WEIGHTING A LOCOMOTIVE

[Trainman4602]

I am always asked what is the weight of the locomotive. Non live steamers are generally the people asking this question. For the most part the locomotive tracks well and can pull a reasonable amount of weight. However sometimes under certain conditions it can be a little slippery.

Jack Bowdenmann posted a method of weighting each axle so I adapted this to my locomotive.

Here is the video.

https://www.youtube.com/watch?v=I4q1b5KY7P0

[JJG Koopmans]

Nice video, thanks! If you do not mind my two cents, you are wrestling with a statically indeterminate construction, a beam on 4 or more supports, the theory of which is partially treated in locomotive design books. The solution was provided by Clapeyron in the 1860's with his "three moments" approach of which a lot can be found on the internet including calculation examples, so I don't have to go into that.
As I have done a calculation recently for a 100 ton locomotive, your results do not appear strange to me, the lower load on the front driver axle is quite predictable in a non-adjusted situation. The beauty of a calculation for such a situation is that the adjustments can be made in an Excel spreadsheet, so all extremes can be investigated.
My advise to you in this situation is to leave both trucks alone, adjusting won't help. Adjustment is done on the three main axles by screwing the spring hangers nuts in such a way that the axle under consideration takes more load.
Start with the front axle and weigh all three because all of them will be different afterwards.
Kind regards
Jos Koopmans

[PRR G5s]

To expand on Jos's comment, in order to keep the back/front of the locomotive at the same height off the rails or to raise it, will require stiffer springs on the driver axles. While adjusting the main axles will apply more weight to the drivers, it will deflect the springs more, and could cause the springs to be overstressed. Obviously, you don't want the springs too stiff, else the axle won't be able to move up in the pedestals.

From a theoretical standpoint, the centerline of the drivers should be set below the centerline of the cylinders, in the unloaded condition, the amount the spring deflects in the loaded condition. That way, once the locomotive has all of its weight on all axles, the centerline of drivers should be at the same elevation as the centerline of cylinders. But in order to do that, you will need to know the amount of weight you're going to put on the drivers, and determine the spring deflection. Which can be done before you begin construction, but it will take a lot of calculations.

I have not tried/verified this yet, as I didn't do this on the engine I'm finishing right now, but the next engine I will probably try this.

Eric L.

[Trainman4602]

I think everyone is forgetting that there is equalization between. The drivers act as a unit not individually.

Koopmans I haven't a clue as to what you are talking about. To complicated in my book. Save the calculations for the full size stuff.

I plan on leaving it alone for now as it runs and pulls fine. I am starting another locomotive shortly and when it is running I will drop the drivers on the K4 and fix the springs, add about 200lbs of steel weights to the locomotive

I plan on doing this by removing the spreaders and replacing them with one big spreader with cutouts for the drive axles and spring hangers. That will do the trick.

BTW Koopmans I figured all this out with a $2.00 junk bathroom scale.

[johnpenn74]

Wrong Wrong Wrong.

Guys lets dispel a few myths about correctly setting up spring equalization on a locomotive.

"Adjustment is done on the three main axles by screwing the spring hangers nuts in such a way that the axle under consideration takes more load."
- The only item that shifts load is changing the position of the fulcrum of the equalizer which changes the ratio of leverage of the equailzer bar between drivers or between the drivers and triling truck. Changing the verticle height of the spring hanger doesn't do diddly. The verticle hangers could be a mile high. From basic statics, the moment is a perpendicualr force.

" in order to keep the back/front of the locomotive at the same height off the rails or to raise it, will require stiffer springs on the driver axles. "
- Springs, whether coil or leaf, are meansured based on the force they carry and push back to the rail. A physical stack of springs is not shimming tool. Necessary springs should be calculated using spring calculation equations. Sure you could put in the lowest leaf since it has the least amount of impact to the leaf stack; add one to the top and you will change the force of the leaf springs. NOT HEIGHT ADJUSTMENT.

"BTW Koopmans I figured all this out with a $2.00 junk bathroom scale."
- Look on that bathroom scale and it will say "not legal for trade" That is, its not accurate or reliable.

-Problem is, if you don't do some calculations your sorta guessing and settling for close enough. For example, your load (boiler frame, cyls, etc) on you journals is NOT the load on the drivers at the rail (due to rod size differences, journal size differences, and driver size differences). On our models we often make all of the spring sets the same, which assumes the equliazers are set up for equal loading on the drivers. The reality is the journals must carry different loads as the equalization is set up to shift load OFF of the main driver onto other lighter drivers. This will keep the wheel/rail loading as equal as possible. This will give the best traction/pull etc. To calculate the loads you need to know the center of mass of the engine (in working order so add water) and weight of the engine WITHOUT DRIVERS RODS JOURNALS. The easier way is to use the scale and weight the axle load and then weight the axles,journal assemble and subtract the moving parts from the main frame/boiler assembly. Tying off or removing the lead truck is wrong when scaling as it shifts the load from the lead to somewhere else on the engine. Leave it on the rails or better yet, block up the pivot point of the lead truck so the LT weight is carried to the rails.

