I'm looking for information on how a robot can map an area, (yard, room etc..) Any informtion will be helpful. Thanks in advance....

You need a.) The means to measure the position and b.)
means to sense the boundary.

The rest is software but by no means obvious.

<nbucska@pcperipherals.com>

We are looking for methods of determining location, other than odometry. Our Budget is very limited....And the enviromental conditions may interfear with IR for use as sensors...

What is the range of the motion and the required accuracy ?
What is the speed ? Is the area different each time ?

<nbucska@pcperipherals.com>

The robot will have to cover about an acre with an avg speed no more than 1.5 m/s. T he accuracy needs to be with in about 1/2 meter over the 1 acre area. The area will be the same each time....but the flexablilty to change may need to be put in at some point in the future.

I would connect tachometers to two wheels and add some
means to calibrate it. e.g. two proximity sensors, corner
reflectors etc. at fixed locations.

You could even get the desired accuracy with ultrasound with 3 transmitters.  

<nbucska@pcperipherals.com>

I think the corner sensors may work is there any way to set up a way to know what corner it's at, if I ounced an IR beam off of some sort of reflector?

Assuming you can tell what corner you're in by the direction you're facing, you can use two compasses and four digital inputs (two from each compass) :
     n                           n
w                 and                e
        e                     w
   s                              s
 Compass 1                    Compass 2

Send current through the compass pointers and set up contacts at the north and south points that prevent the pointers from crossing them.  In this way, compass 1 should never be able to point east and compass 2 should never be able to point west.  This gives you 9 theoretically possible outputs:
Compass 1     Compass 2     Facing Direction
n/c               n/c         (Impossible)
n/c               N           East
n/c               S           East
N                 n/c         West
N                 N           North
N                 S           West
S                 n/c         West
S                 N           East
S                 S           South

Dave.

A corner reflector [CR] = 3 mirrors,90 deg. between any two (like a corner of a box ). It reflects
the beam parallel to the incident one.

You can measure the angle between any two CRs (2 CRs may be very close so their angle is minimum). If you know the position of the CRs and the angles, you can calculate your position.

If you rotate the beam, you can measure the angles very accuretelly. ( Tachom., PLL etc.)

<nbucska@pcperipherals.com>

OK here is the next challange:

We wanna put a wire follow aroung the parimeter of the operational area...simular to the electric dog fences I assume...any thoughts on this? can I use the dog collar? if so how does it work?

thanks