Paul,I've been interested in a CNC mill for quite some time...came
across an old 2-axis Tree mill and decided to take the plunge with
control and software upgrade...then stumbled onto your experience. I
immediately recognized the name because I chased a rotary engine in a
Tailwind for some years. Anyway, I'm more than interested in your
experience.  Checked out MESA only to discover that the two cards you
used for the controls are no longer available and was wondering if you
can recollect(seems you did this project nearly 10 yr ago) why you chose
those and what you'd recommend for a similar project today.Like you, I
intend to use the servos that are on the mill...seems that most of the
CNC community is headed toward stepper motors and I see no need to trash
perfectly good servos, not to mention the advantage of a closed loop
system.  The present system appears to be a concoction of Tree...Once I
get past the controller decision there is the implementation and tuning
of the servos, which may well be over my head...


any advise would be most appreciated...thanks in advance,



Brooks Townsend

My project is on hold. Other things came up with a higher priority.

In the mean time a very good cheap single chip microcomputer
as developed by http://geoffg.net/maximite.html

The Maximite comes completely assembled.
http://www.circuitgizmos.com/
CGCOLORMAX2

It is dirt cheap for what it does.

Uses a PC keyboard and any PC VGA monitor.

Extremely easy to learn to program.

Easy to learn by trail and error. You do some thing and the result can be or
   is printed on the VGA screen. Here is a simple program.

All needed software is free.

PRINT 2+2

END

The number 4 is printed on the screen.

   Buy a Maximite and play with it.

   It comes assembled.

   Ask questions on here or Google.

   Simple program to read an encoder and display the RPM.

SetPin 10,8
SetPin 8, 6, 10
SetTick 1000, 20 'clock hardware interrupt .1 second.

idle: 'wait for clock tick hardware interrupt
GoTo idle

10 start:

RPM = RPM +1

IReturn

20 RPMRoutine: 'clock tick interuppt
RPM=RPM*60 'update RPM
Cls 'clear screen
Locate 30,30 'locate on the VGA row column
Print "RPM = ";RPM
RPM = 0
IReturn

It would be possible to have it do 2D stuff after only few
minutes of programming time.

It will do an arc with a very simple BASIC program.

X^2 + Y^2 = R

Enter R

Increment X or set the X speed with a PWM every 100 msec clock tick.

calculate the Y^2 increment or set the speed with PWM.
every 100 msec or clock tick.

Up load your programs on here or sell them.

The programs are stored on a 64 Gig SD card.
That means tons of storage space as the programs run to
less than 100K. The SD card can be taken out
and read and written by a PC. Many old NC mills were
limited to 10 meg or so. A gig is one thousand meg !!!! :-)

What kind of encoders do you have?
Do you have amps for the servos?

In theory a stp file would be easy to translate to the
NC commands. stp files are out put by Rhino 3D and other 3D software.
Draw the part in rhino. Save a stp file stp file on to the maximite
SD card. Have the maximite read the stp file and make the part.

No need for expensive programs like surface cam.



Paul Lamar



Looks like stl files are easier to work with then stp files.
Here is an stl file for a quarter of cylinder.
Rhino also puts out stl files.

Paul Lamar

Here is how to interpret that STL file  I just up loaded.

https://en.wikipedia.org/wiki/STL_%28file_format%29

STL files create a mesh of the surface with small triangles.
You can control the size and accuracy of the triangles when
you save the STL file in Rhino. See the attached STL control box jpg

STL files can be used with FEA programs. FEA programs can do
a stress analysis on a part.

In any event this might be a bit advanced.

It is possible to just program a G code interpreter in Maximite BASIC

That would be a good first step. Many CNC operator still
program parts in G Code.

https://en.wikipedia.org/wiki/G-code

BTW some people on the net claim the Maximite is 100,000 times
slower than compiled C. Absolute BS.  My time measurements indicate
about 10 times slower than a 1 Ghz ARM. It can turn a bit on in 10 usec.
This is plenty fast enough for NC.


C is a hieroglyphic language anyway and it takes years to learn. After that
it is nearly impossible to figure out what some C programmer was trying
do. BASIC is plain English.

Paul Lamar


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