Pulling power


cncproadwarrior

cncproadwarrior

North of the 49th
What makes for great pulling power? Weight alone? I know that a 6 axle pulls better than a 4 axle but that aside, how can you increase pulling power? I have an Atlas Gold GP50 that can't pull 12 cars with metal wheels. I've added as much weight as I could. I noticed that the loco wheels are very shiny. Should I roughen them up with light sand paper to increase friction with the rails? I know about Bullfrog Snot but would like to get away without using that.
 
cncproadwarrior said:
What makes for great pulling power? Weight alone? I know that a 6 axle pulls better than a 4 axle but that aside, how can you increase pulling power? I have an Atlas Gold GP50 that can't pull 12 cars with metal wheels. I've added as much weight as I could. I noticed that the loco wheels are very shiny. Should I roughen them up with light sand paper to increase friction with the rails? I know about Bullfrog Snot but would like to get away without using that.
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Usually, at least for me, weight does the trick. I have 2 Athearn genesis DD40's stuffed with lead that pull really well. But I have noticed on my loco's that a 4 axle vs. a 6 axle, weight being equal, the 4 axle usually pulls more. more weight per axle. I have also had luck with NWSL wheels improving pulling power. I own the club record of 175 cars pulled by 1 loco! They joke at club that a 100 car train is a local for me. :D
 
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The composition of the driving wheels makes a big difference, too. Athearn's old sintered iron wheels added a lot to the tractive effort because they were not smooth. The tradeoff was they didn't always conduct electricity very well.
 
My understanding is that a loco with the fewest axles, power being equal, and weight being equal, will develop (or maybe better to say apply) more tractive effort because they have more adhesion on the rails. It is for this very reason that diesels outperform steam locomotives when it comes to lifting a train from a standing start. Steamers develop much more torque due to their main cranks and rod applying immense leverage about the centre axis, but they'll spin more easily, and they don't develop the sustaining horsepower until they have gained some 15-50 mph, depending on their gear and driver diameter. So, they are likely to spin, rods flying, if the hogger is overly agressive. A diesel would only spin on a much heavier or stickier consist. Instead, with all axles normally driven, and all the weight on those driven axles, a diesel will begin to pull and continue to build speed to a certain speed and then level off.

If you have the weight of any one locomotive spread over six or twelve axles, the locomotive with the sprung weight on the fewest axles should have the strongest factor of adhesion, meaning all the hp generated by the prime mover, which can rev up quite independently of the axles, gets applied even at crawling speeds. Later, when the diesel's horsepower curve levels, often near 50 mph or thereabouts, the passenger steamers, as an example, those with drivers in the 67" range and higher, develop their maximum horsepower and can continue to accelerate well into the low 100's if the rods, valves, lube systems, and balancing will permit it. Oh, and the track conditions, too! ;)
 

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With respect to weight, you can generally get more lead into an SD than a GP. So, wouldn't extra weight and extra wheels on an SD generally give more pulling power?

I still think the wheels are too smooth on this GP to give adequate tractive power. I'm going to roughen them up a bit and see if it makes a difference.
 
To get better power you need more weight per wheel..........so if you add 2 more axles ( 4 to 6 , 50% increase) you need to add 50% more weight to keep your pulling power the same. Few locos have the room to add that much weight......but as you note, there is more room in an SD (especially a large 50,60, or 70). In the real world, most RRs that ran out west went to 4 axle passenger locos, because the early E units only had 4 powered axles. One axle on each truck was just to support the weight, so you still had 4 drive axles (like an F unit) but less weight per axle for traction. Back in the late 50's, Milwaukee Road had a similar issue with the RS/RSC/RSD units......they bought RSC2s (which were 6 axle units) to use on lighter branch line trackage, but they found they lacked traction to start heavy loads on mainline trains. They also had RS2s (4 axle) and if they were mixed, the 6 axle units would spin while the 4 axle units maintained traction. That's a good example because the difference between the RS and RSC was the trucks.
 
cncproadwarrior said:
What makes for great pulling power? Weight alone?
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That is something I wish someone would do a comprehensive science fair project on. Weight would increase the coefficient of friction between the wheel and rail. There has to be some trade off on number of wheels pulling vs weight per wheel with both theoretical and practical limits. That is the amount of weight on 4 wheels will reach a point of diminishing advantage while adding the weight to an additional 2 wheels would continue to increase the tractive effort. Calculus problem anyone?

The composition of the rail and wheel would also be factors. Brass / NS wheels on NS rail will be different than steel wheels on NS rail.

