How much would each side and main rod weigh on a typical (say USRA) 2-8-2 or 4-6-2? How about something like the Milwaukee 291 or UP 844 or other big Northern?
Disclaimer: This post may contain humor, sarcasm, and/or flatulence.
Michael Mornard
Bringing the North Woods to South Dakota!
1000 pounds for the little engines, 1500 for the big.
Ed
So there's almost three tons of weight hanging off each side of 261?
I'm impressed at how fast you replied, I've spent all day searching Google.
Older locomotives had comparatively heavy rods - the Grande's narrow gauge locos have main and side rods that look like slabs of steel. These are small, comparatively low horsepower machines. Contemporary standard-gauge locos had similar rodding.
More modern locos had shaped rods made of high strength alloys. They did weigh more, but they had to transmit much higher levels of force.
A few WWII era locos couldn't get the best alloy steel (they were competing with the Navy and tank production) so they had truly massive rods. Santa Fe's 2900 class were at least 2000 lbs heavier than their pre-war sisters, much of the difference being heavier rods.
Chuck (Modeling Central Japan in September, 1964)
Bayfield Transfer Railway So there's almost three tons of weight hanging off each side of 261?
Hey! Let's not forget the main rods.
I'm not sure "hanging" is quite the right choice of word. Perhaps for air compressors or exhaust feedwater heaters, but not those. Anyway, since a typical 4-8-4 loco weighs about 250 tons, allocating 3 tons to make the wheels (NOT on the bus) go round and round seems acceptable.
I, uh, sorta cheated:
density of steel = 490 lbs/cuft
rod = 6' x .75' x .5' = 2.25 cuft
490 x 2.25 = 1102.5 lbs
That would be for each segment. For a Mike 3 x 2 x 1000 = 6000 lbs
For the 4-8-4, I figured the length would be greater, plus the cross-section would increase. So I added 50%.
I didn't notice the request for the main rod. I'd ballpark that at twice the side rod. So that would add 4000 pounds.
Total, then, would be 5 tons. A GN O-1 Mike (fairly typical) has an engine weight of 150 tons. Five out of 150 isn't all that bad, considering ALL of that 5 tons is being used for mechanical transmission. As opposed to the air tanks, that are just "sitting" there. And, don't forget, most of a steam locomotive is a void.
As to accuracy: Yup, it's pretty ballparky. But if you start changing the dimensions, you'll see you can't get too far from the number I came up with. For the typical Mike, I would think the lowest would be 750 pounds. And the highest 1250. Too low, and the rods fail. Too high, and they're heavy for no reason.
ndbprrAnd those rods were a main reason for continuous track maintenance. The up and down motion pounded the rails.
Well, yeah. Sort of.....
If you DIDN'T have a main rod (connecting the crosshead to the main driver), the system is perfectly balanced. The side rods are balanced by the counterweights. One locomotive like this is the PRR S2. It had side rods, but not main rods. And no pounding. Track maintenance guys must have loved it.
Main rods have no (simple) way to be counterbalanced. When you first add them, their back and forth motion causes the locomotive to yaw. There is "negligible" vertical pounding. But yaw is not exactly great, either. So the "folks who know" decided to improve the yawing by messing with the driver counterweights and, in doing so, managed to transform a part of that bad yawing into bad vertical pounding. They came up with a happy medium. Or perhaps it would be better called a less-unhappy medium.
OK. I did the unthinkable: more work!
I dug out my old "Model Railroader Cyclopedia" and measured the drawing of the USRA light Mike.
Side rods are made up of two elements: the part near the crankpin and the part connecting those two parts. The former is fatter than the latter. But not as long. So I split the computations into two elements:
Connecting section:
2" x 6" x 39"
And the ends:
6" x 6" x 18" (the end with the rod joint) and 6" x 6" x 12"
Dimensions were "squiged" a bit to account for the hole for the crankpin
So, in feet, you get:
(.17 x .5 x 3.25) + (.5 x .5 x 1.5) + (.5 x .5 x 1)
.27 + .38 + .25 = .9
So: 490 lbs/cuft x .9 = 441 pounds.
Oops. Well, it seemed like a good guess at the time.
I believe the side rods are only "sort of" perfectly balanced. The counterweight is out by the rim while the rods are close to the center of the wheel, so the moment arm is different. They can be perfectly balanced for a specific speed, which should keep the dynamic augment within reasonable limits when travelling slower or faster.
If one is talking only about side rods (say, on the S2, that had no main rods), then the side rods can be easily perfectly statically balanced. Meaning that if you lift the locomotive up in the air, and position the wheels in any position, they will rest there. Without the counterbalances, the wheels would turn until the side rods were in the lowest position.
The reason the counterweights are out at the rim is that they can be lighter. If it's twice as far from the center as the side rod is, it only has to weigh half as much. And this effect works at all rotational speeds.
BUT.
Dynamic imbalance can also be a problem. This happens during rotation over time, not statically. For example, you can statically balance a new tire at a tire shop and have it vibrate when it spins up. That is caused by a dynamic imbalance.
