doctorwayne . . . the loco is fully assembled for the balance test, even though the lead and trailing trucks have little weight to contribute and are mostly supported on their own wheels. As Ed mentions, you can create a balance with a piece of wood and some dowel - I made mine from a sheet of brass, with heavy brass wire soldered across its balance point . . . Wayne
. . . the loco is fully assembled for the balance test, even though the lead and trailing trucks have little weight to contribute and are mostly supported on their own wheels.
As Ed mentions, you can create a balance with a piece of wood and some dowel - I made mine from a sheet of brass, with heavy brass wire soldered across its balance point . . .
Wayne
Thanks, Wayne. And Ed, too. I get the notion that merely establishing a pivot at the mid-point of the driver wheel base is sufficient and that I should not concern myself with the possibility of loading variations from one axle to another.
But I'm inclined to think that any platform upon which the engine is placed for the test must extend equal distances from the mid-point of the drivers' wheelbase. If not, I would think the platform itself will be unbalanced and throw the whole test out the window.
John
peahrens...if we had a 0-8-0 with center of gravity not over the midpoint of the 4 axles, let's say towards the last axle, the forward axles would lose tractive effort and the rear axles would increase their effort and it would tend to come out near the same. Two caveats come to mind. If the drawbar to the tender started picking up some of the out of balance force, some of the loco weight would transfer to the tender for a net (tractive) loss. If nearly all the weight were over the 4th axle, it would be ok (if that axle not on an especially slippery area)??...
It seems to me that if only one wheelset were bearing the bulk of the weight, then yes, you'd think it would still be okay, but were the weight balanced, the friction of eight wheels would, I think, translate to more applied tractive effort.
Given relatively equal specifications an 0-8-0 was generally more capable than a comparable 0-6-0.
peahrens c) leading and trailing trucks. If the trucks had much stronger springs than needed to barely help them track adequately, they would be stealing weight (downforce) from the driven axles / wheels and reduce traction.
c) leading and trailing trucks. If the trucks had much stronger springs than needed to barely help them track adequately, they would be stealing weight (downforce) from the driven axles / wheels and reduce traction.
Paul,
In his presentation on Bluetrain, Wayne did mention that in doing his mods he had to replace trailing truck springs which effectively skewed the driver pressures so that they were unequal for each axle. With all the variables, not to mention the available spaces present in the boiler for additional weighting, it is all an exacting exercise in the art of physics. A few of us become as capable as violin makers, but most of us do well to rise to less exacting results I can see why many throw up their hands and just consign wimpy locos to flatlander or short consist duties - or get rid of them. Arrgh.
The issue of traction tires adds a new factor. The Athearn Mountains have them, but I don't think they're on all four driver axles.
Thanks for your initial observations. Heady stuff, once one begins to reflect a little. Mr. Cargo, my junior college physics teacher from the previous century, would have moved you to a seat in the front row of the classroom - where all the smart ones sat.
John, the loco is fully assembled for the balance test, even though the lead and trailing trucks have little weight to contribute and are mostly supported on their own wheels.As Ed mentions, you can create a balance with a piece of wood and some dowel - I made mine from a sheet of brass, with heavy brass wire soldered across its balance point. Even if the loco is picked up, with thumb and finger on the running boards in a light grip, and at the mid-point of the driver wheelbase, you can get a pretty-good sense of how well it is (or isn't) balanced.Prior to doing the modifications outlined in that thread, I placed one of those locos and its tender on the layout, then draped a "saddle" of folded sheet lead over the boiler, and while restraining the tender with my hand, applied power.
The locomotive attempted to surge forward, then immediately slipped its drivers, a sure sign that the weight was not too much for the motor to handle. As I recall, that "saddle" was well in excess of two pounds, and of more volume than could ever be fit into that locomotive.If you have diesels and think that weight could help increase tractive effort, you can do a similar wheelslip test by coupling a car to the diesel, and holding it in place, as I did with the tender. Most diesels I've owned seem to have been pretty well-balanced, but I did add weight to pretty-well all of them....my layout is mostly grades and curves, usually occurring in the same places.
