Pylon-guided mower | #MagPiMonday

Here’s a robot that takes grass and weed cutting to the next level… literally. This #MagPiMonday, Nicola King wonders at the weed assassin that is Roktrack, the pylon-guided mower.

Living in a mountainous region of Japan has proved inspiring for maker Yuta Suito. The local area has many rice terraces but, as he explains, “With the ageing of the farmers, this beautiful landscape will disappear in about ten years. Many farmers say that the hardest part of maintaining the terraced fields is weeding.” Determined to try and help, Yuta wanted to “solve this problem by providing mobility (with no need to bury boundary wires underground) and intuitive operation (in reality, many elderly people cannot use smartphones or computers).”

 Traffic cones act as a visual guide for Roktrack, helping it to work its way around an identified area
Traffic cones act as a visual guide for Roktrack, helping it to work its way around an identified area

The result is the lightweight, solar-powered Roktrack pylon-guided mower, and it’s perfect for rough terrain. Prompted by a road construction site, Yuta noticed that “by simply enclosing the area with traffic cones, the people inside would understand the scope of the work. I was inspired by the idea that computers could do the same thing.” Applying this logic to his project, Yuta’s mower is able to mow a range of coned-off areas, with a 200 m2 area, for example, taking around two hours. Not only that, but it’s equipped with a speaker, so “if you are in the immediate vicinity, an audible voice will tell you when the mowing is done!”

The word in weeding

With software written by Yuta, Roktrack is programmed to head towards a pylon (or cone) which it recognises through a camera image, and it then starts working its way towards the next one. Equipped with two blades, it cuts backs grass and weeds as it goes, leaving them on the ground. It’s rain-proof and has eccentric front wheels which allow it to traverse less hospitable terrain than you’d find in your average garden. In addition, object detection means that two mowers operating in the same area won’t collide.

The robot is equipped with a camera to spot the pylons (traffic cones) marking the designated area
The robot is equipped with a camera to spot the pylons (traffic cones) marking the designated area

Yuta used a Raspberry Pi 3 Model A+ to control Roktrack for temperature and power consumption reasons. “I wanted to cool the Raspberry Pi only with the fan provided on [Roktrack], not with a dedicated fan for Raspberry Pi. In addition, since this unit uses only one LiFePO4 (4S, 12.6 V) power supply for the control and drive systems, it was necessary to step down the power supply for Raspberry Pi.”

To start mowing, the user just presses the power button – or they can use an Android app, where communication between the robot and the app relies on Bluetooth Low Energy (BLE). Impressively, the app can instruct the mower to make an emergency stop, switch mode instructions, and, as Yuta details, “the coordinates of the past mowing point are recorded by the Android [device]’s GPS, and the current vegetation (weed growth) can be remotely sensed using Sentinel satellite images.”

of the robot shows its two rotary blades which enable pebbles to be ejected
An underside view of the robot shows its two rotary blades which enable pebbles to be ejected

Finding solutions

Testing Roktrack was challenging, says Yuta. “It was very difficult to test the system until I could get it to work stably.” He once took his eyes off of it while testing, and the robot tumbled down a cliff, but his conscientious hard work, testing thoroughly, and solving problems “one by one” now means, “I just leave it on and have a cup of tea in the house, and the weeds are cut.” Yuta is currently developing what he calls “parallel operation with multiple units,” and, by the end of the year, he hopes to experiment with up to six mowers working on several hundred square metres at a time.

 A couple of Roktrack robots in action on tricky terrain
A couple of Roktrack robots in action on tricky terrain

The building of a robotic mower like this is probably not a suitable beginner project: for one thing the creation of the chassis gave Yuta some issues initially, but then he discovered a sheet metal service, which was able to send him “precisely machined” aluminium sheet for his project, and this solved a number of problems. “I don’t think it would be easy to make it from scratch, as it would require a lot of tools and the number of parts is very large,” he notes. “However, you can find the 2DCAD [file] of the body on Hackaday. If you use an aluminium sheet metal service, you can reduce the difficulty of the work.”

A life changer

Pleasingly, Yuta’s project has brought people together. “The field robots are very eye-catching and provide an opportunity to talk to many people, including passers-by,” he notes. More than that, the project appears to have struck a chord with people and, when presented to the Japanese maker community, it became a “hot topic.” Interviews followed and his local government has agreed to support the project, and five additional units will now be built to mow vacant lots in the community. “Together with the two I have built so far, I will have a total of seven units. I feel that this project is definitely starting to change my life,” declares Yuta.

Yuta is now ramping up production of his robot mowers to help out 
local farmers
Yuta is now ramping up production of his robot mowers to help out local farmers

Japan is not the only part of the world with rice terraces and the inherent issues that rice farmers are facing, as other parts of Asia, where rice-eating is an important part of the culture, face potentially the same problems. Happily, Yuta has received well-deserved interest from potential investors, including “venture companies, mower manufacturers, and agricultural corporations. It would be great if this project becomes a business.” Ingenuity and resourcefulness at its best – we wish him well!

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The Magpi issue 133 cover

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