RE: servos

Dean;
I believe low cost computer interface hardware is valuable , for example, in reading quadature signals and interface digitally to a few of the appropriate projects some are involved in. I believe the "opto issolation" requirments might be met on another independent board or within the different black boxs people are constructing.

What do you mean by "Auxilliary ide controllers"? Something other than the ide controller on the motherboard? Is it a card?

What might the system configuration look like through the eyes of an ide controller port to receive quadature inputs and drive various digital outputs (aside from any 8255 which may be used on the business end)? What is the software interface like in terms of configuraing an application program to find its way through the hardware associated with the ide port and hardware used to expand its functionality (such as the 8255)?

How much faster is an ide port than a printer port? I understand that 66 Megabits is possible. There are many programs developed around single, dual, and three printer port computer interfaces. Most drive stepper motors and because stepper motors are limited in speed, the printer ports that drive them are sometimes not the limiting factor. In the case of servo motor drivers, the limitations of slower printer ports may likely come up, so I believe you are on track (for some of us playing in this area).

As you know, there are many really good efforts going on in various directions, with completed developments which are useable as components for various systems. One might want to hear that n number of people have enough interest in <new concept number 625>, to justify etching copper on fiberglass, but it is difficult to get a comitted group behind any one concept because there are many directions depending on what each wants. There are also an amazing number of options.

Let's say, just for fun, we wanted to accomplish this:

We want to utilize as much low cost computer board I/O within the (off the shelf) computer as we can, to interface to 3 quadature inputs, and 3 bi-directional 8 bit parallel ports at high speed (faster than the printer ports).

If we wanted to do this, I take it that we might develop a board that fits into an ide socket on our PC, (or if I understand you correctly, use an off the shelf ide port card?) and connect to our external opto-issolated black boxes next to our computers. If we developed such a card (or what it took to interface to an off the shelf ide card if that exists), can we hope to reduce the cost of interfacing the two kinds of digital data many of us need (quadature and digital inputs, and digital outputs). If we did this, how might one patch this high performance hardware interface into application software? Can it appear as higher speed printer ports at those addresses?

You know, the quadature input piece alone is probably of interest to many. The I/O cards with quadature inputs are big bucks. I think a reasonable card with quadature inputs and digital outputs might get some interest here. Lets see....

Survey. Would you buy a blank ide card for under $50, if you could buy the components for another $35 and put together 3 quadature inputs and 3 8 bit ports whcih may be configured for inputs or outputs? Would you buy it, mostly for the quadature inputs, or the higher speed digital data? Does anyone know what 3 quadature inputs is priced like on any off the shelf PC card?

I for one will buy such a blank PC board, if I can understand how to put it to use with medimum performance motion control software, and complete the mid range motion performance objectives I am considering with DC motors. Others seem to be building black boxes which might find need of this.

On my block box front, I'm searching the web to discover how painful the identification process can be concerning Surplus DC servo motors, and what support can be had with application programs. Those programs suitable for the printer ports, may be "remapped" elsewhere, if they support doing so (or if the ide concept can be addressed as printer port addresses).

The diamond in the pile of possibilities (on my front) may be open loop stepper motor programs, driven through a higher speed interface into a black box which turns a DC motor and encoder into a higher performance stepper motor (a hybrid). This may be realized, if surplus DC servo motors offer more bang for the buck and can be identified and used easily. Some surplus servo motors are neither easy to identify, or appropriate for this use.

Making a DC servo motor out of a regular DC motor and an encoder has a few difficulties. Many DC motors have uneven torque as you rotate them 360 degrees. It becomes impossible to move the motor 1.8 degrees and hold it there. I discovered that it can be done with a timing belt (gearing), however this adds to the complexity. The driver and the DC motor can heat excessively, trying to control too small and poor quality a motor.

I solved this problem with an intelligent motor driver (then a better motor). The major discovery was that the quality of the motor helps ten times while the smart of the driver can work with poor motors, - one. If somewhere there is huge quantities of high quality appropriate DC servo motors for a low price, controlling both the motors and the total cost is within reason.

