Improving Our Steam Engines Performance
- Thread starter beiland
- Start date
I am using a Proto FT-B unit as a pusher for my challenger. The Challenger has plenty of power but lacks traction up the 3.5% grade on my layout. The B unit gets plenty of traction as a pusher. I did have to play with midrange numbers a little to keep it from pushing too much coming out of a curve and causing a derailment of the tender. Once I tweaked that, it works nicely. I made a shell to look like a water tender but didn’t like some of the details and am currently changing it more to my liking. I will post a pic in a couple days when finished.
I understand. I think in most cases this is the reason for a surge at the start because it takes a little more voltage to get everything turning than with a diesel model. The motor selection is a big thing here. The rule of thumb has always been "the biggest one that will fit" which has served me well. I used to buy Sagamis and Mashimas and scoured the internet for them when they became hard to find. Now e-Bay is lousy with cheap can motors and I don't pay more than two or three dollars for one.
Proof that
. Combining them with a 3.24 % grade will kill most steamers.
Proof that more weight does not necessarily mean more pulling power. The loco has to lift itself as well as any cars. On 20 radius curves I wouldn’t run anything larger than a 2-8-0. Most of my large steamers are brass and wouldn’t negotiate a 20” radius curve.
. Combining them with a 3.24 % grade will kill most steamers.It’s been my experience that it’s not as much the voltage as the surging thrust. Let’s look at the physics. When the drivers are at 12 o’clock or at 6 o’clock they are very efficient pushing or pulling but at 9 or 3 o’clock they are mechanically compromised and relying on centrifical force. This is why prototypes have large counterweights to aid in centrifugal force. But most models do not have these counterweights, only fake plastic ones. This linear motion conversion to rotary motion causes a very inefficient surging thrust.
I don’t know that I agree here. True at 3 and 9 they would be compromised, if not for proper driver quartering. The problem with physics is it doesn’t scale. The counterweights are more to balance the driver, being located 180 degrees from the rods and their bearings and hardware. They also offset Torque and lessen stress on the track by smoothing rotation.
I am comparing to a diesel where the drivers are all constant and close to the rotation axis and is a better climber. With a single GP9 I can pull 20+ cars up a 3.5% grade, even though it's not prototypical but with my best pulling steamer, that number is reduced to 12. I do not agree that physics does not scale here.
KriegslokBR52
Well-Known Member
Consider one of my personal interests; class F-1 of the L&NE just managing about 16 coal loaded hoppers by itself up the Summit Grade of 2,74% (few miles north of Bath, Pennsylvania). Your steamer does pretty good. Not sure how diesels did up that grade, since they were run in multiple after dieselization. I have a Pennsy I1 decapod which i'm working on, but i didn't install coupler on the tender yet. I have similar severe grade on my branch line, so it will be interesting to see how many cars this thing will manage by itself when i get around to it.
My 3.5% incline is on the mainline and I can either go up or down it but the preferred direction is up due to some sidings and their direction required to back in. I have been able to do a lot of comparisons and I really like to watch the steamers climb with some slippage. I have a Big Boy (Rivarossi) that I have regeared and installed two motors in and adjust the car numbers so I see a little slippage but not enough to hinder a successful climb. I also have a Rivy Challenger which I haven’t replaced the traction tires on and I use a diesel pusher with a water tender shell. Again, I have adjusted the pusher’s speed to allow the Challenger’s wheels to slip some. Love to watch those steamers work.
Exactly my point! While generally model diesels will pull better than model steamers, mostly because of all geared axles and smaller wheel diameters, when compared to the real thing, they aren't all that far off. I very much doubt the real GP 9 would pull 20+ cars yup a 3.7% grade (if you could find one). Right now, the steepest grade we have is Raton Pass NM at 3.3%. I've never researched the operations on that grade but have seen plenty of pics with double headed steamers. I am somewhat familiar with operations on Saluda Grade, which was 4.7%, site of numerous accidents, and a real bear to get trains over. "Tripling the hill" was very common.
