Re: [CAD_CAM_EDM_DRO] Re: A "simple" Hexapod project - calibration

Chuck,

I'm sorry, I didn't answer your "practical question".

>P.S. A practical question. How are Hexapods interfaced with your
>computer? If my count is right, you need 12 lines to control the motors
>(6 step + 6 direction), plus a few miscellaneous connections. If limit
>switches for each leg are included, that's another 6 as well. We're
>really pushing the limits on a parallel port, since it has only a
>guaranteed 8 data lines, and a few more if we get creative with the
>pins. How is this handled, on a practical level?

In my current machine, I interface the stepper motors through a parallel
port. I also interface an A-D converter and the pendant through the same
parallel port. The schematics are on my web site, buried in the "project
notebook" scans.

The motors are full/half stepped unipolar motors with R-L drive, driven
with phase data. That means that each motor requires 4 bits -- one bit per
coil. The lower four bits of the parallel port data lines are the phase
data, the next three bits define which motor, and the top bit is used as a
clock.

Since only 6 motors are required, the other two values of the "motor
select" bits are decoded to send and receive a serial data stream to the
pendant and the A-D converter.

For the machine which is under construction, I am staying with phase drive,
with come changes. I'm using a serial port to interface to the motor
drivers, each motor driver circuit board drives two bipolar motors, and I'm
using a microstepping chopper driver. Details of the new motor drivers are
also on my web site.

-- Carl