Re: DRO card and future projects

Tom,

I am definitely interested. I noticed that US Digital also offers
linear encoders for $2 per inch, which sounds reasonable. Of course
the electronic "readers" are extra, but the cost should be about the
same as for as a rotary (I presume!). Wouldn't this help address
backlash? At least you should be able to tell where you actually are.
I'm not sure how the slop effect when changing directions - not likely
to be good. But wouldn't this be a problem even with backlash
compensation?

Steve

At 10:02 PM 5/21/99 -0700, you wrote:

>From: Tom Kulaga <tkulaga@...>
>
>I guess you've all seen the posts about the DRO card I built. I've
>got an update to the software, adding metric support, cleaning up a
>few things I didn't like, and changing the 4th axis to display in
>degrees instead of linear units. I haven't posted it to the webpage
>yet because I wanted to add backlash compensation first. That's the
>problem.
>
>The big drawback of backlash compensation is that you are forced to
>make sure that all of the slop is cranked to one side of the travel
>before you can zero that axis. If you don't, the computer doesn't
>know where you are inside the backlash zone, and you can't trust the
>numbers on the display.
>
>My question is this: Do those of you who want to use rotary encoders
>have a problem with this? Keep in mind, you won't be able to zero
>the axis until you are certain that you've moved all the way to the
>left or the right of the slop. I can think of more than one occasion
>where this would be *really* annoying, but usually it would just be a
>matter of getting in the habit of watching what you're doing a bit
>more so than normal.
>
>So, did I get that across clear enough? Is it worth it to add this
>feature? I don't want to spend a whole bunch of time working on a
>feature that nobody will want to use, especially since I've got a new
>project I want to start.
>
>Speaking of that new project, I've been following the comments about
>the EMC software (gotta love the free stuff ;) with interest, and got
>to thinking about how I'd go about trying it out here at home. I was
>thinking that buying a motion control card is pretty pricey, and that
>my DRO card makes a great jumping-off point for bigger and better
>things. With a little extra work, and probably an extra 200 bucks, I
>could come up with a 3-axis servo controller card design. It's a
>little more involved, but using PWM for the output signal cleans it up
>nicely, bringing it into the 'definately doable' range, even for
>beginners.
>
>I think that this group could easily write plans to build the card,
>the servo amps, and the guidance you'd need to assemble the lot into
>a really good webpage. I can handle the card OK, but I need to know
>how the card interfaces with the EMC stuff, or if I could provide all
>the register-level programming info to somebody who could write a
>driver or whatever is needed to get things going. I don't yet have
>Linux here at home, so I can't really experiment much. If there's
>interest in this, I'll order Redhat next month.
>
>What do you say, guys? Sound like fun?
>
>-Tom Kulaga
>
>
>
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