If you just want to reduce this to a pulling contest, model diesels as a rule will pull better. If you compare steam models to what the prototypes were actually capable of, I think our model steamers do quite well, and my favoring prototype operations does influence my perceptions. We make many compromises in the hobby. Sharper radii, steeper grades, deeper flange depths, articulated frames and huge amounts of side slop in mechanisms, and more. Sometimes you have to pick what you want the model to do. Do you want a good puller, or do you need to get around sharp curves? Modifications to get a model to do one of those may impact its ability to do the other.
Last edited:
Yes I am in agreement there but still state that steam locomotives, both models and prototypes, deliver a surging power. We already established that the drivers at 12 and 6 are at peak thrust and at 3 and 9 have a mechanical disadvantage. Properly quartered locomotives will shift their torque from left to right rails and back again twice per revolution of the drivers. Then with models, most of which do not use bearings, just sleeves made of brass or plastic, have a very loose tolerance which allows for the side play which you refer. This develops an even greater loss of effective power transfer to the wheels.
zzr1200guy
Well-Known Member
I have a Bachmann N&W J 4-8-4 and it would pull it sat for 20 years and it sits so low it is pretty much useless Ill be tearing it down to see what happen. it never had traction tires. I saw a vide where they change out the springs that support the drivers the guy tried 3 different springs and in the end he did improve the traction effort of the engine by 6 heavy weight passenger cars
Find the surge:
This is a 20 car train counting the tender on a 2% grade. The cars are weighted to NMRA standards, some maybe a little heavier. As you can see the pulling power is there, no traction tires, no Bullfrog snot, no modifications out of the box. Also no surge. You'll notice it doesn't slip, and I could stop the train in the middle of the grade and re-start it. I think the true difference in our opinions here is in the quality of the models being compared. A Rivarossi Northern or a Bachmann GS-4 won't pull this train. Those two brands are at the bottom of the market, entry level models full of compromises to get them around 18" radius curves, and they are cheaply made. Too much slop, lightweight frames, and in the case of most Bachmann steamers, you just can't add enough weight to make them pull. I know. I've tried. No disrespect intended to the owners of these, I started out with them myself many years ago. This model is a Westside. Japanese brass, vintage 1970's. It pulls as well as any single diesel locomotive in my stable, and I have Genesis, Rapido and Scale Trains, as well as some of the old blue box stuff. It won't go around 18" or 22" curves though. It might get around a 24" radius but I'm not sure. I've never tried. It uses real bearings, and the build quality is very good to excellent. You can buy one for around the same money as modern good quality diesel models. It will still be running long after the plastic is in the dumpster. I think if you try some of the more modern better built steam models you may find you close that pulling power gap considerably! I would stack my Athearn Genesis Mt-4's against any single diesel. One of these days I may have a pull off, the Mt against a single Genesis F-7!
You are taking what I said out of context. A torque surge is not necessarily noticeable but it does cause a loss of traction. Have a good day!Find the surge:
This is a 20 car train counting the tender on a 2% grade. The cars are weighted to NMRA standards, some maybe a little heavier. As you can see the pulling power is there, no traction tires, no Bullfrog snot, no modifications out of the box. Also no surge. You'll notice it doesn't slip, and I could stop the train in the middle of the grade and re-start it. I think the true difference in our opinions here is in the quality of the models being compared. A Rivarossi Northern or a Bachmann GS-4 won't pull this train. Those two brands are at the bottom of the market, entry level models full of compromises to get them around 18" radius curves, and they are cheaply made. Too much slop, lightweight frames, and in the case of most Bachmann steamers, you just can't add enough weight to make them pull. I know. I've tried. No disrespect intended to the owners of these, I started out with them myself many years ago. This model is a Westside. Japanese brass, vintage 1970's. It pulls as well as any single diesel locomotive in my stable, and I have Genesis, Rapido and Scale Trains, as well as some of the old blue box stuff. It won't go around 18" or 22" curves though. It might get around a 24" radius but I'm not sure. I've never tried. It uses real bearings, and the build quality is very good to excellent. You can buy one for around the same money as modern good quality diesel models. It will still be running long after the plastic is in the dumpster. I think if you try some of the more modern better built steam models you may find you close that pulling power gap considerably! I would stack my Athearn Genesis Mt-4's against any single diesel. One of these days I may have a pull off, the Mt against a single Genesis F-7!