Hopefully the speed of the computer interface will not limit the potential performance of my project, and the ide concept might offer something to others as well.


David Howland


-----Original Message-----
From: Dean Franks [SMTP:dean@...]
Sent: Friday, September 24, 1999 6:52 PM
To: CAD_CAM_EDM_DRO@onelist.com
Subject: Re: [CAD_CAM_EDM_DRO] servos

From: "Dean Franks" <dean@...>

One possibility to consider is using ide controller ports. Auxilliary
controllers are cheap, they are very fast and easy to deal with in software.
You do not have to implement a device-side protocol (as in USB or SCSI), ide
is basically a decoded mezzanine bus that is buffered from the actual CPU
bus.

It is still only 8 bits wide, but it much faster than a parallel port. If
you use an ISA bus card, the signals are slow enough to use an 8255 to
generate 24 usable i/o lines. If you use PCI/motherboard ide controllers,
use fast 373's/245's to generate extra ports.

If there is interest, I can do some testing, and generate a tested PCB
layout/schematic (for free distribution). I have been thinking of building
an external stacking bus (physically like pc104, but with pre-decoded board
selects, etc) using an ide port.

Dean

----- Original Message -----
From: David Howland <dhowland@...>
To: <CAD_CAM_EDM_DRO@onelist.com>
Sent: Friday, September 24, 1999 4:49 PM
Subject: RE: [CAD_CAM_EDM_DRO] servos


> From: David Howland <dhowland@...>
>
>
>
> Yes, the Interfaces which are low in cost will place restrictions on
performance, and <real time> goes first, and therefore the speed is
limited. This improves with faster computers, but this scheme probably will
not work on a system with a red hat sitting on top. Still the USB is
available on most newer machines and might play a role of interest to some
exploring their personal interests herein.
>
> The funney part of the converging technologies, may be that as computers
get faster and cheeper, the standard interfaces may begin to work in ways
they were too slow for in the past. Metal will not get softer and easier to
machine as time goes on.
>
> As far as the printer interface goes, I'm thinking of the dual printer
interface card option, giving you 16 bi-directional lines of data, plus an
odd amount of handshaking and status lines between the two parallel ports
available. If you look in your favorite cheep computer catalog, you find
all sorts of standard I/O cards to drop in a slot. It seems to me that the
fancy cards such as Servo to go give you a lot of bang for more bucks.
If you can live
> with less bang, then why not consider the concept that while you are even
thinking about it, computer I/O in the standard formats will be 6% cheeper
by the time you order it.
>
> >
> > Computer Interfacing cards and approximate price:
> > ISA SCSI-II Controller card $50
> > PCI USB I/O Card $40
> > Dual port ISA Bi-directional Printer Card $35
>
> [David Howland]
>
> <In response to comment from Jon >
>
> USB is a real exciting option, but I wonder, how long does it take for a
request from a R/T module to be sent
> through the USB driver to the custom motion box, and then for a reply to
come back through the driver to the
> R/T module. Actually, that can't work, anyway. So, if the R/T module had
the code to manage the USB,
> then nobody else could use it. Maybe with that restriction that the USB
couldn't be used for any other purpose,
> maybe this would work.
>
> Same problem, then, with the SCSI interface, it would have to be a private
resource to the R/T code.
>
> And, the printer interface is just too narrow (8 data bits plus way too
few control lines) to be a good
> data path. Also, there are limits on how many printer ports you can have
(unless you hack the address
> decoder).
>
> Jon
>
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Welcome to CAD_CAM_EDM_DRO@...,an unmoderated list for the discussion of shop built systems in the above catagories.
To Unsubscribe, read archives, change to or from digest.
Go to: http://www.onelist.com/isregistered.cgi
Log on, and you will go to Member Center, and you can make changes there.
For the FAQ, go to http://www.ktmarketing.com/faq.html
bill,
List Manager