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Diversification and sophistication
Journal of Terrarnechanics, Vol. 28. No. 2//3, pp. 137-150. 1991. Printed in Great Britain.
DIVERSIFICATION
AND
0022 -4898/91 $3.00 + 0.0tl Pergamon Press plc. © 199l ISTVS
SOPHISTICATION*
A K I R A OIDA'~
S u m m a r y - - I n this report, progress and state-of-the-art of research on vehicle and machinery designs are described for vehicles such as boat tractors, wheel type vehicles, tracked xehicles and a new locomotion system. The development stages and aspects of off-road vehicles are different in countries/districts, showing many kinds of running devices. Reflecting a high-technology in some countries, the mechanism and the control system of off-road vehicles arc becoming more and more sophisticated.
INTRODUCTION
WITH DIFFERENT objectives in various industries on different terrains in countries/ districts where the levels of technological development are somewhat different, various ideas have been created and grown up to realize new concepts of more effective vehicles and machines from the viewpoint of terramechanics. In this part of Session No. 4, there are nine reports [1-9] which are related to the research and development of vehicles and machines with higher mobility and better maneuverability on some kinds of off-road terrains. If these reports were to be summarized by a few words, one would like to say these papers are reflecting the diversification and sophistication of vehicle and machine designs owing to various demands in various terrains and a rapid development of high technology. These nine papers are classified as follows by the vehicle/machine types: (1) (2) (3) (4)
boat tractor [1 and 6], wheel type vehicle [2, 3 and 8], tracked vehicle [4, 7 and 9], and new locomotion system [5].
They can be also classified as follows according to the objectives of research: (1) (2) (3) (4)
to achieve good propulsion [1, 3, and 8], to decrease running resistance [6], to reduce walking wheel vibration [2], and to improve trafficability, maneuverability and steering controllability [4, 5, 7, and 9].
General views of the papers and related literature are given according to the vehicle types. *State-of-the-art report, Session 4, Vehicle and Machinery Design and Implements, Part I, presented at the 10th International Conference of the International Society for Terrain-Vehicle Systems, Kobe, Japan (August 1990). *Department of Agricultural Engineering, Faculty of Agriculture, Kyoto University, Kyoto 606. Japan. 137
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A. OIDA
BOAT TRACTORS According to ref. [10], research on a boat-type tillage machine started in the early 1960s and a prototype "'Hupeih-12"' was produced for actual field workings. Since then it quickly went on to be tested over very mushy paddy fields in lake and marsh areas in China. In 1978, 12 years ago, there were about 40 kinds and 70000 units of boat tractor. One of the merits of a boat tractor is of course good mobility due to its buoyancy, and it was said that the workable area per unit power of boat tractor was 2-25 times that of a standard tractor. The kinematics and dynamics of the boat tractor had been clarified through some enthusiastic research [such as 11, 12 and 13] from the standpoints of Bekker's theory, earth pressure theory etc. with many experiments. Wang et al, [12] said in their paper that: Through a preliminary statistical analysis of the effects of present boat type tractors, we have reached the conclusion that the boat type tractor, the boat type combine and the combinatory tractor with floating boat which are all based on the "Buoying principle" may be the main developing direction of the PFPU (Paddy Field Power Unit) in the future. In the paper presented in this conference [l], Tao et al. report that much progress has been made in the design of the drive wheel and the geometrical parameters of the wheel blade of boat tractors. They proposed a "Floating Walking Mechanism" shown in Fig. 1. According to the paper, the mechanism is self-adjusted and can create the most desirable vertical load distributions on the boat bottom and drive wheel, resulting in high traction efficiency. It sounds a little strange that a non-controlled self-adjusted mechanism is the best one. There may be some limitations to adopt this mechanism, which are not clear in the paper. Chen et al. [14] showed us a new idea of movable lugs for the driving wheel of boat tractors at the 8th ISTVS conference in Cambridge. As shown in Fig. 2, the mechanism was to keep the lug face vertical during the contact time by a roller-sliding groove mechanism or a chain-sprocket mechanism. That idea seemed very good in order to reduce soil compaction, that is to decrease the running resistance of the
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driving wheel. If this mechanism is applied to the boat tractor, however, the lugs can scarcely support the load. However, the driving wheel would not need to support the load, because the boat tractor body will support almost all the load and the driving wheel is used only to exert the propulsion. This point will become a theme of discussion. Zhuge Zhen et al. [6] present the method to reduce a sliding resistance by charging the air between a sliding part of vehicle and the soil and making a thin air curtain, which causes less sliding resistance. They call the device a Slide Air Curtain Resistance Reducer ( S A C R R ) and did some experiments, applying the S A C R R to the boat tractor as Fig. 3. Figure 4 shows the reduction percentage of sliding resistance when the S A C R R was used, and it is clear that the effect of the device was very great on the adhesive soil where the vehicle having a sliding mechanism can scarcely go easily. The following questions are raised. (1) Are the sliding vehicles like the boat tractor mainly used on a muddy/mushy high moisture soil? Therefore, one would guess that the sliding resistance itself would not be so high, because, if the sliding resistance were high, these sliding mechanisms would actually not be used. (2) Is there no entry of water and soil particles through the air injection holes'? (3) What was the energy balance and the cost balance between the sliding vehicle with the S A C R R and that without S A C R R ?
