Constructing a linkage that works every time and can cope with valve gear that varies in its distance from the cab depending on whether the loco is on a curve or not is the challenge. Whichever end is in reverse gear has to have the die block in the expansion link rigidly held at the top of the link, otherwise it will go out of gear. To achieve the flexibility required for curves and the rigidity required to hold the gear in place would certainly be a challenge. The trick is, of course, to have the linkage running along the loco's centre line to reduce the amount of movement of the power units in relation to the cradle.Keith S:110081 wrote:I don't feel that it would be particularly challenging to build the locomotive with a proper functioning reverse lever in the cab.
Other commercial Garratt manufacturers have also had to tackle the problem:
- The Locobox Darjeeling Garratt is an oscillator (so no valve gear) and has a steam reversing valve under the boiler.
- The Locobox 2-6-0-0-6-2 Garratt was only available with radio control I think ... I've never seen a manual one.
- The Accucraft NGG16 was available with manual reversing achieved by a wheel in the cab that used bevel gears to drive a shaft running the length of the loco. The shaft was then attached to the valve gear weighbar by more bevel gears and universal joints.
The drain cocks on Festiniog Fairlies are pulled open on right-hand curves because the linkage does not follow the loco's centre line.
