Control system and method

A method of controlling a transport device such that the transport device remains in a substantially erect orientation while a platform of the device remains substantially horizontal regardless of a surface pitch, the method comprising steps of:

• a) determining current operational characteristics of the transport device;
• and
• b) automatically changing between a plurality of operation sub-modes of a mode that maintains or restores an estimated location of the center of gravity above a foot print of the device depending upon the current operational characteristics;
• wherein step a) includes determining a value of a balance indicator and step b) includes switching between at least a first sub-mode and a second sub-mode based upon the value of the balance indicator;
• wherein the second sub-mode includes at least two sub-modes;
• wherein step b) includes entering a first sub-mode of the second sub-mode when a control switch value is greater than an entry value;
• and
• wherein the transport device remains in the first sub-mode of the second sub-mode until the control switch value falls below an exit value.