Re: [Gumstix-users] Servo motors

[Nate W <del...@gm...>]

I have a Gumstix/Robostix in a biped with 21 servos.  The Robostix controls
two servos, the other 19 are attached to a PicoPic servo controller, see
http://www.picobotics.com/PicoPic.html for details.  I actually have an SD21
but haven't used it yet - the PicoPic is smaller and I found that it fits
better.   I've also got a hexapod with the same servo controller, but no
Gumstix (it uses bluetooth to connect w/ my laptop).

It's worth investigating the serial protocol of whatever controller you want
to buy - find out how many bytes per command, then multiply that by the
number of channels you need, and make sure the servo controller can accept
data fast enough.  Most will accept 115200bps, which is plenty, but some
have limits as low as 9600.  Most servos only expect 50-60hz, so there's no
point going higher than that, but my hexapod's 'brain' only works at about
15-20hz and the motion is noticeably notchy.  In that particular case the
serial line isn't the limiting factor, but with a 9600bps servo controller,
it would be.  The SD21's I2C interface is probably fast enough, but I
haven't done the math.

On 10/14/06, tc6 <tc...@fr...> wrote:
>
> Hello all,
>
> I plan to build a small hexapod robot using Gumstix and Robostix cards,
> and I would like to know if someone has already tried to control several
> servomotors (at least 18) using those two cards. Is it possible to
> control them using all available ports of Robostix card or would it be
> better to use a specific i2c servo controller card (like SD21 card for
> example)?
>
> Any advice would be appreciated a lot.
>
> Best regards,
> Thomas
>
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-- 
Nate Waddoups
Redmond WA USA
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