WHEELS AND WHEEL TYPE VEHICLES The D e p a r t m e n t of Tractor and Automobile Engineering, Jilin University of Technology, P. R. C. has been conducting a consistent research about a so-called walking wheel. Firstly they made a so-called half walking wheel as shown in Fig. 5 in order to reduce the rolling resistance and to improve the tractive efficiency of a normal tractor wheel [15]. However, the big disadvantage is an intense shock and a vibration when running on a hard ground/road. Thus their efforts have been directed to reduce or, if possible, to eliminate such vibration of a walking wheel. They considered a mechanism of retractable legs as shown in Fig. 6. Because of the complexity of the structure, they developed the next walking wheel utilizing the
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principle of harmonic resultant as shown in Fig. 7. It has a deviated (eccentric) center of rotation of the hub Oi from the rotation center of the wheel 02 and by selecting optimum parameters the vertical m o v e m e n t of the hub could be restricted in a small range. There was a video of a running tractor with the walking wheels at the 2nd Asia-Pacific Conference of ISTVS in Bangkok two years ago and it was found that the tractor ran very smoothly on the road. In this conference Zhang et al. showed a new walking wheel as shown in Fig. 8 [2]. It has a kind of retracting legs with a cam-roller mechanism. It is shown that the bouncing of the wheel should be perfectly eliminated theoretically, the number of legs would be better as 8, and the wheel has good characteristics such as a simple structure, a low price, a high mobility and a high tractive efficiency. There might be some problems of durability of the mechanism and sealing from water and soil at the sliding parts of the legs. The research report [3] of this session by Takai et al. is about a tractor and driven trailer (root crop harvester) system. The authors analysed this driving system statically 5o
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DIVERSIFICATION AND SOPHISTICATION
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and made simulation calculations to find out the effects of some design parameters such as trailer weight, the center of gravity of the trailer, height of the hitch point and the ratio of peripheral velocity of the trailer wheel to that of the tractor wheel. Results of the analysis are summarized in the conclusion in the paper. Let us consider the peripheral velocity difference between tractor and trailer wheels. The authors concluded that in order to avoid pushing the tractor, the peripheral velocity of the tractor wheel should be at least 20% more than that of the trailer wheel when the traction coefficient of tractor wheel is larger than that of the trailer wheel. Tano et al. also studied the peripheral velocity difference between front wheel and rear wheel of a 4WD farm tractor on a paved road [16, 17]. Figure 9 shows the variations of slippages of front and rear wheels, traction and tractive power due to the peripheral velocity difference. The tractive power reached its maximum when the peripheral velocity of the front wheel was about 10% more than that of the rear wheel. In Japan nowadays manufacturers of farm tractors are selling 4WD farm tractors, which
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Fl~i. 7. Ncw half walking v~heel [15I. generally have a peripheral velocity difference of 3-4% (that is the front wheel has a 3-4% faster peripheral velocity than the rear wheel) and have also a special mechanism that when the tractor turns at the end of field the velocity ratio is suddenly increased for example to 100% (it means the front wheel velocity is twice the rear wheel velocity). It helps the tractor turn easily especially in a soft or tilled field. However, the optimum velocity difference has not been found yet in order to make a good turn. Researching is now being carried out on that point from the standpoint of steerability based on terramechanics including a new steering system such as a 4WD-4WS [18]. Reference [g] in this session is related to the design of cage wheels and is presented by Triratanasirichai and Oida. As the simple wheel-type running device for a power tiller, the cage wheel is coming very popular in dry land and paddy field in South-east
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Asia countries like Thailand because of its high mobility with a simple structure and a low cost. Much research has been done on lug-soil interactions in these two decades in the terramechanics field [19-31]. However, it seems that there is not yet a distinct conclusion about design criteria of cage wheels, such as wheel diameter, lug angle and lug pitch. Of course, such criteria will/should vary with soil conditions (that is soil mechanical properties). Almost all past experiments were done under restricted conditions such as a single lug, a constant sinkage and a soil bin test. In this research we aimed to carry out experiments with actual size cage wheels in natural dry land and paddy fields by using fully automated electronic data acquisition and processing systems. For example, Fig. 10 shows distributions of lift and pull forces on the lug along a contact length for the lug angle of 45 ° . As a result of repeated experiments using test cage wheels with double thin rims of 60 cm diameter, 7.5 x 20 cm lug plates, five kinds of lug angle ( 1 5 , 3 0 , 4 5 , 6 0 and 75 °) and four lug pitches (12.3, 16.4, 24.6 and 32.9 cm), it was found that the combinations which gave the m a x i m u m tractive efficiency were 12.3 cm lug pitch and 60 ° lug angle in a dry sand field and i2.3 cm lug pitch and 45 ° lug angle in a wet paddy field. The theoretical analysis will be made soon by utilizing the finite element method of Nakashima [28]. In the case of adopting FEM, it is always an important problem how to express the soil mechanical properties by a constitutive equation. Nakashima took the soil property as a rigid plastic one. In this study the lug-soil interaction is analysed,
144
A. OIDA
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TRACKED VEHICLES Fijalkowski presents an interesting paper about so-called very advanced propulsion spheres in this session [4]. What he wants to say would be that the very sophisticated tracked vehicle would be developed by utilizing the past knowledge, ideas and present high technology. One example which was proposed is shown in Fig. 11. According to this expression, this turtleqike vehicle, the so-called "Terrapin", has the Fijalkowski engine [34] with a constant output, on-board advanced sodium-sulfur d.c. storage battery, and two primary and two secondary twin-bogies each with a rubber all-wheel-driven track. Within the latter, two pneumatic-tyre motorized road-wheels, including two d.c. macrocommutator IPM (interior permanent magnet) electromechanical twin-wheel h u b - m o t o r s [351, are fixed, and there is an o n - b o a r d single-chip m i c r o c o m p u t e r - b a s e d vehicle controller. T h e twin-bogies with r u b b e r track were already shown by Mickelson [36] in the c o n f e r e n c e in C a m b r i d g e . The next p a p e r by Sasaki et al. [7] is a b o u t an articulated tracked vehicle. T h e concept of the articulated tracked vehicle to i m p r o v e mobility and steerability a p p e a r e d at a b o u t the beginning of this century, and m a n y types of articulated tracked vehicle have been m a d e and used. Nuttall listed t h e m in the first issue of Journal o f Terramechanics, 1964 [37], including the Diplock t r a c t o r - t r a i l e r articulated vehicle (1912), the D a v i d s o n S n o - T r a c t o r (1935), the T u c k e r S N O - C A T (1948), the N o r t h King (1952), the C a n a d i a n A r m y R A T , the P O L E C A T , the M U S K - O X (1959), the three-unit, train articulated C O B R A (1959), the M A R K II P O L E C A T
DIVERSIFICATION AND SOPHISTICATION
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FIc~. 1i. TERRAPIN by Fiialkowski [4]. (1962), the W N R E D I N A H (1961) and the U.S./Canadian Army XM571 (1963). Nuttall said in his conclusions in 1964: The steering of tracked vehicles by articulation has, within the past few years, been successfully demonstrated on high-mobility vehicles from 1 ton to 45 tons in gross weight. Experience has shown that this configuration is eminently practical. It improves the mobility of tracked vehicles both directly, through the elimination of constant braking while trying to go ahead, and indirectly, by making practical near-bellyless configurations capable of carrying large loads at unusually low nominal unit ground pressures. Vehicles of this configuration are now demonstrating levels of mobility and of reliability not previously thought possible in tracked vehicles. Hanamoto has done research on a positive pitch control of an articulated tracked vehicle " ' C O B R A " [38,39]. In the 5th International Conference of the ISTVS in Detroit Kamm reported about an articulated armored personnel carrier Coupled M-113, which had two upper cylinders and a ball-joint and an electro-hydraulic control system with force-feedback circuit [40]. The author also saw the field demonstration of the Coupled M-113 in Houghton near Lake Superior. The good performance of the Coupled M-113 was examined, which climbed up a step obstacle about 1.5 m high, raising the head of the front vehicle, climbing and pulling up the rear vehicle.
