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IIUM Engineering Journal, Vol. 6, No. 1, 2005 A. Rahman et al.

DESIGNING FRAMEWORK OF A SEGMENTED RUBBER
TRACKED VEHICLE FOR SEPANG PEAT TERRAIN IN

MALAYSIA

ATAUR RAHMAN, AZMI YAHAYA, MOHD. ZOHADIE, DESA AHMAD AND
WAN ISHAK

Faculty of Engineering, University Putra Malaysia,

43400, Serdang, Selangor, Malaysia

Abstract: The focus of this paper is to present the designing framework of an off-road
special segmented rubber tracked vehicle that may be required to run on low bearing
capacity peat terrain. To complete this study: firstly, mechanical properties of the peat
terrain were first determined by using different type of apparatus. Direct shear test was
performed using a Wykeham Farrance 25402 shear box apparatus to determine the
internal friction angle, cohesiveness and shear deformation modulus of the peat sample.
Load-sinkage test was performed using a specially made bearing capacity apparatus to
determine the stiffness values of surface mat and underlying peat. Secondly, substantiate
the validity of the mathematical model and finally design parameters of the special
segmented rubber tracked vehicle were optimized by simulation.

Keywords: Tracked vehicle, peat terrain, tractive performance.

1. INTRODUCTION

In Malaysia, new requirements for greater mobility over a wide range of peat terrain,
and growing demands for environmental protection and collection-transportation goods by
vehicles on unprepared peat terrain constitute a significant part of the overall
transportation activities. This has led to the necessity of developing segmented rubber
tracked vehicle and establishing mathematical models for the vehicle-peat terrain systems,
that will enable design engineers, as well as users, to evaluate a wide range of options for
the selection of an optimum configuration for a given mission and environment. Various
organizations in Malaysia are introduced different type of machines for performing several
tasks on peat land. The machines suitabilities were justified based on the mechanical
properties [2] of Sepang peat land. It was found that the engine power of all the machines
are quite reasonable based on their carrying capacity. However, the tractive performances
is severely affected due to the higher ground pressure distribution.

 Corresponding author

IIUM Engineering Journal, Vol. 6, No. 1, 2005 A. Rahman et al.

2. MATERIALS AND METHODS
The feasibility of the land locomotion of the tracked vehicle operating on the weak peat

terrain is discussed from the perspective of the terramechanics. Figure 1 shows the
processes for designing a segmented tracked vehicle. This paper presents the discussion
until the design parameter optimization technique.

Fig. 1: Flow chart for the processes of designing a segmented tracked vehicle.

2.1 Mechanical Properties of Peat Terrain

To properly identify the mechanical properties of peat from a vehicle mobility
viewpoint, measurement has been taken under loading conditions similar to those exerted
by a vehicle on the peat terrain. Field tests were carried out at Sepang peat area, located
about 45 km from Kuala Lumpur Malaysia for determining the mechanical properties of
peat terrain including moisture content, bulk density, cohesiveness, internal friction angle,
shear deformation modulus, vane shearing strength, surface mat stiffness, and underlying
stiffness of peat. The mechanical properties of Sepang peat terrain including the terrain
moisture content , bulk density d, peat surface mat stiffness mm, underlying stiffness of
peat kp, cohesiveness c, internal frictional angle , and shear deformation modulus Kw that
are found from an earlier work [2] are given in Table 1.

Segmented Track
Vehicle

Operating Terrain-
Peat

Mechanical Properties
of Peat

Developed Algorithm Algorithm Validity

Engine Power
Requirement

Design Parameters Selection and
optimization

Hydraulic Power
Estimation

Basic Design Parameters
Identification

Auto CAD Design

Construction

Field Test

IIUM Engineering Journal, Vol. 6, No. 1, 2005 A. Rahman et al.

Table 1. Peat terrain parameters.

Parameters Un-drained

Drained

Mean value SD Mean value SD

, (%) 83.51 - 79.58 -
d, (kN/m3) 1.53 0.59 1.82 0.78
c, kN/m2) 1.36 0.21 2.73 0.39
, (degree) 23.78 4.56 27.22 2.19
Kw, (cm) 1.19 0.10 1.12 0.17
mm,(kN/m3) 27.07 13.47 41.79 13.37
kp, (kN/m3) 224.38 52.84 356.8 74.27

Notification: SD-Standard deviation, Source [2].

2.2 Mathematical Model

Consider a rigid link segmented rubber track vehicle of weight W, track size including
track ground contact length L, width B, pitch Tp, and grouser height H, radius of the front
idler Rfi , rear sprocket Rrs, and road-wheel Rw, and height of center of gravity (C.G) hcg,
which is traversing under traction on a peat terrain at a constant speed of vt and applied a
driving torque Q at the rear sprocket by the hydraulic motor as in Fig. 10. If the pressure
distribution in the track-terrain interface is assumed to be non-uniform by locating vehicle
C.G rearward of the track mid point, the vehicle will traverse on the specified terrain by
making an angle ti. Consequently, the track entry and exit angles at the front idler fi and
rear sprocket rs, the reaction pressure at the front idler Pfi, main straight part Po, and rear
sprocket Prs, and the sinkage of the front idler zfi, main straight part zmp, and rear sprocket
zrs and tangential force reveal different values due to the different amount of slippage at
each of the grouser positions of the rigid link tracks at the bottom track elements of the
front idler ifi, main straight parts imp , and rear sprocket irs as shown in Fig. 2.

Fig. 2: Force acting on the track system of the vehicle during traversing on peat terrain
with a slippage of 10%.

IIUM Engineering Journal, Vol. 6, No. 1, 2005 A. Rahman et al.

