Delfshavense Schie Lifting Rail Bridge
Built by Robin Schoolar in September 2024
This is the closest I can come in Meccano to a scale model of the Delfshavense Schie Lifting Rail Bridge which carries a very heavily trafficked four track railway line over an important Dutch inland waterway.
The current bridge was built in the early nineties to replace four side-by-side rolling bascule bridges which were worn out. Although Bascule Lift Bridges are not uncommon on railways (especially in the Netherlands), the current bridge has a unique (and to my eye delightfully intriguing) geometry, a direct consequence of the need to accommodate the significantly oblique angle between rail line and canal.
The designer of the prototype turned what some might have regarded as an awkward angle to real advantage, making the lifting spans trapezium shaped (rather than conventional rectangular) and offsetting the towers for the balance arms to the sides (rather being awkwardly in-line with the tracks). The result is remarkably compact and to my eye elegant and beautiful. A classic piece of modern steel engineering work, which I think deserves to be better known.
The model is 100% genuine Meccano, all in original colours (nothing has been repainted) except for Peco O gauge track (which sets the scale of 7mm:1ft), about 5kg of lead counterweight concealed in the fat ends of the balance arms, and countless commercial washers under every nut and bolt.
As in the prototype, well balanced bascules mean that minimal effort is needed to raise or lower the bridge — well within the capabilities of one small Meccano motor running at 6V in each bascule. The necessary reduction ratio is provided by an epicyclic mechanism with a 19-tooth pinion orbiting adjacent 56- and 57-tooth Gears. The motors are turned off at fully open or closed by limit switches which are all built from Meccano (but contain no Elektrikit parts!).
The model reproduces a superb design feature of the prototype in that bascule arms are pushed or pulled by a long rod moving vertically within each tower. Lower end of each rod is moved by a crank arranged to operate over an exact half turn between top dead centre and bottom dead centre. This brings the valuable characteristic that when the bridge is either fully opened or fully closed, the dead centre action physically locks the bascules from moving.
The crank drive also brings the excellent characteristic that as the bridge begins opening or closing, the initial movement of the bascules from stationary is very gentle … and equally as operation completes, the characteristic of a crank drive brings the bascules to rest just as gently.