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In a series of field experiments we measured the stresses in sand beneath the rubber belt of a prototype belted tractor and beneath single front and dual rear tyres of a radial ply type equipped tractor, using earth stress cells installed beneath the belt or tyres. The stress in the sand increased with increasing axle load for both belt and tyres. The peak vertical stress beneath the belt was about 6 times the average stress calculated as total weight divided by total area of belt. Depending on axle load, the stresses near the soil surface were similar beneath belts and tyres, whereas at 35 to 45 cm depth the stresses beneath tyres exceeded those beneath belts. Stresses beneath individual wheels on the track bogey could be distinguished near the soil surface, but at 35 to 45 cm depth only the average stress could be identified.

For a number of years during cotton harvest in California's San Joaquin Valley, a decrease in cotton plant height was noted in the rows adjacent to the traffic path of the tractor. Studies which measured soil compaction and cotton yields for several tractor configurations were conducted over two growing seasons. The first year's study consisted of sandy and clay test plots with four tractor configurations. The highest yield was with a conventional wheel tractor with dual rear tires and front wheel drive. The plot yielded 27% more cotton in the sandy field and 14% more in the clay field over the least producing tractor plot, which was the belted track tractor. In the second year's study, the highest yield was also with a conventional wheel tractor with dual rear tires and front wheel drive. The plot produced 5% more cotton over the least producing tractor plot, also a belted track tractor. Cotton yields correlated with the soil compaction (cone penetrometer) measurements.

The 9000T track-type agricultural tractors mark John Deere's entry into the high-horsepower, track tractor market. The 360-HP 9300T and the 425-HP 9400T tractors were designed with input from customers to meet customers' needs. Through customer input, on-farm research, and common sense, these tractors have been designed to work light in the spring, heavy in the fall, handle steep hillsides, turn under load and pull like a locomotive. Incorporating many of the already-market-dominating features of the 9000 wheel tractors plus innovative track vehicle features such as the wide stance, long wheel base, controllability, power, and versatility, these machines are truly amazing.

The difficulties and complexities associated with manual backup steering have increased as off-road vehicles have become larger. System components must be optimally designed to produce the most efficient manual steering. To efficiently transfer power from the human operator to the steered wheels, the characteristics of the steering wheel with metering pump must be impedance matched to the operator. Knowledge of the torque-speed characteristics of a human, as related to a steering wheel, is required to determine the maximum power transfer point for impedance matching. Published literature provides little information on human power capabilities in this context. To better define the human power characteristics a study was undertaken at the John Deere Product Engineering Center, Waterloo, Iowa. This paper deals with the results of that study.