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A. O I D A
Ljunggren produced an articulated all-terrain tracked vehicle model BV206 in the 7th International Conference of ISTVS in Calgary [41]. Pitching. roiling and yawing can be controlled by a hydrostatic articulated steering system operated by a stccring wheel and activated by hydraulic cylinders each side of the steering unit. Thc proposed steering system by Sasaki et al. in this conference [7] is similar to that of thc BV206 as shown in Fig. 12. It has three modes such as "float". "'lock" and "'active control" modes for forestry work on steep slopes. In order to go over some obstacles of logs and slash it would be better for the vehicle to have the twin bogies [351. which can keep the vehicle body parallel to the ground surface. Alhimdani et al. presented a paper in this conference about an effect of hydraulic piston on hinge force of simple wagon-type articulated tracked vehicle [9]. Their fundamental theory was already published [42]. They tried to insert a hydraulic piston between the towing tractor and the hinge point of the towed trailer in order to help the straightening up motion from the turning position. As a conclusion they said that this piston should not act when the tractor-trailer system is turning and should act when the system starts to straighten up. To construct their theory they assumed a uniform pressure distribution and constant coefficient of lateral friction and neglected some dynamic parameters. The most important point would be that they did not consider the effects of track slippages. There was much theoretical and experimental research about the forces, which acted on the cleat or track, and about the turning behaviors of articulated tracked vehicle in our terramechanics field [43-49]. If these results are adequately applied, more actual analysis will be done, The author feels that the articulation should be somewhat controlled by sonic actuators such as hydraulic cylinders as mentioned abovc.
NEW I . O ( ' O M O T I O N SYSTEM
Horio produced a new locomotion system using rolling balls [5]. It consists of a big rolling ball and some small balls to drive the big ball by the friction between them as shown in Fig. 13. By changing the rolling directions of the small balls, the rolling direction of the big ball would be controlled directly. Horio earlier studied crab steering, that is a kind of 4-wheel steering to enable the vehicle to move laterally or slantwise like a crab, and hybrid steering composed of crab steering and normal front-wheel steering, in order to use them for the automatic control system of off-road vehicles such as agricultural crop harvesting or pest control machines [50, 51]. As he said in the proceedings through such studies he felt that there was a difficulty to control the vehicle always to be in the optimum position and direction because of involved integral elements in the steering system. Therefore, he developed a new concept of direct steering mechanism without integral elements. It looks like a very interesting method, but at the same time there might be many problems. Is the power transmission efficiency between the driving small balls and the rolling balls considered reasonable? Especially when this device runs on the soil some soil particles will adhere to the ball surface and the contact between the balls will change to a low friction state. Even if this aims at the application for agricultural robots, it will be required to carry a rather heavy load in the handling of agricultural crops. There is also the problem of wear/abrasion of balls. The mechanism of force transmission by friction itself would not be r e c o m m e n d e d . How does one brake the vehicle, if the friction coefficient will decrease from some reason such as water or soil particle
D I V E R S I F I C A T I O N AND SOPHISTICATION Y¢w
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insertion? Furthermore, even if the vehicle sinkage becomes smaller, the rolling resistance will increase on the soft soil compared to conventional tires because the volume of compressed soil would increase. Anyway the question is whether the steerability and controllability of the system (if possible) is so important in spite of some undesirable aspects mentioned above. As a conclusion it is felt that new ideas and concepts to develop more effective vehicles should be welcomed, however, at the same time the reality of proposed ideas should be investigated.
CLOSING R E M A R K S
Progress has been made in vehicle and machinery designs in different districts/coun-
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A. OIDA
tries. In C h i n a t h e b o a t t r a c t o r is b e c o m i n g m o r e e f f e c t i v e , i m p r o v i n g the d r i v i n g w h e e l d e s i g n by a p p l y i n g a f l o a t i n g w a l k i n g m e c h a n i s m , o r t r y i n g to d e c r e a s e the sliding r e s i s t a n c e by i n t r o d u c i n g t h e air c h a r g i n g s y s t e m . In C h i n a a n e w m e c h a n i s m o f w a l k i n g w h e e l was d e v e l o p e d , w h i c h can r u n w i t h o u t m u c h v e r t i c a l v i b r a t i o n . In J a p a n n o w m a n y k i n d s o f 4 W D t r a c t o r are m a i n p r o d u c t s o f m a n u f a c t u r e r s a n d the a d v a n t a g e will b e u s e d in t h e t r a c t o r - t r a i l e r s y s t e m . In J a p a n also a n e w i d e a a p p e a r e d in t h e l o c o m o t i o n s y s t e m to use r o l l i n g balls in o r d e r to a p p l y it to a fully a u t o m a t e d a g r i c u l t u r a l v e h i c l e , t h a t is an a g r i c u l t u r a l r o b o t , utilizing v e r y a d v a n c e d s o - c a l l e d h i g h t e c h n o l o g y , T h e d e s i g n c r i t e r i a o f c a g e w h e e l s will be also e s t a b l i s h e d in t h e n e a r f u t u r e in T h a i l a n d . In P o l a n d t h e h i g h s p e e d t r a c k e d v e h i c l e w i t h v e r y a d v a n c e d p r o p u l s i o n s y s t e m was p r o p o s e d r e f l e c t i n g t h e h i g h t e c h n o l o g y e r a . T h e a r t i c u l a t e d t r a c k e d v e h i c l e was also d e v e l o p e d in J a p a n e s e f o r e s t r y d i v i s i o n . This research progress associates the terms "diversification" and "'sophistication" of o f f - r o a d v e h i c l e s . D i f f e r e n t i d e a s s t i m u l a t e e a c h o t h e r a n d e a c h r e s e a r c h e r gets s o m e hints f r o m t h e t a l k i n g a n d d i s c u s s i o n , so t h a t a n e w s t e p o f t h e r e s e a r c h b e g i n s . T h i s is t h e fruit o f o u r i n t e r n a t i o n a l c o n f e r e n c e o f t h e I S T V S .
