Project of the Month: An Autonomous Lawn Mower

A Neat Lawn For Less

Hubert Pissavin's autonomous mower uses an inexpensive motor and rechargeable nickel-cadmium batteries.Paul Wootton

It took Hubert Pissavin two weeks in his garage to build a machine that would do his least favorite chore for him: mowing the lawn. The retired electrical engineer started with a simple, boxy chassis made of wood. With four motorized wheels and a spinning blade, the battery-powered device moves in a straight line until it bumps into an obstacle, which activates a relay switch that backs the mower up about three feet.

It then turns 30 degrees to the right or left (it alternates each time it hits something) and gets back to work. To ensure that it goes over his entire lawn, Pissavin constructed a border around the perimeter of his backyard out of rocks and driftwood from a nearby beach. The lawn mower takes longer to finish the job than a person would—about an hour to mow 4,300 square feet—but, Pissavin says, the time flies while he's watching from his hammock.

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