Dynamic stability :
The front elevation which is common to all the three Rathas is. shown in Fig 2. It is clear that the foundation of the Ratha rests on the axles of wheels and supports the superstructure divided in four parts vertically. The four divisions indicated as A, B, C & D exhibit heavy concentration of mass in the A division. The concentration of mass covering 1/4th of the plinth area tapers in the ascending order repre¬sented in B, C, & D divisions. Primarily, the mobile heavy structure in A division is responsible for dynamic stability since the weight of the upper portion (B, C & D) is very much less in comparison to division 'A'. Therefore, the scope of this article is limited to the dynamic stability of division 'A' only.
(a) Wheel structure : The wheel structure which is similar to all the three Rathas is shown in Fig. 3. However, the dimensions of the wheels of Nandighosa Ratha are as under;
(i) Rim size : (7" X 9") cross section - 4 nos. per wheel
(ii) Spoke size : (7"x2") cross section -16 nos. per wheel
(iii) Hub diameter: (20"), length (32") 1 no per wheel
(iv) Hoop Iron : (20"dia-x 1/4 x 2") - 2 nos. per wheel
(v) Wedge: (Projections of spokes beyond rim) -16 nos per wheel
(vi) Diameter of wheel : 78 inches
(vii) Bearing in Hub: (7"diax2'X1/4l)-2 nos. per wheel made of iron.
The description of wheel parts is indicated in Fig 9. The wheels are mounted on 7" dia-axles duly lubricated for minimum friction. The wedges protruding beyond the rim circumference are designed to pierce the ground for safe road grip analogous to the treads in rubber tyres used in the automobiles. The wheel plan indicates four lapping joints at A, B, C & D in the plan shown in Fig. 3. These joints are at 90 degrees from each other. During motion, the wheels move in parallel planes and hold to the road through the wedges. The distance covered by the wheel is 20'5" per revolution. As compared to the distance covered by the Devadalana and Talacfhvaja Rathas, this Ratha has the intermediate linear coverage per revolution and hence, has an inter¬mediate speed for the same pulling force. The brake system of the Ratha is confind to a block of rectangular wood which is hung from the plinth level cross members and when dropped, arrests the movement of the two front wheels situated at a distance of 9'3" (centre to centre). This block extends to both sides of the wheels when placed on ground to provide safe breaking. The heavy load of the Ratha ensures static breaking and eliminates any possibility of tilting forward and backward. There is no steering arrangement. However, the ropes made of sisal fibres are directed at suitable angles by the Dahuka (driver) to orient the direction of motion. Depending on the requirement, the speed of the Ratha is controlled by verbal commands of the Dahuka. The cross-section and the elevation of combination of the wheel and axle arran¬gement are dimensionally exhibited.
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