Roughness of the wheel and rail are yet another factor.

I am actually surprised the Atlas GP50 can't pull more than that. Are you certain both trucks are pulling, or are at least pulling at the same speed? I had an F unit with two PFM spuds that couldn't pull a thing. I found out they were turning at just slightly different speeds. I fixed that (replaced one of them with a better matched unit) and instantly could pull 40 cars.
 
cncproadwarrior said:
That makes perfect sense. But why did the most popular diesel ever have 6 axles?
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Prototype is going to be a completely different story. 6 axles = 6 traction motors. More torque along with less heat, less wear, means less maintenance.

The issue with some of the early 6 axle units, such as the Alco PA, and EMD Es were the A1A trucks, were they still had only 4 traction motors. One of the axles was an idler.
 
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I've ensured that both sets of trucks and all wheels are pulling. All it does is spin. I push down on it with my finger and away it goes. It weighs about 14 ounces. I crammed lead into my SD40-2s to the tune of 1.5 lbs.
 
I suggest using a NMRA track/wheel gauge and make sure all your wheels are in gauge. When pulling a long train, do the wheels spin or does the motor stall?

Four axle will handle smaller radius turns, six axle gives lighter load per axle, probably less traction. Prototypical use of six axle is because of light rail/poor roadbed, so this engine spreads the load better, less track wear.
 
Remember that we are talking weight per axle........... virtually all 6 axle modern locos are bigger than the 4 axle locos.........an SD70 weighs around 400,000 lbs, while a GP40 weighs around 245,000 ......so the SD has more weight per axle (66666 vs 61250) At some point you reach a balance between what the rails will carry, what the loco weighs , and the pulling power. So you can only increase the weight to a certain point, and then you need to add another axle just to support the locos weight, but that may mean having less pulling power than a lighter loco with fewer axles.
 
Set the loco on a piece of glass (table top or something) and try to slide a piece of paper under each wheel where they make contact with the glass.
 
That makes a lot of sense. But I never was any good at calculus :p

What I have often wondered is why people clean their rails going with the grain. Wouldn't it be better to lightly scuff across the rails with some very fine scotchbright? You would think it would give a lot more traction that way. Especially if the wheels were scuffed the same way, which would be kind of difficult to do.
 
NScaler said:
...What I have often wondered is why people clean their rails going with the grain. Wouldn't it be better to lightly scuff across the rails with some very fine scotchbright? You would think it would give a lot more traction that way. Especially if the wheels were scuffed the same way, which would be kind of difficult to do.
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I use either alcohol or 600 grit black paper. When I use the paper, I always scrub at a 45 deg angle, but I don't scrub much. I want to avoid leaving micro-grooves to the extent I can and still use the grit paper to clean off any oxidation or gunk. The wisdom is that the grooves become repositories, stubborn ones, where the black gunk wants to set in again over time, except now in less time because it has provided the arcing surface that generates the black gunk.

I have read so many posts about wiping the rails down with Rail Zip, Wahl's Clipper Oil (which someone very recently opined was just Dextron III Mercon auto transmission fluid, which I HAVE used to wipe the rails...), about the gleam method, and Bright Boys.

I believe the gleam method, if done properly and fully, should do really well. I don't understand why coating the surface of the rails with an oil should work, but hundreds swear by it. I did wipe the rails on my last layout quite heavily with the transmission fluid before I decommissioned it to see what, if any, effect it would have on traction, pickup, release of black gunk, or prevention of more black gunk. I didn't let it go for weeks, but there was no apparent change in tractive effort, and I experienced no sudden changes in electrical continuity from rails to the decoders. So, whaddoIknow? I tried it and didn't find the drivers slipping as I was sure they would do. I must have placed close to a full tsp on the rails, wiping a finger dipped in it in about eight or nine places around my main. I had 3.4% grades, too.

One last entry into the, "Let's try this..." list, and that is lacquer thinner. Some very credible modellers I know swear that it cleans the tracks better than anything, and CAN be applied with a cleaner car towed or shoved around the rails.
 
Yeah, I wasn't suggesting scratching the rails. Using a white scotch-bright pad would do more to polish the rails than it would scratch them. But I think going across the rails would be better than going along them, as the cleaner cars do. Which they too just use scotch-bright pads right? I have never owned a working layout. So I have nothing to base my ideas on other than the fact that I have worked with cutting, deburring, and polishing metal for most of my adult life. But it just seems to me it would make sense not to go with the grain as this would make the most slippery surface for the wheels to try to grip.
 
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