There is a formula for calculating the optimum weight of rolling stock, at least partly because ready-to-roll ones are not always made heavy enough. Do the manufacturers of locomotives determine the optimum weight & make them in accordance with it? If that is not always the case, is there is a way to calculate the optimum weight of a specific locomotive, or are there too many variables?
Too many variables. Remember that a locomotive also has to pull it's own weight. Most locomotives will be of sufficient weight out of the box for operation on level track.
I would consider "optimum weight" to be the weight that allows good pulling performance for your particular needs or wants, while not preventing the drivers from spinning when stalled.
Most manufacturers design their locomotives to slip their wheels before the motor current gets so high that the motor burns out. If you add more weight, you run a real risk on having your motor burn out because you have, in effect, tied down the safety valve.
In large scale, I run some locomotives with extra weights and a much higher than normal motor current. This would cause certain failure except for the fans I install to force ventilate the motors (much like the real railroads do on their diesel traction motors.) As yet, I haven't figured out how to do this in H0, particularly in steam locomotives where the motors tend to be small and poorly ventilated.
Consider a 200 ton locomotive. If you scale the weight down to HO, that equates to 9.7 ounces, much too light for good pulling. Doubling that to 18 ounces is probably more realistic. All my GP 35 & 40 weigh about 15 ounces.
I have never found the need to add weight to any of my locomotives. Even my tiny GE 44 ton will pull 15 cars at a good 50 mph speed, yet it only weighs 5 ounces. Of course my track is level, if I had grades I would simply add a helper. I have several powered cars that can be added to the mix if needed, a DCC powered caboose being my favorite.
so it it bad practice to fill your hoppers .and create your own loads for different rolling stock . i plan to have an area of about a 2" rise on the backside of my layout then down. not tunnel height .
regards mf
Not at all, adding scale looking loads adds to the realism. For real railroads, the overall ratio of rolling resistance is less for a loaded car than for an empty car on level track. I haven't as yet figured out a way to measure required pulling force of a car moving at 50 mph.
i had heard that .125 / .190 per 1'-0 is rule of thumb , for ho. so on the 22" rad on the outside loop . i may have to lower my grade to be 2 to 3 % . im adding a 3" to get the full prim of the 4x8
Don't steam locomotives carry sand to release onto the rails for better traction? I don't know exactly how they do that. Since we can't put sand on our tracks, maybe traction tires are the alternative. :)
Quote from: Yampa Bob on February 26, 2009, 01:35:30 AM
Not at all, adding scale looking loads adds to the realism. For real railroads, the rolling resistance is less for a loaded car than for an empty car on level track.
Bob, that's interesting about rolling resistance. I do like my freight cars to carry scale loads: Ballast iron ore, tiny wooden crates (I cut from craft dowels), cattle for my cattle car, scrap metal, logs, barrels, & etc..
Bob, its very interesting that the scale weight of a loco less than the actual weight of our locos. But if we were to scale down the weight of cars, they would weigh an ounce or 2. A lighter loco to pull a lighter load. Unfortunately, they would not track well because of their light weight. I too, like to run cars with prototype loads. I have a car for tea and another one for donuts! ;D ;D ;D
Quote from: pdlethbridge on February 26, 2009, 07:32:06 AM
Bob, its very interesting that the scale weight of a loco less than the actual weight of our locos. But if we were to scale down the weight of cars, they would weigh an ounce or 2. A lighter loco to pull a lighter load. Unfortunately, they would not track well because of their light weight. I too, like to run cars with prototype loads. I have a car for tea and another one for donuts! ;D ;D ;D
They must be awfully small donuts.
Both steam and diesel locomotives use sand for traction - electric, too, I imagine. If you look at the top of a steam locomotive you will see one or more domes with one or more hatches in them. Usually there will be piping running down the boiler side. The dome or domes are the sand domes and the pipes are the delivery system to the wheels. The engineer controls the amount of sand delivered to the drivers. With diesels, all this is hidden.
Gene
Thanks, Gene, for explaining how the sand is applied. I've never seen sanding in action.
