Re: Why is my feedrate slow with stepper motor

Roger,

The relationship between a step motor's output power, power supply
voltage and motor inductance is: V / square root of L

You have several things going against you, low power supply voltage,
a high inductance motor and an unnessesarily high reduction (10 TPI
and 2:1 reduction). Let's take them one at a time.

(1) and (2) These are tied together. The motor you have is 1A, 5V. It
would come into its own at a power supply voltage of 100VDC. You are
using 12VDC. The 100VDC is based on using a voltage 20 times the
motor's rated voltage for maximum performance. It would have 8 times
higher speed potentially (100/12).

(3) Guessing from your motor specs, you have a 50 oz-in motor. From
the gearing you describe (20:1) your thrust or force is: 50 oz-in
times 20 times 2 pi / 16, or 392 lbs of force (neglecting
transmission efficiency). Do you need this much? If not, lower the
gear ratio and trade in force for speed.

Your options are: Decrease your gear ratio, go with a higher power
supply voltage and/or a higher current, lower inductance motor.

Mariss

--- In CAD_CAM_EDM_DRO@y..., "lenskeeper2000" <rnichol1@n...> 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
>
> Is this normal for stepper motors? I'm thinking of designing a
> current limiting or chopper(?) circuit but do not know electronics.
>
> 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)
>
> Any comments / advice?
>
> Roger Nicholas