The following assumptions were made in order for the equation used in the mathematical

modelling to be valided:

i. Vehicle theoretical speed was considered to be 10 km/hr on zero slope terrain

based on various off-road operations ASAE D497.3 NOV96, ASAE standard

(1996).

ii. Vehicle total weight was considered to be 19.62 kN with payload of 9.81kN based

on the in-field maximum fresh bunches collection practiced.

iii. Vehicle’s track critical sinkage was considered to be 0.1m based on experimental

data on Sepang Peat terrain [2].

iv. Aerodynamic resistance was neglected, due to the low operating speed.

v. Vehicle’s belly drag was considered to be zero since the vehicle hull was not in

contact with the terrain.

vi. Vehicle speed fluctuation was considered to be 2.75% based on Wong [7].

vii. Road-wheel spacing was considered to be 0.245m to ensure good drawbar
performance based on Wong [7].

2.2.1 Slippage

Slippage is one of the functional parameters for the vehicle traction mechanism. It
reveals different value at the bottom track part of front idler, main straight part, and rear
sprocket if the vehicle traverses on unprepared peat terrain with non-uniform ground
pressure distribution. Therefore, it is important to compute the slippage of the front idler,
track main straight part, and rear sprocket separately to determine the vehicle performance
over the peat terrain.

For the slippage of the ground contact track of front idler, the relationship between the
front idler slippage ifi , the entry angle of the track at front idler fi , the track trim angle ti,
the slippage ratio i and front idler radius Rfi can be modeled by the following equation [5].

     titififi
fifi

fi
fi iL

R
i  sinsin1 










 (1)

where, the slip ratio,
t

v
vv

i


 , track trim angle,   arcsinti rs fiz z L   , and track
entry angle  fifitifi Rz  cosarccos and  tifififi RL   .

For the slippage of the ground contact track of rear sprocket, the relationship between
the slippage of rear sprocket irs and front idler ifi, rear sprocket radius Rrs, the track entry

IIUM Engineering Journal, Vol. 6, No. 1, 2005 A. Rahman et al.

angle fi,, the track trim angle ti, and exit angle rs can be modeled by the following
equation of Ataur et al.[5] :

    titirsrs
rs

rsrs
firs iL

R
L
L

iii  sinsin1 



















 (2)

where, track exit angle
   
























 
 2

222
arccosarcsin

firsrs

rsfirs
rs

zzR

R
L

zz
 , sinkage of the

front idler,
2

































m

fihfi

hfip

m
pD

m
Dk

z , sinkage of the rear sprocket,

































m

rshrs

hrsp

rshp

m
pD

m
Dk

z , hydraulic diameter of the terrain due to front

idler,
 BL

BL
D

fib

fib
hfi 


2
4 , rear sprocket,

 BL
BL

D
rsb

rsb
hfi




2
4 and  tirsrsrs RL   .

2.2.2 Tractive Effort

The tractive effort is denveloped not only on the ground contact part of the track but
also on the side parts of the ground contact track grouser and on parts of front idler and
rear sprocket. The initial track tension 12% of the total vehicle weight is assumed to be
constant in every point of the track system in order to avoid the track deflection apparently
between consecutive road-wheels.

2.3 Ground Contact Part of the Track

The traction mechanics of the track bottom part of the front idler, road-wheels, and rear
sprocket are different due to its different angle of entry and exit. It is also different due to
the different sinkage of the track front idler, main straight part, and rear sprocket when the
vehicle traverses on the unprepared peat terrain with non-uniform ground pressure
distribution. Therefore, it is important to compute the traction of the individual
components bottom track segment, separately.

For the tractive effort developed at the track ground contact length of the front idler, the
relationship between the tractive effort Fb developed at the ground contact track, track
ground contact length L, track width B, terrain cohesiveness c, normal stress , shear
stress , shear deformation modulus Kw, and slippage ratio of the track-terrain interfaces i
can be modeled by the following equation of Ataur et al.[5]:

 


































wfi

fibfi

wfi

fibfi

wfi
fibfib K

Li
Li

K
Li
Ke

cBLF 1exp1tan2
1

 (3)

IIUM Engineering Journal, Vol. 6, No. 1, 2005 A. Rahman et al.

with  tifififib RL  

The tractive effort of the track main straight part and rear sprocket ground contact track
was computed by Eq. (3).

2.4 Side of the Ground Contact Track

Wong [7] suggested that the traction mechanics of the track at the side of the grouser is
highly significant on the development of vehicle traction if the vehicle sinkage is more
than the grouser height. In this study, it was assumed that the sinkage of the vehicle was
more than the grouser height of the vehicles track.

For the tractive effort developed at the side of the ground contact length of the front
idler track, the relationship between the tractive effort Fs developed at the side of the track
ground contact part, track grouser height H, track ground contact length L, terrain
cohesiveness c, normal stress , shear stress , shear deformation modulus Kw, and
slippage i of the vehicle track-terrain interfaces can be modeled by the following equation
of Ataur et al. [5]:

 


































wfi

fibfi

wfi

fibfi

wfi
fibfis K

Li
Li

K
Li
Ke

cHLF 1exp1costan4
1

 (4)

with 















B
H

cotarctan

The tractive effort at the side of the track main straight part and rear sprocket ground

contact track was computed using Eq. (4).

2.5 Motion Resistance

When the same vehicle as shown in Fig. 2, traverses on the peat terrain with non-
uniform pressure distribution, the vehicle individual components such as front idler, main
straight part, and rear sprocket reveal different values of motion resistances due to the
different sinkages. Therefore, it is important to compute the motion resistance of the
individual component for understanding the vehicle performance.

