Re: [mowbot] What Happene

Raymond Skarratt u (skar9500 nospam at
Tue, 26 Nov 1996 11:09:19 -0500 (EST)

> > 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
> > environment.

I agree. I was just pointing out that if we are dealing with a
relatively structured and small area that if we wanted to we could get
much better than .2m accuracy. I do think that we at some point are
probably going to have to have some sort of either passive or active
beacons or boundary marker.

> 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.

As was mentioned perviously I think that it's not really feesable (sp?)
to examine the whole process through anything more than thought
experiments. (But then again it's that what most fo the theory of
relitivity is based on? :)

> > >
> > 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.
> Agreed. I'm really uncomfortable when it comes to the mechanics of building
> such a beast. Sensing and control electronics and programming are trivial
> compared to the three basic items any project any of us undertakes requires:
> infrastructure, mobility, and cutting. I really wish we could focus here
> and folks could throw out some cookbook recipies for us to try out.

Ok, here's my attempt at throwing out some ideas in these areas. First I
think that the cutting mechanism can be really crude (rasor blades on a
plastic or metal disk) as long as we have some sort of saftey device that
either retracts or totally disables or both the blades when something
gets close to the mowbot or when it gets picked up.

Second, I thnk that the base can be relativly simple. A square frame
made of angle irons comes to mind. We can then build a cover from
whatever (everyone's idea can be different however,) I prefer fiberglass
because it can be worked into whaht ever shape I want and I can paint it
to make the mowbot look really sexy, which fits into the 'have a winning
personality' goal of this project. :)

> > 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. Then
> each of us can choose a point on the curve we,re comfortable with and implement
> it.

And again the already argued point of exploring the whole spectrum not
being feesable can be brought up here. I think that we won't be limited
by intellegence, mircoprocessors are pretty powerful but payload is an
issue. I would like to see a beast that weighs in at less than 10 kg
including batteries.

> >
> > 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.
> Not exactly. From the beginning I've been thinking of active beacons as
> extensions of the passive beacons, their primary job is to artificially
> define "do not cross" boundaries for the Mowbot. Positional info is a bonus
> and need not be mapped a priori. The Mowbot can internalize positional
> info to indicate areas it has already covered. So instead of depending
> on the "seek for uncut grass then flood fill" algorithm solely positional
> information recorded during the session indicating what has already been
> cut can be eliminated from the search. It can also help the Mowbot to define
> a finished condition, when all the areas without the boundaries (natural
> and artificial with the active beacons) has been mapped as cut, it's done
> for now.

I think that this is a valid point. a semi-complete map of the area
coupled with beacons is a good idea I think. It is really the way that
we get around if yyou think about it. We don't know exactly where
everything in our yard or house is, but we know approximately where it is
and use visual beacons (although they are passive) to get to an exact

> >
> > 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:
> > 2) perform a detailed survey of my property

I was thinking about this one and originally I thought that this was not
necesary at all. however after some more thought it turns out my
original thoughts were wrong unless we use beacons as a boundary marker.
I think that infared is probably the best way to do this, or an
underground wire, or laser :).

> 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? Then when the
> Mobots (I'm thinking more than one now ;-) are done, then whole team rolls
> right on back into the shed? Idle speculation mind you.

Yeah but how do the beacons know where to go? GPS? That might get a
little costly. :)

> Active beacons what do not create any a priori situations and don't require
> massive reworking (or mapping) of the property could be useful. Let's not
> dismiss them summarily.

I agree. We could very well end up using a beacon or two. I'm currently
trying to think of a way to use only two beacons (for a rectangular yard
with no obstructions, although this is not ideal once I get this figured
out it can be modified for other yards) at opposite corners of the yard.
I think that it should be possible as long as Mowbot is able to
differentiate between the two beacons.