in the mechanical operation of electrically powered steam model locos? I completely understand why it is mandatory for a real steam powered loco, but I assume the reason for doing it on an electric model is for prototypical appearance. Is this correct?
Depends on the unit.
Most model steam locos have the main set of drivers (the one with the large counterweight) geared to the motor. It then transfers the rotational motion to the other drivers via the driving rods. If the wheels are out of quarter, then you will experience binds…no 2 ways about it…you WILL have binds.
If you are lucky enough to have a steam loco with multiple geared drivers, then the drive rods are usually cosmetic (think N scale Mikado). The drive rods will float above the drivers and not actually turn them.
Quartering is very important. If you have a loco that has jerky or no slow speed operation, 99% of the time, it is either out of round or out of quarter.
David B
David, I will have to disagree partly…the rods on a model steamer, even models that have all driver axles geared and therefore driven, do still impart the same physical requirement to each axle that they do on the real steam locomotives. It isn’t their purpose since the rods aren’t driven as they are by the piston in real steamers, but if you turn only one axle on a steamer, the others must turn since they are all connected to, and by, the same rod. I’m not saying that the rod is doing the turning, but it will keep the drivers turning on axles where a gear breaks and spins, for example. Said another way, if you didn’t have the rods, all-geared drivers would still turn…we agree on that. But if you had a broken gear, all axles would still turn…because of the physical properties, engineered, of each driver connected to a side rod via a crank pin…even on the model.
The rods are not elastic or telescoping…they have a fixed length with fixed distances between their pin orifices, so when the axles turn, driven or not, the rods also require the wheels to turn in concert. That is what quartering provides…that all crank pins are at the same location in the clock-face, so-to-speak. If one crank pin is more advanced or retarded in position along the rotation, then there will be significant binding as the pins try to stretch or compress the rod…which they can’t possibly do.
For the OP, we quarter the model drivers the same way as the real engines are quartered, with one side advanced by 90 degrees so that they look prototypical. The function is not necessary for the models, though, since the impetus for the rods is provided by the turning drivers.
I have read here that some roads had their right side drivers ahead of the left, and vice versa. The purpose is described in a recent thread that may still be on the
Sorry Crandell. I have to agree with David 110% on this one. Quartering can vary drastically from model to model. It really depends on scale and how the drive wheels are connected to each other. (or not…)
The closer you can get to an exact 90 degree clock face offset from side to side will improve your running quality. An 0-8-0 with a one piece side rod will time out differently than an 0-8-0 with a 3 piece side rod. (depending on how well the parts were machined)
I’ve found it’s how well the loco was manufactured and how the drive mechanism was designed. Some need a lot more tweaking than others. But to answer your question, YES, it is VERY important that the drivers be quartered properly.
The example I gave was the N scale Kato Mikado. If the driver has a gear (and they all do), then the side rod just ‘floats’ above it…there is NO physical connection.
David B
On all drivers but the geared one(s), force transmitted through the rods to the other drivers is sinusoidal, due to the reciprocating nature of the rod connection (I could go into a long-winded explanation, but won’t unless someone specifically want to read it). The result is that the driving force of the wheels at the rail is not a constant at a given power setting, but is periodic, reaching two peaks and two minimums for each revolution of the wheel.
With proper quartering (90 degrees out-of-phase between the left and right sides of the loco), one side is at maximum driving force while the other is at it’s minimum. As the wheels turn 1/4 revolution, max and min transition to opposite sides of the loco (that’s why steamers can show a tendancy to waddle down the rails). What was max is now min, and vice-versa. So a graph of the driving force of the wheels on the rails (for any given power setting except zero) looks like a constant value with a ripple imposed on the top (how much of a ripple? Several things contribute to that, but I’m not going to delve into it right now).
As the quartering deviates farther and farther from 90 degrees, the max-one-side-min-the-other-side no longer happens at the same time. Min on one side is no longer max on the other - it leads or trails by the number of degrees the quartering is off 90. The ripple is no longer a smooth, constant-amplitude periodic function. It still periodic, but now what graphed out as a constant value with a 1/4-turn periodic sine wave imposed becomes a lower-value constant with both a one-revolution sine wave and the 1/4-revolution sine wave imposed on it. Not nearly as pretty, and the variation in driving force from minimum to maximum greatly increases. The results as this deviation from 90 degree quartering leads very quickly to a poorly-running locomotive.