For the motion resistance of the vehicle due to terrain compaction Rc, the ground
contact length L, track width B, sinkage of the vehicle z, stiffness of peat surface mat mm
and underlying peat kp can be modeled by equation of Ataur et al. [5]:

 






















































































3

3
2

3
4

23
4

2
2

rsm
hrs

rsprs

mpm
hmp

mppmp
fim

fih

fipfi

zm
D

zk
L

zm
D

zk
L

L
zm

D
zk

L
L

BR
(5)

IIUM Engineering Journal, Vol. 6, No. 1, 2005 A. Rahman et al.

where

 BL
BL

D
fi

fi
hfi 


2

4 ,
 BL

BL
D

mp
hmp 


2

4 , and
 BL

BL
D

rs
hrs




2
4

For the motion resistance of the vehicle due to bull dozing effect, the relationship
between the motion resistance of the vehicle due to bull dozing effect Rb, the bulk density
of the terrain d, the internal frictional angle , track width B, and terrain cohesiveness c
can be modeled by the following general equation of Wong [7]:















 






 

2
45tan

2
45tan2 22


 czzBR db (6)

The total external motion resistance of the rubber track vehicle Rtm, can be computed as
the sum of the individual motion resistance components by:

etm fic msc rsc fib msb rsbR R R R R R R      (7)

2.6 Sprocket Torque

When torque is applied at the sprocket, it starts driving the track and the vehicle starts
moving. A frictional torque appears in the bearings of moving elements of the track
system, resisting the vehicle motion. The forces appear at the track interface due to the
terrain compaction and vehicle bulldozing effect, resisting the vehicle motion. Therefore,
the vehicle needs to develop sufficient tractive effort after developing shear stress at the
track-terrain interface in order to move forward and overcoming all of the motion
resistance. The tension in each track segment does not affect the torque of the vehicle
motion since it was assumed to be constant due to the geometrical arrangement of the
road-wheel and initial tension equals to 12% of the total weight of the vehicle. For the
torque of the sprocket, the relationship between the torque of the sprocket Q, vehicle total
tractive effort Ftt, total motion resistance Rtm, sprocket radius Rrs, track grouser height H,
vehicle total weight W, and vehicle normal reaction force Fn and track ground contact
length L can be modeled by using the following equation:

       tintirscgrsp eWFLRhWHRDQ  cos5.0sin  (8)

where

titt
n

FW
F




cos
sin



2.7 Vehicle Steerability

The force system assumed to be acting on a tracked vehicle in general planar motion is
shown in Fig. 3 and Fig. 4. In these figures, Fot and Fit are the thrusts on the outer and
inner tracks. Rlnot and Rlnit are the longitudinal forces exerted by the terrain to per unit
length of the outer and inner track, fr and l are the coefficients of the longitudinal and

IIUM Engineering Journal, Vol. 6, No. 1, 2005 A. Rahman et al.

lateral motion resistance, respectively, Bstc is the vehicle tracks tread, Fcent is the
centrifugal force and  is the slip angle.

Fig. 3: Force acting on the track during turning at 6 km/hr.

Fig. 4. Force acting on the track during turning at 10 km/hr.

During a turn, centrifugal force appears at the mass centre of the vehicle. When the
vehicle turns at a traveling speed of 6 km/hr with locating C.G at the middle of the track
system, the slip angle of the vehicle is assumed to be zero due to negligible effect of
centrifugal forces. The lateral motion resistance assumed to be equally distributed around
the C.G of the vehicle and represented by equal triangles F1 to F4 as shown in Fig. 3.
When the vehicle turns at a traveling speed of 10km/hr with locating C.G at 0.20 m
rearward from the middle point of the track system, the slip angle of the track system  is
considered significant higher value and significantly affect the vehicle stability and

IIUM Engineering Journal, Vol. 6, No. 1, 2005 A. Rahman et al.

steerability. Therefore, the lateral force distributions on the track system to be congruent
are represented by the triangles F1 to F4 as shown in Fig. 4. The vehicle must have rotated
about an instantaneous center point O located at a distance of D ahead of the vehicle C.G
for the dynamic equilibrium. This force is generated by a shift to the point O ahead of C.G
and the vehicle will be oriented by an slip angle , which can be computed as









lg
L

 4arctan
2

, the yaw velocity  of the vehicle can be computed as

  





 


R

R itotrs 2


,where, Rrs is the radius of the sprocket. The vehicle follows the

dashed trajectory, turning to the right around the instantaneous centre point O with turning
radius R.

2.8 Dynamic Load on the Tracks

From the slippage equations of the outer and the inner track it can be identified that
when the loading condition of the vehicle changes, as the vehicle is accelerating, the
slippages of the vehicle track changes. Therefore, in order to adjust the vehicle slippage
on given terrain it is necessary to estimate the proper loading condition for getting the high
steerability of the vehicle The centrifugal force of the vehicle that will develop during
turning at speed of 10km/hr can be computed as 2 coscentF W R g  , which causes
lateral load transfer. The weight transfer from the inner track to the outer track is mainly
due to the centrifugal force. If the centrifugal force is taken into consideration the dynamic
loads of the outside and inside track will be different. For the dynamic load of the vehicle
outer and inner track, the relationship between the dynamic load of outside and inside
track Wot and Wit, yaw movement of the vehicle , turning radius R, slip angle  and
acceleration due to gravity g, can be modeled using the following equations of Ataur et
al.[3]:

cos
2

gB
RWhW

W
stc

cg
ot


 (9)

cos
2

gB
RWhW

W
stc

cg
it


 (10)

where 








R
D

arctan

Drawbar pull

The drawbar power is referred to as the potential productivity of the vehicle, that is, the
rate at which productive work may be done. It is computed using the following equation:

apd VDP  (11)

with tmttp RFD 

IIUM Engineering Journal, Vol. 6, No. 1, 2005 A. Rahman et al.

