Large Scale Central

Loco weight

Modeling Motive Power
#1

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?

#2

I don’t know much about this but at 2.2 #s to the kilo that 3.5# is over seven pounds. When I was asking this about my 2-6-0 build I was told 3-5 pounds (I think mine weighs in just over 4) so I am thinking 1.5 would be more than ample for a small loco not needing a lot of tractive effort. My understanding is the weight is only their to supply ample down force to the drivers on the rails to get traction (just like the real deal). Considering this I would think the least amount of weight needed to supply adequate traction would be best; Anything more is just extra weight. I would put it on a diet in such a manor that it loses weight until it no longer maintains traction then ad back whatever is needed.

Just like the real thing the more power a loco produces (and supplies to the drivers) the more down force (weight) it needs to keep the drivers from slipping. So on models I would think weight requirements are directly proportionate to the amount of power to the drivers from the motor. If your two locomotives indeed have all the same electronics including the drive motor power output then the weight needed I would think would similar.

That is my uneducated 2 cents worth.

#3

There are more influences here than just weight. A few things to cause pause and thought. Are the motors ‘IDENTICAL’? Are the drives exactly the same - same worm, same gear, same materials of construction (ex. steel worm, brass gear). Is the gear ratio the same and are the drivers the same diameter? Are the axles run through the same bearings (if any)?

Each one of the above conditions affect the overall run time of the locomotive. As an example, my Bachmann K27 has been modified, converted to battery and radio control. The modifications include locking drivers #1 and #4 (removing springs and adding spacers to eliminate side play), adding a spring on the gear box to add stability to the #3 driver. I have also added the weight from an Aristo 0-4-0 a fellow club member purchased as an unrepairable wreck. This had the added benefit of putting a far better balance in the loco (front to back), and I have all but eliminated the pilot truck derailments. I have not weighed the loco, but I believe she is in the 30 pound range. I will have to weigh her one day. And I also added an additional gear reducer to bring the final ratio closer to the 30:1 it should have been.

I am running AirWire R/C and a 5600mha battery. I have run this loco 4 plus hours and still have battery left, not sure how far it will go. I would recommend spending some time looking at the two side by side and see where the differences are. I am sure that weight is not going to be the only difference you will find.

Good luck.

Bob C.

#4

From the other direction, I have a Bachmann 2-4-2. It was a feather weight when I bought it, and lame as freight hauler. I have added 16 ounces of weight to it, and its still kind of lame, but it does pull more cars now before slipping. So while it does take energy to move weight, it takes weight to haul cars. So Devon is on the right track.

Bob is also on the right track, as in there are other things that will reduce run time on batteries. Light bulbs versus LEDs in the engine lights. A bit more binding or stiffness in the wheel bearings and drive train. Different gear ratios in the drive train, requiring more or less power for the same speed as another locomotive.

So weight is part of the equation, but it isn’t all of the equation in power consumption.

#5

David and Bob thanks for chiming in. This gives me much to think in my current loco builds and future ones. One such example of “other” considerations is the smoke unit. I have decided to leave of a smoke unit to save power. But things like gear ratios and the likes I hadn’t considered. All good stuff and when the time comes I will be asking questions.

#6

I added about three lbs to my Lionel Atlantic. Its a bull, now.

#7

I have a USAT Docksider that weighs in at 10#10oz. It’s all die-cast and will pull my Bachmann 2 truck Shay dead with no problem. I have easily pulled 18 freight cars with it and it didn’t know they were there. The thing about loco weight is that you don’t want to over do the weight vs. the strength of the drive train. I would never weight down one of my B’mann 10 wheelers to that level. The gearing couldn’t take it. Three pounds is about all it could take. HTH (http://www.largescalecentral.com/externals/tinymce/plugins/emoticons/img/smiley-wink.gif)

#8

Yes, more weight will give you more tractive force. But the OP, Graeme, is on battery power, and wants to reduce power consumption by removing weight. He could, but I was trying to illustrate that if he removed too much weight, he wont have enough tractive force to move an empty flat and a caboose.

The other thing about steam locomotive weight is, you want it centered above the drivers. If the weight is too far aft, the loco could try and pop wheelies when its running. Too far forward could cause tracking issues. Diesels with 2 trucks aren’t as susceptible to these problems, but you still should have the weight pretty evenly distributed.

#9

Thanks for the replies.

