Re: [mowbot] What Happene

Dave Everett (Deverett nospam at
Mon, 25 Nov 1996 12:34:50 +1100

Byron A Jeff wrote:
> >
> > Surely we should exhaust all possibilities of onboard sensing before we
> > ever contemplate beacons or any other artificial modification to the
> > environment.
> Well like everything else it's a tradeoff. Complete onboard sensing may
> require a significant investment whereas an external source may greatly
> simplify some problems you present below. We should examine the sensing
> problem from one end of the spectrum (complete onboard) to the other
> (completely mapped and beaconed) so that we can understand the tradeoffs.

Tradeoff analysis can only occur in situations where all the factors are
known. For a computer project, this could be done. But this is not a
computer project. A mobile robot poses more unknowns than just about any
other pursuit. Rather than employ a top-down approach, we need to
implement a bootum-up process, where the robot evolves as we discover
problems and solve them.
> Dave, while beacons do bring new issues to the party, they are not that
> difficult to solve. For example I'll take a quick swipe at two of the three
> you presented above: power and failure.
> Power: Rechargable battery contained within the beacon.

FIne, but how does the battery get recharged? Is it connected by a
buried cable to a power supply? Does the beacon beep for a few days
before the battery goes flat so you can replace it? Should the user keep
spare battery packs charging to replace the ones in the field? How much
is all this going to cost?

> Failure. Mowbot stops and signals alarm when a beacon is lost.

That is fine if the beacon is sending a continuous signal, but in the
example Raymond outlined, the beacon responded to a call from the
Mowbot. How would Mowbot know that if a signal is not received a) Mowbot
is not near the beacon, or b) the transducer is full of water, or c) the
battery is flat, or d) the tranducer has failed etc etc.
> > I believe the stages should be:
> > 1) Onboard sensors
> > Until all possibilities of solving a particular problem are
> > exhausted.
> Again I'm not so sure. Onboard electronics can solve a lot of problems, but
> at what cost for load, power, and intelligence? Let's develop a tradeoff
> curve which designates what it takes to solve particular problems onboard.
As I say above, a tradeoff curve implies that we _know_ all the senory
needs of the robot.
> >
> The sensor can even be smart enough to turn itself off until it hears the
> Mowbot talking to it.

However that invites all the possible problems I outlined above.
> And just a cute thought: Any reason the active beacons could not be mobile
> and roll themselves to the right spot at grass cutting time?

Yes :-) If an active sensor can roll itself to a particular location,
why can't Mowbot do that by itself?

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