The effect of a float on power tiller performance

Journal of Terramechanics, Vol. 29, No. 3, pp. 329-339, 1992. Printed in Great Britain.

THE EFFECT

OF A FLOAT ON POWER PERFORMANCE

0022-4898/9255.00+0.00 Pergamon Press Ltd © 1992 ISTVS

TILLER

V. M. SALOKHE* and A. GHAZALIt

Summary--A bow-shaped enamel coated float attachment was developed for a 4.74 kW power tiller and fixed underneath the power tiller between the two cage wheels. The performance of the power tiller with and without the float was studied in flooded and puddled soil conditions. During the general performance test it was observed that the float prevented the cage wheels from digging deeper into the soil when slippage occurred. The float-cage wheel combination eased the operator's work. The statistical analysis showed that there was no significant difference in the pull and power delivered by the power tiller with and without the float in the flooded soil condition. However, in a puddled soil condition the power tiller with the float showed lower performance, in terms of pull and power delivered, than the power tiller without the float, as the cage wheels were prevented by the float from reaching the hardpan layer lying below the top puddled layer to develop enough pull. The drag test of the power tiller with and without the float showed that the presence of a float on a power tiller did not increase the drag force required to pull it.

INTRODUCTION

MECHANIZATION of rice cultivation with power equipment has increased production in recent years. However, the physical environment of the wetland area places certain demands on the design and capabilities of machinery to be used for cultivation. The wetland conditions are amongst the most difficult in which vehicles are ever expected to operate [1]. Various prime movers have been used to improve the traction and flotation of the vehicles used for wetland. Improvement of traction and mobility of rolling type prime movers has served as the backbone of mechanization in Asian countries. However, low bearing capacity, poor field levelling and uncontrolled water depth limits the prime-mover operation on these sites. The combination of float and wheel has improved machine mobility in the case of transplanters. The float mainly supports the machine weight and the wheel provides the driving force.

LITERATURE REVIEW

Kokubun [2], Kisu [3], Ayub [4] and Kobuta [5] related machine trafficability of wet soil with cone penetrometers. In Japan, Kokubun [2] and Kisu [3] stated that a power tiller could possibly work on areas having a cone index between 196 and 284 kPa at 20 cm depth. Four wheel tractors and semi-crawler combine harvesters could possibly work on areas having a cone index value of 284-490 kPa at 20 cm depth. * Division of Agricultural and Food Engineering, Asian Institute of Technology, Bangkok, Thailand. t Malaysian Agricultural Research and Development Institute (MARDI), Malaysia. 329

330

v.M. SALOKHE and A. GHAZALI

Jayasundera [6] and Wimalawansa [7] observed that 30 ° lugs on cage wheels gave maximum tractive performance. They found that the optimum number of lugs on a cage wheel should be 12-15 depending on the size of the wheel. Hossain [8] observed that under similar conditions, the performance of a 4.47 kW power tiller with cage wheels was better than one with rubber tyres. Verma [9] developed a pair of cage wheels with retractable lugs. He observed that the performance of the wheels was higher than the high lugged tyres and conventional cage wheels. Yeoh [10] tested a four row, pedestrian-controlled float-wheel type transplanter. H e found that this transplanter could be used in soils with a cone index of more than 147 kPa at 25 cm depth. Later, similar results were obtained by Abu et al. [11] with a six-row pedestrian-controlled float-wheel type transplanter. Shah [12], based on his studies of floats, stated that the float for agricultural purposes should be long, narrow and bow-shaped. A normal pressure between 1.25 to 1.6 kPa over the float gave a lower drag coefficient in his study. He also found that a standing water film on the soil surface decreases the drag coefficient substantially. Wang and Zhu [13] stated that for Chinese boat tractors the bow should be lifted up while working in the field to reduce motion resistance. Govino [14] found that to use the turtle tractor for land preparation the field should have 3.5 cm of standing water. Thai and Chancellor [15] used boat-design theory to minimize drag force of the buoyant flotation. They found that a hull-shaped boat tractor with maximum curvature at the rear was the most efficient, and that a cross section of elliptical shape tended to minimize drag. Salokhe and Gee-Clough [16, 17] reported that enamel coated plates mounted on cage wheel lugs reduce the soil adhesion considerably. Salokhe et al. [18] found that the performance of a power tiller with and without enamel-coated plates on its cage wheel lugs was almost the same, although the cage wheels with enamel coated plates performed slightly better than the cage wheels without plates on them. Power tillers are quite widely used for wetland cultivation in the Far East countries. Bogging down of the power tillers in the wet paddy fields is a common problem. To avoid this problem, a float attachment was developed which can be fixed underneath the power tiller and between the cage wheels to assist the power tiller working in soft-soil conditions [19]. The float was coated with an enamel, based on the benefits demonstrated by Salokhe and Gee-Clough [16, 17]. The performance of the power tiller with and without the float in flooded and puddled soil was tested.