One place dynamic imbalance will happen with locomotive side rods occurs because the side rod and the counterweight do not rotate in the same plane. This can be eliminated by placing a counterweight on the other driver in the pair in exactly the same position as the crankpin of the first wheel (but at the edge of the wheel, of course). It should weigh approximately 10% of the weight of the basic counterweight. Also, the counterweight for the first wheel will have to be recalculated up a bit. The same effect can be had by repositioning the opposing counterweight slightly off of directly opposite its own crankpin--essentially average the main counterweight on that wheel and the one that accounts for the other side.
This, of course, throws off the previously perfect static balance. This may be acceptable because imbalance at low speeds is less destructive. And the extent of static imbalance is less (see noted 10%). I expect that, if one were charged with balancing a steam loco's drivers, that there would be a lot of best possible solutions rather than perfect solutions.
In fact, these imbalances may well be masked by the problems with balancing the main rod.
I have a treatise before me entitled Locomotive Rods For 100 M. P. H. by T. V. Buckwalter, of the Timken Roller Bearing Axle Co. dated Feb. 18, 1938.
I will include some of the excerpts from this study and the reader can digest this information at his leisure.
This is a very interesting study where "Dynamic Augment" was the prime concern for high speed locomotive performance.
https://en.wikipedia.org/wiki/Hammer_blow
Timken states that over 6000 tests were performed and the application of new type rods were studied on the Pennsylvania K4-s 5371; The Burlington "Aeolus"; Union Pacific 2906; New York Central "Commodore Vanderbilt" and J-3-a 5450.
An interesting note is that the piston rod is forged from tubing with a wall thickness of 3/4" compared to the standard practice of using a 4-1/2"ø solid rod and the strength is 33% higher with the tube. The weight of the piston and the rod is 350 lbs a reduction from the 750 lbs. of the conventional design.
Perhaps when time permits I can make a .pdf available for anyone wishing to read the entire study.
Hope this helps,
Regards, Ed
I would certainly like to obtain such a thing for my reading pleasure.
Hi, Ed
I'll get to work on it in the next few days and drop you a PM when ready.
Another Ed
7j43k I would certainly like to obtain such a thing for my reading pleasure. Ed
Ed, I sent you a PM a few days ago...
gmpullman 7j43k I would certainly like to obtain such a thing for my reading pleasure. Ed Ed, I sent you a PM a few days ago... Ed
Ed.,
I replied on the 10th with the info you requested. Did it fail to go through?
I just checked my messages and didn't see a reply
I re-sent one with my email address. Hopefully that will get to you.
I received the Timken booklet. Great reading, especially since it's original source.
Thanks, a lot, for copying and sending it,
Glad to help get information out to people who really appreciate the value of the hard work that the designers and engineers of the locomotive builders' and their suppliers did to refine the operating characteristics and efficiency of these amazing machines.
Wouldn't it be great to have a repository of this kind of data available in a cataloged, searchable database for the future locomotive historians to access?
I can dream, at least...
A bit of a side-note...my understanding is that a large part of why early Mallets (like the USRA 2-6-6-2 modelled by Bachmann) were limited to 20 MPH was because their small drive wheels made it impossible to counterbalance the weight of the siderods properly. Over time engines with larger drivers, like UP's Challengers, were developed which could run at passenger train speeds with no problems.
Ed, rather than just dreaming, you might contact the Railroad and Locomotive Historical Society. They have a vested interest in obtaining and maintaining all sorts of data on past locomotives, and may already have (or be developing) such a data base. I'm sure they would welcome a copy of your work if they don't have it already.
Chuck (Modeling Central Japan in September, 1964 - with steam locos that never heard of roller bearings)
Thanks, Chuck
Good idea! My dad was a member of R&LHS for many years.
After I'm gone my kids would probably just Ebay this stuff or toss it!
Thanks for the suggestion...
wjstix A bit of a side-note...my understanding is that a large part of why early Mallets (like the USRA 2-6-6-2 modelled by Bachmann) were limited to 20 MPH was because their small drive wheels made it impossible to counterbalance the weight of the siderods properly. Over time engines with larger drivers, like UP's Challengers, were developed which could run at passenger train speeds with no problems.
It's certainly true that there's less room for counterweight in smaller drivers. But, as I noted earlier, you also need less counterweighting the farther from the axle the counterweight is placed. Or, put another way, you need more counterweight the closer the counterweight gets to the axle. So, little drivers get a double whammy.
gmpullmanWouldn't it be great to have a repository of this kind of data available in a cataloged, searchable database for the future locomotive historians to access?
The T1 Trust has just such a repository, and I think it would be valuable to put a copy of this Timken report there (it would be particularly appropriate as there is nothing quite like it, and it contains a number of details that have had to be 'extrapolated' from other references).
I'd like to put my 'oar in the water' for a copy, too...
RME, I sent you a PM.