Tractive efficiency

Tractive efficiency is used to characterize the efficiency of the track vehicle in
transforming the engine power to the power available at the drawbar. It is defined by the
following equation:

d
d P

P
 (12)

3. MATHEMATICAL MODEL VALIDATION

The drawbar pull and the tractive efficiency of light peat prototype Kubota Carrier
RC20P track vehicle having track width of 0.43 m, track ground contact length of 1.85 m,
total weight of 2645 kg including payload 1000 kg and three pneumatic road-wheels on
each track, operating on a peat terrain were predicted through simulation. Basic
parameters of the reference vehicle that used in the study are shown in Table 2.

Table 2. Basic parameters of Kubota Carrier RC20P track vehicle.

Parameters Symbol Values

Vehicle parameters
Machine weight, kN W 1645
Max. loading capacity, kN Wl 1000
Rated power, kW@rpm P 8.2@3200

Track parameters

Ground contact length, m L 1.85
Width, m B 0.43
Grouser height, m H 0.05

Machine parameters

Length, m Lt 2.98
Width, m Bt 1.76
Height, m Ht 1.45
Ground clearance, m Gc 0.27

Source: Ooi [6]

Table 3 shows that the regression model is highly significant at a significance level of
Pr0.01. In the regression model, t values of 11.74 for i and –7.84 for i2 are higher than
t*16 (0.01)=2.69. Hence, the null hypothesis is rejected. This implies that the slippage of
the vehicle has significant effect on the drawbar pull of the vehicle. A standard error value
of 0.032 for i and 0.00067 for i2 are concluded that both of the predicted and measured
drawbar pull is pretty tightly bunched together. The variability of the predicted and
measured drawbar pulls of the vehicle has the less variability around the best fitted
regression line,   )(005.0385.0916.0 2iiDp  where, Dp is the drawbar pull of the
vehicle in kN and i is the slippage of the vehicle in percentage. Therefore, based on the

IIUM Engineering Journal, Vol. 6, No. 1, 2005 A. Rahman et al.

vehicle estimated standard error of 0.032 and the R-square values of 0.967, it can be
concluded that the predicted and the measured drawbar pull are strongly correlated.

Table 3: Regression analysis on the drawbar pull of Kubota Carrier RC20P track vehicle.

Source df SS F value P value R square

Model 2 99.97650 49.98825 0.0001 0.9667

Error 16 4.52226 0.28264

C total 18 104.49876

Estimated
Parameter

Coefficient

T for H0:

Parameter=0

Standard Error

Pr T

Intercept
i
i2

0.916190
0.385447
-0.005228

3.431
11.794
-7.842

0.26699892
0.03268138
0.00066673

0.0034
0.0001
0.0001

Table 4 shows that the slippage of the vehicle significantly (Pr 0.01) affects the vehicle
drawbar pull. While, the non-significant value of treatments (predicted and measured
drawbar pull) indicates that there is no significant difference between the treatments.
Therefore, the close agreement between the predicted and measured drawbar pull of the
vehicle substantiates the validity of the simulation model.

Table 4: ANOVA on the drawbar pull of Kubota Carrier RC20P track vehicle

Slippage 18 201.47489383 143.21 0.0001

Treatment 1 0.14455325 1.85 0.1906

Error 18 1.40688027

Total 37 203.02632735

Table 5 shows that the regression model is highly significant at significance level of
Pr0.01. In the regression model, t values of 2.91 for i and -3.81 for i2 are higher than
t*35(0.01) = 2.67. Hence, the null hypothesis is rejected. This implies that the slippage of
the vehicle has significant effect on the tractive efficiency of the vehicle. The standard
error values of 0.23 for i and 0.0087 for i2 concluded that both of the predicted and
measured drawbar pull are pretty tightly bunched together. The variability of the predicted
and measured drawbar pulls of the vehicle have less variability around the best fitted
regression line,  20034.0)(25.161.56 iiT  where, T is the tractive efficiency of the
vehicle in percentage and i is the slippage of the vehicle in percentage. Therefore, based
on the standard error estimated values of the vehicle of 0.23 and the R-square value of
0.79, it can be concluded that the predicted and the measured drawbar pulls are strongly
correlated.

IIUM Engineering Journal, Vol. 6, No. 1, 2005 A. Rahman et al.

Table 5: Regression analysis on the tractive efficiency of Kubota Carrier RC20P track
vehicle.

Source df SS F value P
value

Model 2 2604.69 13.31 0.000
1

0.79
3

Error 35 3426.12

C total 37 6030

Estimate
d

Coefficien
t

T for H0: Standar
d Error

PrT

Intercept 56.61 15.83 3.51 0.0001

Table 6 shows that the slippage of the vehicle significantly (Pr 0.01) affects the
tractive efficiency of the vehicle. The non-significant value of treatments (predicted and
measured tractive efficiency) indicates that there is no significant difference between the
treatments on the model. Therefore, the closed agreement between the predicted and
measured tractive efficiency of the vehicle substantiates the validity of the simulation
model.

Table 6: ANOVA on the tractive efficiency of Kubota Carrier RC20P track vehicle.

Source df SS F value
P value

Slippage 18 6153.59 2556.23 0.0001

Treatment 1 0.006 0.05 0.83

Error 18 2.28

Total 37 203.026

4. VEHICLE DESIGN PARAMETERS OPTIMIZATION

Tractive performance of the rigid link segmented rubber tracked vehicle has been
computed with the computer simulation method based on the new mathematical model for
undrained peat terrain. It appeared that the engine size and tractive performance of the
vehicle on peat terrain vary with: the variation of vehicle weight, track size including track
ground contact length, width, pitch and grouser height track entry and exit angle, idler
diameter and location, sprocket diameter and location, road-wheel diameter, spacing and
geometrical arrangement, and location of center of gravity. Therefore, for the selection and
optimization design parameters of the vehicle track size, idler diameter and location,
sprocket diameter and location, number of road-wheel, road-wheel diameter, spacing and
geometrical arrangement, ratio of the road wheel spacing to track pitch, ratio of the
sprocket diameter to track pitch, and the location of the center of gravity are taken into
account. The optimization design parameters of the vehicle have been performed by using
the Microsoft Excel software with performing calculations, analyzing information and
managing lists in spreadsheets.

