NZFMM 1993 Auckland Convention page 15 of 17

Railway Breakdown Crane by Doug Harris

This model is based on Super Model Number 30.  The original weakly designed gearbox has been redesigned to provide hoisting, luffing, slewing and travelling outputs from a single input, all contained in a space of 4 by 4 by 7 holes.  Each movement is braked by a worm gear.  The travelling drive is automatically disengaged when the slew drive is engaged to avoid the tow locking up.  Each output has forward, neutral and reverse positions, each retained by a spring loaded detent.