line trimmer

3 Articles

Teardown Shows Why Innovative Designs Sometimes Fail

January 7, 2019 by 28 Comments

Some ideas are real head-scratchers from a design standpoint: Why in the world would you do it that way? For many of us, answering that question often requires a teardown, which is what [Ben Katz] did when this PCB motor-powered weed whacker came across his bench. The results are instructive on what it takes to succeed in the marketplace, or in this case, how to fail.

The unit in question comes from an outfit called CORE Outdoor Power. The line trimmer was powered by a big lithium-ion battery pack, but [Ben] concentrated on the unique motor for his teardown. After a problematic entry into the very sturdy case at the far end of the trimmer’s shaft, he found what looks like a souped-up version of [Carl Bugeja]’s PCB brushless motors. The rotors, each with eight large magnets embedded, are sandwiched on either side of a very thick four-layer PCB with intricately etched heavy copper traces. The PCB forms the stator, with four flat coils. The designer pulled a neat trick with the Hall-effect sensors needed for feedback; rather than go with surface-mount sensors, which would add to the thickness of the board, they used through-hole packages soldered to surface pads, with the body of the sensor nestled in a hole in the board. The whole design is very innovative, but sadly, [Ben]’s analysis shows that it has poor performance for its size and weight.

Google around a bit and you’ll see that CORE was purchased some years back by MTD, a big player in the internal combustion engine outdoor power market. They don’t appear to be a going concern anymore, and it looks as though [Ben] has discovered why.

[Jozef] tipped us off to this one. Thanks!

Lawn From Hell Saved By Mower From Heaven

June 19, 2018 by 94 Comments

It’s that time of year again, at least in the northern hemisphere. Everything is alive and growing, especially that narrow-leafed non-commodity that so many of us farm without tangible reward. [sonofdodie] has a particularly hard row to hoe—his backyard is one big, 30° slope of knee-ruining agony. After 30 years of trudging up and down the hill, his body was telling him to find a better way. But no lawn service would touch it, so he waited for divine inspiration.

And lo, the answer came to [sonofdodie] in a trio of string trimmers. These Whirling Dervishes of grass grazing are mounted on a wheeled plywood base so that their strings overlap slightly for full coverage. Now he can sit in the shade and sip lemonade as he mows via rope and extension cord using a mower that cost about $100 to build.

These heavenly trimmers have been modified to use heavy nylon line, which means they can whip two weeks’ worth of rain-fueled growth with no problem. You can watch the mower shimmy down what looks like the world’s greatest Slip ‘n Slide hill after the break.

Yeah, this video is two years old, but somehow we missed it back then. Ideas this fresh that tackle age-old problems are evergreen, unlike these plots of grass we must maintain. There’s more than one way to skin this ecological cat, and we’ve seen everything from solar mowers to robotic mowers to mowers tied up to wind themselves around a stake like an enthusiastic dog.

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Robot Lives In Your Garden And Eats The Weeds

May 18, 2017 by 50 Comments

You can’t deny the appeal of gardening. Whether it’s a productive patch of vegetables or a flower bed to delight the senses, the effort put into gardening is amply rewarded. Nobody seems to like the weeding, though — well, almost nobody; I find it quite relaxing. But if you’re not willing to get down and dirty with the weeds, you might consider deploying a weed-eating garden robot to do the job for you.

Dubbed the Tertill, and still very much a prototype, the garden robot is the brainchild of some former iRobot employees. That’s a pretty solid pedigree, and you can see the Roomba-esque navigation scheme in action — when it bumps into something it turns away, eventually covering the whole garden. Weed discrimination is dead simple: short plants bad, tall plants good. Seedlings are protected by a collar until they’re big enough not to get zapped by the solar-powered robot’s line trimmer.

It’s a pretty good idea, but the devil will be in the details. Will it be able to tend the understory of gardens where weeds tend to gather as the plants get taller? Can it handle steep-sided raised beds or deeply mulched gardens? Perhaps there are lessons to be learned from this Australian weed-bot.

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