IIUM Engineering Journal, Vol. 6, No. 1, 2005 A. Rahman et al.

4.1 Track Width and Ground Contact Length

The length of the track in contact with the ground and the level of pressure within the
ground are the most important factors that influenced tracked vehicle tractive
performance. To evaluate the effects of track system configuration on the vehicle ground
pressure distribution and surface mat stiffness, it is important to study track ground contact
length and width. Figures 5(a) and 5(b) show that the vehicle ground pressure distribution
decreases with increasing vehicle track ground contact length and width. The vehicles
under consideration are traversing on a zero slope terrain with a travel speed of 10 km/hr.
From the field experiment on Sepang, it was found that the bearing capacity for the un-
drained peat terrain was 17 kN/m2. It appears that if a ground contact pressure of the
19.62 kN vehicle, with a moderate payload of 5.89 kN, is limited to 16.35 kN/m2 by
designing a track with ground contact area of 30x2000 mm2 then the sinkage and external
motion resistance of the vehicle will be low and tractive effort will be high, yielding a
desired travel speed of 10 km/hr and vehicle productivity.

0.2 0.25 0.3 0.35 0.4 0.45 0.5

Track w idth,m

G
ro

un
d

co
nt

ac
t p

re
ss

ur
e,

kN
/m

11.77kN vehicle 17.65kN vehicle 21.52

1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2 2.1

Track Ground contact length,m

G
ro

un
d

co
nt

ac
t p

re
ss

ur
e,

k
N

/m
2

11.77kN vehicle 17.65kN vehicle

21.52kN vehicle

Fig. 5: Variation of ground pressure distribution with (a) variation of track width at
constant track ground contact length of 200 cm and (b) variation of track ground contact

length at constant track width of 30 cm.

Figures. 6 (a) and 6(b) show that the sinkage of the vehicle decreases with increasing
track width and track ground contact length. If the track size of the vehicles is limited to
300 x 2000 mm2, then the sinkage of the 11.77 kN, 17.65 kN, and 21.52 kN vehicles will
be 61, 81.8, and 110 mm, respectively. From the field experiment, it was found that the
surface mat thickness of the Sepang peat terrain was 100 mm, which will support the
maximum load of the vehicle during static and dynamic as well. Therefore, if the vehicle
sinkage is more than 100 mm the vehicle will sink rather than traverse. If the vehicle total
weight is considered to 19.62 kN and the track ground contact area to 300x2000 mm2, the
vehicle will traverse on the peat terrain with sinkage of 90 mm or 10 % less than the
Sepang peat terrain surface mat thickness and exit ground pressure of 16 kN/m2 or 6 %
less than the worst condition Sepang peat terrain bearing capacity. Based on the 19.62 kN
vehicle sinkage and ground contact pressure, it may be conclude that the vehicle will not

IIUM Engineering Journal, Vol. 6, No. 1, 2005 A. Rahman et al.

in risk to traverse on peat terrain if the vehicle used the track ground contact area of
300x2000 mm2.

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5

Track width,m

S
in

ka
ge

11.77kN vehicle 17.65kN vehicle

21.52kN vehicle

120 130 140 150 160 170 180 190 200 210
Track Ground Contact Length,cm

S
in

ka
ge

,c
m

Vehic le weight, 11.77kN Vehic le weight,17.65kN

Vehic le weight, 21.52kN

Fig. 6: Variation of vehicle sinkage with (a) variation of track width at constant track
ground contact length of 200 cm and (b) variation of track ground contact length at

constant track width of 30 cm.

Therefore, the best choice is to select a vehicle track ground contact area of 300x2000
mm2 for the vehicle to produce an effective tractive performance.

The conclusion is further supported by the relation between the track size and motion
resistance with keeping option either track width or track ground contact length could
increase to adjust the track ground contact area for getting the desired vehicle ground
contact pressure. Figures 7(a) and 7(b) show that the motion resistance coefficient of the
vehicle increases with increasing track width and decreases with increasing track ground
contact length. Figure 7(a) shows that the motion resistance coefficient increased 18.12 %
for 13.73 kN vehicle, 16.99 % for 17.65 kN vehicle and 24.12 % for 21.58 kN vehicle
with increasing the track width from 0.2 to 0.4m when the track ground contact length
considered to keep in constant at 2.0m. Whereas, Fig. 7(b) shows that the vehicle motion
resistance coefficient of the vehicle decreased 21.09 % for 13.73 kN vehicle, 24.07% for
17.65 kN vehicle and 24.5 % for 21.58 kN vehicle with increasing the track ground
contact length from 1.3 to 2.2m when the track width considered to keep in constant at
0.3m. From the justification of vehicle motion resistance coefficient based on vehicle track
width and track ground contact length, it could be noted that the vehicle track ground
contact length should be considered to increase instead of increase the track width in order
to get the vehicle lower ground contact pressure of 16 kN/m2 on Sepang peat terrain.
Therefore, it was found that for a given overall dimension of 300x2000 mm2 track system,
the maximum motion resistance coefficient of the 19.62 kN vehicle is 5.4 %, which could
be good enough for a track vehicle on soft terrain [7].

IIUM Engineering Journal, Vol. 6, No. 1, 2005 A. Rahman et al.

