1980 - Volume #4, Issue #1, Page #05[ Sample Stories From This Issue | List of All Stories In This Issue | Print this story | Read this issue]
Drive Two Tractors Instead of One
A master/slave tractor control system developed in Denmark by Svend Aage Christiansen, Agricultural University, Copenhagen, permits the driver on the master tractor to control a slave tractor working immediately behind or offset to either side.
Distance between tractors and the offset angle are maintained automatically and the engine speed of the slave tractor is proportional to the distance between units. If the distance between tractors decreases to a specified minimum, or exceeds a pre-determined maximum, the clutch and brakes of the slave are activated.
The clutch and brakes of the slave tractor are also remotely controlled by the driver of the master tractor, and are automatically applied in case of certain other equipment failures or malfunctions. The gear shift, hydrauliclift and differential lock of the slave are also controllable from the master tractor.
A hydraulic motor, controlled by a 4-way solenoid valve, turns the steering wheel shaft of the slave tractor through an idler gear. Penumatic cylinders control gear shifting, differential lock and fuel cutoff to the engine. The fuel cutoff is spring-loaded so that when there is no air pressure, the spring will automatically stop fuel flow to the engine. Diesel fuel is also cut off whenever the control button on the master tractor is pushed; when lubricating oil pressure drops too low; when engine coolant temperature gets too high; or when the electrical system fails.
An inductive connection system is used to control the slave tractor. A horizontal loop coil located on top of the cab of the master tractor carries an alternating current which produces an alternating magnetic field that is picked up by three sensing coils arranged in a horizontal triangle on top of the slave tractor. The voltage induced in the front center coil on the slave tractor measures distance between the two vehicles, and the ratio of that voltage to the voltage picked up in the other two coils mounted slightly to the rear and to each side of the tractor measure the offset angle of the slave from the master tractor. Remote control signals are carried by an amplitude modulation of the exciting current.
Christiansen stresses that development of a master/slave control system requires particular attention to safety and the possibility of using the tractors separately. In fact, being able to use the tractors individually could be a prime advantage of buying a master/slave combination instead of a single larger tractor. For instance, if one machine in a master/slave team fails, the other could continue operating compared to halting all field work if a single large tractor or machine is down.
The master/slave system developed by Christiansen is not available commercially in the U.S. or Denmark.
For more information, contact: FARM SHOW Followup, Svend Aage Christiansen, Senior Lecturer, Dept. of Agricultural Engineering, Agrove 10, 2630 Taastrup, Denmark.
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