Robots at home alone

On a knife’s edge

The automatic lawnmower from Husqvarna sneaks past its hand-propelled compatriots with a working volume of well under 64 decibels. But that is not the only thing the robotic vacuum cleaner has in common with the Automower®. Above all the cutter drive, which is supplied by ebm-papst Landshut, represents a prime example of a product that has been optimised with respect to cost and performance. “At first we were not sure whether the requirements for the new motor were maybe a bit too much,” admits Siegbert Hartauer from the lower Bavarian sales organisation, describing the early misgivings. After all, Husqvarna was counting on continuing its success story.
Since 1994, the Swedes have been using a single-core, brush-less direct current motor from Landshut to turn the cutter blades in the four Automower models 210 C, 220 AC and 230 ACX and solar Hybrid. Husqvarna employs a mechanical trick to overcome the weak start-up torque, which is the drawback of the low priced single-core motor. The razor-sharp blades are not fixed to the rotating disk. Rather, they fold out once the working speed has been reached.
The 260 ACX was launched at the beginning of 2009. The largest model of the automatic mowers is designed for semi-professional use and has a mowing range of around 6,000 square metres, so it needs a more powerful motor. Until now, the BG 3633 has been used as a fan drive in heater blowers, with a service life of up to 20,000 hours. Yet the 50 watts power output required by Husqvarna still caused the motor to overheat. Until the engineers at Landshut found the solution. A modified cooling blade now expels even more heat, allowing the motor to defy the greater power. Its ideal operating point is at 1,750 rpm with a power output of more than 45 watts – and an efficiency of 63 percent. This energy efficiency allows the Automower® to cut a lot of grass before it needs to return to the charging station. And there is another characteristic that links it to its vacuum cleaning compatriot. You don’t have to persuade it to work, and it doesn’t demand any praise afterwards.

Within a limitation cable laid out along the borders, the Automower® automatically carves its way over the lawn. Day or night, sun or rain, even on gradients of up to 35 percent.

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