Published in Radio-Electronics, April 1961.
The Lazy Man's Delight … An Automated Lawnmower
By GORDON CARLSON – Development engineer, DeVry Technical Institute. Chicago, Ill.
MUCH has been done with remote control, but a remotely controlled device that must maneuver in tight spaces (such as a grass cutter near the wife's flower beds) and in near panic situations (like a very close miss) requires constant and close observation. This means radio control from the lawn chair is out. Instead, a completely reliable, fully automatic device that doesn't require watching, that does not run over the neighbor's dog or the children's toys is the type of easy living lawnmower that allows plenty of time for relaxation.
Basically, the operation of this automatic lawnmower is this: A length of ordinary plastic-covered hookup wire is buried about 1 inch under the lawn in the pattern the grass is to be cut (Fig. 1). The distance between wires depends on the width of the cutting blade and the amount of overlap desired.
Mounted about 16 inches in front of the steerable wheel of the mower are two pickup coils (Fig. 2), about 6 inches apart and 2 inches above the lawn. When a small alternating current is passed through the buried wire, an electromagnetic field is set up around it. When the coils are near the wire, the magnetic field induces voltages in them. The amplitude of these voltages increases as the coils move nearer the wire. If the coils are equally distant …. see attached pdf for complete text.
See other early remote-controlled and robotic lawn mowers here.