AutoTrac System Accuracy

Accuracy Equation

AutoTrac System Accuracy = GPS Signal Accuracy + Steering Kit Type + Vehicle Setup + Tracking Mode + Implement Setup + Field/Soil Conditions

GPS Signal Accuracy

The starting point of any system is the receiver. Guidance begins with that receiver receiving raw GPS signals from satellites and a differential correction to that signal. Raw GPS tells the receiver approximately where it is, and the differential correction signal hones into its actual position. Fifteen-minute pass-to-pass accuracy is the range of accuracy that a customer will experience in typical conditions. For example, the SF1 signal has a 15-minute pass-to-pass accuracy of 33 cm (13-in.) 95% of the time. This means that the accuracy of a StarFire iTC with SF1 signal will show a location 33 cm (13-in.) or less to its actual position 95% of the time and 16 cm (6.5-in.) or less 68% of the time. The signal accuracy that the customer is using helps determine the accuracy they can expect.

Steering Kit Type

Steering Kit Type refers to which type of AutoTrac vehicle kit, ATU, or integrated AutoTrac steering kit is being used on the machine. While performance can be similar between a properly set up ATU kit and an integrated kit, testing has shown that total system error may be greater with the ATU kit than with the integrated kit. Customers may notice delayed line acquisition and higher off-track errors with the ATU kit. AutoTrac universal kit on 2WD machines may also have less accuracy due to less steering authority on the front end. For maximum accuracy, both the integrated kit and the ATU kit need to have sensitivities properly set up and monitored for field conditions.

Vehicle Setup

Proper setup of vehicles is crucial to the performance of AutoTrac. This includes making sure the vehicle is ballasted by increasing weight on the steering axle up to, but not exceeding the weight capacity of the tires to improve steering authority. Please note that if additional attachments, such as side or front mounted saddle tanks, are installed, ballast can be affected. Additional attachments need be taken into account when selecting proper ballasting. Along with increased ballast, it is important to remember AutoTrac performance will vary by platform due to inherent vehicle design differences. For example, track tractors give an operator very good accuracy control, but a sprayer or 4WD tractor loses some of that accuracy control due to differences in drive train and steering response. Ground speed also affects performance. With the ability to operate at higher speeds, operators need to remember higher speeds impact performance. Using AutoTrac above 19 km/h (12 mph), especially when using Curve Track, will give accuracy on the ground that may be less than desirable for some row-crop applications.

Please refer to machine operator’s manual for complete recommendations on ballast.

Tracking Mode

Tracking Mode refers to the AutoTrac mode being used with the system (Straight Track, Circle Track, or Curve Track). With Straight Track and Curve Track, multiple A/B lines can be set based off the initial track and implement width. In Adaptive Curve mode, multiple Adaptive Curves can be recorded and stored on the display. While John Deere Curve Track software "smooths" the track to record a better curved line, there is still the opportunity for greater error on the ground with Curve Track than in both Straight Track and Circle Track. Once all tracks have been laid and the vehicle is operating in repeat mode, the vehicle still has the possibility for increased error due to the machine characteristics while navigating through a curve pass. GPS Signal Accuracy, Vehicle Setup, Implement Setup, and Field/Soil Conditions still affect the accuracy equation.

Implement Setup

A common cause of unsatisfactory performance of the AutoTrac system is improper implement setup. It is best to ensure AutoTrac performance of the vehicle alone is sufficient prior to attaching to an implement. Once the vehicle is proven to sufficiently track up and back on the same line, connect the implement to ensure overall system performance. The implement must pull straight and level behind the vehicle, meaning all parts (shanks, planter units, etc) need to be spaced appropriately and should not be damaged or worn unevenly from one side to the other. A good exercise is to measure from the center line of the tractor to each individual engagement point to ensure the implement is symmetrical. This helps avoid uneven side-to-side draft on the tractor. When using integral planters on flat and level ground, sway blocks should be set to allow the free travel of the tractor separate from the implement, approximately 3.8—5.0 cm (1.5—2.0 in.) of travel without allowing the lower arms of the three-point to come in contact with the tires. Sway blocks may need to be adjusted more tightly to accommodate side slopes and other side draft operations to achieve desirable implement performance.

Field/Soil Conditions

The environment in which the vehicle is operating also affects the performance of the AutoTrac system. For example, loose soil conditions can reduce the effectiveness of the steering system because traction is lost. Firm soil conditions can cause uneven loads in high-draft applications. Differential Lock can provide some compensation to lost traction and uneven loads or terrain, depending on the situation and operation being performed. However, it must be used at the operator’s discretion and only if the operator feels it is beneficial to the particular operation. Slope of the land can also play a key factor in performance because the machine or implement may slide down a slope while trying to operate AutoTrac resulting in a motion called ‘crabbing’. Currently, AutoTrac does not compensate for crabbing along a slope.

There are many factors affecting accuracy and performance of the GreenStar AutoTrac system. It is imperative to understand these factors and what can and cannot be adjusted to achieve optimal performance. For more information on expected accuracy, please visit the accuracy calculator on www.StellarSupport.com.

Points To Remember

It is very important to remember:

• Receiver has to go through a warm-up period upon start-up.
• Vehicle is setup properly (ballasted according to vehicle operator manual, etc.)
• Implement is setup to run properly (wear parts such as shanks, shovels, and sweeps are in good working condition and correctly spaced).
• Understand how field/soil conditions affect system (loose soil requires more steering than firm soil, but firm soil can cause uneven draft loads).