And just to throw more on top of that -
I too, must side with Loather and David. Like it’s been said, most model steam locos have only one drive axle geared to the motor. It may however, not be the axle with the large counter weight, but that makes no difference. The only reason for that larger counter weight is to balance the driver for the added weight of the connecting rod from the cylinders. Now if we take away the side rods, we have only one axle transfering power to the rails. Like this, that loco may do good just to pull it’s own tender around the layout. Here’s where it gets interesting, the model makers follow the same rules and practices as the full size locomotive makers did. Rather then gearing each axle together which would eliminate the side rods, it’s much simpler to and more easily maintained to connect all the drivers with side rods. On a full size loco, "quartering’ serves two purposes. It makes sure that when the loco stops, one of the cylinders is in a power position for restarting. Secondly, it provides equal power to both sides of the loco. Since our models are not powered by the steam cylinders only the second part still applies here. Also interesting is that it takes less energy to move the loco when the crank pins are at either top dead center or bottom dead center. Anyway hope this explains why our models must be quartered, just as the real ones. Proper quartering also keeps our model’s “walking” down the track to a minimum. Hope this helps. Ken
Fellas, drivers out of quarter with each other mean a big problem because the rods won’t stretch. As Mark has pointed out, you must have each crank-pin on one side at the same position relative to the clock-face as you look at the drivers from 90 deg out to the side.
On the other hand, you could have a perfectly functioning model steam locomotive with both sides of the engine having their crank pins at precisely the same mirrored location. IOW, with those on the left having cranks at 0600 and those on the right having cranks at 0600. Power that loco and no matter how it is geared internally, fully driven or only one axle, it will move off smartly.
So, quartering on a model means nothing at all, except that the individual crank pins must be oriented the same as the others on the same side. It won’t look realistic, and so we insist that the manufacturers provide them quartereed…for looks.
Mark?
I think the original question was relating to whether it really mattered on a model if the drivers were set at one-quarter the way they are on real engines, as opposed to say 180 degrees or the same on both sides…nothing in there about being “out of quarter” i.e. out of alignment. I believe it wouldn’t matter on a model, in fact one set at 180 degrees might run better since the drive rods would be opposed to each other an in better balance than at one-quarter offset, since I don’t know that model drivers have proper counterweights. Of course the drivers would need to be in perfect alignment with each other on each side, but on a model I don’t think it would make that much difference otherwise.
Sorry, Crandell, but I"ll have to disagree. The rods transmit force along their length - only. Think about a bicycle. The pedals are ‘quartered’ at 180 degrees - and only the fact that your foot can push forward or backward as well as downward keeps the system from locking up. Automotive engines are carried past that lock-up point by the flywheel, and have to be started with an external motor or crank.
Three cylinder locomotives are ‘thirded’ - rods are offset 135 degrees, rather than 90 - but that is about as far out of quarter as it is practical to get. (The prototype also has that third main rod, which is ‘thirded’ to both sets of external rods.)
Going back to the OP’s original question, proper quartering makes all the difference. Any difference in quartering between will result in poor performance and excessive wear of the rods and crankpins - and possibly of the driver axles/bearings as well.
Chuck (Modeling Central Ja
Chuck, we must be talking about two different things. Of course it matters if the cranks on any of the two sides are not matched. And of course the metal rod imparts directional force causing the crank pins to force their host drivers to rotate. But on our models, which is the subject of interest, the rods are not really functional or purposeful, although they are able to be both, depending on the construction of the model. They don’t connect to a force-inducing piston. They respond to wheel rotation.
If one were to physically spin all the drivers on one side, with a quartering tool, so that all the cranks on one side were mirrored with the other side, is anyone going to argue that the can motor won’t be able to turn the gears and cause the loco to advance? Imagine it…no pistons, no working valve gear, no expansion link, no operating radius arm…all we have is a fake piston rod hooked up to a cross head which gets its impetus from the main crank. All cranks are linked by the rod, which we agree can’t change its length. So the driving force is gearing, and not (mostly) the rod. The rod will become the driving force if the cranks on one side are not oriented properly.
The rods can be in any position you’d like on a model, provided you have all the linked crank pins on the one side oriented to match the main…say. Then, all that matters is that the internal gearing is working well linked to the can motor since the can motor provides all the locomotion.
There is no appreciable dynamic augment to worry about, no piston to balance. So the quartering is only for looks, not functional on a model.
My contention in my first post is that the rods still provide motive continuity in the event that a gear should fail or if only one driver axle is powered.
David, I am not familair with the N s
In models the drivers can be out of quarter without causing problems so long as all the drivers are out of quarter the same. I have an old PFM MA & PA light consolidation which i wore out the gearbox with 30 years of running. I decided to replace the gearbox and repower while i was at it. It was then that i discovered that “Old Faithful” #27 had been badly out of quarter the whole time! (I corrected the quartering curt of NWSL and “Old Faithful” now has a new lease on life, running better than ever thanks to a can motor and new gears) but the point is the quartering didn’t matter so long as the wheelsets were all equally out.