0.2 0.25 0.3 0.35 0.4 0.45 0.5

Track width,m

M
ot

io
n

re
si

st
an

ce
c

oe
ff

ic
ie

nt
,%

11.77kN vehicle 17.65kN vehicle 21.52kN vehicle

15.5

16.5

17.5

18.5

19.5

1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2 2.1

Track ground contact length,m

M
ot

io
n

r
es

is
ta

nc
e

co
ef

fic
ie

nt
,%

11.77kN vehicle 17.65kN vehicle

21.52kN vehicle

Fig. 7: Effect of track size on vehicle tractive performance (a) track width and (b)
track ground contact

Based on Figs. 8(a) and 8(b), it could be pointed out that if the 19.62 kN vehicle track
size is considered to be 300x2000 mm2, the vehicle ground pressure exit on track-terrain
interfaces is 16 kN/m2 with sinkage of 90mm and motion resistance coefficient of 5.4%.
Therefore, the 19.62 kN vehicle track system overall dimension can be optimized by
selecting track width of 300 mm and ground contact length of 2000 mm.

0.25 0.29 0.33 0.37 0.41 0.45 0.49 0.53

Idler diameter,m

Tr
ac

k
en

try
a

ng
le

,d
eg

re
e

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18
S

in
ka

ge
,m

Track entry angle, degree Sinkage,m

Fig. 8: Relationship between track entry angle, sinkage and idler diameter.

4.2 Track Grouser Size

To fully utilize the shear strength of the peat surface mat for generating tractive effort,
the use of grouser on tracks would be required. From the field experiment on Sepang, it
was found that the shear strength of the peat surface mat is considerably higher than that
of the underlying peat deposit and that there is well defined shear-off point beyond which
the resistance to shearing is significantly reduced. This would, however, considerably

IIUM Engineering Journal, Vol. 6, No. 1, 2005 A. Rahman et al.

increase the risk of tearing off the surface mat unless the slip of the track is properly
controlled. Thus, the use of aggressive grouser on vehicles for use in organic terrain does
not appear to be desirable from traction as well as environmental viewpoints. The surface
mat thickness of Sepang peat terrain was found to be about 0.1m. In order to fully utilize
the shear strength of the surface mat and to increase the traffic ability of the terrain the
grouser height of the track is considered to be 0.06 m.

4.3 Sprocket Location and Size

The location of drive sprocket has a noticeable effect on the vehicle tractive
performance. Wong et al. [6] (1986) reported that in forward motion, the top run of the
track is subjected to higher tension when the sprocket is located at the front than when the
sprocket is located at the rear. Thus, with a front sprocket drive, a larger proportion of the
track is subjected to higher tension and the overall elongation and internal losses of the
track will be higher than with a rear sprocket drive. With higher elongation, more track
length is available for deflection and the track segments between road-wheels take fewer
loads and the vibration of the track increase, which will cause the fluctuation of the track.
Consequently, the sinkage and motion resistance will be higher and the mobility of the
vehicle will be affected severely on the unprepared peat terrain. Therefore, the sprocket
could be considered to locate at the rear part of the track system configuration in order to
distribute the vehicle normal pressure to the track-terrain interfaces uniformly. The center
point of the sprocket is considered the (0,0) coordinate system of the vehicle.

Generally, it could be mentioned that the sprocket is the most important component of
the vehicle track system, which propels the vehicle with sufficient torque, control the
vehicle speed fluctuation and maintain the vehicle tractive performance. Therefore, the
size of the sprocket can be determined from the relationship between the relationship
between the sprocket torque, vehicle speed fluctuation, and vehicle turning radius. From
the simulation result, it was found that the ratio of the sprocket diameter to track pitch
have significant effect on the vehicle tractive performance. Therefore, the ratio of the
sprocket pitch diameter to track pitch should be a value which will stand to meet the field
requirement.

Further support to optimize the sprocket size of the vehicle track system, the following
equation on vehicle speed fluctuation can be considered. For the relation of vehicle speed
fluctuation and the ratio of the vehicle sprocket pitch diameter to tract pitch the following
mathematical model of Wong [7]can be used:

2
1

1 1
p r s pD T


  
         

(13)

where  is the speed fluctuation in percentage, pprs TD is the sprocket pitch diameter to
track pitch in proportion.

Using pprs TD equals to 4.00, the computed value of  is 3.17%. According to Wong
[7], the industrial and agricultural track vehicle speed fluctuation should be in the range of
3.72 to 2.75%. Since the speed fluctuation of the vehicle was found of 3.17%, the ratio of

IIUM Engineering Journal, Vol. 6, No. 1, 2005 A. Rahman et al.

the vehicle sprocket pitch diameter to track pitch can be optimized at 4.00. Consequently,
the sprocket pitch diameter was optimized at 400mm by using the track pitch of 100mm.

4.4 Idler location and size

Idler is located at –2.0 m front of the track system. It was earlier reported that the
surface mat thickness of Sepang peat terrain in the ranged of 100 to 250 mm which is
considered the supporting platform of the vehicle. It could be noted that if the sinkage of
any vehicle on the Sepang peat terrain is more than 100mm will cause the vehicle to bog
down. Furthermore, from the simulation it was found that the track entry angle was
significantly affect the vehicle front idler size and tractive performance. Therefore, from
the relationship between the vehicle sinkage, track entry angle and idler diameter, the idler
diameter can be identified. Figure 8 shows that the vehicle track entry angle at front idler
and sinkage decreases with increasing vehicle front idler diameter. If the vehicle critical
sinkage of the vehicle is considered to 100 mm, the corresponding front idler diameter and
track entry angle were found 400 mm and 78, respectively.

This conclusion can be further supported from the relationship between the track entry
angle, slippage and vehicle tractive performance. Figure 9 shows that the relationship
between the vehicle track entry angle, slippage, and tractive efficiency. At track entry
angle 78, the vehicle slippage and tractive efficiency were found 18% and 70.5%,
respectively, which was found at sprocket pitch diameter of 400mm. Therefore, the front
idler diameter 400mm can be optimized at 400mm for getting the tractive efficiency of the
vehicle 70.5% and high productivity.

