AVR-Chat

Research Numerical Control (NC), Dave.  That will get you where you want 
to go, albeit not very inexpensively nor will it be simple.  You'll have to:

1.  Have complex servo motor controls with fast accel/decel characteristics
2.  Have motors to match, with low inertia rotors and they'll draw high 
currents
3.  Your drive profile will be complicated
4.  Absolute encoders are expensive
5.  Resolvers, instead of absolute encoders, are expensive as are their 
decoding circuits
6.  DC servo motors will also have a large number of windings to 
minimize cogging at low speeds.

DC servos are used in NC and CNC machine tools because their operation 
is smoother than steppers and give a smoother finish to the work piece.  
They also operate at higher speeds, fast start/stop times with 
regenerative drives, fast accel/decel rates due to low inertia rotors, 
and can be current hogs.  The systems are expensive, you won't be able 
to do much with a Radio Shack motor in those applications.  You'll also 
need some sort of braking mechanism if you don't use a regenerative 
drive, as well as a reversing scheme that you can ensure won't let all 
the smoke out of either the drive or the motor.  Steppers came into 
vogue because their control schemes are more easily accomplished but 
they have their own set of drawbacks and problems.

If you do a comparison of the characteristics of steppers and 
series/shunt wound, permanent magnet, and servo motors you'll se that 
there isn't any way to "step" the input to a "regular" DC motor and 
obtain the same effect as using a stepper.  They're 2 entirely different 
critters.

Hope this helps.


REB



Dave Mucha wrote:

>Hi all,
>
>I am wondering if nayone know if there is anything on using DC motors
>as stepper motors.  using a step and direction input and an encoder to
>feedback to the driver circuit with the position or the shaft ?
>
>This is different than the R/C servo motor applicaions.  
>
>Any ideas ?
>
>Dave
>  
>