An improved mobile X-ray unit has a counterweighted articulating X-ray tube support arm that allows positioning of an attached X-ray tube virtually without the need for moving a supporting carriage. The improved mobile X-ray unit also allows the X-ray tube to be locked to the supporting carriage during travel and the articulating X-ray arm includes several electro-magnetically actuated disk brakes capable of locking the articulating X-ray arm in a predetermined position. In the event that the carriage movement is required, the carriage may be moved by application of force on a force sensing handle engaged with the carriage by two strain gage assemblies. The strain gage assemblies provide signals to a motor drive control circuits which in turn propel two driven wheels in the direction and proportional to the force applied to the handle relative to the carriage.