Newsgroups: comp.robotics
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From: shane@cs.sunysb.edu (Shane Bouslough)
Subject: Re: robot parts: info and question
Message-ID: <1993Jan31.155957.7778@sbcs.sunysb.edu>
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Date: Sun, 31 Jan 1993 15:59:57 GMT
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Allen Brown (abrown@hpcvcec.cv.hp.com) wrote:

: I am assembling the people, expertise, and parts to make a robot.  It
: will be a cat sized six legged creature modeled after a beetle.

: References so far:
: 1. Minimalist Mobile Robitics by Jonathan H Connel
:    ISBN 0-12-185230-X
:    This talks about a Brooks inspired wheeled robot designed to
:    collect soda cans.

I sure wish there was an equivalent volume on the genghis/attila/hannibal
series.

: We also bought for evaluation about ten motors from a couple of
: surplus houses.  Several of those motors were approximately what we
: were looking for.  I recommend you get catalogs from:
: 
: 1. American Science and Surplus
:    (708) 475-8440
: 2. Mendelson Electronics Co., Inc
:    (800) 422-3525

: We considered stepper motors but settled on DC motors.  Steppers tend
: to take too much power, even when doing nothing.  They tend to be more
: expensive than DC motors.  Steppers have the advantage of one pulse
: translating to a fixed amount of motion.  But you have to have some
: additional sensor to find out where you are when you start.  (This is
: generally a limit switch.)  But if you are going to install an
: additional sensor, why not use a pot and measure position directly?

Is there a reason you didn't consider servos? Price?

: We have discussed various ways to translate the energy from the motor
: to the leg.  We haven't found a source for gears at anywhere near a
: reasonable price.

I have heard of, but been unable to obtain so far, a catalog from
the "Berg" (sp?) Corporation. They are the "Digikey" of gears, joints,
etc. I'm not sure about pricing, but I've been told it's relative to
its competitors in the same way Digikey is to its competitors.

: The main structural components such as body and legs will probably be
: made of model aircraft plywood and fiberglass.  High strength and low
: weight are what makes me lean toward them.

Any references on using fiberglass?

: The uC will be the Pic.  (I don't know if that is how it is spelled.
: Others in my group are familiar with this computer.)  The Pic is in a
: quartz lid 18 pin DIP.  It has 8 digital I/O lines and 4 analog input
: lines.  There is a 8 bit ADC multiplexed onto the analog inputs.  As I
: recall the Pic has 512 bytes EPROM and 32 bytes RAM.  I expect we will
: use one Pic per leg and one to supervise.

Is the miniboard too expensive a solution? It does the same thing, and
has a pretty nice development environment :-).

: We do not yet have the motor drive electronics.  I am hoping we find a
: suitable IC.

How about the SGS-Thompson L293D on the miniboard?

: We have also not worked out how to measure foot force.  But we know
: two of the constraints: its gotta be small and cheap.

There seems to be a deafening silence in c.r about this issue.

: Now the question:
: Any advice?  Do you know of a good cheap source for gears or pullys?
: (Like about $0.50 per gear.)  Do you know of a better way to deliver
: force to the legs?  I don't really want to design and build my own
: motor to cable interface.  Do you know where I can get this for less
: than $2.00?  How about a small cheap strain guage?

See above about Berg Corp. I'm looking for strain gauges too. Let me know
if you find any leads.

:   Allen C. Brown  abrown@cv.hp.com or hplabs!hpcvca!abrown or "Hey you!"

-Shane

--
Shane Bouslough       | #include <stddisc.h>
shane@sbcs.sunysb.edu | "Follow your bliss" - Joseph Campbell