REFERENCES [1] ,h~Nn'N TAO and ZHON~;IONC~LJu, The essential technical matters of boat-tractor design in the respect of driving and loading condition. Proc, 10th Int. Conf. ISTVf, Kobe, pp. 755-766 (19901. [2] SHI:JUN ZHANG, DEXING CIIEN, LUQUAN YEN and BINGCONG CHIN, Study on a new kind of walking wheel. Proc. 10th Int. Conf. ISTVS, Kobe. pp. 767-770 (1990). [31 K. SAY,M, M. TAKAI and S. HA'IA, Theoretical analysis of a wheel driven root crop harvester. Pro('. 10th Int. ('on[~ ISTVS, Kobe, pp, 771-782 (19901. [4] B. m. FIJALKOWSI
DIVERSIFICATION AND SOPHISTICATION
[19] [201 [21] [22] [23] [24] [25] [26] [27] 128] [29] [31)] [31]
[32]
[331 [34] [351 [36] [371 [38] [39] [40] [411 [42] [43] [44] [45] [46]
[47] ]48]
149
J. W. DICKSON, D. (_JEE-CLOUGH and J. K. HENSHALI., The tractive performance and comparison produced in agricultural soils by open, flat-lugged wheels m o u n t e d alone. Prec. ?th Int. Conl~ ISTVS, Calgary, pp. 551-583 (19811. x t , DA, A research of the dynamic performance of the paddle driving wheel working in soft terrain. Prec. 9th Int. Conf. 1STVS. Barcelona, pp. 381-388 (19871. Z. L. ZHANG and Y. J. SHAO, The analysis on the dynamic performance of a single lug. Prec. 8th hit. Conf. ISTVS, Camt~ridge, pp. 575-591 (19841. H. Z. Lu and Y. J. SHAO. Experimental research on the soil flow and soil reaction beneath lugs of powered wheel. Prec. 9th Int. Conf. ISI'VS. Barcelona, pp. 373-380 (19871, V. M. S~,LOKHE and D. G~E-GLou~H, Behavior of wet clay soil under single cage wheel lug../, a~,,ric. Engng Res. 37, 255 266 (19871. V. M. S.~,LoKm- and D. GL~ -CLot~on, Formation of a boundary wedge on a single lug in wct claw soil. J. agric. Engng Res'. 38, 113-125 ( 19871. T. TAr-,.~,KA and H. NA~,ASHIM~',, Interactions in soil-lug system (Part l) Characteristics of soil reaction on a lug with lug angle of 30 degrees. J. J S A M 48(2), 225-232 ( 19861. H. NAIq,~SHJ~,IA and T. TANAKA, Interactions in soil-lug system (Part 2)--Effect of lug angle on soil reaction. J . . I S A M 50(6), 3-10 (1988). H. NAKASHM-', and T. TANAKA, Interactions in soil-lug system (Part 3)--Soil behavior under lug and sinkage variation of lugged wheel, J. J S A M 51(2), 47 55 (19891. H. NAKAStlIMA and T. TANAKA, Interactions in soil-lug system (Part 4)--Numerical simulation of interactions. ,1. J S A M 52(11, 77-83 (1990). X. L. WA:-;c;, T, TANAKA and M. YaM~,Z.XKI, Study on soil-lugged wheel interaction (Part 1)--Dynamic behavior of a lugged wheel. J. J S A M 51(31,33 40(1c~89). X. L. WANG, f . TANAKA and M. YAMAZAKI, Study on soil-lugged wheel interaction (Part 2)--Characteristics of soil reaction on a lugged wheel. ,I, .ISAM $1(51, 11 18 (1c,~89). X. L. WANe;, f . TANAKA and M. YAMAZAKI. Study ori soil-lugged wheel interaction (Part 3)--Characteristics of behavior and reaction of a lugged wheel in a high moismrc, h o m o g c n c o u s paddy soil and a paddy soil with hardpan..I. J S A M 52(2), 11 18 (lttg()). K. TRIRAFANASIP,ICHAI, A. On)A and M. Hoyt),x, Study on dcsign criteria of cage wheel (Part l)--Effccts of lug angle and lug pitch on tractive performance of cage wheel in dry hind and paddy field. J. J S A M 52(4), 21 27 (19901. A. ()u)A, Analysis of rheological deformation of soil by mcans of finite clement method. ,I. Terrumechanie,~ 21, 237-251 (1984). B. T. Fl¢~Ai ~owsKi, Novel ahernative prime movers for agricuhural tractors. Prec. t)th lnl. ('onf. ISTVS, Barcelona, pp. 881-897 (19871. B. f . Fl.l,XlkOWSkl. Electronic-commutator A C / D C motor-driven tracked all-terrain vehicles with extremely high mobility. Proc, 8th Int. Conf. ISTVS, Cumbridge. pp. 1045 1063 (1¢t84). P. 1. MJ(E
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[49] L.F. LITTLE, The Alecto tracklayer. J. Terramechanics 1(2). 7¢~ ,q2 (1964). [50] H. HoRio, On-off control of crab-steering. The Science Report ~[ kFtcul(v ~/'A~ri('.. Kohe Univ., 18(2). 185-206 (1988). [51] H. HORIO and H. NAKA~AURA.Automatic steering of off-ro~ld vehicle: calculatixlg detcctioll of desired pass and double modes steering (Part 1)..1. JST 9, 15 21 (1989).