Sanding....of course the rail yards are not as they once were, but if you get the chance to visit a rail yard somewhere, check on the ground for little (or large sometimes) piles of sand along the rails. Until a few years ago I never knew what that was about. That is from the sanding actions of the locomotives. If you see a big pile, the engineer forgot to turn of the sand! lol Stephen
The optimal weight for a model locomotive, without traction tires, is to cram as much weight as you can into the body shell, keeping the weight balanced around the centre of the driving wheels on steam, so that the loco can still spin it's drivers under full throttle.
If the loco cannot spin it's drivers under full throttle, then you risk motor burnout so remove some weight. Traction tire fans, please note that little tit-bit.
casings and frame made out of depleted uranium ( black hole stuff ). but it would be tough to isolate all elements of DCC system.
Another use for sand is to clean the flues in a steam locomotive. A couple of shovels of sand thrown in the firebox will go swirling through the flues and up the chimney, taking soot and creosote with it. Then the heat transfer from the hot air/flames to the water is much improved. This also helps clean coal dust and stuff off the shovel, getting it ready for cooking the bacon and eggs for breakfast. No, they don't use steam cylinder oil for greasing the shovel - that was what the bacon is for.
While on the subject of breakfast, you also need to know about the metal shelf attached to the back of the firebox. Officially, it was to keep the oil cans warm in cold weather so the oil wouldn't be like molasses. Unofficially, that was where the coffee pot was kept. Back in the days before water treatment, hot water for coffee or tea was drawn from the bottom tri-cock. Now you know why there are three when two would do. Cream for the tea and coffee as well as the eggs were often from a trackside farmer who would from time to time get one of the crew to pick up something from town, or maybe deliver something.
I can't swear to any of this, except the bacon and eggs on a shovel and the shelf for the coffee pot. It is all rumour from a long time ago when schedules were looser, trains were shorter, speeds were slower, and superintendents were fewer and farther between. I suspect the railways were aware of what was going on but chose to ignore it as long as the freight arrived reasonably on time and nobody was booking off sick from stomach problems when 100 miles days turned into 20 hour days. I also suspect that the superintendents were fellows who had come up through the operating trades, not university boys who would faint at the thought of working 12 hours of overtime on top of a a full day's work.
That reminds me of a picture of a B&M switcher carrying a block of ice on the pilot. Don't ask me why.
(http://s167.photobucket.com/albums/u134/pdleth/th_443.jpg)
Quote from: rogertra on February 27, 2009, 03:20:32 PM
The optimal weight for a model locomotive, without traction tires, is to cram as much weight as you can into the body shell, keeping the weight balanced around the centre of the driving wheels on steam, so that the loco can still spin it's drivers under full throttle.
If the loco cannot spin it's drivers under full throttle, then you risk motor burnout so remove some weight. Traction tire fans, please note that little tit-bit.
That's a simple formula to remember. I guess it's okay if, at full throttle, the steamer moves at 130 mph, instead just its wheels. :) BLI informed customers that metal drivers are available to replace the wheels with traction tires that came on our Heavy Mikados.
Jim, that's some colorful train lore!
Stephen, now I'll now those aren't anthills. ;)
My first HO kit engine was an original Penn Line mike. I built it as instructed. When I joined a large HO club I brought my engine along to run. It was greeted with much disdain as the club members told me that my mike would barely pull five cars. The reason, of course, was the heavy tender and trucks that didn't have the best rolling qualities. It was quite a disappointment.
If I remember from my days in HO weight in an engine needs to be over the driving wheels and balanced. Sticking lead in a cab roof might make an engine heavier but it is just adding drag.
Quote from: WGL on February 28, 2009, 03:43:21 AM
That's a simple formula to remember. I guess it's okay if, at full throttle, the steamer moves at 130 mph, instead just its wheels. :)
Spinning wheels under full throttle has nothing whatsoever to do with the top speed. If the loco's top speed while running free is a scale 55 mph, then you fill it with weight enough so that under full throttle, the wheels will still spin.
Speed has nothing to do with it.
Quote from: Woody Elmore on February 28, 2009, 11:17:03 AM
My first HO kit engine was an original Penn Line mike. I built it as instructed. When I joined a large HO club I brought my engine along to run. It was greeted with much disdain as the club members told me that my mike would barely pull five cars. The reason, of course, was the heavy tender and trucks that didn't have the best rolling qualities. It was quite a disappointment.