MATERIALS AND METHODS For this study a 4.74 kW Kubota power tiller with 600 mm diameter and 240 mm wide cage wheels was used. The lug angle and lug spacing were 30 ° and the lug height was 75 mm. Enamel coated plates were mounted on the leading faces of the lugs. In order to improve the flotation of the power tiller, a float attachment was fabricated and mounted under the main body of the power tiller engine between the two cage wheels [2]. The specifications of the float are given in Fig. 1. The bow-shaped float was coated with enamel to reduce the soil adhesion on it. The weight of the float with the enamel coating was 19 kg. A sliding attachment with a single front holder and two rear holders was used to attach the float to the power tiller (Figs 1 and 2). In the general performance test, effective field capacity, field efficiency and fuel consumption were found. These tests were conducted on Bangkok clay soil. The tests were performed in flooded soil conditions with the hardpan 15-25 cm below the soil

FLOAT EFFECT ON POWER TILLER

331

4

I

All dimensions in mm Q - 2mm thick low carbon steel sheet ( ~ ) - 5 x S O x 6 5 0 mm steel plate

~

- 5 0 x 5 0 x 4 mm steel plate 25x25x5 mm steel plate 11.7 mm dio. screw and nut 19 mm dio. steel bar

~

- 4 5 x 4 5 x S m m steel plate 27ram dia. 3mm thick hollow steel bar ( ~ - 42ram dia.:3mm thick hollow steel bar (~)- 50xSOx240mmangle iron bracket

FxG. 1. Assembly drawing of a float.

surface, in undulating depth with the hardpan 10-30 cm below the soil surface and in a ditch, 40 cm deep and 30 cm wide, formed previously by a bogged tractor. The mobility of the power tiller with and without the float in each of the above soil conditions was observed. In the second part of testing, pull and drag tests of the power tiller with and without the float were conducted. These tests were conducted in flooded and wet soil conditions with hardpan depths of 15-20, 20-25 and 25-30 cm. Each test plot area was 270 m 2, The average hardpan cone index was 213-365 kPa. Each test was

332

V.M. SALOKHE and A. GHAZAL!

ii!;'

,

FIG. 2. Float attached underneath the power tiller. replicated three times. The test power tiller was connected to another four wheel tractor by a wire rope. This tractor was outside the field on firm soil. Load on the power tiller was increased slowly by applying the brakes of the tractor till the power tiller cage wheels showed 100% slip. The pull of the power tiller with and without the float was measured as a function of slip. The pull was measured by a load transducer. The slip was calculated from the theoretical forward speed and actual forward speed was measured. Bicycle dynamos were used to sense the wheel rotational and forward speeds. For the drag test, the tractor towed the power tiller with and without the float in flooded and wet field conditions. The signals from the sensors were amplified and recorded on a tape recorder and were later down loaded to a microcomputer through a data logger for detailed analysis.

RESULTS AND DISCUSSIONS

General performance tests During the performance of the power tiller without the float on a hardpan with undulating depth, it was observed that the power tiller began to slip at a sudden change of hardpan depth. At this condition, the cage wheels dug the soil deeper and deeper and were finally blocked with soil. Though the power tiller with the float also started to slip at the same condition the cage wheels were prevented by the float from digging deeper and hence they did not get blocked. The power tiller without the float was difficult to move when it started slipping at one place. However, the same power tiller with the float on it could be moved forward by pushing or sledging to either side. In general, the power tiller with the float eased the operator's job compared to the power tiller without the float. The float prevented the power tiller wheels from going deeper. The bow shape of the float improved maneuverability and facilitated sledging of the power tiller, especially when the cage wheels lost their grip on the soil. Table 1 shows the results obtained during the general performance test. At hardpan depths of 5-25 cm, the performance of the power tiller with and without the float was

