Re: [CAD_CAM_EDM_DRO] Why is my feedrate slow with stepper motor

lenskeeper2000 wrote:

> Hello, I'm new to this discussion (any discussion) group so I hope
> I'm not asking an ofter repeated question.
>
> I've just created my first CNC router/mill. I used small Oriental
> 200 set/rev stepper motors 5V 1A. I'm running through a 10pitch screw
> and 2:1 reduction - 4000 steps per inch.
>
> I'm driving through a home made driver from some chips I found on the
> net for this purpose (Allegro 5804) and K-cam software.
>
> My problem is that as I increase speed, the torque falls off to the
> point that motors stall. I've upped the voltage to 12V and this
> helped but am still limited to about 2.5 IPM

This sounds like a resistorless R/L driver, ie. it depends on the resistance
of the motor winding to limit current. If you have resistors there to limit
current, you need higher value resistors and higher voltage to charge
the inductance of the windings faster.

> Is this normal for stepper motors? I'm thinking of designing a
> current limiting or chopper(?) circuit but do not know electronics.

Bipolar chopper drives perform much better, even with the same motors,
especially if you can raise the power supply voltage.

> I'm guessing others have been here already. Will a chopper circuit
> work? could the k-cam software be part of the problem (I get
> a "stop" for one cycle every rev that gets more pronounced with speed
> rate)

A hitch in the pulse stream is death for any stepper system that can't
smooth out the pulses in the driver. Some microstepping drivers will
smooth this out for you, but the hitch will cause any other driver/motor
setup to lose sync at that moment, once the speed reaches a certain
point. A completely smooth pulse train is essential for maximum speeds.

Jon