Automatic steering systems save time, fuel and costs by reducing overlaps and improving overall accuracy.

Moreover, unlike an operator – they don’t get tired.

But, until quite recently, this extra precision cost from £10,000 to £20,000, and usually came with a vehicle attached to the integral system.

Now, however, there is a range of lower cost, retro-fit units that steer the tractor by either replacing the steering wheel, turning the existing wheel or by tapping into the hydraulic steering system.

Costing from £5000 up to £8800, the retro-fit units offer pass-to-pass accuracies from +/-15cm (8in) to +/-30cm (12in).

This may not appear that precise but it is, arguably, better than many operators can achieve.

They can also see in the dark and through clouds of dust.

They not only cost less than the integral system, they are also more versatile.

As well as fitting various different makes and models of machines, they can also be swapped between vehicles.

Just like the integral units, these assisted-steering devices guide vehicles in either straight or curved parallel lines using signals from a GPS satellite network, plus a differential or correction service to improve precision.

Suppliers claim the biggest potential to make savings comes from the improved accuracy of tramline placement.

Accurate guidance and steering when drilling will improve precision by between 5% to 10%.

This then reduces all inputs by the same amount over the season.

For work outside tramlines on grassland or when cultivating, the systems also prevent misses and overlaps.

And when it comes to harvest, switching the system to the combine ensures the header not only works at full capacity, but setting up lands exactly parallel to each other cuts the amount of shortwork, again saving time.

John Deere autotrac

Indeed, the savings accumulate to such an extent that John Deere says its new Universal AutoTrac system can almost pay for itself in just one year on a typical 500ha (1250 acre) arable unit (see costs box).

John Deere is the latest firm to now offer an entry-level, retro-fit steering system.

The unit is not only available for fitting to a wide range of Deere’s own models, but also many tractors and combines from other manufacturers as well.

After removing the steering wheel the Deere system uses a splined boss to clamp onto the steering column.

A chain connected to an electric stepper motor provides positive drive to the steering.

Swapping between vehicles is said to take experienced users about 30mins.

The firm’s own StarFire service provides the differential correction signal.

An entry-level package, including the subscription-free SF1, providing an accuracy of accuracy of +/-30cm (12in), costs £8800.

A more accurate SF2 system which will operate at +/-10cm (4in) is available for an extra £4100.

At the headland operators need to steer the tractor to within 40% of the distance from the next bout at an angle of no more than 45 before it will resume auto-steering.

Trimble Ez-steer

An interesting alternative is the Trimble EZ-Steer from Precise-Solutions, which simply bolts to the steering column and uses a soft rubber wheel to turn the steering wheel.

Although the actual steering unit is priced at just £2650, it must also be connected to the firm’s £2250 EZ-Guide system.

It is claimed to work to an accuracy of between 15cm (6in) and 30cm (12in), and uses Trimble’s own receiver to acquire the GPS signal. EZ-Guide uses the free EGNOS differential signal.

At the headland operators resume steering, following guidance from a lightbar.

When the tractor is within 1.8m and at an angle of 15 the system can resume steering automatically.

Transferring the unit between vehicles is said to take just a few minutes.

Outback e-drive

Instead of using the steering wheel and column, the Outback E-drive system plumbs into the vehicle’s hydraulic steering circuit.

While the unit will fit to a wide range of vehicles, it is now the preferred system for Claas tractors, available through its dealers with back-up and support from Soyl.

It costs 5300 for the steering, but requires the 2500 Outback unit to provide the signals.

E-Drives offers an accuracy of +/-15-30cm (6-12in), using the EGNOS correction service.

It includes software, which compensates for any brief losses of signal by providing its own correction for the local area.

At the headland the tractor needs to be within 3.6m of the next bout before auto-steering is reactivated.

It works by tapping into the steering’s plumbing and timing how long the valves on each side stay open.

From this it determines the oil flow, which is then used by the system’s computer to calculate the current steering angle.

For this reason it is more difficult to switch between vehicles.

fwmachinery@rbi.co.uk