Steam locomotive wheel connecting/driving rods.

[Guest]

 


Wheel train: As far as the connecting rods of the driving wheels are concerned, are the 2 sides of steam locomotives  a) mirror images, or b) one side rotated 180°, or c) rotated 90° (to hinder locking)?


Or, in other words, when the main connecting rod of one side is at its lowest position, the position of the connecting rod on the other side is a) also in lowest posiotn, or b) highest position, or c) halfway between the 2?

[Guest]

Bob 90 degrees to one another it's called quartering. I think you can see it in this pic.


Bob

[Guest]

Thanks Bob.  Lovely model in your pici


Bob (boblalux)

[Gwyn]

Good question and a very useful answer from Bob, a bit of info to store away for the future.

[Guest]

Good question and a very useful answer from Bob, a bit of info to store away for the future.

Yes, interesting. Given  double-acting cylinder/pistons, quartering, I guess, would give a left/right/left/right forward thrust to the engine per full forward/back piston stroke. This, at low speeds but maximum force, might cause the engine to rotate slightly about a verticle axis.


If the crank pins were in unison (when one was up, the other was up as well) (which could be called "zeroing"!) the forward thrust from both pistons would occur at the same time, probably causing a back-and-forth pulsating force on the engine. The same would apply to "halving" (when one pin was up the other would be down). This might actually be helpful when pulling away with a heavy load because, whatever the part of their cycle the pistons were in, the pulling force (small or large) would be exerted on both wheels at the same time, so minimising the risk of slipping. That's my theory anyway.

[Gwyn]

Yes, interesting. Given  double-acting cylinder/pistons, quartering, I guess, would give a left/right/left/right forward thrust to the engine per full forward/back piston stroke. This, at low speeds but maximum force, might cause the engine to rotate slightly about a verticle axis.


If the crank pins were in unison (when one was up, the other was up as well) (which could be called "zeroing"!) the forward thrust from both pistons would occur at the same time, probably causing a back-and-forth pulsating force on the engine. The same would apply to "halving" (when one pin was up the other would be down). This might actually be helpful when pulling away with a heavy load because, whatever the part of their cycle the pistons were in, the pulling force (small or large) would be exerted on both wheels at the same time, so minimising the risk of slipping. That's my theory anyway.

My understanding is that when in the zeroing position and when in the halving position there is no power to the wheels. A train could not pull away from a standstill with the pistons in this position. With quartering there is always power to one of the wheels.