By Jack Desbiolles, Agricultural Machinery R&D Centre, University of South Australia

Implement guidance is still an emerging technology in North America, but it is being utilized in other parts of the world to improve agricultural production. This recent article from Ag Contractor & Large Scale Farmer looks at some of the considerations for adding implement guidance to a farming operation. 

Accurate sub-inch RTK guidance of the tractor and stable implement tracking are both necessary to achieve guided row sowing. Accurate tractor guidance increasingly uses sophisticated ‘terrain compensation’ software to accurately steer the tractor hitch along the guidance path. Different towed seeder bars have different tracking abilities, so accurate auto-steering of the tractor alone may not always be sufficient. The stability of the seeder is influenced by the forces applied onto the bar in relation to the tractor pulling force. The forces applied on the seeder bar include:

• forces at the implement hitch, including tractor pull;
• the weight of the seeder bar;
• tyre reactions, including rolling resistance;
• opener draft, penetration and side forces;
• drag forces from a tow-behind air-cart.

Design Principles for Good Tracking

A balanced bar design is the first requirement for a good tracking stability. This includes symmetrical layouts of both openers and wheels, and a uni-form distribution of the seeder bar weight, including over the wing sections.

An air-seeder fitted with a ProTrakker steerable draw-bar hitch for active implement guidance.

Where the wheels are positioned relative to the tines can improve or worsen tracking. For example, working depths will be affected if they ride into the fur-row or over soil throw ridges during skewing. Wide tires placed on a walking beam are typically least sensitive to the above. A longer A-frame gives an advantage by stabilizing drift at smaller skew angles. A common rule of thumb is that the draw-bar length should be half the implement width to give sufficient restoring power to rig-id frame wheels.

Constant tillage depth across the bar is critical. It is best achieved by openers that follow ground contours. This is especially important on wider, less-stable bars and undulating land.A poorly set-up bar or inadequate floatation in soft soils can create a constant force imbalance that causes systematic drift to the left or right. You can check the extent of systematic drift by sowing up and back on flat land and checking for alternate ‘closed’ and ‘open’ spaces between adjacent passes.

To maximize the stability of a tine seeder bar, avoid steep narrow openers because they absorb some of the bar weight by generating an upward soil reaction, especially when dry seed-ing in hard soils. Conversely, shallow rake angle points (less than 60 degrees) with optimum wear at the cutting edge can both add to the existing frame weight and decrease the seeder draught requirement.Avoid castor wheels because they take on the weight of the frame but do not help restore tracking.

A fully mounted air seeder box placed near the rearmost supporting (rigid) wheels of the seeder bar and openers placed close to the towing tractor can improve tracking. A tow-between air-cart adds another ‘link’ to the tow-chain, and places the implement further behind the tractor. On side slopes, this can increase the extent of implement drift down-slope, especially when the air-cart is near-empty.

On the other hand, a tow-be-hind air-cart acts as a damp-ing force on the flat. It tends to reduce the amount and suddenness of random implement drift by decreasing the impact of a force imbalance. However, when operating on a side slope, the tow-behind cart drag force increases the downslope-pull on the seeder which increases its skew angle. Twin axle air-carts with steerable wheels can minimize this impact relative to single axle carts.

Implement Guidance

Guiding implements to targeted pathways gives the most accurate implement control. Implement guidance falls into two categories: Passive guidance: These systems combine GPS data from mounted receivers on both the tractor and implement to auto-steer the tractor such that the implement always remains on the intended guidance path.

This is the cheapest option but requires the tractor to move on and off track to keep the implement on the targeted path.It is best suited to gradual and systematic drift so it is combined with a stable seeder bar to minimize transient and sudden random drift. Example technologies include John Deere IGuide, Trimble TrueGuide.

Active implement guidance: These systems guide the implement independently of the tractor. Active implement guidance is more expensive but the extra accuracy may be warranted to improve cropping returns.

This technology is based on dedicated ‘auto-steering’ systems for the implement, of which there are two main types:

• A) Hitch correction is where the tractor draw-bar or the implement hitch tongue is hydraulically adjusted side-to-side to guide the implement. A system controller reacts to GPS receiver position data from the implement itself or to data from a stubble row or furrow/ridge tracking sensor fitted to the implement.
  This approach adjusts implement position up to a maximum offset but without correct-ing any skew angle. With large offset drift (such as on side slope), this approach may not always be sufficient. Example technologies include SunCo Farm Equipment AcuraTrak guidance system, John Deere hitch-based iSteer, MBW ProTrakker Guidance Systems (GPS, Side-Hill Sensor and SonicTrakk), Seed Hawk SBR technology, SeedMaster SmartHitch and AgriParts I-till.
• B) An implement steering kit actively directs the implement frame over the guidance path using steerable wheels or disc blades to generate a corrective force. Their action is con-trolled by GPS position data from both the implement and the tractor.

This approach corrects an implement skew angle in order to track squarely behind the tractor over a common guidance path. Provided they achieve sufficient penetration, piloted disc blades can generate larger restoring forces than steerable, surface running wheels. Example technologies include John Deere wheel-kit iSteer, Orthman Agriculture Shad-ow Tracker and Tracker IV.

To read the full article, visit www.agcontractormag.com.