Re: [mowbot] What Happene

Dave Everett (Deverett nospam at
Sun, 24 Nov 1996 14:14:05 +1100

Raymond Skarratt u wrote:
> We can probably get <10cm accuracy with ultrasonic beacons, depending on
> humidity and temperature variances. I think that the idea of having

Surely we should exhaust all possibilities of onboard sensing before we
ever contemplate beacons or any other artificial modification to the

We need to build a base first, then build the sensing system bit by bit.
Sovling the simplest problems first and building on those foundations to
solve more of the problem.

Beacons sound nice when you first consider them, but all they really do
is move the problem from the robot to another location. Worse, they are
extra entities that bring their own problems. An active beacon is a
major undertaking: power needs to be run to the beacon, the beacon needs
to be installed to certain specifications, a method must be implemented
to ensure that failure of the beacon is reported in a timely fashion
(don't want Mowbot rolling off to regions unknown). Failure can take
many forms, simple power failure, frequency failure, even failure of the
transdure itself.

I believe the stages should be:

1) Onboard sensors
Until all possibilities of solving a particular problem are
2) Passive beacons
fences, wires, posts etc, that the existing onboard sensors can use.
3) Active beacons
when all else fails.

Any talk of positional information (like XY co-ords, multi-beacon
referencing) creates another problem; They imply that the robot carries
a detailed co-ordinate map of the environment. That means that before
the robot ever moves, a detailed survey of the property must be made.
These are in my opinion just more entities that do little to add value
to the project, in fact they are good reasons for not pursuing it. If,
to get a robot lawnmower going on my property I had to:
1) build the robot
2) perform a detailed survey of my property
3) install beacons (at considerable expense and modification to my
property, ie digging cable trenches, installing concrete bases for the
4) ensure the security of said beacons from weather damage, vandalism
I would consider that an unreasonable venture.

Dave Everett                                Email: deverett nospam at
(c) 1996 - Copyright remains with the author unless explicitly stated