This may seem a silly question -but how DID they make the wheels go round? I like to make my models work in as near as possible the same way that the originals did. I admit that they may all have batteries and electric motors rather than steam -I have a number of small nieces and nephews... But I have tried to make it a point of honour that the wheels go round as realistic and true to the original as a I can!

Valve Gear

Normally steam is associated with pistons and cylinders. Most model makers, (such as me), have problems with the types of valve gear that seem to abound -I think P. Ransome Wallis's "The Encyclopedia of Railway Locomotives" lists 37 variations.... As a modeller there are really only two types that I can produce with any degree of fidelity. They are HACKWORTH and JOY valve gear.

In the Hackworth everything is timed from the drive wheel with a rod to the D valve over the cylinder and everything moves in the same direction with it.

In the Joy everything is timed from the piston rod and a reverser moves the rod to the D valve in the opposite direction of motion to the piston rod.

I have found the Hackworth type easier to build -although the Joy type is visually more interesting...

Conrods

This is normally the abbreviation for connecting rods and they are used to transfer the drive from the driving wheel to the other wheels. But normally they had split sections to allow for cornering and the springing of the locomotive. For instance an 0-6-0 locomotive would have a conrod of two sections -joined in the middle.

Certain designers have built locomotives with no conrods... While others have used the conrods for more than transferring power.

Francis Webb is perhaps the most (in)famous proponent of the no conrods design. He designed locomotives with a central LP cylinder and two external HP cylinders. The LP drove the front pair of drivers and the HP drove the rear pair thus giving 2-2-2-0 with no connection between the two driving axles. The designer Alfred de Glehn produced a locomotive that was similar except that there were two central HP cylinders driving the front wheels and two external LP cylinders driving the rear pair. The two driving wheels were connected by conrods. The Nord sold these locos to both the GWR in the UK and the PRR in the USA.

The Klose system used the conrods between the wheels as a steering aid.

Below is a simplified drawing of the Klose linkage!

What you are looking at is the lever differential system for a KLOSE type loco.

In this system as the loco corners the distance between the driving wheels varies...

So, as the loco turns LEFT, the left hand side diamond rotates counter clockwise shortening the effective distance between centres and the right hand side diamond rotates clockwise lengthening the effective distance between centres. The diamond is connected to the central driving wheel pin (and goes around with it) and the triangle bounces up and down.

Tension on the blue lever to the support tender causes the rotation of the triangle and thus the diamond.