DIVERSIFICATION
AND
0022 -4898/91 $3.00 + 0.0tl Pergamon Press plc. © 199l ISTVS
SOPHISTICATION*
A K I R A OIDA'~
S u m m a r y - - I n this report, progress and state-of-the-art of research on vehicle and machinery designs are described for vehicles such as boat tractors, wheel type vehicles, tracked xehicles and a new locomotion system. The development stages and aspects of off-road vehicles are different in countries/districts, showing many kinds of running devices. Reflecting a high-technology in some countries, the mechanism and the control system of off-road vehicles arc becoming more and more sophisticated.
INTRODUCTION
WITH DIFFERENT objectives in various industries on different terrains in countries/ districts where the levels of technological development are somewhat different, various ideas have been created and grown up to realize new concepts of more effective vehicles and machines from the viewpoint of terramechanics. In this part of Session No. 4, there are nine reports [1-9] which are related to the research and development of vehicles and machines with higher mobility and better maneuverability on some kinds of off-road terrains. If these reports were to be summarized by a few words, one would like to say these papers are reflecting the diversification and sophistication of vehicle and machine designs owing to various demands in various terrains and a rapid development of high technology. These nine papers are classified as follows by the vehicle/machine types: (1) (2) (3) (4)
boat tractor [1 and 6], wheel type vehicle [2, 3 and 8], tracked vehicle [4, 7 and 9], and new locomotion system [5].
They can be also classified as follows according to the objectives of research: (1) (2) (3) (4)
to achieve good propulsion [1, 3, and 8], to decrease running resistance [6], to reduce walking wheel vibration [2], and to improve trafficability, maneuverability and steering controllability [4, 5, 7, and 9].
General views of the papers and related literature are given according to the vehicle types. *State-of-the-art report, Session 4, Vehicle and Machinery Design and Implements, Part I, presented at the 10th International Conference of the International Society for Terrain-Vehicle Systems, Kobe, Japan (August 1990). *Department of Agricultural Engineering, Faculty of Agriculture, Kyoto University, Kyoto 606. Japan. 137
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BOAT TRACTORS According to ref. [10], research on a boat-type tillage machine started in the early 1960s and a prototype "'Hupeih-12"' was produced for actual field workings. Since then it quickly went on to be tested over very mushy paddy fields in lake and marsh areas in China. In 1978, 12 years ago, there were about 40 kinds and 70000 units of boat tractor. One of the merits of a boat tractor is of course good mobility due to its buoyancy, and it was said that the workable area per unit power of boat tractor was 2-25 times that of a standard tractor. The kinematics and dynamics of the boat tractor had been clarified through some enthusiastic research [such as 11, 12 and 13] from the standpoints of Bekker's theory, earth pressure theory etc. with many experiments. Wang et al, [12] said in their paper that: Through a preliminary statistical analysis of the effects of present boat type tractors, we have reached the conclusion that the boat type tractor, the boat type combine and the combinatory tractor with floating boat which are all based on the "Buoying principle" may be the main developing direction of the PFPU (Paddy Field Power Unit) in the future. In the paper presented in this conference [l], Tao et al. report that much progress has been made in the design of the drive wheel and the geometrical parameters of the wheel blade of boat tractors. They proposed a "Floating Walking Mechanism" shown in Fig. 1. According to the paper, the mechanism is self-adjusted and can create the most desirable vertical load distributions on the boat bottom and drive wheel, resulting in high traction efficiency. It sounds a little strange that a non-controlled self-adjusted mechanism is the best one. There may be some limitations to adopt this mechanism, which are not clear in the paper. Chen et al. [14] showed us a new idea of movable lugs for the driving wheel of boat tractors at the 8th ISTVS conference in Cambridge. As shown in Fig. 2, the mechanism was to keep the lug face vertical during the contact time by a roller-sliding groove mechanism or a chain-sprocket mechanism. That idea seemed very good in order to reduce soil compaction, that is to decrease the running resistance of the
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driving wheel. If this mechanism is applied to the boat tractor, however, the lugs can scarcely support the load. However, the driving wheel would not need to support the load, because the boat tractor body will support almost all the load and the driving wheel is used only to exert the propulsion. This point will become a theme of discussion. Zhuge Zhen et al. [6] present the method to reduce a sliding resistance by charging the air between a sliding part of vehicle and the soil and making a thin air curtain, which causes less sliding resistance. They call the device a Slide Air Curtain Resistance Reducer ( S A C R R ) and did some experiments, applying the S A C R R to the boat tractor as Fig. 3. Figure 4 shows the reduction percentage of sliding resistance when the S A C R R was used, and it is clear that the effect of the device was very great on the adhesive soil where the vehicle having a sliding mechanism can scarcely go easily. The following questions are raised. (1) Are the sliding vehicles like the boat tractor mainly used on a muddy/mushy high moisture soil? Therefore, one would guess that the sliding resistance itself would not be so high, because, if the sliding resistance were high, these sliding mechanisms would actually not be used. (2) Is there no entry of water and soil particles through the air injection holes'? (3) What was the energy balance and the cost balance between the sliding vehicle with the S A C R R and that without S A C R R ?