The Athearn USRA locos (Mikados and Pacifics) both came with springs on the trailing truck, and I think that its main purpose was an attempt to shift some of the imbalanced weight forward. If you complete the outlined modifications, the spring should be removed - the truck tracks well without it, and leaving the spring in place will create another imbalance. I had intended to add more weight inside the cabs, and then re-install the springs, but I went on a bit of a tear adding crews to all of my locomotive cabs. The weights likely would have served as seats for the surgically modified engineer and fireman, but they'd then block access fror the screwdriver needed to remove the cab if the loco needed to be disassembled.
I've never thought about it so will be interested in what can be offerred.
I'm recalling that friction force is proportional to the friction coefficient (wheel to rail) times the force (weight) applied.
https://en.wikipedia.org/wiki/Adhesion_railway
That being the case, if we had a 0-8-0 with center of gravity not over the midpoint of the 4 axles, let's say towards the last axle, the forward axles would lose tractive effort and the rear axles would increase their effort and it would tend to come out near the same. Two caveats come to mind. If the drawbar to the tender started picking up some of the out of balance force, some of the loco weight would transfer to the tender for a net (tractive) loss. If nearly all the weight were over the 4th axle, it would be ok (if that axle not on an especially slippery area)?? I may be missing something here.
This would be complicated by:
a) one axle having traction tires, perhaps, where the friction factor for that axle is higher, so the more weight force there, the better. I'm assuming that the traction tire and bare wheels have equal radii and are touching simultaneously.
b) sprung drivers, but that might not matter much as long as none are bottomed out. While the axles with least spring compression would get less weight (downforce) the other axles would make up for that (the weight sum being the same)??
I'm thinking the keys are:
(a) the more weight, the more traction, and the center of gravity (if there are leading or trailing trucks) should simply be within the front and rear driven axles (more precise centering may not matter much), and
(b) excess weight that is sprung to the lead and/or trailing trucks is wasted weight = lost traction.
It's late, so I may have forgotten some physics or am overlooking practical basics that apply. I'm guessing that only extreme out of balance / springing could be an issue of significance. Just my hypothesis, may be way off! Be kind with pointing out what I am missing.
Paul
Modeling HO with a transition era UP bent
Attuvian 1) I presume that the balancing should take into account the entire engine upon its reassembly...
1) I presume that the balancing should take into account the entire engine upon its reassembly...
I'm not sure I follow you. If you're talking about the lead and trailing trucks, they're mostly decorative on a model. The balance point should be the middle of the driver wheelbase.
2) what method and devices (jigs, etc.) are used in the balancing process?
Place the locomotive on a "plank" that is strong enough to support it. Balance this assembly on a dowel or pencil. The balance point should be as mentioned above.
Ed
Late last night Dr. Wayne provided responses on the Electronics and DCC Forum in a string entitled "How to Repair the Wiring Harness on a Athearn Genesis 282 Light". In his last response he included a link to a 2009 spread that he did on 2-8-2 mods on the Bluetrains forum. As is all his stuff on behalf of the community, it is a masterful presentation, replete with photos and step-by-step instructions - including particulars on the casting of customized weights from scrap lead to maximize loco pulling power. He spoke of the importance of the engine's weight being evenly distributed across the wheelbase of the drivers for best effect.
This piqued my interest immediately as I have two Genesis SP Mountains that likely will need the treatment once I generate enough courage to open them up. But I am a bit unclear on two points: 1) I presume that the balancing should take into account the entire engine upon its reassembly, and 2) what method and devices (jigs, etc.) are used in the balancing process?
I fully expect Wayne to chime in here - in spite of all the other stuff that he has to do. But I will also look forward to what other advice (and gizmos) come from the rest of you steamer mechs out there. Photos will be icing on this cake.
With much appreciation, as always,