19 January 2001

On course for moreoutput?

At £30,000 Trimbles AgGPS

Autopilot automatic tractor

steering system is not cheap.

But, with its claim to boost

outputs by up to 30%, it might

be a viable option. Andy Moore

takes a closer a look

HAS Trimble achieved the ultimate? The company has developed a guidance system which automatically steers tractors within  20mm accuracy, reducing driver fatigue and boosting productivity.

Developed over four years at Trimbles US base at Sunnyvale, California, AgGPS Autopilot uses "centimetre level" GPS technology.

"Autopilot enables the operator to keep his hands completely free from the steering wheel, allowing greater attention to be paid to monitoring and controlling machines and implements," says Neil Ackroyd of Trimble, which has its UK headquarters at Hook, Hants. "Autopilot can boost machinery productivity by up to 30% by steering accurately. This eliminates human error and allows faster forward speeds and workrates."

The system, believes Trimble, should appeal to large root crop and vegetable growers seeking a more efficient and accurate way of operating inter-row cultivators, drills and harvesters.

"Autopilot is based on existing GPS technology used for recording functions, for example soil mapping and yield monitoring," says Mr Ackroyd. "The driver first records a field map by driving around the field boundary and then enters the implement width. A monitor displays the shape of the field with the intended bout widths to be covered."

DGPS signals are picked up by an AgGPS RTK receiver fitted on the cab and then processed through an in-cab terminal and Navigation Controller.

"The controller checks the exact position of the tractor 20 times a second against the planned path previously recorded on the computer," he says. "A highly sensitive sensor fitted to the tractors steering arm monitors the deviation of the front tractor wheels through signals sent by the Navigation Controller."

Complicated? It gets easier.

The Navigation Controller then calculates the optimum path for the tractor and implement down the length of field which is displayed on the monitor providing two views.

Similar to a flight simulator, the Perspective View displays the intended path of the tractor, while a Plan View shows an overhead picture of the field and the area covered.

Digital signals from the Navigation Controller are converted to analogue and sent to a proportional valve plumbed in parallel to the tractors regular power steering control valve.

It is then, says Mr Ackroyd, that the magic really starts, with Autopilot automatically guiding the tractor through the machines power steering system.

Autopilot is designed to compensate for the tractor working on steep ground and varying forward speeds; GPS signals can be interpreted up to 600m/s, says Mr Ackroyd.

Should the tractor approach a telegraph pole, an unsuspecting farm animal, person or parked Land Rover, Autopilot can be disengaged by manually turning the steering wheel. If such close encounters arise, the system activates the tractors regular power steering control valve, as would happen if the cab doors were opened or the operator became unseated.

"Autopilot is even sufficiently clever to steer the tractor at headlands, although operators with a nervous disposition may prefer to take the helm to make tighter turns," says Mr Ackroyd. "When the tractor is a few metres away from the new bout, Autopilot can then be re-engaged. And when the driver packs up work for the night, the Navigation controller remembers the exact location where work finished so the operation can recommence the next day."

But the technology does not stop there. Autopilot is also designed to operate in dark, foggy or dusty conditions, enabling the operator to work longer hours and the tractor and implement to perform a more efficient and accurate operation in the field.

In poor visibility, Autopilot can be operated with a lightbar which illuminates red and green lights in series, to let the driver know the correct direction to manually steer the tractor.

"Autopilot has been successful with vegetable and root crop growers operating large tractors and cultivators in America where the system has been in operation for the past six months," says Mr Ackroyd. "The main challenge will be to tailor the system to suit smaller European growers where economies of scale are less and farming practices are different."

In addition to cultivation kit, he believes the system could be used with cereal drills and spreaders for reducing inputs such as seed, fertiliser and sprays through its ability to minimise overlap and skip.

Autopilot can be fitted to larger Case MX Magnum and Caterpillar Challenger tractors, although there are plans to introduce the system to lower horsepower machines in the future. &#42

Autopilot comprises Trimbles AgGPS GPS receiver (right) and a AgGPS70 remote display (left) which can be used in combination with an AgGPS 170 field computer.

Dead straight lines and extra productivity… Autopilot can be fitted to larger Case MX Magnum and Caterpillar Challenger tractors.