Re: Low cost Servo Controller

Hi David - I have posted in the past on a similar product called a PicServo
by J R Kerr Engineering ( http://www.jrkerr.com/ ) He has something
similar to your concept that I am trying to use on my mill conversion.
Basically he has a board with custom programmed PIC microcontrollers reading
encoders and running a PID servo loop. I am using one of his boards that
makes a stepper motor think it is a brushless servo motor. He also has an
adapter board that lets the servo board use standard step and direction
signals from the EMC or similar software, although the system is designed to
use a serial interface. I have one axis moving at the moment using the
serial interface.

Costs:
Board with 5 amps of driver capacity $170 one per axis
Stepper signal adapter $45 per axis.
Also need a RS 232 to RS 485 serial adapter $60 and steppers with encoders.
(usual disclaimer - no connection etc. )

I also hope to get better that stepper performance and no step loss out of
this setup. I may need bigger motors than my 125 oz-inch stall steppers with
a 3.7:1 timing belt drive on a .125 lead acme screw. The slow speed seems to
have plenty of power but the best I have been able to run the rapid is about
15 in/min. ( I seem to have a variable friction in the table which may need
some work. )


If I was starting over I would look at the closed loop stepper system that
may be possible with Dan Mauch's $225? 3-axis 5 amp stepper control board
kit and Tom Kulaga's DRO encoder interface board ($100? kit ) if it can be
made to run with the EMC software.


Andy Olney

----- Original Message -----
From: David Howland <dhowland@...>
To: <CAD_CAM_EDM_DRO@onelist.com>
Sent: Friday, September 10, 1999 12:24 PM
Subject: [CAD_CAM_EDM_DRO] Low cost Servo Controller


> From: David Howland <dhowland@...>
>
> I am working on specifications for a Servo driver board which will allow
any low or medimum cost DC motor to be converted to a Servo motor and
connected to a parallel I/O board. I hope this electronic assembly will
allow high performance motion control for a reasonable cost. Steppers +
Stepper controllers seem to be less expensive and easier to use than Servos
+ Servo controllers. Many of us use steppers and put up with speed - torque
limitations. I know that many low cost DC motors will not perform as well
as a low inertia high quality servo motor, however the board development
I am considering will out perform most steppers for less or equal system
cost.

{snip}