Hagans ‘J’ Type
When I first started to explore this model I was convinced that it would be impossible to do prototypically! So all my initial work and investigation was aimed at producing a model that looked as if it worked... I do not blame anyone for not knowing anything about this locomotive. It was the only one of its kind and it worked on a small tramway in Tasmania. But it does have some very famous stable mates K1 and K2.
I am grateful to Mr David Fletcher -who shipped me literally KILOS of photostats on this locomotive from Australia. But more importantly in there was a complete piece by piece drawing set of all the Hagans linkage.
The question was now "How can I NOT make it work like the original?"
The lever form of articulation is an extinct technology. Although in principle it is merely an application of the laws of levers -the mental imagery needed to imagine a variable fulcrum offset system required a lot of practice...
Here is a simplified picture of the Hagans linkage
The piston pushes on the first green lever and moves it backwards transmitting power through the red lever to the wheels and conrods. Power is also taken off the blue push rod to the second green lever and thence to the wheels and conrods via the red lever. Thus power is sent to both bogies from one set of pistons. The rear bogie swivels in the manner of a Mallet. How the power is transmitted to the rear bogie during cornering is done by the pivot point of the rear green lever moving forwards or backwards... This is done by taking the position of the rear bogie from a measuring bar and moving the pivot with it. In practice the device looks like an inverted J with the pivot point slung between the two halves of the J.
This shows the brass shapes and levers with their 3mm nuts and bolts. The two transfer levers can be seen with the moving pivot arm.
This shot shows the lever linkage has been screwed to its lengths of 25mm aluminium angle and then bonded to the bottom of the body.
Here you can see the inverted body with the fitting of the rear chassis (yes an IP Eng 0-4-0 with an 0-6-0 for the front one). You can see the rear power take off lever from the push rod and the measuring arm from the same position as the centre of the first axle of the rear bogie.
At this time I was still intending to have a motor in each chassis...
Call it personal gripe -but if I had gone to all the trouble of working out the levers and linkages -surely I was defeating the object of this by having two motors and not powering the rear chassis from the front? I unlimbered the rear motor and put it into the front chassis, took a deep breath -and applied power. It squeaked horribly!!! A quick once round with a tin of WD40 removed that and wonder of wonders the thing mooved smoothly and if a little jerk along the track. After a couple of runs up and down the workshop floor test track -even that disappeared.
The loco is now resplendant in Forest Green, White and Black.
