Steerable power drive for gantry crane

A self-propelled steerable gantry comprising:

• a. an elevated load carry beam;
• b. individually adjustable downwardly divergent pairs of legs spaced apart lengthwise of said beam proximal the ends thereof for supporting said beam;
• c. tie means between the lower ends of the legs of each said pair of legs to maintain and adjust the angularity between said legs;
• said tie means having a length which is substantially shorter than the length of said beam;
• and
• d. ground engaging mobile mountings for said gantry including:
• i. a castering wheel disposed adjacent the lower end of one leg of each said pair of downwardly divergent legs, each said castering wheel being capable of swivelling about an upright axis perpendicular to the longitudinal axis of said tie means;
• ii. a fixed orientation wheel disposed adjacent the lower end of the other leg of each said pair of legs and being aligned with the longitudinal axis of said tie means, the distance between the two fixed orientation wheels and the distance between the two castering wheels being substantially greater than the distance between the caster wheel and the fixed orientation wheel of each said pair of downwardly divergent legs in all adjustement positions of said legs;
• iii. a prime power mover operatively connected to each of said fixed orientation wheels and capable of independently rotating each said fixed orientation wheel in a forward or reverse direction;
• and
• iv. control means operable to independently actuate said prime mover means for forward or reverse rotation of said fixed orientation wheels.