|Be aware that problems may arise when expanding your use of precision technologies.
To achieve the sub-inch steering precision required for strip-till and controlled traffic, farmers rely on real-time kinematic (RTK) auto-guidance to take the wheel. Even though the technology is becoming more trouble-free, farmers can still find themselves frustrated in the midst of a busy planting or spraying season.
"Sometimes farmers find their A-B lines don't line up precisely for subsequent operations," says University of Kentucky ag engineer Scott Shearer. "This can become an issue if you want to run in the same wheel tracks for planting and spraying. If you deviate, you can run over the standing crop and miss strips with the sprayer. At harvest, if you are off more than 4", you could have yield loss."
The problem usually results from using RTK systems set to the relative mode, multiple RTK systems or different steering controllers in machinery. Solutions range from recording a new A-B line with your sprayer to buying all your components from one manufacturer.
If you are mixing manufacturers, ask which coordinate system the new steering controller uses, Shearer advises.
"Deviations between two coordinate systems can be a concern when switching between guidance systems, especially in fields of 3,000' or more," he says.
Portable base stations can be problematic since they must be placed for 24 hours to set an absolute reference.
"Otherwise, you get only a relative location," Shearer says. "So when the base station is returned to the field, you may not be lined up with the original A-B line."
A permanently mounted base station, or access to an RTK network, eliminates that problem.
"Before you buy an RTK system, ask your dealer if you will have access to a network signal," says Kyle Collins, a marketing rep for John Deere Ag Management Solutions.
Where Jim Ellis farms with brothers Mike and Bob, in Shelby and Henry counties in Kentucky, no network is available, and all of their scattered fields can't be reached by one permanent base station.
"One solution is to drive a stake to mark an absolute base station location for each field," Jim says. "Then, mount the base station on that stake when you get to the field, and manually input the coordinates."
The Ellises have another solution. They place several base stations—probably a total of three—on towers to create a local network.
If you're after sub-inch precision, you may need to steer your implements, as well as your tractor. "Even on undulating terrain, manufacturers can guide a tractor within a few inches, and it should run in the same tracks again and again," Shearer says. "But implements don't necessarily follow the tractor with the same accuracy." FJ
How Distortion Happens With Auto-Guidance real-time kinematics
One of the reasons it's difficult to combine real-time kinematic (RTK) auto-guidance systems from different manufacturers is that manufacturers record locations in different manners.
"Some manufacturers build steering controllers that operate on geographic coordinates—latitude and longitude—and some on Cartesian coordinates," says University of Kentucky ag engineer Scott Shearer. "If you take an A-B line recorded in geographic coordinates and project it onto a system of Cartesian coordinates, there will be slight differences that translate to the field when using multiple guidance systems."
The difference becomes much greater in more Northern regions. "It usually is small in Texas but huge in Canada," says Clay Mitchell, a Buckingham, Iowa, farmer who has worked with RTK auto-guidance since 2000. "Setting the A-B line in the middle of the field can reduce the error, but there's no easy way to share A-B lines between different brands of equipment."
Other problems can occur when laying out your A-B lines, Mitchell notes. "Always make your A-B lines in the same direction," he says. "In some machines, an A-B line made from north to south will create different guidance lines than one made from south to north."
- December 2008