DPRG mailing list archives: [DPRG] Tarzan's lessons learned at the DPRG Outdoor Challenge

Sun May 18 12:34:48 CDT 2008

Just wanted to bring up a small point. My father was captain of a diesel submarine and he told me a story about subs and magnetism that I think would put some -insight into the discussion.  Randy, you were a naval officer, you may know a little about this too. 
Back in 40's and 50's they fitted the subs with degaussing coils to reduce the magnetic signature.  So they would sit in port and run the degaussing coil and demagnetize the sub. Worked great!  Then of course they would power up the large electric motors and and change the electric field in the sub. . 

So I think you will at least need to have the robot moving to get a "reasonable" reading. But I think with all the variable magnetic fields around the robot, you really would need to put the compass as high and as far away from the robot as possible. 

Bill
Know the following?
Can dead men vote twice?
C D M V T
compass + deviation = magnetic heading + variation = true heading. 
And the other way. 
true virgins make dull company

----- Original Message ----
From: Randy M. Dumse <rmd at newmicros.com>
To: Robert F. Scheer <rfscheer at speakeasy.net>; dprglist <dprglist at dprg.org>
Sent: Sunday, May 18, 2008 11:08:57 AM
Subject: RE: [DPRG] Tarzan's lessons learned at the DPRG Outdoor Challenge

Robert F. Scheer said: Saturday, May 17, 2008 5:59 PM
> Haven't a clue.  I've never seen 3-D maps of magnetic flux on 
> the scale of parking lots and robots near the earth's 
> surface.  It would be an interesting science project.
> 
> I do have a comment though.  Raising and lowering a mast is 
> not a practical way to equip an outdoor robot unless you 
> don't care if it stops to make the measurements, because it 
> would be critical to make the z measurements at the same x,y 
> coordinate.
> 
> Perhaps more than one magnetometer placed at different 
> heights could give you simultaneous data that would be 
> useful, but I've never heard of anyone actually doing this 
> and certainly haven't seen a study of it.

Bringing this post back to the DPRG, think it came to be
directly...

Yes I'd thought of using three separate magnetometers, but I'd
think that would be much more expensive than a single one with a
lifting arm.

Also I rather like the idea of stopgging to take a reading. It's
a fine tradition we humans do: "stopping to take our bearings",
as it is said. 

Further, I've always been concerned about jBot wacking that mast
on a picnic table or bench, because it is above the range of the
sonars to see. Dpa and I have discussed this, and as I recall
it, it does pretty well avoiding those situations, but we were
able to set it where it had that trouble at UTA once. The other
behaviors got it out of the situation, but it is possible to
have it hit the mast on a something like a low plane, or bar.

So I like the idea of keeping the compass tucked down, and
occassionally sensing where to stop to hoist it into clean air. 

I don't know, it's more moving parts, but then, I think we are
perhaps more fascinated by robots with more moving parts, et?

Randy

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