GPS on Tractors for Precision Farming

Commercially available GPS receivers provide you with 3 meters to 5 meters accuracy. That’s roughly a little more than 3 yards to 5 yards (add 3 inches per yard to get a closer number). However, this is not good enough to let the tractor drive itself. You would also miss soil areas where adjustments in chemical application or planting need to be done. There is a way around this problem: RTK or real time kinematic GPS systems can provide sub-inch accuracy. The precision can be up to a centimeter. A base station sends out a corrective signal that can be used by several moving stations to arrive at accurate positions.

What you need is one such set up and a GPS-based tractor auto–steer set up per tractor that you want to run. The accurate readings obtained by these on-board GPS are used to steer the vehicles. The auto steer system also takes the attitude of the vehicle (roll, yaw and pitch angles) into account so that undulations in the field are handled.

The RTK-based GPS systems can compensate for atmospheric delay, orbital errors, and other variables in GPS geometry. Because of the accuracy that can be derived, it is used by engineers, topographers, surveyors, and others in applications in civil engineering and dredging, and now in precision farming. RTK systems use the Wide Area Augmentation System (WAAS) to generate initial corrections. The base station receives the corrections transmitted by the WAAS system and correct them further. Typically you can get 1.0 metre (3 ft 3 in) laterally and 1.5 meters (4 ft 11 in) vertically correct data. RTK provides differential corrections to produce the most precise GPS positioning. Typical corrections derived by current RTK systems are up to 1 cm. System examples can be found from John Deere, Trimble, AutoFarm, and Garmin. John Deere, for example, provide you with precise corrections and charge a monthly subscription for it. Sauer-Danfoss is an example of a company who provide steering subsystems. If your skills include the ability to assemble systems, this could be a good source.

Auto-steer systems use the corrected GPS signals from base stations that are transmitted to moving tractors. These tractors are then steered automatically to follow a path. The movement commands take into account the roll, yaw, and pitch attitudes of the vehicle. The outlay for equipment may vary over a wide range from about $10,000 to $30,000. Good equipment is available in the $20,000 to $30,000 range. Hopefully we have provided the necessary pointers to launch you in the right direction.

You can view couple of examples in the following image section.