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[DPRG] Re: new pictures

Subject: [DPRG] Re: new pictures
From: Earl Bollinger earlwbollinger at comcast.net
Date: Sat Sep 6 09:26:01 CDT 2003

That is most interesting. But in my experiences with a Hexapod, sending
commands to each servo via the serial port limits your walking speed
severely. The most I was able to achieve was very slow motion walking in
this manner.
The Servopod on the other hand can make the servos move fast enough to
get a brisk walk going. Maybe even a slow run. Your mainly limited by
how fast the servos can move. 
On a hexapod you've got 18 servos to command to move all six legs, three
servos per leg. Thus you have to send a lot of commands down that serial
wire to make each servo move some distance. Now you've got to throw in
velocity methods to make it move smoothly too. Thus you could send 100+
commands per leg in a second to move it smoothly. Doing through the
serial port starts to become a big bottleneck.

My thinking was to use a ISOPOD (I have them, not a sevopod yet), to
perform set command, such as walk forward, walk backwards, turn right,
turn left, slow, medium, fast, et cetera. Then another MASTER ISOPOD
would send the commands via one of the serial ports (lot of choices on
the ISPOPOD,CAN Bus looks good) to the Leg control ISOPOD, which handles
all the movements for me.
Oh yeah on each leg, you would want to have a simple pressure sensor to
let you know when it made contact (with the floor for example) so you
could stop it, thus you could gain more level movement on irregular
surfaces. I am also thinking about bump sensors or IR sensors on the
legs for detecting obstacles too.
Then we get to a arm with a gripper, now we have a bunch more servos to
control. Yup you guessed it another, Arm ISOPOD on the CAN bus.
The MASTER ISOPOD gets to handle things like the ultrasonic detectors,
minicams (note plural) with zoom in oom out abilities, and such maybe.

When I think about it, I tend to walk pretty much autonomously, thus it
would make sense to break up the movements and processes into different
ISOPODS to handle it all. 
If I use the Devantech chip, which is a good chip, I still need a second
processor to send it the basic movement commands, thus limiting the
movements to a slow crawl. Thus I have two MCU's to control the legs,
two MCU's to control the arm, and a master CPU that controls them. The
MCU networking is now getting complicated.

I can only say, until you do it, you can't imagine how much wire goes
into one of these things, until you start to wire it all up. :)




-----Original Message-----
>From: dprglist-admin at dprg.org [mailto:dprglist-admin at dprg.org] On Behalf
Of Dale Wheat
Sent: Saturday, September 06, 2003 8:21 AM
To: Dan Gates; LLYONS
Cc: DPRG
Subject: Re: [DPRG] Re: new pictures

Dan,

Have you taken a look at Devantech's 20 servo controller?

http://www.robot-electronics.co.uk/htm/sd20tech.htm

It's somewhat cheaper & smaller than the ServoPod.  :)

Thanks,

Dale Wheat
http://dalewheat.com
(972) 486-1317
(800) 330-1915, access code 00

----- Original Message ----- 
>From: "Dan Gates" <topazx2 at yahoo.com>
To: "LLYONS" <llyons at flash.net>
Cc: "DPRG" <dprglist at dprg.org>
Sent: Saturday, September 06, 2003 12:40 AM
Subject: [DPRG] Re: new pictures


> 
> --- LLYONS <llyons at flash.net> wrote:
> > Really Great legs!!!   LL.
> > 
> > 
> 
> 
> Thanks, I'm looking forward to getting them walking with a Servopod
> from New Micros when I get them mounted to the body. I was excited to
> see that there was a servo control board that was capable of handling
> all 20 of the servos I'll have in this walker. I'll keep everyone
> posted as it progresses, and when it's finished I plan on writing an
> article for the new Servo Magazine.
> -Dan 
> 
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