Newsgroups: comp.robotics
Path: brunix!uunet!mdisea!mothost!merlin.dev.cdx.mot.com!sgi.dev.cdx.mot.com!johnb
From: johnb@sgi.dev.cdx.mot.com (John Bottoms)
Subject: Arm Position
Message-ID: <1993Aug18.165654.153@merlin.dev.cdx.mot.com>
Sender: news@merlin.dev.cdx.mot.com (Merlin News System)
Nntp-Posting-Host: sgi.dev.cdx.mot.com
Organization: Motorola Codex, Canton, MA
Date: Wed, 18 Aug 1993 16:56:54 GMT
Lines: 30

I am interested in building an arm. It looks like this:

                 o
                 |\
                 | \
                 |  \
                 |   o---o
                 |        \
                 |  _
            /    | |\
            |        |
            \-------/

Pretty good, huh?

So it's got 4 degrees of freedom and is a small arm used 
to do pick and place.  It is driven by something using 
tendons running up the arm to each joint. Since it's 
small I can't put limit switches on it like you might 
with a big arm. Some of the motors may need to turn more 
than 360deg to get the required forced to move the arm. 

Here's my problem. Now do I tell the starting position of
the arm? Even if I use servos which have a zero position I
won't know where the various joints are.

Sorry if this is a Robo101 questions but I'm a hacker and
don't have much mechanical experience.

 -johnbottoms, SGML guru
