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[DPRG] New sensor for robots
Subject: [DPRG] New sensor for robots
From: Kipton Moravec
kip at kdream.com
Date: Tue Feb 12 14:07:06 CST 2008
On Mon, 2008-02-11 at 17:39 +0100, Redouane Boumghar wrote:
> Hello everyone,
>
> Motus' product code named Darwin is said to measure absolute position
> but well.. I wonder how it is doing using only gyros and accelerometers.
> Compared to the wii controller, I guess they wanted to say that the "zero"
> direction is measured by absolute mean (magnetic north).
> So the user does not have to use an infrared to get a initial direction and may just have
> to press a button. else Does the user have to turn his/her screen face to the north ? :-)
>
> I doubt the user is able to know where he/she is on earth.
> Anyway, correct me if I am wrong.
You are correct. Looking at it from a very top view (with a lot of
details missing,) Accelerometers can tell you what direction you are
going and how fast and how your speed is changing. Gyroscopes can tell
you how you are turning and how fast you are turning, and how fast your
rate of turning changes.
A compass tells you which way is magnetic north.
Nothing so far can tell you where you are or where you started.
In theory if you know where you started the data produced should be able
to tell you where you are. That is how Inertial Management Units (IMU)
in airplanes work. In practice the errors start building up. For
example, an accelerometer measures acceleration. It does not tell you
directly how fast you are going, or where you are. But if you started
from a known position at rest, by measuring acceleration you can
integrate and get velocity. Little errors in acceleration make bigger
errors in velocity the longer it goes. If you know your velocity, you
can integrate and get position. But again small errors in velocity mean
larger errors in position over time.
So the Aircraft have very very expensive IMU systems. But if you don't
put the right starting coordinates in then it will never be right.
Kip
>
> It's my first time writing on this list,
> Should I introduce myself ? :-)
>
> Have a good day,
--
Kipton Moravec KE5NGX
"Always do right; this will gratify some people and astonish the rest."
--Mark Twain
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