Re: [Autopilot] Integration drift...

[Anthony B. <bal...@op...>]

Hi

As far as I understand, a 6 DOF gyro / acc. / mag. module
is useable in a VERY accurate INS. (inertia navigation system)

An onboard INS computer reads the sensors, and tracks
the actual 3D position, ground track & speed, flight path & velocity
and attitude of itself.
It also recognizes wind direction and speed at all times.

The module also gives the flight computer all necessary flight info
for flight control. ( attitude, IAS, TAS, altitude, vertical speed, heading, 
track, ground speed, rate of roll & turn, global position)

The module also gives the navigation computer all necessary position
info for navigation.

In a General Aviation environment, INS's are installed as a primary
navigation aid, provided an accurate fix can be obtained every hour.
This is to counter the slight drift inherent with INS.
Usually this is done with conventional nav-aids like VOR, DME etc.

In a UAV this could be a GPS fix.
The errors recorded would probably be acceptable for UAV use
anyway , negating the need for a hourly position fix.

They do need an accurate position fix at start-up.

INS navigation is FAR more reliable and accurate than GPS base
navigation

I think that is all correct.

Regards
Anthony Ball
BallTech UAV's
Australia

----- Original Message ----- 
From: "Bradley Parcels" <bpa...@ho...>
To: <aut...@li...>
Sent: Friday, October 14, 2005 3:00 PM
Subject: [Autopilot] Integration drift...


> Hello all,
>   Just signed up, so a quick intro, and a quick question:
>
> I'm a 4th year (and a half ;-)...) computer engineering student in 
> Calgary... Last year, myself and a 3 other students built a quad-rotor 
> heli as our design project - as it was from scratch, we were pretty 
> pleased just to get it in the air! Now I'm back taking another course, in 
> which my goal is to improve the control system, and take it a bit closer 
> to the long term goal of autonomy. Complicating the situation, the heli is 
> intended for indoor/outdoor use (ie - inspecting an unsafe building) and 
> as such, GPS is automatically ruled out.
>
> My question is this: has anyone attempted to integrate the accelerometer 
> readings to estimate velocity (or go even further as to position)? Or even 
> more basically - in it's current form, what kind of attitude accuracy can 
> one expect from the AHRS, using only the gyros, accelerometers, and 
> magnetometers?
>
> Essentially, I'd be pretty thrilled if I could get even SOMEWHAT 
> reasonable estimates of velocity for now... Even if not by integrating the 
> AHRS, could I trouble anyone for a suggestion? At the moment, I'm 
> contemplating very crude vision of some sort to fuse with the 
> accelerometers... TV-GPS looks good, but doesn't look like it'll be a 
> viable option for a while to come...
>
> Anyhow, thanks for taking the time... If anybody has any thoughts at all, 
> please let me know!
>
> Cheers,
> Brad Parcels
>
>
>
>
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