Source: Turnbull, S.. (2004). (War chariot) Siege Weapon of the Far East. Osprey Publishing Ltd. pp 21
War Chariot
Catapult had evolved to a new structure. As the name shown in subtopic, the catapult started to equip with wheels on the bottom instead of burying the stands under the ground.
Reference Needham, Yates, R. D. S. (1988). Science and civilisation in China. Vol. 5, Chemistry and chemical technology. Part 6, Military Technology: Missiles and Sieges (pp 142-181) . Cambridge [England]: Cambridge University Press. Turnbull, S.. (2004). Siege Weapon of the Far East (pp 20-22) . Osprey Publishing Ltd.