Re: [mowbot] Questions?

Dave Everett (deverett nospam at
Sat, 01 May 1999 10:47:37 +1000

At 14:32 30-04-99 -0700, david steinke wrote:
>I actually tried to post about 3 weeks ago but had lost the new address
>due to a virus attack (wonderful java code that just modified files by
>rearranging contents). I was hoping someone would post. So if I can
>remember, here is what I wrote.
Good to see some mail here again. Just when I got time to work on my mowbot
>a. How sensitive are the electronic compasses to permanent magnet motors
>nearby (within 4")?
The short answer is, quite sensitive. The problem is that a motor is
hundreds of times stronger than the Earth's magnetic field. Don't let that
discourage you though, a bit of experimentation should find you a spot
where the motor field is too weak to effect the compass. Field strength is
the inverse of the sqr of the distance.

Take into account heading errors caused by tilt. If your lawn is not flat
you may experience substantial error. From the Vector manual "For example,
in Mountain View, CA, for each 1deg of tilt, there would be about 3deg of
heading error. In Greenland, for 1deg of tilt, there can be 10deg of
heading error. I bought the 2XG model for this reason, it has gimballed
sensor coils which can tilt up to 15deg to remain level.

Dave Everett

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