AI weed killer uses sunlight and Raspberry Pi

Maker Nathan brought together Raspberry Pi, AI, and the sun’s rays to create a weed-burning robot. It’s billed as the “world’s first autonomous, intelligent weed burner”, and it’s so gloriously shonky we don’t even care whether that’s true or not.

This is one of those YouTube videos that got sent round Pi Towers like wildfire, which is what we really hope does not occur as a result of this project or any like it. Absolutely do not make one of these then leave it to roam around and end up setting fire to your entire region. We do not want that to happen. Please take all kinds of care if you are having thoughts about using the energy of the actual Sun to make fire. We hope we are making you feel like there’s a lot that can go wrong here. Stay safe.

Parts list

  • Raspberry Pi 3 Model B+ (you don’t need a lot of processing power because the robot needs to travel very slowly in order to do its job, so any board should be OK for this build)
  • Fresnel lens (aka giant magnifying glass PLEASE BE CAREFUL)
  • Photoresistors to track the sun
  • Old phone charger for power
Close-up of the hardware attached to the robot rig

How does it work?

The Raspberry Pi camera is mounted to the underside of the robot rig. It captures bird’s-eye images of the ground as the robot travels through the garden.

This is brilliant – watch it! And also subscribe to Nathan’s YouTube channel for more autonomous builds.

A TensorFlow custom image classification model taught the robot to differentiate between weeds and plants that Nathan wants to keep. When the Raspberry Pi identifies a weed, the motors flip out the giant lens and manoeuvre it into place directly above the hapless plant. Photoresistors track the direction from which the light is coming, and provide the information needed to focus the sun’s beam through the lens. Then the weed burns to death. Sounds bleak, but nature is cruel by necessity.

Two motors move the lens roughly into the right position. Then three additional motors do the fine-tuning, focusing the sunlight directly on top of the weed. The big lens has a cover that’s only lifted when it’s in the right place, which saves grass and other plants from being burned while the robot is driving around. There is a lot going on here.

Fresnel lighthouse lenses

Nathan explains the interesting way this build repurposes a Fresnel lens. You’d usually see one in use at the top of a lighthouse. When fulfilling its originally intended purpose, it sits in front of a powerful light source and focuses it into a narrow beam. Fresnel lenses do this while using less material than a conventional lens, and they can be overall flat in shape. Ships’ crews can see this strong, focused beam from greater distances. That makes it easier to avoid the dangerous rocks the lighthouse is built on.

Nathan showing off the lid of the Fresnel lens

The flat Fresnel lens is used in a similar way in this weed-killing project: it focuses sunlight on a point about two feet beneath it. While the light source doesn’t need to travel far enough to warn boats miles away, it does need to be concentrated into one strong beam in the same way.

Alternative weed killing

We love this project but we’ll have to chalk it up as one that we won’t get proper use out of, here on our often-cloud-covered isle. We’ll have to stick to that Shake ‘n’ Vac-type stuff we sprinkle over the really weedy parts of the garden, then our bare hands when we’re digging them out of flower beds. Or just make friends with the weeds.

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