-Adding steel isn't really the solution. If your equalization is set up wrong and the leaves are not calculated to match the actual load, then the leaves are probably too stiff (caused by someone guessing it looked right or assuming the equilzer ratios should be symetrical) and the engine can't get any traction.

My Allen was wrong the other way where the springs were too light based on load and crushed down all the time.

JP

[Trainman4602]

I say RIGHT RIGHT RIGHT

In live steam work you should always use the KISS principal.


PLEASE No more rocket science explanations.

[JJG Koopmans]

Well, rights and wrongs are tumbling over each other!
Probably I was misunderstood, any change in the springing system that results in a change of a vertical force will give a reaction on all the drivers, that is the consequence of such a system, whether it has levers or not. Since this is counterintuitive, I was trying to prevent a further excursion into the realm of the last letter of KISS.
Rocket science?? This is 1860's knowhow, 40 years before the invention of the superheater!
Seasons greetings
Jos Koopmans

[6491]

MERRY CHRISTMAS CHAPS....MAY THE DRIVING FORCE BE WITH YOU. (Oops, I mean tractive effort )

[PRR G5s]

Dave, nothing wrong with keeping things simple. Since we’ve turned down the road of complicated explanations, when Jos mentioned that you are wrestling with a statically indeterminate construction, he was describing in engineering terms the equalization of the drivers/whole system.

John, you misunderstood my explanation. First off, I never said to add leaves as a shim, I said will require stiffer springs. (I’m not going to use all caps, it’s rude and unnecessary) This applies to any type of spring, leaf, coil, torsion, etc. Further in your explanation, you were basically saying the same thing I was. I think part of the problem was my explanation. I was trying to over simplify it so as not to go into a dissertation, but I think we’re going down that road now. So, here’s a little more detail in what I was trying to explain.

If you’re modeling a certain prototype, as Dave has done, the equalization has already been done for you. Or at least very close. The only difference will be in the relative stiffness of the springs and equalizing levers. If you can find the general arrangement of the engine you’re modeling, as you can with PRR locomotives, it will tell you what the weight is on each axle. From that, you can determine what percent is applied to the drivers. Based off that information, you can doing the following steps:

1. Determine weight of the model engine applied to all axles (you can do calculations, or make an educated guess)
2. Determine load applied to each axle (based off the prototype’s percentage)
3. Determine the size of spring required for all axles (based on the load from step 2 divided by 2 to get it in terms of wheel)
4. Determine the deflection of the spring for all axles (based off the load from step 3)
5. Set all axles below their final location using the deflection determined in step 4, in the unloaded condition (for drivers, that would be below centerline of cylinders)
6. Determine load on axles minus wheel weight, axle weight, etc. (as Dave did, or any other method you choose to use)
7. Adjust spring stiffness as necessary (I said stiffness, not add leaves, you can increase stiffness without adding leaves)

For those developing their own design, determine what percent you want applied to the drivers, and go from there. If you want to get really complicated, and have the means, model this in a structural analysis program if you so desire, but like Dave, I would prefer to keep it simple.

That is all from me. Hope everyone has a Merry Christmas!

Eric L.

[Dick_Morris]

The only item that shifts load is changing the position of the fulcrum of the equalizer which changes the ratio of leverage of the equailzer bar between drivers or between the drivers and trailing truck

I've got to agree with JP on this. To put more weight on the drivers I would experiment with moving the fulcrums for the equalizers to the front and rear trucks.

[FLSTEAM]

KISS, I took my engine to the local truck scales. Plus or minus 20lbs. Close enough for me.

oops. I guess you are trying to weigh each axle. Oh well

John B.

[JJG Koopmans]

The only item that shifts load is changing the position of the fulcrum of the equalizer which changes the ratio of leverage of the equalizer bar between drivers or between the drivers and trailing truck

I've got to agree with JP on this. To put more weight on the drivers I would experiment with moving the fulcrums for the equalizers to the front and rear trucks.

Sorry, I have to disagree, there are enough locomotives without levers that get their spring system adjusted to equalize the axle loads on the rail. The 4-6-0 locomotives of the GWR in the UK are an example.
Kind regards
Jos Koopmans