Re: Sensors: "Where is the other end of my tether?"

On Tue, 04 Oct 2005 21:58:29 GMT, Ben Bradley <ben_nospam_bradley@xxxxxxxxxxxxxxx> wrote:
> On Tue, 04 Oct 2005 14:12:31 GMT, Frnak McKenney
><frnak@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
>
>>
>>There are several different approaches to determining a robot's
>>position "absolutely" (okay, relative to the Earth) such as GPS.
>>There are others for determining position relative to beacons and
>>walls where sound, light or RF are at least partially unobstructed.
>>
>>But... suppose you want to build a tethered (remotely powered)
>>tunnel crawler to explore and map complex networks of metal piping,
>>such as sewers, conduits, and ventilation ducts? Odometry would be a
>>bit "sloppy" (especially in sewer pipes), and one couldn't depend on
>>light or sound.
>>
>>Is there some simple method for determining where one end of a cable
>>is relative to the other end? (Okay, how about a complex method?)
>>I know that if you throw enough money at the problem one can measure
>>the _length_ of the cable (via signal travel time), but what if you
>>want to know the far end's XYZ location relative to the beginning of
>>the cable after your robot has snaked its way through fifteen
>>air-duct conduit joints and created a replica of the Gordian knot?
>
> Presuming you're on a "tether" cable, you're probably unwinding it
> (either at the base end or on the robot, and from this (calculations
> from rotation count and winding diameter) you know the total distance
> of the tether you've unwound. With onboard gyroscopes, you can know
> how far you went in each direction as you unwound the cable.
> Calculation of current position is done with this info and
> trigonometry.

Ben,

Thanks for the reply.

A "Theseus thread" would certainly give the explorer a way home (or a
way to attempt to haul it back or send another explorer after it).

Will the cable be taut enough to yield a good approximation of the
distance travelled? I'm wondering about making multiple turns in large-
diameter pipes, where the cable might "hike up" the wall and represent
the szhortest path to the explorer, but not necessarily represent the
distance actually travelled.

Of course, I may be overly optimistic on how much accuracy I can
expect. <grin>


Frank McKenney, McKenney Associates
Richmond, Virginia / (804) 320-4887
Munged E-mail: frank uscore mckenney ayut minds pring dawt cahm (y'all)
--
Some see private enterprise as a predatory target to be shot,
others as a cow to be milked, but few are those who see it as
a sturdy horse pulling the wagon.
-- Winston Churchill, 1874-1965
--
.

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