Newsgroups: comp.robotics
From: pcats@cryton.demon.co.uk (Patrick Arnold)
Path: brunix!news.Brown.EDU!agate!howland.reston.ans.net!pipex!dis.demon.co.uk!cryton.demon.co.uk!pcats
Subject: Re: Cheap gyros 
Distribution: world
References: <9401161437.AA23227@algol.demon.co.uk>
Organization: The Serial Port
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Date: Mon, 17 Jan 1994 19:02:46 +0000
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In article <9401161437.AA23227@algol.demon.co.uk> bruce@algol.demon.co.uk writes:

>I read in this newsgroup a few weeks ago about there being gyros
>available for under $200. More recently I was browsing through some
>magazines belonging to an aeromodelling enthusiast. It seems that
>there are gyros available for model aircraft for around 60 UKP (that's
><$100). If anyone reading this knows about these devices I'd be
>interested to hear:
>
>1. How they work, e.g. whether they're inertial or magnetic.
>
>2. Whether they drift.
>
>3. What sort of outputs they produce. I'd guess that they output a
>couple of PWM signals suitable for feeding straight to servos.
>
>4. Anything else about them that would be of interest to someone
>building mobile robots on the cheap!

The gyros that you have seen adverts for are almost certainly designed mainly
for radio controlled helicopters. These are rate gyros, used to sense the 
rate of turn about a particular axis (usually vertical, for tail rotor 
control), and are designed to connect between an R/C receiver and a servo. 

The gyros work by modifying the PWM signal that the rx produces, before it
gets to the servo. The sensing is usually done by a linear hall effect device,
which senses the position of a magnet on the bottom of the flywheel assembly.

The gyros have both sensitivity and gain controls, and some can be switched 
on and off remotely. I have used them for sensing rotation about an axis for
a VR headset, with some success, but I'm not sure whether they would be much
use for most robotics applications.

Hope this is some help.

Patrick.

-- 
The shortest distance between two points has not yet been built.

pcats@cryton.demon.co.uk vox+44(749)670058 fax+44(749)670809 dat+44(749)670030