88 84 81 79 77 76 75 74 73 71

Track Entry Angle,degree

T
ra

ct
iv

e
ef

fic
ie

nc
y,

35
S

lip
pa

ge
, %

Tractive efficiency,% Slippage,%

Fig. 9: Track entry angle, tractive performance and slippage.

4.5 Roadwheel diameter, Track pitch, and Number of Roadwheel

Wong [7] reported that the ratio of road wheel spacing to track pitch is a significant
parameter that affects the tractive performance of tracked vehicle, particularly on soft
terrain. The decrease in the track motion resistance coefficient with the increase of the
number of road wheels was primarily due to the reduction in the peak pressures and

IIUM Engineering Journal, Vol. 6, No. 1, 2005 A. Rahman et al.

sinkage under the road wheels. The longer track pitch would lead to an improvement in
tractive performance over soft terrain. But, it may cause a wider fluctuation in vehicle
speed and higher associated vibration.

Consequently, a proper compromise between tractive performance and smoothness of
operation must be struck. Road-wheel diameter can be predicted based on the following
equation:

G
DD

Sr  22
21 (14)

where, Sr is the road-wheel spacing in mm, D1 is the first road-wheel diameter in mm, D2
is the second road-wheel diameter in mm and G is the gap between consecutive road-
wheel is assumed to be 5mm for avoiding the track deflection between the consecutive
road-wheel.

In the track system all the road-wheel dimension (D1 = D2=------= D7) are considered
as equal size. If the roadwheel spacing equals to 225mm, the gap between two
consecutive road-wheel on the track system equals to 5 mm, the computed value of road-
wheel diameter equals to 220 mm.

Figure 10 shows that the vehicle drawbar pull increases with increasing the ratio road-
wheel spacing to track pitch and tractive efficiency increases with increasing the ratio of
road-wheel spacing to track pitch until 2.1 and then decreases with further increasing of
the ratio of road-wheel spacing to track pitch. If the ratio of road-wheel spacing to track
pitch is considered to be 2.25, the tractive efficiency of the vehicle is found 70.5%.
Whereas, the tractive efficiency of the vehicle is found 70.5% for the optimum sprocket
pitch diameter of 400 mm and idler diameters of 400 mm. Therefore, the ratio of road-
wheel spacing to track pitch should be 2.25 if the optimum sprocket pitch diameter and
idler diameters each is limited to 400 mm. By using Sr/Tp equals to 2.25 and Sr equals to
225mm, the computed value of Tp equals to 100 mm.

The number of road-wheels can be computed based on Fig. 2 by the following equation
[5]:

  
 
( ) 2r s f i

r
r

L D D
n

D G

 



(15)

where, L is the total ground contact length in mm, Drs is the outside diameter of the
sprocket in mm , Dfi and Dr are the diameter of the front idler and road-wheel in mm and nr
is the number of road-wheel. The outside diameter of the sprocket (i.e, 2HDD prsrs  )
is considered to 460mm based on the grouser height.

By using L equals to 200 mm, Drs equals to 460 mm, Dfi equals to 400 mm, Dr equals to
220 mm, G equals to 5mm, the computed value of nr is 7. Therefore, total number of road-
wheel seven with diameter of 220 mm on the 19.62 kN vehicle track system would
significantly reduce vehicle vibration during traversing on the unprepared peat terrain by
making zero deflection of the track between two consecutive road-wheel.

IIUM Engineering Journal, Vol. 6, No. 1, 2005 A. Rahman et al.

4.6 Center of Gravity Location

Center of gravity of a tracked vehicle is a most important design parameter for getting
the high tractive performance. Figure 10 shows that the tractive efficiency of the vehicle
increases steeply with increasing the slippage of the vehicle until a certain value and then
start to decrease with increasing the slippage of the vehicle. The vehicle under
consideration with total weight 19.62 kN including payload of 5.89 kN is traversing on a
zero slope terrain with traveling speed of 10 km/hr. Figure 11 shows the maximum tractive
efficiency of 79.8% at 11% slippage for the vehicle with center of gravity located at 300
mm rearward from the mid-point of the track ground contact length and 70.5% at 12%
slippage for the vehicle with center of gravity located at the mid-point of the track ground
contact length.

1.5 1.65 1.8 1.95 2.1 2.25 2.4 2.55 2.7 2.85 3
Ratio of roadw heel spacing to track pitch

T
ra

ct
iv

e
ef

fic
ie

nc
y,

2.5
3.5
4.5
5.5
6.5
7.5
8.5
9.5
10.5
11.5
12.5

D
ra

w
ba

r
pu

ll,
kN

Tractive efficiency,% Drawbar pull,kN

Fig. 10: Relationship between tractive efficiency, drawbar
pull and the ratio of the road-wheel spacing to track pitch

0 5 10 15 20 25 30 35 40
Slippage, %

T
ra

ct
iv

e
ef

fic
ie

nc
y,

Center of gravity at midpoint of track

Center of gravity at 0.2m rearward track middle

Fig. 11: Relationship between tractive efficiency and slippage.

IIUM Engineering Journal, Vol. 6, No. 1, 2005 A. Rahman et al.