WHEELS AND WHEEL TYPE VEHICLES The D e p a r t m e n t of Tractor and Automobile Engineering, Jilin University of Technology, P. R. C. has been conducting a consistent research about a so-called walking wheel. Firstly they made a so-called half walking wheel as shown in Fig. 5 in order to reduce the rolling resistance and to improve the tractive efficiency of a normal tractor wheel [15]. However, the big disadvantage is an intense shock and a vibration when running on a hard ground/road. Thus their efforts have been directed to reduce or, if possible, to eliminate such vibration of a walking wheel. They considered a mechanism of retractable legs as shown in Fig. 6. Because of the complexity of the structure, they developed the next walking wheel utilizing the
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principle of harmonic resultant as shown in Fig. 7. It has a deviated (eccentric) center of rotation of the hub Oi from the rotation center of the wheel 02 and by selecting optimum parameters the vertical m o v e m e n t of the hub could be restricted in a small range. There was a video of a running tractor with the walking wheels at the 2nd Asia-Pacific Conference of ISTVS in Bangkok two years ago and it was found that the tractor ran very smoothly on the road. In this conference Zhang et al. showed a new walking wheel as shown in Fig. 8 [2]. It has a kind of retracting legs with a cam-roller mechanism. It is shown that the bouncing of the wheel should be perfectly eliminated theoretically, the number of legs would be better as 8, and the wheel has good characteristics such as a simple structure, a low price, a high mobility and a high tractive efficiency. There might be some problems of durability of the mechanism and sealing from water and soil at the sliding parts of the legs. The research report [3] of this session by Takai et al. is about a tractor and driven trailer (root crop harvester) system. The authors analysed this driving system statically 5o
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DIVERSIFICATION AND SOPHISTICATION
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and made simulation calculations to find out the effects of some design parameters such as trailer weight, the center of gravity of the trailer, height of the hitch point and the ratio of peripheral velocity of the trailer wheel to that of the tractor wheel. Results of the analysis are summarized in the conclusion in the paper. Let us consider the peripheral velocity difference between tractor and trailer wheels. The authors concluded that in order to avoid pushing the tractor, the peripheral velocity of the tractor wheel should be at least 20% more than that of the trailer wheel when the traction coefficient of tractor wheel is larger than that of the trailer wheel. Tano et al. also studied the peripheral velocity difference between front wheel and rear wheel of a 4WD farm tractor on a paved road [16, 17]. Figure 9 shows the variations of slippages of front and rear wheels, traction and tractive power due to the peripheral velocity difference. The tractive power reached its maximum when the peripheral velocity of the front wheel was about 10% more than that of the rear wheel. In Japan nowadays manufacturers of farm tractors are selling 4WD farm tractors, which
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A. ()II)A
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Fl~i. 7. Ncw half walking v~heel [15I. generally have a peripheral velocity difference of 3-4% (that is the front wheel has a 3-4% faster peripheral velocity than the rear wheel) and have also a special mechanism that when the tractor turns at the end of field the velocity ratio is suddenly increased for example to 100% (it means the front wheel velocity is twice the rear wheel velocity). It helps the tractor turn easily especially in a soft or tilled field. However, the optimum velocity difference has not been found yet in order to make a good turn. Researching is now being carried out on that point from the standpoint of steerability based on terramechanics including a new steering system such as a 4WD-4WS [18]. Reference [g] in this session is related to the design of cage wheels and is presented by Triratanasirichai and Oida. As the simple wheel-type running device for a power tiller, the cage wheel is coming very popular in dry land and paddy field in South-east
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Asia countries like Thailand because of its high mobility with a simple structure and a low cost. Much research has been done on lug-soil interactions in these two decades in the terramechanics field [19-31]. However, it seems that there is not yet a distinct conclusion about design criteria of cage wheels, such as wheel diameter, lug angle and lug pitch. Of course, such criteria will/should vary with soil conditions (that is soil mechanical properties). Almost all past experiments were done under restricted conditions such as a single lug, a constant sinkage and a soil bin test. In this research we aimed to carry out experiments with actual size cage wheels in natural dry land and paddy fields by using fully automated electronic data acquisition and processing systems. For example, Fig. 10 shows distributions of lift and pull forces on the lug along a contact length for the lug angle of 45 ° . As a result of repeated experiments using test cage wheels with double thin rims of 60 cm diameter, 7.5 x 20 cm lug plates, five kinds of lug angle ( 1 5 , 3 0 , 4 5 , 6 0 and 75 °) and four lug pitches (12.3, 16.4, 24.6 and 32.9 cm), it was found that the combinations which gave the m a x i m u m tractive efficiency were 12.3 cm lug pitch and 60 ° lug angle in a dry sand field and i2.3 cm lug pitch and 45 ° lug angle in a wet paddy field. The theoretical analysis will be made soon by utilizing the finite element method of Nakashima [28]. In the case of adopting FEM, it is always an important problem how to express the soil mechanical properties by a constitutive equation. Nakashima took the soil property as a rigid plastic one. In this study the lug-soil interaction is analysed,
144
A. OIDA
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TRACKED VEHICLES Fijalkowski presents an interesting paper about so-called very advanced propulsion spheres in this session [4]. What he wants to say would be that the very sophisticated tracked vehicle would be developed by utilizing the past knowledge, ideas and present high technology. One example which was proposed is shown in Fig. 11. According to this expression, this turtleqike vehicle, the so-called "Terrapin", has the Fijalkowski engine [34] with a constant output, on-board advanced sodium-sulfur d.c. storage battery, and two primary and two secondary twin-bogies each with a rubber all-wheel-driven track. Within the latter, two pneumatic-tyre motorized road-wheels, including two d.c. macrocommutator IPM (interior permanent magnet) electromechanical twin-wheel h u b - m o t o r s [351, are fixed, and there is an o n - b o a r d single-chip m i c r o c o m p u t e r - b a s e d vehicle controller. T h e twin-bogies with r u b b e r track were already shown by Mickelson [36] in the c o n f e r e n c e in C a m b r i d g e . The next p a p e r by Sasaki et al. [7] is a b o u t an articulated tracked vehicle. T h e concept of the articulated tracked vehicle to i m p r o v e mobility and steerability a p p e a r e d at a b o u t the beginning of this century, and m a n y types of articulated tracked vehicle have been m a d e and used. Nuttall listed t h e m in the first issue of Journal o f Terramechanics, 1964 [37], including the Diplock t r a c t o r - t r a i l e r articulated vehicle (1912), the D a v i d s o n S n o - T r a c t o r (1935), the T u c k e r S N O - C A T (1948), the N o r t h King (1952), the C a n a d i a n A r m y R A T , the P O L E C A T , the M U S K - O X (1959), the three-unit, train articulated C O B R A (1959), the M A R K II P O L E C A T
DIVERSIFICATION AND SOPHISTICATION
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FIc~. 1i. TERRAPIN by Fiialkowski [4]. (1962), the W N R E D I N A H (1961) and the U.S./Canadian Army XM571 (1963). Nuttall said in his conclusions in 1964: The steering of tracked vehicles by articulation has, within the past few years, been successfully demonstrated on high-mobility vehicles from 1 ton to 45 tons in gross weight. Experience has shown that this configuration is eminently practical. It improves the mobility of tracked vehicles both directly, through the elimination of constant braking while trying to go ahead, and indirectly, by making practical near-bellyless configurations capable of carrying large loads at unusually low nominal unit ground pressures. Vehicles of this configuration are now demonstrating levels of mobility and of reliability not previously thought possible in tracked vehicles. Hanamoto has done research on a positive pitch control of an articulated tracked vehicle " ' C O B R A " [38,39]. In the 5th International Conference of the ISTVS in Detroit Kamm reported about an articulated armored personnel carrier Coupled M-113, which had two upper cylinders and a ball-joint and an electro-hydraulic control system with force-feedback circuit [40]. The author also saw the field demonstration of the Coupled M-113 in Houghton near Lake Superior. The good performance of the Coupled M-113 was examined, which climbed up a step obstacle about 1.5 m high, raising the head of the front vehicle, climbing and pulling up the rear vehicle.