333

FLOAT EFFECT ON POWER TILLER TABLE 1. RESULTS OF GENERAL PERFORMANCE TESTS

Hardpan depths Power tiller Effective field capacity (ha/h) Field efficiency (%) Fuel consumption (1/ha)

5-25 cm

Undulating

More than 40 cm

With float

Without float

With float

Without float

With and without float

0.17

0.19

0.15

0.13

Power tiller bogged down

68.6

67.7

63.3

58.6

5.9

5.4

6.5

7.5

almost the same. In undulating soil conditions the power tiller with the float showed improvement in perfomance compared to performance without the float. Pull and drag tests The pull vs slip data of the power tiller with and without the float were obtained in flooded as well as in puddled soil conditions at different hardpan depths. Figure 3 shows a pull vs slip characteristic of the power tiller with and without float attachment in flooded and puddled soil conditions for different hardpan depths. In the flooded soil condition, the pull increased up to about 50-60% slip; then it remained almost the same for power tiller with and without float. The pull developed by the power tiller with the float was always higher than the pull developed by the power tiller without the float. The trend of the pull vs slip curve was different in puddled soil than that observed in the flooded soil. The pull was exerted after about 20% slip and then it increased as slip increased further. The pull generated by the power tiller with the float was lower than the pull of a power tiller without the float at all hardpan depths (Fig. 3). For all situations in puddled soil, the power tiller with the float generated less pull than the power tiller without the float because the soil layer above the hardpan did not have sufficient strength compared to flooded soil condition to help the cage wheels generate enough traction. Also, the presence of the float restricted the cage wheels from sinking downward to bite the hardpan below this soft top soil layer. Due to this unfavourable soil condition, even at the beginning, wheels have to slip about 20-30% before they generate some pull to move the power tiller forward. Two different equations could be fitted to pull vs slip data obtained in the two field conditions. The data obtained in the flooded soil condition followed the relationship P = A (1 - e-BS).

(1)

While the data obtained in puddled field condition could be represented by P = A [1 - e -(B(s-c))] where P S

(2)

= pull exerted by the power tiller (kN); = wheel slip (%);

A, B and C = constants A summary of Duncan's multiple range test for the maximum pull obtained in different soil conditions of a power tiller with and without a float is given in Table 2.

334

V.M. SALOKHE and A. GHAZALI Flooded

soil

Puddled

2.0

2.0

1.5

15

soil

n

o

o

4

80

I00

]0

LO

05

05

0 .C 0

I

I 20

i 40

:

I 60

,

81t~

O0 I00

{a)

z

o

20

15-

cm

0

20

hardpan

depth

2.0

20

1.5

15

LO

Io

40

o

60

x x

n 0.5

05

i

o,o

I

I

20

40

I

I

i

60

I

J

80 (b)

20 - 25

O01 I00

0

cm

hardpan

2.0

2.0

1.5

15

io

I0

20

40

60

80

I00

60

80

I00

depth

! 05

O0 20

60

40

I00

0

20

40

Slip(°/o)

Sfip(%) (c)

25-30

cm

hardpan

without

float~

~x----

depth with

float

FIG. 3. Comparison between power tiller pull with and without float under flooded and puddled conditions for three hardpan layer depths The average pull developed by the power tiller with and without a float at 15-20 and 2 0 - 2 5 cm hardpan depth in flooded soil was almost the same. However, it was different in puddled soil conditions. Table 3 shows the values of constants (equations 1 and 2) obtained by the regression analysis. From the pull vs slip data, power vs slip characteristics of the power tiller in different soil conditions were obtained. Figure 4 shows the power vs slip curve of the power tiller with and without the float in flooded and puddled soil conditions. It was observed that the power tiller with the float gave a little higher power than the power tiller without the float in flooded soil conditions. In puddled soil, the power

FLOAT EFFECT ON POWER TILLER

335

TABLE 2. SUMMARYOF DUNCAN'S MULTIPLE RANGE TEST FOR THE MAXIMUMPULL (kN) Flooded

Conditions (Hardpan depth)

Without float

With float

15-20 cm Mean*

1.78 1.77 1.74 1.76(A)

1.80 1.75 1.78 1.78(A)

Mean*

1.74 1.74 1.75 1.74(A)

1.76 1.76 1.82 1.78(A)

Mean*

1.60 1.74 1.69 1.68(A)

1.42 1.25 1.33 1.33(A)

Mean*

1.73(A)

Average

Flooded

20-25 cm

25-30 cm

Puddled Mean*

Without float

With float

Mean*

Mean*

1.77(A)

