unlurking

Hi,
I have been lurking here for a couple of months and feel that I should
contribute. My name is Bob Dring and I do electronic design for a job and
metalwork for a hobby. I have taken on a project for a friend to build a 'V
groover' for PCBs. (My friend is a PCB manufacturer.) The Mechanical part
was already done by someone else, it has stepper motors (200oz/in) linear
bearings and ballscrews.
For my part of the project I am designing the motor drivers, power supply,
etc. I hope to finish the first PCB layout for the driver in the next few
days. The spec of the driver is overkill for this application but I intend
to use the same design for my own uses. The spec is 2 phase microstepping
bipolar chopper drive of up to 80V @ 8Amps for driving one motor. I have
put a fast micro in the design and because of this I can give it new and
novel features, I am taking the opportunity to ask the group for advice on
what features would be desirable. I have made a list of the ones I am
currently thinking of implementing but I would like comments and ideas.

1. Optoisolated inputs (step, direction, lowpower1, shutdown)
2. Optoisolated outputs (fault, lowpower2)
3. Takes DB25 pin cable (printer port style)
4. Pass through to another DB25 to daisy chain the next motor driver(s)
5. A jumper matrix (ball of solder type) on the PCB allowing any DB25 pin
to be connected to the any driver input, output, ground.
6. A signal that allows automatic power reduction when all drivers have
stopped (lowpower2).
7. Motor parameter setup up by RS232 port. (max phase current, lowpower
phase current, low power delay time, etc)
8. Signal polarity setup by RS232 port (step, direction, lowpower1,
shutdown, fault etc)
9. EEPROM to store parameters.
10. LEDs to show signals (clockwise, step, fault etc)
11. Motor connection and motor power via un pluggable terminal block style
connector.
12. Logic power 12Vac plug pack (wall wart).
13. Motor drive short circuit protection.
14. Fits in a snazzy aluminium extrusion.

I will be doing a similar module for limit switch detection and spindle
control.

Before going further I should mention what stage I am up to.

I have prototyped one phase of the motor driver on strip board and
controlled it from a DAC driven from the micro. I have only run it at 60V
at 4 Amps at the moment because the circuit becomes unstable at higher
currents because stripboard is unsuitable for this type of circuit (at
least I think that it is the reason!) No firmware has been written at this
stage (except the code to drive the 12 DAC that sets the max phase
current). Hope to have some PCBs in a week.

I know that many of you are probably saying to yourselves that this project
is going to cost a lot of money and I have to agree that it certainly isn't
a low budget design but in my defense I can only say The PCBs are being
made for me at no cost and I can have as many prototype iterations as
needed without financial penalty and so I am taking the opportunity to make
this design as interesting as possible. Just to allay any ethical fears. My
friend will pay me in full for the parts that I use but I will only get a
fixed amount for my labour. He knows my intention to make more for my own
use in the future.

If anyone has any comments please feel free to share them.


I am planning to use Maxnc deluxe as the PC based control software for this
project but I have been experimenting with Linux my future uses. Last week
I bought a book "Red Hat Linux Secrets 2nd ed" which came with a CDROM
containing linux 2.0.33 (and a lot of other stuff) My intention was to
install it and upgrade it to 2.0.36. My Hard drive is removable (ultimate
virus protection when PC is shared with my daughter!) and I went out and
bought another drive and drawer for the linux install. I founds it all
quite straight forward following the step by step instructions in the book
and I ended up with a dual boot system (Win 98 and Linux 2.0.33). Then I
went to the Redhat site thinking about upgrading to 2.0.36 and to be honest
I started to get confused (a normal state with linux users?) I couldn't be
sure what files I needed to download. Finally I shelled out money for the
Redhat 5.2 boxed set and reinstalled that. So far so good. The I went to
the EMC site and downloaded the release9J version of RTlinux. I have
installed that using the instructions on the EMC site and despite the patch
file not running clean RT linux appears to work. When I have time I will
try to install the EMC software.


Bob