PHYSIOLOGICAL BASIS OF TRACTOR DESIGN

Energy expenditure of tractor driving varies from 1-4 kcal/min depending on the particular agricultural task performed. The paper is concerned with principles underlying the design and positioning of tractor controls and seats in such a way as would enable the operator to carry out this strenuous work under the most favourable conditions.

Energy consumption and electrical skin capacity of the operator were measured during tractor driving with a number of different types of seat. The most satisfactory seat had a parallel seat suspension and hydraulic damping of tractor vibration. The extra cost of this seat above that most commonly supplied was insignificant in relation to the total cost of the tractor.

A study was made of the positioning relative to the operator of brake and clutch pedals, foot rest, steering column and steering wheel. The techniques employed in this study were : measurement of O₂ consumption and heart rate of the operator and of forces required in depressing the pedals and turning the steering wheel. In each instance the optimal positions of control and operator are illustrated by a detailed diagram.

In many existing tractors there is a separate brake pedal for each wheel (for rapid turning) and for both wheels together (for braking). A new type of brake with a single pedal (accident proof) is described. This brakes both wheels unless the steering wheel is also turned, when the brake on the outer wheel is released.

A standard commercial tractor was modified according to the principles described. Energy consumption of operators was found to be 13-29 per cent below that with unmodified equipment and the heart rate 40-45 per cent lower. It is believed that fatigue is reduced more than the energy figures suggest.