1.69 1.70 1.69 1.69(A)

1.40 1.40 1.49 1.43(B)

1.55(A)

1.66(A)

1.56(A)

1.75 1.67 1.67 1.69(A)

1.04 1.03 1.10 1.05(B)

1.37(A)

1.37(A)

1.49(A)

1.40 1.38 1.49 1.42(A)

0.75 0.65 0.87 0.75(B)

1.08(B)

1.29(B)

1.62(A)

1.60(A)

1.07(A)

1.68(A)

Puddled

1.34(B)

1.66(A)

Average without float Average with float

1.35(B)

* Means with the same letter are not significantly different at 5% level of signficance.

TABLE 3. RESULTS OF REGRESSION ANALYSIS OF PULL VS SLIP DATA

Constants Test conditions* FL FL FL FL FL FL PD PD PD PD PD PD

P H1 P H2 P H3 F H1 F H2 F H3 P H1 P H2 P H3 F H1 F H2 F H3

Corr. Coef. (R 2)

A

B

C

1.7811 1.8034 1.7774 1.7878 1.8391 1.3293 1.7036 1.8391 1.5140 1.4502 1.2213 1.8568

0.0442 0.0336 0.0294 0.0578 0.0342 0.0431 0.0727 0.0299 0.0328 0.0461 0.0281 0.0073

---18.35 12.36 16.21 21.0 30.21 28.53

0.939 0.907 0.947 0.849 0.907 0.725 0.896 0.887 0.953 0.973 0.88 0.935

F-statistic Computed

Table Fo.ol

Table F0.0~

10.12 12.57 14.13 15.37 17.33 8.91 20.68 13.47 11.49 7.05 24.0 13.78

12.25 9.65 9.65 9.33 10.56 10.04 9.65 10.56 11.26 12.25 10.04 12.25

5.59 4.84 4.84 4.75 5.12 4.96 4.84 5.12 5.32 5.59 4.96 5.59

F0.01= Significance at 99% confidence limit. F0.05= Significance at 95% confidence limit. *Test conditions: FL = flooded condition; PD = puddle condition; P = power tiller without float attachment; F = power tiller with float attachment; H1 = hardpan at 15-20 cm depth; H2 = hardpan at 20-25 cm depth; H3 = hardpan at 25-30 cm depth. developed by the power tiller without float was higher than the power developed with t h e f l o a t a t all h a r d p a n d e p t h s . Table 4 summarizes Duncan's multiple range test for the maximum power obtained in different working conditions. The power developed by the power tiller with and

336

V.M. SALOKHE and A. GHAZALI Flooded

soil

Puddled

06

soil

06 x

05

o5

x 0.4

04

03

03

02

O2

OI

OI i

O0

] 20

L

I 40

J60

L ~

i 80

((1)

15 - 2 0

__ I00 cm

20 hardpan

06

05

05

"~ o4

04

O~

03

02

02

o a.

CI

',,\,.,

,/I,

O0

06

~

f

\~ 4O

60

8O

I00

depth

o D

a

0.1

0.13 0

20

40

60

80

(b)

20

I00 -

25

am

0.0

0

20

hardpan

depth

40

60

80

100

60

80

I00

O~ 05 04 I

o.~ 02 OI 0.0 20

40

60

80

I00

20

40

slip(%)

Slip ( % ) (el --0---

25 - 30 without

cm float,

hardpan x

depth with

float

Fl(;. 4. Comparison between the power delivered by power tiller with and without float under flooded and puddled conditions for three hardpan depths. without the float in flooded soil conditions was almost the same. H o w e v e r , they were different in puddled soil conditions. The reason for low power output was due to low operating speed of the power tiller to avoid overturning the power tiller due to braking of the towing tractor. The average speed of the power tiller in flooded and puddled soil condition was 0.125 and 0.33 m/s respectively. The pull values at m a x i m u m power were also compared since these values represent the actual working pull or the necessary pull required to work in wet or flooded soil conditions. The results are given in Table 5. The results of combined analysis of pull in flooded and puddled field conditions by the 'F' test showed that the

337

FLOAT EFFECT ON POWER TILLER TABLE 4. SUMMARYOF DUNCAN'S MULTIPLERANGE TEST FOR THE MAXIMUMPOWER (kW) Conditions

Flooded

(Hardpan depth)

Without float

15-20 cm 20-25 cm 25-30 cm

0.51 0.35 0.25

0.54 0.36 0.20

Mean*

0.38(A)

0.37(A)

Average

With float

Flooded

Puddled Mean* 0.52(A) 0.35(AB) 0.25(B)

Without float 0.42 0.29 0.26

0.33 0.13 0.06

0.352(A)

0.17(B)

0.35(A)

Average without float Average with float

With float

Puddled

Mean*

Mean*

0.37(A) 0.21(AB) 0.16(B)

0.45(A) 0.28(B) 0.20(C)

0.27(B)

0.37(A) 0.25(B)

*Means with the same letter are not significantly different at 5% level of significance.

