You could pay for the most accurate satellite signal corrected with a ground station, and your tractor could still waver a foot or two off line. That’s because many other factors influence pass to pass accuracy. John Deere has an accuracy equation that looks like this:
AutoTrac accuracy = GPS signal accuracy + AutoTrac software type + implement set-up + vehicle set-up + steering vehicle kit type + tracking mode + field/ soil conditions
You may find you can increase accuracy significantly by taking care of some of these other factors before investing in a more accurate signal. While this information comes from John Deere, it applies to any system. Here are more details for each:
performance of the AutoTrac system is improper implement setup. It is best to compare AutoTrac performance of the vehicle alone to when it is attached to an implement. For the best accuracy, the implement must pull straight and level behind the vehicle and all parts must be in good working condition. When using a three-point-hitch mounted implement, sway blocks on the vehicle should be set to limit the free travel of the implement.
From John Deere: Proper vehicle set-up is crucial to the performance of AutoTrac. This includes making sure the vehicle is ballasted with increased weight on the steering axle to improve steering authority and making sure the sway blocks are set appropriately. Along with increased ballast, it is important to remember that AutoTrac performance will vary by platform due to inherent vehicle design differences. Another vehicle factor that affects performance is speed. Generally, the higher the speed, the less accuracy an operator will experience.
STEERING KIT TYPE
If you have an integrated AutoTrac that taps right into the hydraulic steering system, this will provide more accuracy than a kit that attaches to the steering wheel — either by a gear kit on the steering shaft (such as John Deere’s AutoTrac Universal (ATU) kit) or by a rubber friction wheel on the steering wheel.
The John Deere website says: While performance can be similar between a properly set up ATU kit and an integrated kit, testing has show that total system error may be greater with the ATU kit than with the integrated kit. Operators may notice delayed line acquisition and higher off-track errors with the ATU kit. Additionally, an ATU kit on a 2WD machine may have even less accuracy due to less steering authority on the front end. For maximum accuracy, both the integrated and ATU need to have sensitivities properly set-up and monitored for field conditions.
STRAIGHT TRACKS ARE MORE ACCURATE
If you are going up and down the field in straight lines, your tracking will be more accurate. If you’re doing a lot of curves, John Deere provides these pointers to improve accuracy:
A vehicle with an integrated AutoTrac steering kit is more accurate than a vehicle with the AutoTrac Universal steering kit.
Slower speeds are more accurate than faster speeds.
Gentle curves are more accurate than tight turn radius curves.
GreenStar 2 curves are more accurate than the Original GreenStar Display curves.
FIELD AND SOIL CONDITIONS
From John Deere: The environment in which the vehicle is operating is one of the most overlooked factors that affect the performance of the AutoTrac system. For example, loose soil conditions can reduce the effectiveness of the system because traction is lost.
Finally slope of the land plays a key factor in performance. Machine and implement drift can occur in these conditions when the machine slides down the slope while trying to operate AutoTrac.