding Torque: 2100 g/cm
Detent torque: <220 g/cm
Rotation inertia: 20 g/cm2

Power supply : 12v 8.5A switching

can anyone tell me what is wrong? the motors are not powerful enough to handle higher speeds?

and Why when I click on "GOTO Z" in Mach3 software, it ignores the motor tuning settings and makes the motors spin at high speed? so my machine can't handle that speed and starts jerking!

Thank you

[vlmarshall]

http://www.cnczone.com/forums/showthread.php?t=32284

Read that thread, the dampeners really work!

[MechanoMan]

and Why when I click on "GOTO Z" in Mach3 software, it ignores the motor tuning settings and makes the motors spin at high speed? so my machine can't handle that speed and starts jerking!

Thank you

Because your Jog Speed (hit TAB key) is set to keyboard-jog at a fraction of the max speed you entered in Motor Tuning. When you hit Goto Z, it uses 100% of the speed in Motor Tuning. Set Jog Speed to 100% if you want that to be the speed.

[Crevice Reamer]

Hi kooroshi60. Welcome to the Zone.

You are using Nema 42 motors, internally wound to Bipolar Series, and they have HUGE inductance. Series wound motors don't run well except at low rpms.

Stepper motors work from pulsed current, not steady current. Higher voltage per pulse will charge the coils quicker and produce more power at higher RPMs.

Formula for best/max power is 32 times the square root of the motor inductance.

This motor has inductance of 32 mH. So 32 times 5.657 = 181 Volts max/best.

If you could power this motor with 180 volts, you might get a LITTLE more speed, but it's not a good candidate for fast rapids. A low-inductance Nema 23 or 34 motor, wired Bipolar Parallel, will give much faster performance.

CR.