In answer to these questions "Are the motors ‘IDENTICAL’? Are the drives exactly the same - same worm, same gear, same materials of construction (ex. steel worm, brass gear). Is the gear ratio the same and are the drivers the same diameter? Are the axles run through the same bearings (if any)?

The answer is no to all, so many variables, but both will haul the same train with no worries that is why I went to the weight difference.

I think I will remove some more weight as I think I actually added weight when I put the battery into the boiler on top of the standard weight that came fitted but I will definitely look at the other factors if the weight removal doe not work.

XX

#10

i don’t remember where, but two or three years ago this was discussed at length. many test results were reported and compared.

i then wrote down a number. that was 1.3 kilograms per axle. (nearly three pound)

everything exceeding that was consented upon as superfluous.

i adopted this standard for most of my locos and motorized tenders - with very satisfying results.

edit: the forrunner axles were not counted. so the Bachmann big hauler was in for thrice 1.3 kg. and the stainzes twice.

#11

Some folks used to say the cube root of the prototype’s weight would give you the ball park figure.

John

#12

John,

Korm’s method seems about right for a G gauge loco. Cube root seems way too heavy. For example, my B’mann 38 ton Shay would have to weigh over 42 pounds by the cube root method. I doubt the electric motors in the trucks could move that much weight for very long. Here is an on-line cube root calculator. Try it yourself… http://www.calculatorsoup.com/calculators/algebra/cuberoots.php

#13

Joe,

Is it ok if I take your word for it?

John

#14

Cube root would give you scale weight, and you are right, I doubt that many of the small electric motors and plastic gears could handle that.

2.866 pounds per axle. Well, that explains why my 2-4-2 is such a poor puller. Even after adding a pound of weight, I know she doesn’t come in anywhere close to 5.732 pounds.

#15

An engineering friend told me you can figure on the wheels slipping when the tractive effort is roughly .22 times the weight on the drivers. Varies a bit by what the wheels and rails are made of and what’s between them. At 1.3KG per axle, my slightly overweight mallet is still a hair light. Well, about 4 pounds light. She has pulled dead dash 9s.

#16

this makes me want to get mine running. I have to weigh it again but I believe I have it a shade over 4 pounds. with suggestions here it might need to weigh twice that. (http://www.largescalecentral.com/externals/tinymce/plugins/emoticons/img/smiley-cry.gif)will be a challenge getting more in there. But I won’t do it until after i do some pulling. I don’t expect it to pull more than 4-5 cars at a time as that is prototypical.

#17

Whoa!

We are not pulling scale weights either.

The biggest influence will be the drag of your cars wheels. Check for burrs and lube.

Add cars and see how it starts and stops, you’ll see where it moves easily and where it struggles.

I suggest bags of shot hung over the loco to temporarily add /subtract weights while testing and looking for a happy medium.

No wheel slip at start and no pushing the engine during braking. Too much weight and you’ll treat it like a stump puller when the gearing supports easy running…

Doubling the hill, was a common experience when the yard boss would over load your engine… break it in the middle, leave the conductor protecting the rear of the left half, while the loco takes half up the hill, parks it in a siding and comes back for the rest.

Happy Rails

John

#18

Doubling the hill??? That sounds like real work! The roundy-rounders will be upset. (http://largescalecentral.com/externals/tinymce/plugins/emoticons/img/smiley-tongue-out.gif)(http://largescalecentral.com/externals/tinymce/plugins/emoticons/img/smiley-laughing.gif)(http://largescalecentral.com/externals/tinymce/plugins/emoticons/img/smiley-innocent.gif)

#19

Steve Featherkile said:

Doubling the hill??? That sounds like real work! The roundy-rounders will be upset. (http://largescalecentral.com/externals/tinymce/plugins/emoticons/img/smiley-tongue-out.gif)(http://largescalecentral.com/externals/tinymce/plugins/emoticons/img/smiley-laughing.gif)(http://largescalecentral.com/externals/tinymce/plugins/emoticons/img/smiley-innocent.gif)

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)

Great topic, I want to go home and weigh my engines now to see where they shake out. I’m pretty sure my EBT 12 will be about 10LBS per axle!

Did driver size matter when “the group” came up with the “3 pound per” rule?

#20

Did driver size matter when “the group” came up with the “3 pound per” rule?

i do not remember having read about that.

what was mentioned, were the not powered axles. consense was, to count them in, because part of the weight would be carried by them.