If I remember from my days in HO weight in an engine needs to be over the driving wheels and balanced. Sticking lead in a cab roof might make an engine heavier but it is just adding drag.
That's what I wrote: -
" ... keeping the weight balanced around the centre of the driving wheels on steam..."
gravity does not scale ;)
look at the front and rear trucks of a steamer. if they have a spring that pushes down on the truck it removes weight from the drivers.you can cut a coil or two out to get more weight on the drivers. one thing alot of people think is that the more drive wheels a loco has the better it will pull.. this is not always true... if the weight is the same between a 4 driven axels and 6 driven axels the 4 axel will likely pull better. this is also tru with steam..
Here is a bit of information about "Adhesive Weight".
http://everything2.com/e2node/adhesive%2520weight
The total weight of a train includes both the cars and the locomotive. Therefore a percentage of available power is lost just moving the locomotive. For the way I operate, I estimate about 20% for the loco. Of course I only run short trains.
thats a great link Yampa! that about sums it up about traction and weight
I thought you would like it. The section about steam locomotives is interesting. All drive wheels coupled together gives "total adhesion" but lack stability at speed.
Here's another good site, scroll down to "running gear".
http://www.answers.com/topic/steam-locomotive-mechanical-engineering
Site also has a great animation and lots of other information about steamers.
Another great link about the workings of steam engines!
Locomotives with "compensating levers" connecting the ends of plate springs have often been deemed a complication but locomotives fitted with them have usually been less prone to loss of traction due to wheel-slip.
is this compensating lever a way to balance weight across drivers or does it give one axel the ability to have a greater weight on it? intresting read!
Bob,
I read with interest your links to adhesive weight & steam locomotives. However, I don't understand why, if a 0-4-0 has the same weight on each axle as a 2-10-2 ("Also known as Santa Fe class locomotives, these brutes were typically employed in drag freight service."), the bigger locomotives were used to pull longer trains. ???
The axle load was limited by the track the engine ran on. A high axle load engine such as the C&O 2-6-6-6 Alleghenies required the heaviest rail made to support the train. Some areas in Canada, for instance, used very light rail and used diesels with 6 axles rather than 4 to spread the weight.
Quote from: pdlethbridge on February 28, 2009, 02:57:10 AM
That reminds me of a picture of a B&M switcher carrying a block of ice on the pilot. Don't ask me why.
(http://s167.photobucket.com/albums/u134/pdleth/th_443.jpg)
It's the coolest place on the engine to carry it.
Quote from: WGL on March 02, 2009, 03:48:02 AM
Bob,
I read with interest your links to adhesive weight & steam locomotives. However, I don't understand why, if a 0-4-0 has the same weight on each axle as a 2-10-2 ("Also known as Santa Fe class locomotives, these brutes were typically employed in drag freight service."), the bigger locomotives were used to pull longer trains. ???
a 0-4-0 switcher can have the same axel weights as a big Santa Fe class and is able to push around heavy trains but it cant maintain the movment for a long time. reason is that the 0-4-0 is not a large engine and has a smaller firebox and boiler.. the larger 2-10-2 has a larger boiler and firebox so it can maintain its steam and thus move the freight at a higher speed and a further distance. each engine was built for a diffrent service even tho they basicly can pull the same weight
Driver size would also have an effect on tractive effort
Thanks for the explanations, pdlethbridge & Imackattack. Since our models don't run on steam, can we expect a model of a 2-10-2 to pull more than a model of an 0-6-0, for example?
If the model 2-10-2 weighs more than a 0-6-0 then it should be able to pull better. if they both weigh the same I would think the 0-6-0 would pull a few more cars due to more axel weight across less drivers. most model 2-10-2 will weigh more than a 0-6-0 so dont worry LOL
Thanks, lmackattack. I am eagerly looking forward to receiving the DM&IR 2-10-2 next week. Maybe, I'll have to get a few more ore cars. :)
This is an interesting thread. I have some other thoughts about weight and tractive effort versus actual traction, but I'll reserve comments until later. In the meantime here's a homework assignment for all wannabe engineers: Define tractive effort in its simplest terms.
locomotive weight divided by its factor of cohesion.