14(~
A. O I D A
Ljunggren produced an articulated all-terrain tracked vehicle model BV206 in the 7th International Conference of ISTVS in Calgary [41]. Pitching. roiling and yawing can be controlled by a hydrostatic articulated steering system operated by a stccring wheel and activated by hydraulic cylinders each side of the steering unit. Thc proposed steering system by Sasaki et al. in this conference [7] is similar to that of thc BV206 as shown in Fig. 12. It has three modes such as "float". "'lock" and "'active control" modes for forestry work on steep slopes. In order to go over some obstacles of logs and slash it would be better for the vehicle to have the twin bogies [351. which can keep the vehicle body parallel to the ground surface. Alhimdani et al. presented a paper in this conference about an effect of hydraulic piston on hinge force of simple wagon-type articulated tracked vehicle [9]. Their fundamental theory was already published [42]. They tried to insert a hydraulic piston between the towing tractor and the hinge point of the towed trailer in order to help the straightening up motion from the turning position. As a conclusion they said that this piston should not act when the tractor-trailer system is turning and should act when the system starts to straighten up. To construct their theory they assumed a uniform pressure distribution and constant coefficient of lateral friction and neglected some dynamic parameters. The most important point would be that they did not consider the effects of track slippages. There was much theoretical and experimental research about the forces, which acted on the cleat or track, and about the turning behaviors of articulated tracked vehicle in our terramechanics field [43-49]. If these results are adequately applied, more actual analysis will be done, The author feels that the articulation should be somewhat controlled by sonic actuators such as hydraulic cylinders as mentioned abovc.
NEW I . O ( ' O M O T I O N SYSTEM
Horio produced a new locomotion system using rolling balls [5]. It consists of a big rolling ball and some small balls to drive the big ball by the friction between them as shown in Fig. 13. By changing the rolling directions of the small balls, the rolling direction of the big ball would be controlled directly. Horio earlier studied crab steering, that is a kind of 4-wheel steering to enable the vehicle to move laterally or slantwise like a crab, and hybrid steering composed of crab steering and normal front-wheel steering, in order to use them for the automatic control system of off-road vehicles such as agricultural crop harvesting or pest control machines [50, 51]. As he said in the proceedings through such studies he felt that there was a difficulty to control the vehicle always to be in the optimum position and direction because of involved integral elements in the steering system. Therefore, he developed a new concept of direct steering mechanism without integral elements. It looks like a very interesting method, but at the same time there might be many problems. Is the power transmission efficiency between the driving small balls and the rolling balls considered reasonable? Especially when this device runs on the soil some soil particles will adhere to the ball surface and the contact between the balls will change to a low friction state. Even if this aims at the application for agricultural robots, it will be required to carry a rather heavy load in the handling of agricultural crops. There is also the problem of wear/abrasion of balls. The mechanism of force transmission by friction itself would not be r e c o m m e n d e d . How does one brake the vehicle, if the friction coefficient will decrease from some reason such as water or soil particle
D I V E R S I F I C A T I O N AND SOPHISTICATION Y¢w
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insertion? Furthermore, even if the vehicle sinkage becomes smaller, the rolling resistance will increase on the soft soil compared to conventional tires because the volume of compressed soil would increase. Anyway the question is whether the steerability and controllability of the system (if possible) is so important in spite of some undesirable aspects mentioned above. As a conclusion it is felt that new ideas and concepts to develop more effective vehicles should be welcomed, however, at the same time the reality of proposed ideas should be investigated.
CLOSING R E M A R K S
Progress has been made in vehicle and machinery designs in different districts/coun-
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A. OIDA
tries. In C h i n a t h e b o a t t r a c t o r is b e c o m i n g m o r e e f f e c t i v e , i m p r o v i n g the d r i v i n g w h e e l d e s i g n by a p p l y i n g a f l o a t i n g w a l k i n g m e c h a n i s m , o r t r y i n g to d e c r e a s e the sliding r e s i s t a n c e by i n t r o d u c i n g t h e air c h a r g i n g s y s t e m . In C h i n a a n e w m e c h a n i s m o f w a l k i n g w h e e l was d e v e l o p e d , w h i c h can r u n w i t h o u t m u c h v e r t i c a l v i b r a t i o n . In J a p a n n o w m a n y k i n d s o f 4 W D t r a c t o r are m a i n p r o d u c t s o f m a n u f a c t u r e r s a n d the a d v a n t a g e will b e u s e d in t h e t r a c t o r - t r a i l e r s y s t e m . In J a p a n also a n e w i d e a a p p e a r e d in t h e l o c o m o t i o n s y s t e m to use r o l l i n g balls in o r d e r to a p p l y it to a fully a u t o m a t e d a g r i c u l t u r a l v e h i c l e , t h a t is an a g r i c u l t u r a l r o b o t , utilizing v e r y a d v a n c e d s o - c a l l e d h i g h t e c h n o l o g y , T h e d e s i g n c r i t e r i a o f c a g e w h e e l s will be also e s t a b l i s h e d in t h e n e a r f u t u r e in T h a i l a n d . In P o l a n d t h e h i g h s p e e d t r a c k e d v e h i c l e w i t h v e r y a d v a n c e d p r o p u l s i o n s y s t e m was p r o p o s e d r e f l e c t i n g t h e h i g h t e c h n o l o g y e r a . T h e a r t i c u l a t e d t r a c k e d v e h i c l e was also d e v e l o p e d in J a p a n e s e f o r e s t r y d i v i s i o n . This research progress associates the terms "diversification" and "'sophistication" of o f f - r o a d v e h i c l e s . D i f f e r e n t i d e a s s t i m u l a t e e a c h o t h e r a n d e a c h r e s e a r c h e r gets s o m e hints f r o m t h e t a l k i n g a n d d i s c u s s i o n , so t h a t a n e w s t e p o f t h e r e s e a r c h b e g i n s . T h i s is t h e fruit o f o u r i n t e r n a t i o n a l c o n f e r e n c e o f t h e I S T V S .