Thanks for all the answers. It’s been interesting reading them. As the OP, I meant “quartering” in the sense of the rods on one side of the loco being 90 degrees out of phase with those on the other side. I realize the rods cannot stretch or contract.
All things considered, Selector’s explanation seems the most logical to me.
The opposing views seem to rest of the principle of force emanating from reciprocating pistons, which an electric model lacks.
While reading this material, I thought about a model 4-2-2 steamer, such as Emily in the Thomas series. I’m pretty such Emily is based on a real prototype. In the model Emily I don’t see how quartering the drivers could possibly make any difference. It seems like it would run just as well with the rods removed, for that matter.
Anyway, thanks for the answers. All were appreciated.
Given an electric 4-6-0 locomotive model with only a gear on the middle driver axle, how would the basic physics of powering the first and third driver axles via the side rods differ from a real (prototype) steam locomotive? If the crank pins are 180 degrees apart or zero degrees apart would the mechanism not reach a top dead center, or bottom dead center point where the side rods have no leverage to make the first and third axles turn?
On real steamers, the 60+ tonners, yes. On models, makes no never mind because there is no force driving the side rods except for the pins themselves…no piston stroke with piston driving a stem that drives the cross head, etc. It’s all pin driven on our models, and as long as the inner electric motor is turning gears connected to a single driver axle, the pins do all the turning. They turn through 360 degrees, and the rod turns with them…the whole way, same speed.
-Crandell
On our un-sprung, un-equalized models of six or eight coupled locomotives, the single, solid rod with three or more crankpin holes can transmit force perpendicular to the length of the rod, so the offset angle between crankpins on one side of the loco and crankpins on the other side is non-critical just as long as it is equal on all axles.
On a four-coupled engine (or two un-linked four-coupled engines in a rigid frame like a PRR T1) the rod will not transmit force perpendicular to its length. The same is true of models with accurately knuckle-jointed or tandem siderods. For those locomotives, the offset angle needs to be reasonably close to 90 degrees, and not less than 45 degrees or more than 135 degrees. Again, the crankpins must have an equal offset angle on every axle.
If every axle is driven by its own gear tower, the rods are purely cosmetic and can be removed without any adverse effect on pulling power. My stable of iron horses doesn’t have a single example with all axles directly powered, although I do have some where the geared axle isn’t the one with the biggest counterweights.
So, the offset angle must be the same on all axles of any model steam locomotive. How critical that angle is depends on the axle count and the prototypical accuracy of the siderod set.
Chuck (Modeling Central Japan in September, 1964 - with a couple of four-coupled locos)
Why the difference? It would seem to be the same principle.
What Tomikawa is saying is 100% correct. When a loco chassis is sprung or compensated, the distance between the coupled wheels will extend, though only by a few thou of an inch when a set of wheels move vertically due to the springing. If the quartering is not the same on each axle then you could experience binding thereby causing rough running. It is normal for sprung chassis’s to sit down on the springs, this allows the wheels to drop rather than rise on uneven track.It is almost impossible to build a loco that sits midway on the springs as a full size loco does and it is all to do with balance and is to big an issue to go into here.
Have fun modelling CPPedler.
.
But Tomikawa was talking about unsprung rigid chassis locos, as I understood it. Also, my original question dealt with different quartering on opposite sides of the loco, not different quartering between wheels on the same side of the loco.
But regardless, I intended my question to Tomikawa to be simple - why does a 4 coupled loco differ from a 6 coupled loco in their ability to exert perpendicular force on the connecting rods?
Ah, but it ISN’T the same principle. The rod with three or more crankpin holes, attached to drivers which cannot move vertically, will transmit thrust applied to one crankpin in any direction, not just longitudinally. Think of digging a hole with a shovel. with one hand on the shovel’s cross handle and another half way down the shaft, it’s easy to lift the dirt on the blade.
Now, try digging using ONLY the cross handle. Unless your grip would put Hercules to shame, the shovel will rotate in your hand - no lifting force. The same occurs if the siderod has only two crankpin holes, or a crankpin hole at one end and a working knuckle joint at the other. Consider, too, that the rod MUST be free to rotate around the crankpin.
In summary:
- A rigid siderod with three or more crankpin holes can transmit rotational force in any direction.
- A siderod with only two crankpin holes, or a longer rod with flexible joints, can only transmit force applied longitudinally. In order to transmit rotational force, there must be TWO siderods, offset from each other by at least 45 degrees (and preferably 90 degrees - “Quartered.”)
Chuck (Modeling Central Japan in September, 1964)