Building a seed-planting drone on a tight budget

Johnny Appleseed became an American legion in the first half of the 19^th century for his apple tree-planting endeavors. In the first half of the 21^st century, a group of nine SDSU engineering students are hoping to make tree planting a viable high-tech operation anywhere in the world.

They form a senior design team that is creating a seed pod drone and dispenser that is sponsored by Jerry Natzel of Owatonna, Minnesota.

Natzel thought of the idea after observing large-scale tree death on his 42 acres, but this project is intended to go well beyond the low rolling hills of Steele County, Minnesota. Each year, fires and floods wipe out thousands upon thousands of acres around the world, much of that in areas not well suited for manual reforestation efforts.

That makes aerial seeding via drones just the ticket, said Natzel, who intends to put the final product design on open source through the internet.

“You must remember drone seeding is not really new with regard to reforestation, but the drones being used at present are very expensive. The idea is that the drone could be built with products available in any developing nation,” said Natzel, a 1975 mechanical engineering graduate from SDSU. 

Hence the drone is being built with PVC pipe and an aim of making it reproducible for $3,000. It measures 5-feet, 6-inches from one side to the other, weighs just under 55 pounds and has a maximum motor thrust of 110 pounds.

Navigating construction turbulents

Cole Hulstein, an electrical engineering major from Sioux Falls, said most team members were attracted to the project because of the benefit it could bring to mankind.

But as with any worthwhile endeavor, team members have experienced their share of trials. 

None of them had previous drone experience. Natzel knew what he wanted the drone to perform, but the design was left to the students. So fall semester was spent researching — What is the optimal size? What are the optimal type and size of motors? How should the seeds be dispensed?

The internet helped. This is novel technology, but not unbroken ground, to borrow an agricultural phrase. Trevor Brezen, a mechanical engineering major from Savage, Minnesota, created a spreadsheet with 250 different motor possibilities. That was narrowed to 10 and eventually one, a 110-kilovolt, multi-rotor, brushless motor designed for drones.

Encapsulating the seeds in a nutrient-rich package, a key element for this technology to have life beyond a senior design project, is a crucial element.

Another team, which is composed of four mechanical engineering majors, undertook that task. They were looking to encapsulate the seeds into balls. But in late November, about a week before teams were to present their final designs to faculty, the drone crew learned the seed technologists had switched to a wafer or a miniature hockey puck.

The design team came up with the idea of using PVC pipe stacked vertically on a platform like a lazy Suzan. The pucks are loaded into the 12 pipes. Each time the drone flies over a predetermined GPS point, the dispenser rotates 30 degrees and releases a puck, ideally with enough speed to penetrate the soil.

A chance to rebuild

As of late March, that is untested technology, but students are confident they can combine lab-tested flight and seed-dispensing methodologies.   

Seed dispensing was tested using a drone borrowed from the SDSU Robotics Club and connected to an LED device. Each flash of the LED symbolized the dropping of a seed puck. All went well in that inside test, said Cris Hernandez, an electrical engineering major from Oakdale, Minnesota.

The same could not be said of a March 21 test of the drone in a field just outside of Brookings. The team was anxious to test its as-of-yet unnamed drone and didn’t give heed to outdoor conditions — the temperature was in the mid-20s, and the east wind was gusting to 20 mph.

The flight lasted long enough for the PVC pipe to become brittle, and the ground that was warm and soft earlier in the month had become cold and hard. “It was a sad day,” Hernandez said of the drone’s collision with the ground. The silver lining: the electronics survived, and the team was well versed in cutting PVC pipe.

“Measure twice, cut once,” said future mechanical engineer Justin Clarke, when asked to identify his most meaningful takeaway from the project.

A couple days after the parts were carried back to campus, a spring snowstorm closed campus. However, by March 26 the team was back in manufacturing mode with an aim to have a flyable drone by month’s end.

Like all senior design projects, the seed-planting drone needs to be ready to go by Engineering Expo April 23, which, appropriately, is just three days before Arbor Day.

The goal is to have a drone that can uniformly deploy about 200 seeds over an acre of land in under 10 minutes. That would also be about the life of the batteries, so it needs to have batteries that can quickly be exchanged. The team settled on lithium polymer batteries, which are typically used for drones. However, they are not quick-release batteries.

Consequently, team members used a 3D printer to build their own battery holders and made their own wiring connections.

The entire project has been a lesson in teamwork and communication, members said.

It could also be a lesson in accepting a challenge and literally seeing your idea take off.

Team members, hometown and major:

Adam Breuer, Madison, mechanical engineering

Trevor Brezen, Savage, Minnesota, mechanical engineering

Daniyal Khurram, Pakistan, mechanical engineering

Justin Clarke, Slayton, Minnesota, mechanical engineering

Alison Hall, Minnetonka, Minnesota, mechanical engineering

Landon Schulte, Geddes, mechanical engineering

Cole Hulstein, Sioux Falls, electrical engineering

Cristian Hernandez, Oakdale, Minnesota, electrical engineering

John Harmon, Rochester, Minnesota, electrical engineering