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'[EE]: Vector 2X Compass for use in a Robot'
2001\02\14@164716 by Tom Handley

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  I'm about ready to add a Vector 2X compass to my robot. I took a look at
Precision Navigation's web site and I found it a bit `pathetic'. I could not
read all of the on-line manual, for example. I'm using NetScape v4.76.

  Anyway, it looks easy enough to talk to. Has anyone used this module? If
so, does it include a manual (or a few pages...)? Has anyone used it in a
robot? I looked at the calibration procedures. Since my little robot wanders
around the house (not installed in a vehicle), there should'nt be a problem
with nearby magnetic fields. The dual PM motor drive will be about 6" from
the compass but a standard R/C servo will be about 3" away. That's used to
scan the ultrasonic sensor to build a picture of terrain 180 deg in front of
the robot. I've looked at the raw data calibration equations for the
compass but I'm hoping to do that during the installation and not have to
update it while the robot is moving around. Thanks,

  - Tom


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Tom Handley
New Age Communications
Since '75 before "New Age" and no one around here is waiting for UFOs ;-)

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2001\02\14@171649 by David VanHorn

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>
>around the house (not installed in a vehicle), there should'nt be a problem
>with nearby magnetic fields.

Well.. Concrete pad has re-bar, that's a problem.
Steel beams used underneath houses too.

>The dual PM motor drive will be about 6" from
>the compass but a standard R/C servo will be about 3" away.

The servo is likely less of a problem than the motor.
The motor will leak field from the internal magnets, but it's also a big
field-distorting lump of stuff.

Check with a hand-held compass. If it wiggles when you add-remove parts,
then you're distorting the field significantly.

Fields around wires carrying motor currents could be interesting too.
Try to get the source and return wire routed as a pair.


Good luck!

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2001\02\14@190610 by Stephen Holland

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I tried it in an autonomous robot I designed, but removed it because it was
far too sensitive. I was picking up all kinds of nearby magnetic fields, and
even found that it could be affected by water pipes or electrical wiring in
the floor or walls. Just to show how sensitive it is, I think the
documentation describes that it could be used in a car to detect another car
nearby. Every once in a while it would receive a reading of 400deg or
something, so the software would have to know enough to throw it out. I
ended having to do some sort of oversampling to get good results, and the
eventual sample rate was too slow for me to use in my application.

Stephen

> {Original Message removed}

2001\02\15@230733 by Tom Handley

picon face
  Stephen, thanks for the info! I can compensate for sudden changes in
heading but there is still some old knob and tube wiring in this old house
which could add a constant error if I was traveling above it. I did see
the warning about the module detecting passing cars even after being
calibrated in a vehicle. That's what started giving me second thoughts
about this... Others have used it in small robots so I'm going to try
and track down their experiences.

  - Tom

At 04:04 PM 2/14/01 -0800, Stephen wrote:
{Quote hidden}

>> {Original Message removed}

2001\02\15@230750 by Tom Handley

picon face
  David, thanks for the info. I can do a hard calibration to compensate
for fixed fields on the bot but I'm not sure of the effect of the motors.
They are small F160-style motors drawing around 250ma once running up to
speed. Rebar and steel beams are not a problem in this house but Stephen
mentioned how sensitive the module is to water pipes and power wiring. I
would have to compenstate for that in software checking to see if a
heading suddenly jumps several degrees. I need to take a hard look at this
before I place an order. I know other small robot projects have used it
and Matt pointed me to a web site which I'll check out. Thanks,

  - Tom

At 05:09 PM 2/14/01 -0500, David VanHorn wrote:
{Quote hidden}

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Tom Handley
New Age Communications
Since '75 before "New Age" and no one around here is waiting for UFOs ;-)

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