There's nothing particularly difficult or expensive about a wooden differential. edit: no seriously, zoom in on this pic here https://upload.wikimedia.org/wiki

There's nothing particularly difficult or expensive about a wooden differential. edit: no seriously, zoom in on this pic here https://upload.wikimedia.org/wikipedia/commons/d/d6/South-pointing_chariot%2C_China_Court%2C_Ibn_Battuta_Mall%2C_Dubai.jpg https://upload.wikimedia.org/wikipedia/commons/d/d6/South-po...