T A B L E 5. SUMMARY OF D U N C A N ' S MULTIPLE RANGE TEST FOR THE PULL

Conditions

Flooded

(Hardpan depth)

Without float

15-20 cm 20-25 cm 25-30 cm

1.56 1.51 1.37

1.71 1.51 1.20

Mean*

1.48(A)

1.47(A)

Average Average without float Average with float

With float

Flooded

(kN) AT THE

MAXIMUM POWER

Puddled Mean* 1.64(A) 1.51(AB) 1.28(B)

1.47(A)

Without float

With float

1.62 1.37 1.13

1.12 0.77 0.42

1.37(A)

0.77(B)

Puddled

Mean*

Mean*

1.37(A) 1.07(AB) 0.77(B)

1.07(B)

1.43(A) 1.10(B)

*Means with the same letter are not significantly different at 5% level of significance.

average pulls in these two different soil conditions were different from each other. The pulls developed by the power tiller with and without the float at 15-20 cm and 20-25 cm hardpan depths were almost the same in flooded soil conditions but they were different in puddled soil conditions. As hardpan depth increased, the pull developed decreased in all cases. The machine performance in most cases was evaluated by pull developed at maximum power and the maximum pull produced at 100% slip. These data have been summarized in Table 6. The results indicate that the power tiller with and without the float attachment delivered almost the same pull in flooded soil conditions except at 25-30 cm hardpan depth. However, the power and maximum pull delivered by the power tiller with the float was lower than that produced by the power tiller without the float at all hardpan depths in puddled soil. The drag test of the power tiller showed that the power tiller without the float required 1.59 and 1.79 kN of drag, while with the float it required 1.58 and 1.66 kN of drag in flooded and puddled soil conditions respectively. The high values of drag were due to cage wheel blocking. However, it was noteworthy that the addition of the float on power tiller did not increase the drag of the power tiller.

338 TABLE6.

V . M . S A L O K H E and A. G H A Z A L I RESULTS

OF THE

DYNAMIC

PERFORMANCE

TEST OF THE

POWER

TILLER

WITH

AND

WITHOUT

FLOAT

ATTACHMENT

Test condition* Test parameter

Pull at 100% slip (kN)

Pull at max. power (kW)

delivered (%)

Slip at max. power (%)

With float

1.76 1,78

1,56 1.71

0.51 0,54

50 54

2

Without float With float

1.74 1,78

1.51 1.51

0.35 0.36

50 50

3

Without float With float

1,68 1,33

1.37 1.20

0,29 (t.20

50 54

4

Without float With float

1.69 1.43

1.62 1,12

0.42 0.33

60 63

5

Without float With float

1.69 1.05

1.37 0.77

0.29 0.13

58 66

6

Without float With float

1.42 0.75

1.13 0.42

0.26 0.06

58 64

1

Without float

Max. power

*Test conditions: 1 = flooded condition at hardpan depth of 15-20 cm; 2 = flooded condition at hardpan depth of 20-25 cm: 3 = flooded condition at hardpan depth of 25-30 cm; 4 = puddled condition at hardpan depth of 15-20 cm: 5 = puddled condition at hardpan depth of 20-25 cm; 6 = puddled condition at hardpan depth of 25-30 cm. CONCLUSIONS

