A wooden robot with a large fresnel lens in a sunny garden

Gardening Robot Uses Sunlight To Incinerate Weeds

Removing weeds is a chore few gardeners enjoy, as it typically involves long sessions of kneeling in the dirt and digging around for anything you don’t remember planting. Herbicides also work, but spraying poison all over your garden comes with its own problems. Luckily, there’s now a third option: [NathanBuildsDIY] designed and built a robot to help him get rid of unwanted plants without getting his hands dirty.

Constructed mostly from scrap pieces of wood and riding on a pair of old bicycle wheels, the robot has a pretty low-tech look to it. But it is in fact a very advanced piece of engineering that uses multiple sensors and actuators while running on a sophisticated software platform. The heart of the system is a Raspberry Pi, which drives a pair of DC motors to move the whole system along [Nathan]’s garden while scanning the ground below through a camera.

Machine vision software identifying a weed in a picture of garden soilThe Pi runs the camera’s pictures through a TensorFlow Lite model that can identify weeds. [Nathan] built this model himself by taking hundreds of pictures of his garden and manually sorting them into categories like “soil”, “plant” and “weed”. Once a weed has been detected, the robot proceeds to destroy it by concentrating sunlight onto it through a large Fresnel lens. The lens is mounted in a frame that can be moved in three dimensions through a set of servos. A movable lens cover turns the incinerator beam on or off.

Sunlight is focused onto the weed through a simple but clever two-step procedure. First, the rough position of the lens relative to the sun is adjusted with the help of a sun tracker made from four light sensors arranged around a cross-shaped cardboard structure. Then, the shadow cast by the lens cover onto the ground is observed by the Pi’s camera and the lens is focused by adjusting its position in such a way that the image formed by four holes in the lens cover ends up right on top of the target.

Once the focus is correct, the lens cover is removed and the weed is burned to a crisp by the concentrated sunlight. It’s pretty neat to see how well this works, although [Nathan] recommends you keep an eye on the robot while it’s working and don’t let it near any flammable materials. He describes the build process in full detail in his video (embedded below), hopefully enabling other gardeners to make their own, improved weed burner robots. Agricultural engineers have long been working on automatic weed removal, often using similar machine vision systems with various extermination methods like lasers or flamethrowers.

Continue reading “Gardening Robot Uses Sunlight To Incinerate Weeds”

Upgrading A Line Trimmer With 3D Printed Parts

Many have complained about the hassle of rewinding their weed whackers with fresh trimmer line. Manufacturers responded by making models with solid plastic blades instead. Some of these suck, though, like this Ozito model belonging to [Random Sequence]. 3D printing was the way forward, adapting the blade trimmer to use traditional line.

The design is simple. [Random Sequence] created a small plastic tab which matches the attachment tab of the Ozito trimmer’s plastic blades. On the end of the tab, in lieu of a blade is a round slot into which a length of trimmer line can be inserted. The trick is to use a cigarette lighter to slightly melt a bulb onto a length of trimmer line so that it doesn’t pull through the slot. Centrifugal force (argue about it in the comments) keeps the line from falling out.

[Random Sequence] prints them in PETG, but notes that the part could benefit from additional strength. They do break when hitting tough objects, much like the stock trimmer blades do. Also, unlike a bump-feed trimmer head, there’s no way to auto-feed more line. Instead, one must simply assemble more of the tab-adapters with fresh line manually.

Overall, though, it’s a great way to fit stronger, more capable trimmer line to a weed whacker otherwise hamstrung by weak blades. It’s reported to work with Ozito and potentially Bosch tirmmers, and parts are on Thingiverse for those wishing to print their own.

Just as string trimmer line was once used as 3D printing filament, you can also go the other way, turning old plastic bottles into trimmer line. If you’ve whipped up your own fun hacks for tools in the garden, don’t hesitate to let us know.

Sound off with your best name for a weed whacker in the comments, too. The Australians may hold the title with “whipper snipper,” but we’re open to other submissions!

Weed Eater String Made From Plastic Bottles

For those who don’t mind constantly adding tiny but measurable amounts of microplastics to their landscaping, string trimmers are an excellent way of maintaining edging around garden beds, trimming weeds, or maintaining ground covers on a steep hill. One problem with them, though, is that not only is the string consumable but it can be expensive. Plus, if you have a trimmer with a proprietary spool you need to hope the company never goes out of business. Or, you can simply refill your string spool with this handy tool.

The build uses plastic bottles to create the string from what would likely become garbage anyway. First, a sharp roller-style knife slices the plastic into a long thin strip. Once cut, it is fed through a heater similar to a hot end on a 3D printer which allows the plastic to be deformed or forged into a cylinder. From there the plastic is added onto a spool, which also has the motor in it that drives the entire mechanism. In this case it is using an old variable-speed drill.

From the comments on the video, there is some discussion about the economics of using this string in a weed eater. It’s likely the plastic won’t last as long as specialty string trimmer string, and the time and expense of making the plastic may never save much money. But we have to give credit to the ingenuity nonetheless. And, if you’re really into recycling plastic just for the sake of keeping it out of the landfill, there are plenty of other ways to go about accomplishing that goal.

I will NEVER buy weed whip line again! from landscaping

DIY Lawnmower Doesn’t Cut Grass Short

[nodemcu12ecanada] is serious about saving water, which is why they built this strange lawnmower that can cut grass taller.

Short lawns are one of those clever marketing victories, like convincing people to eat a lot of sugar, that’s been doing more harm than good ever since the victory was won. Short grass is weak grass, with shallow roots, weakness to weeds, and a lot of water requirement. On top of that the grass is always in a state of panic so it grows extra fast to get to a more “natural” height. It’s great if you want to sell fertilizer, seeds, and lawnmowers. Maybe not so great for the environment.

Most lawnmowers can’t even be set high enough for healthy grass so [nodemcu12ecanada] took three electric weed whackers and bolted them to an angle iron frame. It has a lot of advantages. It’s light. You don’t need to sharpen a blade. It’s quiet. It’s electric. It’s strange appearance will scare your neighbors off from borrowing any of your tools. We love it!

Chainsaw Powered Bicycle


We’ve covered weed whacker bicycles before and you can even buy 66cc conversion kits now. [geoff390] posted a few videos over on YouTube about another motor option. In the first video embedded below, he goes over the basic parts of his bike. The chainsaw motor is mounted to the side of the back tire and a metal drive wheel extending from the chainsaw shaft makes contact with it. The motor assembly is mounted on a hinge and the friction between the drive wheel and the back tire is adjusted with a turnbuckle. He posted a more detailed second video in which he goes over some of the finer details of the bike and some of the issues he’s had. Continue reading “Chainsaw Powered Bicycle”