The RMG consists of lifting mechanism, trolley traversing mechanism, gantry mechanism and sway-dampening mechanism. The lifting, gantry and trolley mechanisms are mostly equipped with AC frequency conversion control system. Normally the lifting mechanism is of the single drum type. It can also be designed to be double drum type if needed.

Table 31-1 shows some technical parameters about RMG.

Rubber-tyred gantry cranes (RTGs) are the specialized equipment for loading and unloading standard containers. They are used in both container terminals and specialized container storage yards.

Each RTG is powered by an AC diesel generator. It is equipped with digital frequency-converting drives, which enable both longitudinal and transverse movements in the container yard. It is also equipped 20ft-40ft telescopic spreaders. Most spreaders are with fixed flippers. Mechanical anti-sway system is installed to reduce swing of spreader. The spreader can also be skewed a little bit to expedite container positioning. The gantry wheels can turn for 90°, so that RTGs can move between different lanes. The standard span of RTGs is 23.47m (six containers plus one truck lane). RTGs with various spans can also be supplied. The lift height is big enough to ensure a 9.6-foot-high container passing over containers stacking four (five or six) high. A RTG stays on four (or eight or sixteen) tubeless tires. The number of wheels can be decided by the allowable load of the container yard. Gantry travel mechanism is also driven by either four wheels or two wheels. To avoid collision between two RTGS, or between a RTG and containers, manual steering system and gantry anti-collision-free equipments are installed.

Trolley travel mechanism can be driven either by rack and pinion, full-wheel drive or two-wheel drive. The move is very smooth. An operator’s cab is installed underneath the trolley, where the operator can drive the crane.   

RTGs adopt AC or DC drives systems, which is very good in speed control and constant-power control. The hoisting and lowering speeds can be adjusted automatically as per weight of the cargo.  

For safe operation, RTGs are installed sensors to detect over-load, diesel over-speed, water over-heat and low oil pressure, wind speed, setting of storm tie-down and other sensors for various mechanisms. Emergency stoop push buttons are also installed.

Furthermore, optional features like DGPS, ECMS, RCCMS, and elevator can be implemented as option. The customers can also purchase as an option a special crane jack up system, which will expedite the changing of gantry travel direction and reduce the wear and tear of the tires.

There are many important technical parameters for RTG such as lifting capacity, span, base distance, lifting height, velocity. Table 31-2 shows the common parameters for RTG. The parameters are only for reference and can be adjusted according to different use.

•         basic parameters Stack height(containers)1 over 4       1 over 5   1 over 6  

•                             Lift height (m)      15.24       18.1    21     

•                                      Rated hoist capacity  40.6-61   40.6-61   40.6-61  

•         velocity parameter Hoist speeds(m/min) Full load  20-23      23-25      25-35     

•                                      No load   40-52      52-60      55-70     

•           Trolley travel speeds(m/min)               70    70    70   

•           Gantry travel speeds(m/min)        Full load  25-50      25-50      25-50     

•                                       No load   100-130   100-130   100-130