Few chores evoke such dread as the weekly lawn cut, and new grass munching bots that take over that job promise to make more than a few Christmas lists this year. Robomow ($695) from Friendly Robotics and Auto Mower ($1999) from Husqvarna run off rechargeable batteries and mow lawns with up to 20-degree grades. The computerized cutters pack on-board sensors that receive RF signals generated from a permanently installed perimeter wire that defines the area in which the mowers roam. If the mower moves beyond the perimeter wire, it stops.

Husqvarna's Auto Mower is making its U.S. debut this year after a two-year run in Sweden where the company has sold more than 5000 devices, according to Dennis Willis, product manager for Husqvarna. Auto Mower can handle up to half an acre of grass and is designed to maintain the property daily, rather than on the typical once-a-week schedule. Because it's trimming the grass rather than going for a full cut, the mower can cover a wider area in less time than it could take on a less frequent mowing schedule with longer grass. That startegy is dictated largely by battery capacity. The nickel-metal-hydride battery run for 1.5 hours off a single charge and requires an hour for recharging. When the mower reaches half its battery capacity it looks for a signal that comes from the docking station and moters itself over for a recharge. A recharging wire extends from the docking station that guides the mower onto its power booster. The Auto Mower cuts in a random pattern, which Willis says hits all the different areas of the property frequently enough that grass will be kept at the length you've programmed the mower to maintain. It takes about an hour to cut 1000 sq. ft. The robotized mowers make strong environmental claims as well. Since the mowers don't use a gasoline powered engine, there are no emmissions and blade noise is barely perceptible. In fact, says Willis, you can program Auto Mower to do late-night manicures without disturbing the neighbors.

Under the hood, the Auto Mower has a 24-MHz processor, software and sensors. Two collision sensors react to obstacles the mower hits, such as a tree or an object in the yard. When the mower hits an object, it stops, backs up and then turns right or left to continue mowing. A lift sensor shuts off the blade rotation if someone tries to raise the 15-pound mower above .75 in., and a tilt sensor stops the blades if the mower shifts from its level plane. And if the neighbor's curious 5-year old tries to reach under the machine while no one' s looking? The blades only rotate when the machine is moving forward, Willis says. The only way for someone to be cut is to walk along the side of the machine as it's moving and reach an arm under the mower without touching the machine's collision sensors, which is an unlikely feat.

Rather than mowing in a random pattern as the Auto Mower does, Friendly Robotics' Robomow scoots in a forward-and-back "V" pattern from one side of the lawn to the other. Its navigational system is a floating compass that uses two settings for forward and backward direction. Once the mower reaches the perimeter wire and knows it can't go any farther, the on-board computer issues two new compass settings and the mower mows in the same V-shaped pattern against the previous path. In the process the mower fills in any spots it missed on the last pass, according to John Bunton, who heads sales and marketing for Friendly Robotics. "It mows in the most efficient way possible," he says. Robomow measures 42 in. long x 23in. wide x16.8 in. high and weighs in at 120 pounds due largely to its two 12 volt lead-acid batteries. The mower will cover 5000 to 6000 sq. ft. at a clip, depending on the thickness of the grass and turf type, according to Bunton. Robomow cuts until the owner shuts off the machine using the remote control.

Robomow packs 10 sensors, including four bumpers on each side of the machine. When the bumpers hit an object, the impact sends a puff of air through a hose to a diaphragm on the mower's computer sensor board. The senser board issues a command for the mower to stop and change direction. In addition, proximity sensors in the front and rear send out a sonarlike signal that tells the mower to slow down when it comes within 3 ft. of an object, Bunton says. Robomow comes with batteries, charger, perimeter switch and wire, pegs to secure the wire, a manual controller, instruction manuals and video. Bunton says users can have the mower out of the box and running in 4 hours, which includes tacking down the perimeter wire, programming in a security code and programming on/off times for the mower to operate. A 16-bit Hitachi microprocessor is the brain of the mower and it's supported by 128KB RAM and 512KB upgradable flash memory.

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