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General

Module 1. Tractor Mechanics

Module 2. Traction

Module 3. Introduction to Transmission System

Module 4. Clutch System

Module 5. Gear Box

Module 6. Differential and Final drive

Module 7. Brakes

Module 8. Steering system

Module 9. Hydraulics

Module 10. Power Transmission

## Lesson 2. Calculation of location of Centre of Gravity of a wheeled rear wheel drive tractor

As discussed in the previous lesson, weighing method can be applied for determining the location of the centre of gravity in laboratory conditions.

From the Fig.s 2.1 and 2.2, the various parameters can be determined.

Following parameters are measured before taking the tractor to a weighing balance:

Wheelbase of the tractor

Radius of front and rear wheels

Height of the centres of front and rear wheels from the ground

When on the weighing balance, the parameters noted are:

Total weight of the tractor

Weight coming on the front and rear tyres.

These parameters are also measured when the front wheels are lifted by a height ‘h’.

From Fig. 2.1

Wx_{2}-R_{f} X_{1}=0

or ………..(1)

so, a vertical transverse plane containing C.G. can be determine by the equation (1)

the front wheel of the tractor are raised distance Y_{2 }and R’_{f }is determined by weighing.

From Fig.1.2

Wx’_{2}-R´_{f} X´_{1} = 0

From fig. 1.2

tan β_{1 }= x_{4 }/ y_{3} (2)

and tan β_{1 }= (x_{2 }- x_{3}) / y_{3 }(3)

or y_{3} = (x_{2 }– x_{3}) / tan β_{1 }

and cos β_{1 }= x_{2}´/ x_{3 }(4)

or x_{3} = x_{2}´/ cos β_{1}

(5)

Hence the height of CG from the ground is given by

where is the diameter of the rear wheel.

Some assumptions while doing this analysis were:

The displacement of the point of contact of rear wheel on the ground as the front wheels are lifted is negligible.

There is no deformation of the pneumatic tyre at the point of contact i.e. height of centre of rear wheel is same as the radius of the rear wheel.