With the rip of a chain saw, a robot lumberjack is preparing to clear pastureland. Using coordinates captured by a drone, it’s on a mission to seek, find and destroy.
Researchers in Oklahoma are using unmanned ground and aerial vehicles as a wedded pair to attack invasive eastern red cedar trees, a scourge of Great Plains producers. As the technology unfolds, the framework carries a host of possibility for all areas of agriculture.
A 4'-long and 42"-wide unmanned ground vehicle (UGV) sits on the shop floor of the Oklahoma State University (OSU) Department of Biosystems and Agricultural Engineering, waiting patiently for a chance in the field. Reminiscent of a lunar rover, painted cowboy orange and built from 1" square tubing, it is the brainchild of OSU grad student and research engineer Collin Craige, designed and developed by him as a doctoral project. With a mechanical arm able to reach 3' beyond the frame, the 275-lb. vehicle is a lethal hunter, capable of finding, securing and slicing its prey in half.
Craige’s UGV hunts eastern red cedar trees, an incessant and costly nuisance species for Great Plains landowners. Initially brought to the Great Plains to create windbreaks and control erosion, red cedar has thrived and taken over ground as a water-sucking beast, reducing forage growth and boosting fire risks. Control costs can be a heavy burden on producers, sometimes nearing $200 per acre.
“Cedar is a big problem for producers, and it’s expensive to control and brings no financial return. It would be awesome if we could cut down cedar trees before they become a big problem,” Craige says.
“We brought cedar here, and it got out of control, kind of like kudzu in the South,” echoes Mike Buser, OSU ag engineer who oversees Craige’s project. “Just one cedar 12" in diameter can draw 40 gal. of water per day.”
Craige aims to use an aerial-ground vehicle combination to cut down saplings (2" to 4" diameter): “If this functions properly, we can make a bigger machine to handle larger trees. It’s too expensive to go big from the start.”
Craige has developed mapping software to work with a hectacopter unmanned aerial vehicle (UAV). The UAV will fly over a given pasture or field and transmit imagery and positional information (pitch, roll, elevation and more). The software will identify red cedar and produce a map of GPS coordinates for each tree. The hectacopter has autopilot and can operate in response to set waypoints.
“After the UAV is finished, we’ll go to processing,” Craige says. “We’ll visually check and make sure everything is correct. Then we take the data and go to the ground robot with something like a flash drive. Plug in and activate. The robot goes on its course using the coordinates as waypoints.”
However, Craige acknowledges the limitations of GPS. “The UAV can only pinpoint GPS coordinates to a certain degree. The ground robot has a camera and LIDAR system so it can travel to the waypoint and look for cedar. If it doesn’t see a cedar, it will send a message saying it can’t find the tree, and then go to the next waypoint.”
The UGV is electric, powered by two 12-volt, 120-minute batteries. Potentially, the UGV will recharge in the field through solar panels or return to a home base station.
DC motors operate a 60" grappling arm and clamp for tree felling, and a 0.25-hp motor powers a 14" chain saw. Craige is configuring the control system to operate the arm and chain saw from his laptop. After remote control testing, he’ll implement autopilot for autonomous testing.
The biggest challenge for Craige is keeping the components in unison while trying to maintain budget. A 1-gigahertz, credit card-sized computer (BeagleBone Black) runs the entire shooting match, controlling 10 motors and the actuators on the arm leading to the clamp and saw.
“It’s tough to push this little computer. If something malfunctions I’ve got a 275-lb. robot with a running chain saw,” he says.
Technological capability often moves too fast forcing Craige to adapt and reconfigure. In April 2017, he purchased an autopilot for the UAV and began work on the UGV. Months later, when he turned back to the UAV, the autopilot was already outdated. Multiple components of Craige’s system are open-sourced: schematics, drawings, code and the BeagleBone Black computer.
“The research arena is moving away from patents and shifting to shareware. We’re developing it and will allow someone else to make it better,” Craige explains.
Craige’s technological advances will have a direct application in 2018 research on automated contamination retrieval in cotton fields. “We may have a UAV fly over fields to identify contamination and note anything that isn’t cotton,” Buser says. “The UAV will send the location of potential contamination to a mobile app and if the contamination is small, such as plastic shopping bags, then we’ll send out an autonomous vehicle with an arm to suck up the plastic into an onboard storage container. The long-term goal is a swarm of these bots. The longer-term goal would be expanding bot capabilities to include weed removal.”
“Right now they’re looking at a prototype to control cedar trees with a chain saw, but we’d like to adapt the tech and remove plastic contamination from cotton fields,” says Ed Barnes, senior director of agricultural and environmental research at Cotton Incorporated. “If you’re already using the robot, go ahead and use it to get plastic out as well.”
Buser emphasizes cost when determining the potential of unmanned technology. “When you see these technologies, run an economic analysis to figure if they are justifiable,” he says. “Cost plays a big part of Collin’s proposal: He’s going to find out if the system is economically feasible.
“Farmers should keep watching. If a particular technology makes economic sense, then try it. If it doesn’t, hold off because things are changing fast,” Buser adds.