[mowbot] Extract from Risks Digest

robin nospam at acm.org
Sat, 5 Oct 1996 13:31:35 +0100

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.


Copyright (C) 1996 R.M.O'Leary <robin nospam at acm.org>  All rights reserved.
For licence to copy, see http://dragon.swansea.linux.org.uk/mowbot/
The Risks Digest Volume 15: Issue 75
Weds 13 April 1994 
Forum on Risks to the Public in Computers and Related Systems
ACM Committee on Computers and Public Policy, Peter G. Neumann, moderator

Robot mower (designed by Belgians, built by Swedes, driven by no-one)

Pete Mellor < pm nospam at csr.city.ac.uk > Sun, 3 Apr 94 03:54:47 BST

The Daily Mail of 1st April 1994 carried a full-page report (p3) of a new design of mower called the Solar Turtle.

This is a little robot that runs around your lawn on wheels, cutting the grass ALL ON ITS OWN! The picture that accompanies the article shows a low-profile object about 3 feet long by 2 feet wide, elliptical in outline, and with its top surface sloping down from about one foot at the front to 6 inches at the back. (I am guessing: the exact dimensions are not given.) It is so light that "it can be carried by a child." It is also (mercifully!) almost completely silent.

Its flat upper surface is covered with an array of solar panels which provide it with sufficient power to trundle around even on dull days, and charge its little batteries so that it can keep going if it runs into a shaded patch of garden. Its maximum speed is 1.8 kph (slower in the shade). Three separate electric motors drive its two front wheels and rotating cutting blade. Since it is intended to operate continuously, the grass never gets a chance to grow. Therefore trimmings are very fine, and are simply left on the lawn as a mulch, so that no collector box is required, and it doesn't even require periodic attention from the gardener to empty it.

A single machine can look after 2000 sq. ft. of lawn. Price {pounds} 1,500 to 2,000 (still TBA). Manufacturers are Husqvarna of Sweden, and the inventor is Andre Coles (Belgian). So far, it has been demonstrated at the Spring Gardening Fair at Olympia, London. Look out for it next at the Chelsea Flower Show. It will probably go on sale next year. (British outlet: Husqvarna Forest and Garden.)

Risks? Well, what if it a) cuts your toe off, b) mows your prize dahlias, c) gets stuck, or d) gets nicked?

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."

a) Safety (1): If it hits anything (tree, chair, foot) "a shock detector stops it in its tracks". The picture shows a sort of white band around the front edge, which is presumably a collision sensor. Since it moves "backwards and forwards a few feet at a time", it presumably has a similar sensor at the rear. Its sensor seems to be a few inches off the ground. Could it give a sleeping cat a short back and sides?

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. The photo shows the Turtle standing proudly in the foreground with a smiling and highly photogenic young lady (who obviously never got her hands dirty with a bit of weeding in her life!) lolling in a deck-chair in the background. The scenery includes (as well as the happy Turtle user) about 50 acres of garden containing a lake, irregular patches of shrubbery, occasional trees, and artistically arranged lumps of rock. Even assuming the Turtle can negotiate the rocks, shrubs and trees without help, burying a boundary cable around that little lot must be a major logistical exercise.

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! :-)

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 ...

After all that, risks to the public? Err ... getting fat through not having to mow the lawn? :-)

[There is a disclaimer in the Mail article which states that this is NOT an April Fool joke! :-) ]

Peter Mellor, Centre for Software Reliability, City University, Northampton Sq. London EC1V 0HB +44 (71) 477-8422, p.mellor nospam at csr.city.ac.uk