The developed float gave sufficient flotation to the power tiller in both flooded as well as puddled field conditions. Adding the float did not affect the effective field capacity, field efficiency and fuel consumption. On the contrary, it improved the maneuverability of the machine. Addition of the float did not increase the drag of the power tiller. The performance of the power tiller with the float in flooded soil conditions was satisfactory. The float did not allow the wheels to sink deeper and bite the hardpan when working up to 30 cm hardpan depth. The pulls developed by the power tiller with and without the float in flooded soil conditions up to 25 cm hardpan depths were almost the same but decreased as sinkage increased more than 25 cm. However, this hardpan depth is generally difficult to work in actual field cultivation practices. The pull developed by the power tiller with the float in puddled soil condition was less than that developed without the float at all hardpan depths. This was because the cage wheel lugs were not able to generate enough traction from the top soft layer of the puddled soil. Also, the float did not allow the lugs to go deeper to bite the hardpan. This problem could have been overcome by using larger diameter cage wheels so that they could bite the hardpan. However, it may not be a feasible solution as biting of hardpan is not desirable. To overcome the problem of hardpan biting, one may think of mounting additional rotor at the front of the power tiller which should rotate at a much faster speed than the cage wheels so that it would generate enough traction from the soft top layer.

REFERENCES [1] D. GEE-CLouGH, The special problems of wetland traction and flotation. J. agric. Engng Res. 32 (3). 279-288 (1985).

FLOAT EFFECT ON POWER TILLER

339

[2] K. KOKUBUN, Relations between trafficability and physical properties of soil in paddy field. I. agric. Res. Q. 5 (3), 33-37 (1970). [3] M. Klsu, Soil physical properties and machine performances. J. agric. Res. Q. 6 (3), 151-154 (1972). [4] S. Avun, Machinery mobility problem in mechanized rice production in Malaysia. MARDI report no. 03-83 (1983). [5] T. KOBUTA, Soil structural index as a measure of bearing strength of clayey lowland soils. J. agric. Res. Q. 17 (4), 292-299 (1984). [6] L. JAVASUNDERA,Study of factors affecting the design of the fiat lugged cage wheels in paddy soils. Asian Inst. Techn. M. Eng. Thesis (unpublished), No. AE-80-15 (1980). [7] L. S. WIMALAWANSA,Study of optimum lug angle and spacing for cage wheels for medium powered tractor (46 kW). Asian Inst. Techn. M. Eng. Thesis (unpublished), No. AE-82-15 (1982). [8] M. M. HOSSA~N, Field performance evaluation of power tiller manufactured in Thailand. Asian Inst. Techn. M. Eng. Thesis (unpublished), No. AE-81-9 (1981). [9] S. VERMA, Development and testing of retractive lugged cage wheels. Asian Inst. Techn. M. Eng. Thesis (unpublished), No. 84-12 (1984). [10] K. C. YEOH, Evaluation of the performance of four row mechanical transplanter. Teknologi Pertanian, Jil 2 Bil 2, pp. 98-104, MARDI, Serdang (1979). [11] H. D. Aau, A. GHAZAU, C. W. CHAN, A. W. CHEONG, M. A. SUPAAD, M. D HUSSAIN, S. MINHAD and M. Y. SHAHRIN, A Practical Guide on Mechanical Transplanting System. MARDI, Serdang (1988). [12] N. G. SHAH, Study of float devices for wetland machinery. Asian Inst. Techn. M. Eng. Thesis (unpublished) No. AE-80-20 (1980). [13] W. L. WANG and Y. ZHU, Buoying principle of tractor and its applications. Trans. Chinese. Soc. Agric. Machinery 2; 2-9 (1980). [14] R. B. GAVINO, Field performance evaluation of the turtle brand manufactured in the Philippines. Asian Inst. Tech. M. Eng. Thesis (unpublished), No. AE-84-8 (1984). [15] N. C. THAI and W. J. CHANCELLOR.Boat-tractor hull design to minimize drag forces. Agric-Mechanization in Asia, Africa and Latin America 16 (1), 11-17 (1985) [16] V. M. SALOKHEand D. GEE-CLOUGH,Studies on effect of lug surface coating on soil adhesion of cage wheel lugs. Proc. 9th lnt Conf. of ISTVS, Barcelona, Spain, pp. 389-396 (1987). [17] V. M. SALOKHEand D. GEE-CLOUGH,Coating of cage wheel lugs to reduce soil adhesion. J. agric. Engng Res. 41 (3), 201-210 (1988). [18] V. M. SALOKHE, D. GEE-CLOUGH, S. MANZOOR and K. K. SmGH, Improvement of the tractive performance of cage wheels by enamel coating. J. agric. Engng Res. 45 (3), 209-224 (1990). [19] A. GHAZALI,A float attachment for power tiller. Asian Inst. Techn. M. Eng. Thesis (unpublished) No. AE-89-8 (1989).