I don't mean to lean on you or be overly argumentative here, but I've been tuning steamers for over 20 years. Some plastic, mostly brass. Some ran well right out of the box, some were real stinkers. In all that time I've never heard of "torque surge". It's an interesting theory, but a characteristic or condition that can' be perceived is irrelevant. The four big things that cause traction loss in model steamers are: 1: Insufficient weight. 2: Weight not centered over drivers. 3: Excessive downforce on lead or trailing trucks (improper springing). 4: Poor suspension caused by unsprung axles or overly stiff springs on the driver axles. To a lesser degree, motor selection can help. I've re-motored many models with higher torque lower RPM motors for better overall performance. I've seen plastic steamers where all axles are geared and the rods are for decoration only that still had traction issues. The old Atlas N scale 0-8-0 comes to mind, as well as the old MRC N scale 2-8-4. Like the prototype, large drivered engines are more slippery than small drivered ones. This is why freight engines generally had smaller drivers than passenger engines. The model diesel's biggest advantages here are more weight, and better weight distribution to the driving axles.
The discussion on getting a powered chassis into an aux tender, a freight or passenger car is a good one. The Coach Yard, a brass importer offers a powered bogie that can be installed in a passenger car. A pair of these in a mail/express car with some added weight is an elegant solution. One of our club members has an all brass Santa Fe passenger train powered by a Blue Goose Hudson with a powered car behind it which gives a very nice prototypical appearance of the prototype's tractive effort. No single model diesel could pull this train around our layout. Brass consists can get very heavy. I have a combination brass and plastic version of the SP Lark (19 cars) which takes three E or PA units to get it up a 2% grade. Two E-units or two of my GS-4's can do it, but they struggle, and if I stop the train on the grade they won't restart it.
Sorry if I irritated you. I do that to people sometimes, but we're here to learn from each other.
Torque surge is a phenomena which has plagued mechanical engineers and engine designers even before the invention of the first steam locomotives. It exists whenever liner motion is converted to rotary motion or the inverse. Prototype steam locomotives had pistons which created power every 2 or 4 strokes of the piston and then converted that motion into rotary motion. Then, when that power was transferred it was then converted back to liner at the drivers and then back to rotary at the wheels. Diesel electric converted all their linear motion to rotary before the generator and that motion remained rotary there after.
Model trains do not have pistons which create power as they get their power from electric motors . Most 5 pole or greater electric motors do not have measurable torque surge but when a steam model transfers the rotary motion to linear at the drivers and then back to rotary at the wheels it creates a measurable torque surge. A well balanced model will not show this surge to the human eye but it is measurable. If you read through this and I didn't put you to sleep congratulations. I am a retired engineering professor.
Model trains do not have pistons which create power as they get their power from electric motors . Most 5 pole or greater electric motors do not have measurable torque surge but when a steam model transfers the rotary motion to linear at the drivers and then back to rotary at the wheels it creates a measurable torque surge. A well balanced model will not show this surge to the human eye but it is measurable. If you read through this and I didn't put you to sleep congratulations. I am a retired engineering professor.
Interesting. So, is there a way to calculate the loss of efficiency?
KriegslokBR52
Well-Known Member
That is also very realistic to see on model steam, because when you see real steam coming at you, you can see this thing snake from side to side. Even large steam has that fenomenon and it's a normal thing. Watch this clip:
I know the steam experts and engineers count this as "loss of efficiency", and also the fact that supposedly even the most efficient steam locomotives use only 6% of the created heat for actual pulling power. But i look at this different way. In a car or truck engine the pistons do only maybe 25% of actual work (four stroke engines). Consider that in steam locomotive every stroke is a power stroke (and exhaust stroke). Data might be a data, but being a logical thinker i disagree with the assesment of that data. So if we compare the steam with diesel and limit ourselves to "efficiency" as desceibed by bean counters we might as well compare piston driven aircraft to a jet and call that piston driven airplane as "inefficient", fact is they work on different principles and that piston powered aircraft is a lot simpler to maintain as being more elementary.
KriegslokBR52
Well-Known Member
Not true, every stroke is a power stroke on steam locomotive, it either pulls, or pushes the main rod causing the main driver set to rotate.
Ok I stand corrected on that. Thank you. I had another couple paragraphs about internal combustion engines and decided my post was getting too long. With the editing process I mistakenly included some of the information about IC engines.
Last edited:
