Large Scale Central

Loco weight

Modeling Motive Power
#21

Randy Lehrian Jr. said:

Fortunately roundy-rounders generally have the same disdain for grades as they do switching! (http://largescalecentral.com/externals/tinymce/plugins/emoticons/img/smiley-surprised.gif)So things ought to work out fine for them. (http://largescalecentral.com/externals/tinymce/plugins/emoticons/img/smiley-wink.gif)

Hey now! (http://largescalecentral.com/externals/tinymce/plugins/emoticons/img/smiley-surprised.gif)I am a roundy rounder. You know that. I also have a constant 2.58% grade on my mainline. And that you know too. So, are you saying that I am just different then the general roundy rounder? (http://largescalecentral.com/externals/tinymce/plugins/emoticons/img/smiley-frown.gif)

Ok. (http://largescalecentral.com/externals/tinymce/plugins/emoticons/img/smiley-laughing.gif)I can accept that.(http://largescalecentral.com/externals/tinymce/plugins/emoticons/img/smiley-wink.gif)

#22

Thanks Korm, not sure I agree with that logic though.  If an axle was unpowered, adding weight to it would do nothing to add tractive effort.

 

I knew you'd chime in on that David!    And if memory serves, you often seem to be the exception to generalizations I make.  You truly are a rare bird!

#23

Randy Lehrian Jr. said:

Thanks Korm, not sure I agree with that logic though. If an axle was unpowered, adding weight to it would do nothing to add tractive effort.

Randy,

On a steam engine, all wheels are powered by means of the rods. Whether a full size or a model steam loco all the wheels that are mechanically turned add to tractive effort if they are on the rails. (http://www.largescalecentral.com/externals/tinymce/plugins/emoticons/img/smiley-wink.gif)

#24

Joe Zullo said:

Randy Lehrian Jr. said:

Thanks Korm, not sure I agree with that logic though. If an axle was unpowered, adding weight to it would do nothing to add tractive effort.

Randy,

On a steam engine, all wheels are powered by means of the rods. Whether a full size or a model steam loco all the wheels that are mechanically turned add to tractive effort if they are on the rails. (http://www.largescalecentral.com/externals/tinymce/plugins/emoticons/img/smiley-wink.gif)

No Joe,

Not all wheels on a steam locomotive are powered by rods. Now I am sure you meant to say all drivers are powered by rods. The pilot and trailing wheels most certainly are not powered. I believe Korm was referring to those such wheels. There would be little to no point in my opinion to weight the pilot or trailing wheels of a locomotive, prototypical or model, beyond what is necessary to keep them in positive contact with the rails for the purpose of keeping the locomotive on the tracks in a corner. In my minds eye weighting a locomotive evenly over all wheels including those not powered would defeat the purpose of the weight in the first place which is to provide tractive effort. If you distribute weight to all wheels evenly then you are actually robbing the wheels providing traction. This would in essence be causing a double negative, less traction to weight ratio and also requiring the locomotive to pull more weight without the benefits of the weight thereby again reducing it efficiency. I would say that on the real deal and on the model most of the weight needs to be over the drivers and only that amount of weight required to make the non-powered wheels should be applied to keep them in positive contact. I am no engineer but this just makes common sense.

Brings up another question for another post maybe but what is the point of the trailing wheels on a loco. If the pilot leads the loco into a corner what is the purpose of the trailing truck. The only thing I can think of is the fire box and boiler extends so far behind the drivers that it weight must be supported. But if your creating such a large power plant why not add drivers?

#25

Graeme Price said:

A question about what would the weight of an 0-4-0 steam loco should be.

I have an LGB Stainz loco that weighs about 2Kg but an LGB “Shorty” loco that weights in at a rail crushing 3.5Kg.

Both are battery powered with the same electronics and battery capacity, but every time I run them the “Shorty” runs out of power first I ran them with identical wagons for the purpose of testing.

I am assuming that the extra 1.5Kg is causing the motor to draw to much out of the battery and am considering removing some more weight (I took some out when I converted to battery power).

What is the average weight that others use on small shunting type locos?

I’d say they were both too heavy. My small shunters are around 1kg.

#26

Thanks Devon, That was exactly my point, and the way that I interpreted what Korm said.

You are also correct on your secondary question about trailing trucks. Indeed some of the fire box weight and the weight of the cab need supporting. Adding more drivers wasn’t possible for a few reasons. Fire boxes got wider as designs evolved allowing for more grate area to pull in fresh air. Because of this the could no longer fit between the drivers or between a spaced out set of drivers as in an early American or Ten wheeler. Why not just add another set of drivers spaced out for behind the boiler on the aforementioned early types? Well by this point locos were already getting quite long so on a something- 4 - something adding a fifth set of drivers back there would have made an extremely long ridged wheel base and limit the ability of the engine to go around curves.

#27

Randy,

I took Korm’s method to mean drivers, not pilot or trailing wheels. I thought he had said that. Sorry if it confused you.(http://www.largescalecentral.com/externals/tinymce/plugins/emoticons/img/smiley-cry.gif)

#28

well, let me try to confuse you more:

let us take the big hauler as example.

i gave mine three times 1.3 kg weight. and it ran good - untill split gears made for forced retirement. (before, without additional weight, it could not even haul its own tender up the 6% grade)

the two axles of the ponytruck (the “4” in 4-6-0) do not carry any/much of the loco weight. so, forget them. (and weight them individually against derailments)

the drivers (“6” in 4-6-0) all take part of the locos weight. if powered, or not. so to have 1.3 kg upon any powered axle, every axle that is fixed to the chassis, has to be counted in.

sure, a loco, with one or more not powered axle(s) never can be as good at towing, as a loco with powered axles only.

i think, that is the secret, why our smallest locos often are our best workhorses.

like the Stainz, the Köf etc. - axles rigid, both powered, all weight used for traction.

(and that is, why i use for my layout with 6% grades only stainzes plus powered tenders.

a 0-8-0 loco with all axles powered would have one or more axles hanging in midair, everywhere the track angles up or down.

0-4-0 loco plus 0-4-0 tender always have all (powered) axles pressing on the rails.)

#29

Hey Joe, It’s no thing. (http://largescalecentral.com/externals/tinymce/plugins/emoticons/img/smiley-wink.gif)And Devon did the hard part typing it all so it could only be interpreted one way. (http://largescalecentral.com/externals/tinymce/plugins/emoticons/img/smiley-smile.gif)

I think the dynamics of steam and diesel cassis design definitely have different effects on how the weight and position of it translate in to tractive effort.

#30

Randy yes, Diesels are different, but the ideal weight per axle is probably about the same.

As for the trailing trucks, yes they were added to support the larger fireboxes. The locomotive designers saw that the weight there was “dead”, it wasn’t adding to the tractive force, and was essentially trailing weight. Weight like a freight car. So there were attempts to power trailing trucks, with small steam motors, to add to the tractive force when starting out, or at slow speeds. The added power wasn’t worth the added weight, complexity, and maintenance of the booster motors, so the idea was eventually dropped.

#31

from Wikipedia…

#32

Korm Kormsen said:(before, without additional weight, it could not even haul its own tender up the 6% grade)

Actually, that is probably right in line with reality.
Let’s see here, according to reprint of Porter locomotive catalog, we’ll take a 92,000 pound 2-6-0 of 48 inch drivers and 16x24 cylinders, weight on drivers 79,000 pounds, with 52,000 pound tender, both weights in working order. Locomotive was order-able with telegraph/telegram code word “HATEAR”
Rated to pull 2,770 tons on the level. On a 1.5% grade it could pull only 37 percent of that flat land weight, 1,045 tons. On a 3% grade that dropped to 205 tons.

#33

Yeah and after I go and explain it Korm comes back and indeed was only talking about powered and un-powered drivers (http://largescalecentral.com/externals/tinymce/plugins/emoticons/img/smiley-surprised.gif). In that case I have to agree with Joe. A Bachmann 10 wheeler only has one axle directly powered by the motor but then the side rods indeed drive the other two sets of drivers. So they are powered drivers and would require weight as they are adding to the tractive effort.

#34

Yea, 6% grade is in geared locomotive territory. Most rod locomotives wouldn’t (normally) go above 3%. 4 if its the DRGW

#35

And the one critical item prototype has over (most) models is equalization. Most models are RIGID framed, which dictates the interior drives will be suspended on vertical up curves, and one end or the other will be suspended on vertical down curves. With equalization all drivers are powered as all drivers will contact the rail at all times, and equalized drivers all bear a somewhat equal share of the weight. Depending on track work, the six drivers of a ten wheeler could potentially be sitting (worst case scenario) on front axle left driver and rear axle right driver with all the others suspended. There are many off beat scenarios in between, but I think I got my point across.

Pulling power is also a function of differential materials and the coefficient of friction between. I am no expert in this area, but considering the varied materials used in our models there is a wide range of possibilities. A bit of my history goes back to the oldest modeling club in the country, he New York Society of Model Engineers. My sponsor/mentor taught me that the best tire material for loco drivers was cast iron because it had the highest coefficient of friction. I can only say for certain that thy pulled a 65 car coal drag on that driver material. hey also used steel rail.

#36

Devon Sinsley said:

Yeah and after I go and explain it Korm comes back and indeed was only talking about powered and un-powered drivers (http://largescalecentral.com/externals/tinymce/plugins/emoticons/img/smiley-surprised.gif). In that case I have to agree with Joe. A Bachmann 10 wheeler only has one axle directly powered by the motor but then the side rods indeed drive the other two sets of drivers. So they are powered drivers and would require weight as they are adding to the tractive effort.

And the middle driver doesn’t even touch the rail.

#37

Bruce Chandler said:

And the middle driver doesn’t even touch the rail.

I beg to differ Bruce. My Bachmann 10 wheeler (generation 5) middle driver most certainly is on the rail…

#38

the conversion from prototype to scale weight involves the prototype weight divided by the cube of the scale. Has worked pretty well for me with diesels so far.

The earlier comment of taking the cube root of the prototype weight does not take into account scale at all, clearly does not make sense.

the cass scenic 3 truck shay #6 weighs 162 tons, so 324,000 pounds / 8,365 (that is 20.3 cubed) = 38.7 pounds … pretty darn heavy, but not really crazy for a 3 truck shay.

an emd e8 weighs about 315,000 pounds, and converting to 1:29 is 315,000 / 24,389 = 12.9 pounds, perfect for how I have run them

Seems to work fine… also if you weight your rolling stock to the prototype empty weight, they will track well and run in long trains… you just won’t be able to pull them up non-prototypical grades and curves…

Greg

#39

This whole discussion of loco weight still confuses the prototype… BNSF recently ordered some new locomotives that are 6 axle units, but the middle axle is an idler axle (no traction motor). BuNSniF ‘thought’ that these new fancy locomotives would work great and be the best thing since sliced bread. Well, from the folks on the ground, I’m hearing that these locomotives suck! They don’t pull worth a darn, and have numerous traction problems, and GE keeps saying “No, no our locomotives are great”.

Long story short to say that what we are dealing with in the models sometimes is replicated by real life… (http://www.largescalecentral.com/externals/tinymce/plugins/emoticons/img/smiley-tongue-out.gif)(http://www.largescalecentral.com/externals/tinymce/plugins/emoticons/img/smiley-undecided.gif)

#40

Craig Townsend said:

Long story short

Hmm, that has me wondering, how come you never hear anyone say, “Well, to make a short story long …”