Robotics club builds autonomous sprayer

Connoisseurs say a good wine can’t be rushed. Perhaps the same could be said about a good autonomous vineyard sprayer.

Since spring 2022, the SDSU Robotics Club has been working on a project for alum Jerry Natzel of Owatonna, Minnesota, to build an autonomous sprayer for his vineyard. The project’s history predates that. But by late April, the club hopes to have all the bugs worked out of this bug-spraying machine.

That will certainly make Natzel, a 1975 mechanical engineering graduate, happy.

He operates a vineyard as a part of his 42-acre farm that has been in the family since 1917. A few years back, the vineyard was hit with an infestation of Japanese beetles that killed numerous plants. “We were spraying about every seven days” using sprayer mounted on a Bobcat, said Natzel, who was concerned for his health.

“It took us three years to understand the beetles and how to control them,” said Natzel, who noted he still must spray the beetles as they crave new plant growth.

Natzel, who spent his career as a design engineer and holds several patents, said he first dreamed of a drone sprayer. However, FAA regulations kept that plan from taking off. 

A COVID era project

Therefore, he spent two years creating a proof of concept for a ground-based autonomous sprayer. He created sketches using the frame of a Ryobi zero-turn lawnmower for its base. Natzel initially pitched the idea as a senior design project, but it deemed as a better choice for the robotics club.

He submitted the information late in fall semester 2021. The following semester the club was anxious to tackle a NASA design project, but NASA still had COVID restrictions in place that eliminated the possibility of qualifying a large team to a NASA contest. Because the project was a good fit for the club and it was funded, it was an easy decision to instead undertake the project, adviser Jason Sternhagen said.

Nothing has been easy since, but the hours of labor has certainly been worthwhile, according to project manager and mechanical engineering major Jonah Coffel.

He is one of six members of the current team, which also includes mechanical engineering majors Devin Hemmelman, Draix Wyatt, Cherish Stern and Haley Evenson and electrical engineering major Tyler Loecker.

None are computer science majors, but many were taught SolidWorks, a computer-aided drafting software, their freshman year, Coffel said.

Coding project’s biggest challenge

Club members were able to take Natzel’s sketches and produce a design using a standard pump motor, a 25-gallon tank, a metal shell and easily accessible electronics to build the sprayer in the 2022-23 school year. They later switched to polypropylene tubing, the type of plastics used in food processing operations because it doesn’t break down.

But the students found the biggest challenge to be in coding for autonomous operations.

Coffel, who became the project manager at the start of the 2023-24 school year, said, “The trickiest part is the coding if it’s not working. Mechanical failures you can look at it and see the problem. Computer coding is harder to diagnose. The past year or so has been focused on the coding.”

Coffel explained that the battery-powered servos and servo controls that came with the lawn mower were adapted to the robotic sprayer. “Mapping servo outputs to the sprayer’s radio-controlled device has been challenging but necessary because the sprayer needs to be able to move quickly when not spraying,” he said.

ArduRover Mission Planner was the software used to process GPS and compass data as well as adjusting the throttle for left and right turns. In addition, Arduino software was used to measure the different voltage signal values to make they are in the right range.

“The arduino is an additional layer of safety that can shut off the robot if need be,” Coffel said. Because the mechanics of the sprayer is still a zero-turn mower, it was challenging to write a code that would adjust to the sharpness of the turn that is required, he said.

“What is coming out of the microcontroller has to match what the mower is looking for,” Sternhagen, an electrical engineering research associate, said.

A labor of love

For the past four semesters, students have been putting in six hours per week — two-hour sessions on Mondays, Thursdays and Sundays. It’s a labor of love. While Natzel got a $9,000 grant from the USDA’s Sustainable Agriculture Research and Education program as well as putting in “a bunch of my own money,” that only covers equipment and supplies.

The students receive no pay or academic credit. However, it is a chance to socialize. “I enjoy it. It’s a lot of fun,” Coffel said.

They also will enjoy delivering the finished product to Natzel’s vineyard. He was on campus in April for Senior Design Day, where the project was on display. On Feb. 5 the sprayer completed its first fully autonomous test when students coded a path for the robot to take around the engineering buildings on campus, club president Hailey Gruber said.

In addition to a photo op outside the Campanile, the outdoor outing gave students an opportunity to learn what needs to be finetuned.

Principal among that was recalculating the GPS parameters to the right values. “GPS should be accurate to within a couple of inches, but sometimes we’re getting readings that are off a couple of feet, which would put us in the vines,” Sternhagen said. Finetuning also needed to be done to steering rates and speeds.

In addition, some safety features needed to be added before the sprayer was turned loose in the vineyard. “For example, if it has poor communications with the remote, you might have it shut off, or if there is too much GPS or compass variance, you might have to shut it off,” Sternhagen said.

Students’ benefit: World of experience

Coffel said, “The final test will be when we bring it to the vineyard and spray it without crashing into anything.”
Sternhagen had confidence. “It will. It’s just a question of when and how. The fact we are driving autonomously means we are getting very close.”

While the robotics club has other projects, such as building combat robots for collegiate contests, the sprayer has been a different animal.

Coffel said, “A lot of us have never seen a full project like this from start to finish. We are getting a lot of experience. We’re mostly mechanical engineers. But this has given us experience in mechanical, electrical and coding. The experience of working various coding programs will help us in the future.”  

Natzel, meanwhile, is excited to see a finished product, not only for what it will mean to his health, but also because of the interest he expects it to create in the industry.