REFERENCES [1] ,h~Nn'N TAO and ZHON~;IONC~LJu, The essential technical matters of boat-tractor design in the respect of driving and loading condition. Proc, 10th Int. Conf. ISTVf, Kobe, pp. 755-766 (19901. [2] SHI:JUN ZHANG, DEXING CIIEN, LUQUAN YEN and BINGCONG CHIN, Study on a new kind of walking wheel. Proc. 10th Int. Conf. ISTVS, Kobe. pp. 767-770 (1990). [31 K. SAY,M, M. TAKAI and S. HA'IA, Theoretical analysis of a wheel driven root crop harvester. Pro('. 10th Int. ('on[~ ISTVS, Kobe, pp, 771-782 (19901. [4] B. m. FIJALKOWSI
DIVERSIFICATION AND SOPHISTICATION
[19] [201 [21] [22] [23] [24] [25] [26] [27] 128] [29] [31)] [31]
[32]
[331 [34] [351 [36] [371 [38] [39] [40] [411 [42] [43] [44] [45] [46]
[47] ]48]
149
J. W. DICKSON, D. (_JEE-CLOUGH and J. K. HENSHALI., The tractive performance and comparison produced in agricultural soils by open, flat-lugged wheels m o u n t e d alone. Prec. ?th Int. Conl~ ISTVS, Calgary, pp. 551-583 (19811. x t , DA, A research of the dynamic performance of the paddle driving wheel working in soft terrain. Prec. 9th Int. Conf. 1STVS. Barcelona, pp. 381-388 (19871. Z. L. ZHANG and Y. J. SHAO, The analysis on the dynamic performance of a single lug. Prec. 8th hit. Conf. ISTVS, Camt~ridge, pp. 575-591 (19841. H. Z. Lu and Y. J. SHAO. Experimental research on the soil flow and soil reaction beneath lugs of powered wheel. Prec. 9th Int. Conf. ISI'VS. Barcelona, pp. 373-380 (19871, V. M. S~,LOKHE and D. G~E-GLou~H, Behavior of wet clay soil under single cage wheel lug../, a~,,ric. Engng Res. 37, 255 266 (19871. V. M. S.~,LoKm- and D. GL~ -CLot~on, Formation of a boundary wedge on a single lug in wct claw soil. J. agric. Engng Res'. 38, 113-125 ( 19871. T. TAr-,.~,KA and H. NA~,ASHIM~',, Interactions in soil-lug system (Part l) Characteristics of soil reaction on a lug with lug angle of 30 degrees. J. J S A M 48(2), 225-232 ( 19861. H. NAIq,~SHJ~,IA and T. TANAKA, Interactions in soil-lug system (Part 2)--Effect of lug angle on soil reaction. J . . I S A M 50(6), 3-10 (1988). H. NAKASHM-', and T. TANAKA, Interactions in soil-lug system (Part 3)--Soil behavior under lug and sinkage variation of lugged wheel, J. J S A M 51(2), 47 55 (19891. H. NAKAStlIMA and T. TANAKA, Interactions in soil-lug system (Part 4)--Numerical simulation of interactions. ,1. J S A M 52(11, 77-83 (1990). X. L. WA:-;c;, T, TANAKA and M. YaM~,Z.XKI, Study on soil-lugged wheel interaction (Part 1)--Dynamic behavior of a lugged wheel. J. J S A M 51(31,33 40(1c~89). X. L. WANG, f . TANAKA and M. YAMAZAKI, Study on soil-lugged wheel interaction (Part 2)--Characteristics of soil reaction on a lugged wheel. ,I, .ISAM $1(51, 11 18 (1c,~89). X. L. WANe;, f . TANAKA and M. YAMAZAKI. Study ori soil-lugged wheel interaction (Part 3)--Characteristics of behavior and reaction of a lugged wheel in a high moismrc, h o m o g c n c o u s paddy soil and a paddy soil with hardpan..I. J S A M 52(2), 11 18 (lttg()). K. TRIRAFANASIP,ICHAI, A. On)A and M. Hoyt),x, Study on dcsign criteria of cage wheel (Part l)--Effccts of lug angle and lug pitch on tractive performance of cage wheel in dry hind and paddy field. J. J S A M 52(4), 21 27 (19901. A. ()u)A, Analysis of rheological deformation of soil by mcans of finite clement method. ,I. Terrumechanie,~ 21, 237-251 (1984). B. T. Fl¢~Ai ~owsKi, Novel ahernative prime movers for agricuhural tractors. Prec. t)th lnl. ('onf. ISTVS, Barcelona, pp. 881-897 (19871. B. f . Fl.l,XlkOWSkl. Electronic-commutator A C / D C motor-driven tracked all-terrain vehicles with extremely high mobility. Proc, 8th Int. Conf. ISTVS, Cumbridge. pp. 1045 1063 (1¢t84). P. 1. MJ(E
150
A. OII)A
[49] L.F. LITTLE, The Alecto tracklayer. J. Terramechanics 1(2). 7¢~ ,q2 (1964). [50] H. HoRio, On-off control of crab-steering. The Science Report ~[ kFtcul(v ~/'A~ri('.. Kohe Univ., 18(2). 185-206 (1988). [51] H. HORIO and H. NAKA~AURA.Automatic steering of off-ro~ld vehicle: calculatixlg detcctioll of desired pass and double modes steering (Part 1)..1. JST 9, 15 21 (1989).