|In this illustration the side plates of the gearbox have been made transparent|
Any model with several individual movements and only one power source, tends to have the "crash and smash" gear engagement system. To this end, the gearbox described here was born. It uses dog clutches to engage the drives and utilises their robust nature to eliminate damage to the gears. After all, surely this is the reason they were introduced. At worst, you have to wait half a revolution for them to engage.
I built a prototype in 1980 and tested it on a Derrick crane powered by a Mamod steam engine. It worked well. In 1989, Laurie Webb (Wellington Meccano Club) and I each built a matching Craven Railway Steam Crane. These were inspired by a picture of two such cranes lifting a locomotive, which was shown on the dust cover of a book called "Railway Steam Cranes" by John S. Brownlie. Each crane was powered by one E15R electric motor with this same gearbox and both had four separate movements. These models were displayed at the 1991 Wanganui convention.
The advantage of this gearbox is that the input can be left running in one direction and all movements can be operated individually or any number together, forwards or in reverse. Also it can be easily extended to obtain more outputs.
Basically the input is split so that two trains of gears (31/26) along each side of the gearbox revolve in opposite directions. The gears are loose on the output shafts and are connected to half a dog clutch by a socket coupling. The other half of the dog clutch is fixed to the output shaft back to back with another half dog clutch. Nineteen tooth pinions (26) are placed between these shafts as a space saving measure and so keeping the length of the gearbox to a minimum. The spring-loaded selector shafts ensure that the gear trains are kept in neutral when not in use. Collars act as stops on these shafts to limit movement. These are adjusted so that the dog clutches engage properly and also prevent excessive pressure being applied by the selector forks to the grooves of the socket couplings.
Plan view of Gearbox
Plan view of Selectors
|return to previous page|