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'[EE]: Botboard'
2001\08\31@165125 by Lawrence Lile

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Y'know, with all this talk about optical sensors, keep this in mind: Cutting
grass is a dirty job.  If you are not careful, any optical sensor is going
to soon be covered in gook.  I nixed several ideas for optical grass height
gauging, concrete sensing, edge sensing etc. after watching the bits of
juicy stick grass flying all around a mower.   That's why I keep coming back
to my axiom - Cochroach Stupid! or Keep It Simple Stupid!  Cochroaches have
feelers that are more use than their eyes, if they even have eyes.


-- Lawrence Lile
Sr. Project Engineer
Salton inc. Toastmaster Div.
573-446-5661 Voice
573-446-5676 Fax

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2001\08\31@172213 by Dan Michaels

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Lawrence.L wrote:
>Y'know, with all this talk about optical sensors, keep this in mind: Cutting
>grass is a dirty job.  If you are not careful, any optical sensor is going
>to soon be covered in gook.
...........


Tiny "windshield" wipers.
Or tiny eyelids.
Or mount the sensor on a servo and pan to limit to squeegee the lens.
Or mount the sensor in a clear plastic hemisphere and dribble water
 down out of a bucket to keep the surface clean - plus water the
 grass at the same time - drain comes out "behind" the mower.
Or have the mower come over to its hutch every few passes for a
 lens cleaning.
Or have the sensor retractable into a box with auto cleaning as it
 goes in and out.
Or only mow on rainy days.

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2001\08\31@173701 by Lawrence Lile

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Or have a midget captain pop out and give a carrot to a rabbit, who must
squeeze his furry hide past the sensor thus wiping it...
{Original Message removed}

2001\08\31@224433 by Byron A Jeff

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On Fri, Aug 31, 2001 at 03:50:40PM -0500, Lawrence Lile wrote:
> Y'know, with all this talk about optical sensors, keep this in mind: Cutting
> grass is a dirty job.  If you are not careful, any optical sensor is going
> to soon be covered in gook.  I nixed several ideas for optical grass height
> gauging, concrete sensing, edge sensing etc. after watching the bits of
> juicy stick grass flying all around a mower.   That's why I keep coming back
> to my axiom - Cochroach Stupid! or Keep It Simple Stupid!  Cochroaches have
> feelers that are more use than their eyes, if they even have eyes.

I understand. Since I posed this query I just wanted to update my thoughts.

I always liked the beacon idea. The problem I always had with it was trying
to figure out how to sense on a moving plane. Between hills, valleys, and
obstacles, along with a continuous slope in the yard it will be very very
difficult to sync the transmitter and receiver. But the discussion on the
rotating VOR mirrors I realized that creating a verticle sweep could help
quite a bit because then the receiver could sense the transmission even
with a height disparity.

After thinking about it some more, I realized that putting a complex motorized
mechanism on a number of stationary beacons probably isn't a good idea. The
stationary part of the system needs to be as simple and reliable as possible.
I also figured that the mowbot really only needs to know which beacon it's
talking to and the angle of the front of the bot relative to that beacon.

So here my idea:

1) Flip flop the system and make the mowbot the transmitter and have stationary
receivers mounted that detects the transmittions.

2) Design a two dimensional sweep. The transmitter will rotate horizontally
360 degrees. On this platform have a vertically rotating light transmitter.

3) The receiver system will passivly wait for transmittions and then
transmit their id when they detect a transmission. Thinking of using wireless
for that.

4) So the way it'll work is that the mowbot does a 360 degree horizontal
sweep with vertical sweeps up and down. When a receiver detects it transmits
its ID to the mowbot. The mowbot can then record the angular position of
the receiver and move on. The set of angles uniquely identifies the position
presuming you have a minimum of two receivers.

After that you can use the data for tracking, planning, etc. You can dead
reckon based on the angular data from the stationary receivers. You can define
spots that are out of bounds, the home position, the start position, where to
turn, etc.

Since the receivers are no longer actively transmitting, they may be low power
enough that they can be solar powered. The receivers do not have to interact
with one another, simply report that they are currently receiving a signal.

Maybe it's time to start some testing of the idea...

BAJ

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2001\08\31@232248 by Dan Michaels

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BAJ wrote:
........
>I always liked the beacon idea. The problem I always had with it was trying
>to figure out how to sense on a moving plane. Between hills, valleys, and
>obstacles, along with a continuous slope in the yard it will be very very
>difficult to sync the transmitter and receiver. But the discussion on the
>rotating VOR mirrors I realized that creating a verticle sweep could help
>quite a bit because then the receiver could sense the transmission even
>with a height disparity.
>
>After thinking about it some more, I realized that putting a complex motorized
>mechanism on a number of stationary beacons probably isn't a good idea. The
>stationary part of the system needs to be as simple and reliable as possible.
>I also figured that the mowbot really only needs to know which beacon it's
>talking to and the angle of the front of the bot relative to that beacon.
>

This is basically the same as my idea. The beacons are fixed, and don't
rotate, but each probably has 3 LEDs wired in series to fire together
with the separate LEDs pointing 90 degrees apart - thus 180 deg xmit
coverage, so the bot can see it from anywhere within a room. Each
beacon has a separate output pulserate, and maybe a 555 or PIC508,
and costs $1-2.

In my case the beacons are always placed along a wall in a room,
and the bot swivels to determine the angle to the beacon, moves and
swivels again - else the bot uses a servo to pan the IR pickup. You
don't need 2 beacons for triangulation, either, because the bot
can only be on one side of it - ie, inside the room with the beacon
up against the wall. However, in my case, the bot uses the beacon as
an absolute reference point, and then uses other means to map out
the room - #wheel rotations, ultrasonics, etc.

- dan
========

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'[EE]: Botboard'
2001\09\01@135843 by Peter L. Peres
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> Or have a midget captain pop out and give a carrot to a rabbit, who must
> squeeze his furry hide past the sensor thus wiping it...

Put the snesors behind a rapidly spinning transparent disk, part of the
mowing mechanism or driven by it. But I said RF is better than optical.

Peter

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