From Wikipedia:
Tractive effort is the pulling force exerted, by a locomotive or other vehicle. The term is used specifically in railway terminology.
The tractive effort value can be either a theorectical or experimentally obtained value, and will usually be quoted under normal operating conditions. The actual value for a particular locomotive vaaries depending on speed and track conditions, and is influenced by a number of other factors.
When a figure for tractive effort is quoted in technical documentation it is either for the starting tractive effort (at a dead start with the wheels not turning) or as the continuous tractive effort which will be quoted at a particular speed.
I agree Yampa this is a great thread with lots of good info. I rember years ago I spoke with a retired Engineer at the Illinois railway Museum and he said something that alwasy stuck in my head regarding that age old Diesel vs steam pulling power. He said in simple terms a Diesel can start a train that it cant pull and a steam engine can pull a train that it cant start. not sure if you can follow that? but after learning more about trains it makes some sence. but then im biased and think steam still rules!
diesel depends on its traction motors. They can overload them at the start but if they keep it up or they will burn out. Thus they can start more than they can pull. A steam loco, on the other hand, doesn't get to be at full horse power until its above usually 20 mph. Its pulling power increases as it gains speed.
Another often overlooked factor in a locos ability to pull is balance, both on the prototype and the model. For instance, how many times have you heard of a leading or trailing truck spring being removed - or added in some cases - to improve the balance of the locomotive.
There are probably several ways of balancing your steam loco, but the one that is easiest uses two postal scales. With the leading and trailing trucks removed, place the leading set of drivers on one scale and the rear on the other. If the weight on both is about the same it is balanced. If they are dissimilar, either add weight to the end of the loco that is on the lower value, or remove weight - milling etc - from the heavier end. Though I would normally recommend the addition of weight.
I have seen notoriously light pullers dramatically improved when properly balanced. A certain 2-10-2 springs to mind .... :)
Steve Magee
Newcastle NSW Aust
Weight distribution is important, however the weight transfer caused by pulling a string of cars also has to be considered. When pulling a load, a greater weight is imposed on the rear drivers, a lesser weight is imposed on the front drivers, unless all forces are balanced. The drawbar hitch point location has a direct effect on the trim attitude of the locomotive.
thats another good point about the angle of the coupler in relation to the driven wheels. that angel can help or reduce traction for anything that pulls a load behind it. I compete in sled pulls with a old Mack semi tractor. hitch hight is very important. hight is set by the circut that we pulled in but that hight could change with the diffrent types of suspention the trucks had. We tried to get the frame hight just right so that hitch hight was in spec thru tech inspection but after a load was chained to the frame it diffred a little. We wanted the wheels spinning as we left the line to get the RPMs up fast then let the truck build its speed before all the weight came up to the front of the sled. This gave us the speed needed shortly out of the gate so that when the weight was at the front of the sled the engine was at its full RPM. The only thing that slowed us down was not having the HP needed to drag all 40,000lbs of dead weight when it was at the front.
heres a vid of the old dog pulling last year at the local fairgrounds
http://www.youtube.com/watch?v=gNigPBpwvQU
Hey Mack, now we know how you got your nickname. That is a great video, thanks for sharing. Did "Last Call" make a full pull? I'm loading the other one, but it will probably take an hour on my slow dialup.
I love the open class tractor pulls with the multiple Allisons. I attended one and the sound was awesome.
Quote from: Yampa Bob on March 07, 2009, 01:56:48 AM
Hey Mack, now we know how you got your nickname. That is a great video, thanks for sharing. Did "Last Call" make a full pull? I'm loading the other one, but it will probably take an hour on my slow dialup.
I love the open class tractor pulls with the multiple Allisons. I attended one and the sound was awesome.
Yea I live in the mid west so if it has a motor and wheels you will find a place to hook it to a sled. I have seen a few allisons pull and if they do great. but Im a little old school and like the manual transmissons.
regarding that vid,It pulled short. it went about 282' 300' is a full pull. that truck is a bone stock 1976 Mack with a 237 HP diesel. the only real mod was the stock fuel pump was turned all the way up. in the other vid we made the year before the truck had a 100% stock fuel settings and only pulled to about 220' but it was on wet ground after a morning rain storm. it had no traction at all