[mowbot] Husqvana Solar Mower

Dave Everett (Deverett nospam at vir.idx.com.au)
Sun, 06 Oct 1996 09:34:52 +1000

robin nospam at acm.org wrote:
> I vaguely remembered seeing a mention of robot lawnmowers in the
> excellent Risks Digest and went back to look for it---sure enough,
> there was a report on the Husqvarna in April 1994. I enclose
> a copy without permission.

Concidentaly the latest issue of Choice magazine (an independent that
unbiased tests on products) contains a review of the Solar mower.

> It is so light that "it can be carried by a child." It is also (mercifully!)
> almost completely silent.

According to the Choice review, it gives different beeps depending on
what it is doing. When it's working it gives a beep every 5 seconds, and
at night once every 10 seconds.
> This is where the relevance of all this to the RISKS forum becomes apparent.
> For the Turtle is controlled by (you've guessed it, folks!) "an on-board
> computer [which] analyses conditions 500 times a second, enabling it to adapt
> to the amount of light, humidity and temperature, and to negotiate slopes
> and particularly overgrown patches."

The mower is only able to negotiate slopes of 20deg or less, there is a
photo of the mower hard up against a rock on a slope greater than 20deg,
the mower is unable to back away from the obstacle due to the slope. A
large part of my lawn is at 30deg, and on a brief tour of other lawns in
my neighborhood, I found slopes up to 50deg in some places. The
limitation for the Solar mower is no doubt because it relies heavily on
solar power.
> b) Safety (2): It will not operate outside an area delimited by a buried
> "boundary cable". An "electronic sensor" detects the cable, and "tells it
> to turn back". The article does not go into this, but (IMHO) this is a
> serious marketing weakness.

One problem with the buried wire (as discovered by Choice), is that the
mower leaves an unmown boundary of about 30cm width because it can't get
any closer to the buried wire. This means you are going to have to hand
mow some of the property anyway.
> c) Reliability: This must depend on precisely how intelligent its program is.
> It can't simply stop when it hits a tree, so what does it do? Back up and
> charge again? Try a random turn? What happens if it hits your foot, and you
> then move out of the way? You can bet that even if you have more sense than
> to get in its way, your kids will have hours of fun trying to convince it
> that they are a tree! If it maintains a database of the terrain, this could
> seriously blow its tiny mind! :-) On the other hand, it must somehow avoid
> mowing the same little patch over and over again. Does it remember where it's
> been? (Software Engineering coursework assignment: "Design an algorithm using
> a pseudo-random number generator to ensure that a Turtle covers the whole of
> a piece of lawn 2,000 sq. ft. in area in a given time irrespective of the
> shape of the perimeter or the presence of interior obstructions." - That
> should keep the students busy! :-)

It has no memory of where it has cut. The mower is totally random,
except when it reaches long grass, it then cuts the patch in a square
pattern much as the Lawnranger did.

Choice also found that the mower avoided shaded areas, "You may still
need to mow your lawn occasionally during the peak growing season and
under permamently shaded areas, which the solar mower tends to avoid for
lack of light (although it has tow nickel cadmium battery packs that
provide power for short periods on cloudy days or in shaded areas.)"
> d) Security: If the Turtle is picked up, "a loud alarm goes off ... and is
> turned off only when an individual code is punched in. And it cannot operate
> outside the electronic boundary." ("I say, Alice! What's the code for this
> ****** Turtle? I can't turn the frigging alarm off!") Also, if it's *carried*
> outside the boundary cable, how does it detect this? Mmmm ...

It can't tell it's been taken outside the boundary, it can only tell
when it is within 30-40cm of the boundary.

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