[nzlug] Controlling a basic servo-motor ...

[Bernard O'Leary]

Thanks for the feedback (so-far) guys, it is very much appreciated - and
significantly excedeed what I was hoping for!

If there is anyone from an Auckland based robotics enthusiast group reading,
then yeah, I would certainly be keen to get involved with something like
that.

Bernard.


On Dec 3, 2007 1:03 AM, Andrew Errington <a.errington at lancaster.ac.uk>
wrote:

> Hi,
>
> I agree with the advice given so far.  Although it is possible to drive
> the
> servo directly from the PC it is preferable to us something else to
> control
> it, which itself is under control of the PC (via the serial port).  A
> PICAXE
> is a great low-cost way to get started quickly, or you could get something
> like the Scott Edwards SSC:
>
> http://www.seetron.com/ssc.htm
>
> If you want to do the whole thing on the PC I recommend using the parallel
> port.  You will have to grab a pin and have low-latency code which runs to
> set the pin's state.  See here for a discussion of how to do that:
>
> http://www.andrew.cmu.edu/user/suppe/mobot/mobot2.html
>
> The technique on that page could also apply to the serial port if you can
> grab
> control of a pin (such as one of the handshake outputs), but you will need
> a
> level converter.
>
> A servo needs a fairly grunty power supply at 5V.  It can draw quite a
> high
> current when it moves to a new position, or if it meets any (mechanical)
> resistance.  Use an external bench PSU.  The 'control' pin (driven by the
> micro) is a logic-level signal and only draws a small current.
>
> I'd recommend you go to the local library and look for books on hobby
> robotics.  Christchurch has a few good ones, and I expect things to be the
> same in Auckland.  Incidentally, there is a (fairly active) robotics group
> in
> Christchurch- go here to subscribe, and ask away:
>
> http://lists.ourshack.com/mailman/listinfo/chchrobotics
>
> We also have links to a group of enthusiasts in Auckland (are you
> listening,
> Keith?).  Maybe you could meet up for a beer.
>
> A
>
> On Saturday 01 December 2007 18:08, Bernard O'Leary wrote:
> > Hi all,
> >
> > I'd like to spend a bit of time over Christmas messing with a
> servo-motor.
> > Initial goal is to get my head around how to control it via the serial
> > port, more long term to be able to apply the techniques I learn to
> > small-scale robotics projects.
> >
> > Am hoping to be able to be able to do things from (more-or-less) first
> > principals - write the device driver that will be the source of the PCM
> > signal, some sort of controlling application, etc. I'm aware that there
> is
> > some risk of damaging the servo if it is sent a PCM signal that is out
> of
> > range.
> >
> > At this stage I'm looking for pointers, advise, and answers to a few
> > questions. For example - is it advisable to test the serial port output
> > using an oscilloscope prior to hooking up the servo? And is it sweet to
> > hook the serial port output directly to the PCM signal input on the
> servo,
> > or should there be some hardware in-between? What is the recommended way
> to
> > power a servo (I assume the serial port lacks the necessary juice
> > requirements)? etc ...
> >
> > Clearly I'm no electronics engineer. I do have some basic digital
> > electronics experience and knowledge though, and tons of textbooks. One
> way
> > or the other I'll be going ahead with this project - so some time (and
> > potentially harware) saving guidance would be appreciated ;-)
> >
> > Ta,
> >
> > Bernard.
> > _______________________________________________
> > NZLUG mailing list NZLUG at linux.net.nz
> > http://www.linux.net.nz/cgi-bin/mailman/listinfo/nzlug
>
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