April 2021
By Eric Buchanan, Renewable Energy Scientist
The Cowbot is an autonomous mower being developed to control weeds in cow pastures at the WCROC. The project is a collaboration between the WCROC, The Toro Company, and the U of MN's College of Science and Engineering’s Robotic Sensor Lab.
The project began with Toro converting one of their diesel turf mowers to run with an electric motor. Toro also replaced the deck mower with a flail mower, a better choice for pasture weeds, and made some other changes to make the mower ‘drive by wire’. For example, the mower was originally designed with a standard manual steering mechanism, but in order to be steered by a computer, called drive by wire, an electronic actuator was added to convert a steering command into actual movement of the steered wheels. Several other changes were needed to adapt the mower to computer control and provide safety features like bumpers around the robot to disable it if it were to run into something.
Post-docs and graduate students working under the direction of Dr. Volkan Isler, a Professor with the U of MN's College of Computer Science Department, have been developing the control and navigation code to allow the Cowbot to operate autonomously. The approach has been to define the perimeter of the area to be mowed by entering GPS coordinates for the corners. This can be done by direct entry into the onboard laptop or by manually driving the perimeter. The control system then calculates a path to mow the selected area including turning around at the end of each row. The Cowbot uses differential GPS for navigation which means there is a GPS receiver on the Cowbot and a second one on a tripod set up in the pasture. This improves the accuracy of a GPS system down to the centimeter level. Other sensors include Inertial Measurement Units (IMU), to monitor the mowers orientation, cameras, to monitor weeds, and LIDAR, which can be used to monitor the terrain and detect obstacles. Essentially there are two basic systems needed to make the Cowbot autonomous: navigation to define the path related to the environment, and control to interface with the mower and keep the mower on the defined path.
One project goal is to power the Cowbot with solar energy. Towards that end, a cargo trailer was converted into a solar charging station that can be parked near the pasture and used to recharge the mower’s batteries. Ten solar panels were installed on the trailer roof using drawer slides which allow panels to extend out on both sides of the trailer and also to be secured within the roof boundaries for highway travel. A charge controller, power inverter, and battery bank are all contained within the trailer along with a level 2 car charger used to charge the Cowbot. The Cowbot can mow for 2 to 3 hours on a charge and the charging trailer can easily replenish that charge on a typical summer day.
Testing the Cowbot began in the usual way for new research projects: in fits and starts. However, like a toddler learning to walk, progress has been steady and the Cowbot can now reliably mow a pasture without stumbling while eliminating, essentially, all weeds in the mowed area. Final testing will be done this summer comparing the Cowbot to its human driven tractor competition so stay tuned!
A local PBS show, “The Prairie Sportsman”, came to the WCROC last September to interview team members and get video of the Cowbot in action. They produced a nice segment explaining the project which can be viewed online.
This project was supported by The Minnesota Environment and Natural Resources Trust Fund* as recommended by the Legislative ‐ Citizen Commission on Minnesota Resources (LCCMR).
* The Trust Fund is a permanent fund constitutionally established by the citizens of Minnesota to assist in the protection, conservation, preservation, and enhancement of the state’s air, water, land, fish, wildlife, and other natural resources. Currently 40% of net Minnesota State Lottery proceeds are dedicated to growing the Trust Fund and ensuring future benefits for Minnesota’s environment and natural resources.