From the comparison of the vehicle based on the location of center of gravity, it is
found that the tractive efficiency of the vehicle with center of gravity is located at 200 mm
rearward from the mid point of the track ground contact length is 13.2% higher than the
tractive efficiency of the vehicle with the center of gravity is located at the mid-point of
the track ground contact length. The variation of tractive efficiency is found between the
vehicle with the locations of center of gravity due to the difference of external motion
resistance. It could be pointed out that the vehicle with location of center of gravity at
200mm rearward from the mid point of the track ground contact length reveals lower
sinkage at the frontal part of the track ground contact part causes the lower external
motion resistance and the vehicle consume lower engine power for developing effective
tractive effort in order to traverse the vehicle easily on the low bearing capacity peat
terrain. Whereas, the vehicle with location of center of gravity at the midpoint of the track
ground contact length reveals the equal sinkage to all over the ground contact part causes
the higher external motion resistance and vehicle consume maximum engine power for
developing the required tractive effort in order to traverse the vehicle on the low bearing
capacity peat terrain. Therefore, the vehicle center of gravity location of 300mm rearward
from the mid-point of the track ground contact length could be optimized the center of
gravity location for the vehicle. The basic design parameters of the vehicle found from the
simulation study are shown in Table 7

Table 7. Basic design parameters of the special segmented rubber tracked vehicle

Vehicle Parameters
Total weight including 9.81kN payload, kN W 19.62
Vehicle traveling speed, km/hr vt 10
Center of gravity, x coordinate, m

xcg

-0.80
Centre of gravity, y coordinate,m

ycg

0.45
Sprocket pitch diameter , m Drs 0.40
Idler diameter, m Dfi 0.40
Idler center, x coordinate, m xcfi -2.0
Idler center, y coordinate, m ycfi 0
Number of road-wheels (each side) n 7
Road-wheel diameter, m Dr 0.22
Road-wheel spacing, m Sr 0.225
Number of supporting rollers (each side) ns 3
Supporting rollers diameter, m Ds 0.20

Track Parameters
Track total length (each side), m Lc 5.90
Track pitch, m Tp 0.10
Track width, m B 0.30
Track ground contact length, m L 2.00
Road-wheel spacing to track pitch

Sr/Tp

2.25
Vehicle speed fluctuation, percentage  3.17
Grouser height, m H 0.06

Note: Coordinates origin is at the center of the sprocket. Positive x and y coordinates are to the rear and top, respectively.

IIUM Engineering Journal, Vol. 6, No. 1, 2005 A. Rahman et al.

5. CONCLUSION

The following conclusions were made based on the analysis of this paper:

Based on the results of mechanical properties of peat in the area studied, the mean
values for moisture content of 79.58 %, bulk density of 1.53 kN/m3, cohesiveness of
1.36kN/m3, internal friction angle of 26.22, shear deformation modulus of 11.2 mm,
surface mat stiffness of 13.6 kN/m3, and underlying peat stiffness of 171.54 kN/m3.

Based on the results of detailed study on vehicle parameters, an optimized track system
configuration for the 19.62 kN vehicle has seven roadwheels with diameter of 0.24 m, a
track pitch of 0.1m, a ratio of the initial track tension to vehicle weight of 12 %, a location
of center of gravity at 30cm rearward of the mid-point of the track ground contact length
ensure the vehicle to develop the maximum tractive efficiency of 74 % during traversing
at 10km/hr on the specified peat terrain.

Based on the simulation study, it was found that the track pitch, number of road wheels,
and location of centre of gravity have noticeable effects on the tractive performance of the
vehicle. The maximum tractive efficiency of the vehicle is in the range of 74 to 72 % and
50 to 48% with the slip range of 9 to12 % when the vehicle traveled at 10km/hr without
payload and with payload, respectively. Furthermore, the tractive efficiency of the vehicle
with center of gravity located at 300mm rearward of the mid-point of track ground contact
length are 10% higher than the vehicle center of gravity located at the mid-point of track
ground contact length.

ACKNOWLEDGEMENT

This research project is classified under RM7 IRPA Project No. 01-02-04-0135. The
authors are very grateful to the Ministry of Science, Technology and the Environment of
Malaysia for granting the financial assistance.

REFERENCES

[1] ASAE, Agricultural Engineers Yearbook of Standards, American Society of Agricultural
Engineers, Michigan,1996.

[2] R. Ataur, Y. Azmi, M. Zohadie, A. Desa, W. Ishak, and A. Kheiralla, ” Mechanical
Properties in Relation to Vehicle Mobility of Sepang Peat Terrain in Malaysia”, Journal of
Terramechanics, 41(1), pp24-45, 2004.

[3] R. Ataur, Y. Azmi, M. Zohadie, D. Ahmad, and W. Ishak, “Simulated Steerability Of A
Segmented Rubber Tracked Vehicle During Turning On Sepang Peat Terrain in Malaysia”,
Int. J. of Heavy Vehicle Systems (IJHVS), Inderscience Publisher, UK: Vol.12, No. 2, pp.
139-168, 2005a.

[4] R. Ataur, Y. Azmi, M. Zohadie, D. Ahmad, and W. Ishak “ Design and Development of a
Segmented Rubber Tracked Vehicle for Sepang Peat Terrain in Malaysia”, Int. J. of Heavy
Vehicle Systems (IJHVS), Inderscience Publisher, UK: Vol.12 No.3, 2005b

IIUM Engineering Journal, Vol. 6, No. 1, 2005 A. Rahman et al.

[5] Ataur, R., Azmi, Y., Zohadie, M. Ishak, W and Ahmad, D. “Design Parameters Optimization
Simulation of a Segmented Rubber Tracked Vehicle for Sepang Peat in Malaysia”, American
Journal of Applied Science, Science Publications, New York, USA: Vol.2(3), pp.655-671,
2005c.

[6] H.S. Ooi “Performance of Modified Kubota Carrier RC20P and Porter P6-121 on peat soil”,
MARDI Report no.110, 1986.

[7] J.Y. Wong “Optimization of design parameters of rigid-link track systems using an advanced
computer aided method”, Proc. Instn. Mech. Engrs, 208(D), pp153-167, 1998.