Large Scale Central

Pulling power

Track and Trestles
#1

What makes a locomotive a good puller? I ask because i have a USA Trains 44 tonner, with 2 motors, and it is easily outpulled by both an aristo pacific and an aristo Mikado, which both have only one motor. I have a Bachmann annie that pulls remarkably well even though it only has four wheels doing the work–it pulls much more than the LGB 0-4-0s I also run

Is it the size of the motor? The material the wheels are made of? The weight of the engine? It’s just for curiosity–I would not expect a prototype center cab switcher to outpull a prototype mikado. But what factors make for a good puller in large scale?

#2
mike omalley said:
SNIP Is it the size of the motor? The material the wheels are made of? The weight of the engine? It's just for curiosity--I would not expect a prototype center cab switcher to outpull a prototype mikado. But what factors make for a good puller in large scale?
All of the above. You have answered your own question.
#3

Mike, as stated earlier, I have the same engine. I find it to be a good puller for its size. It does have r/c and batteries which puts a lot of weight right on top of the trucks. I don’t have any large diesels, so I really don’t have a lot to compare it with,

#4

While all of the factors you mention are important, I think weight over the wheels is one of the most important, so long as the motor is powerful enough to handle the weight. There is a critical balance with weight, too much and your no longer adding to adhesion, but just taking the motor. The Aristo SD-45 is a good example of that. Most folks say it pulls better without the optional fuel tank weight. A good example of a too-light engine is the Bachmann Indy, it will barely pull two cars on level track without some added weight.

#5

Also gearing, though I think all the ones you mentioned have enough torque to slip wheels.

#6
mike omalley said:
What makes a locomotive a good puller?
Last summer, I did a lot of experimentation with a Dash-9 and several USA diesels (SD40, GP38, GP30) pulling consists of different weights and configurations up a 6' long six-and-a-half degree slope. Herewith observations based on these trials:

  1. The number of axles makes no difference. The 6-axle Dash-9 creamed the USA SD40, but so did the USA four-axle diesels.

  2. More weight can be pulled on a straight without derailing compared to a curve, though a regular bend of appx 15’ diameter wasn’t a limitation in the tests. The four-axle USA locos handled twisty sections marginally better than the Dash-9, but there is a limit to how twisty the track can be before a derailment is inevitable when pulling a heavy load.

  3. As the weight increases, the strain on the couplers makes them the most likely point of failure, especially on curves. I use H&L couplers exclusively, so can’t comment on whether knuckle couplers behave similarly.

Jon’s point about a “critical balance with weight” is well taken. Our Dash-9 has no extra weights, but the loco is both hefty and well-balanced. I was able to put a lot of weight behind all the locos mentioned above, except the SD40, without inducing wheel spin.

While accepting that thinking by analogy is primitive, let’s disregard Beard and do it anyway. With cars, CCs rule. Ergo, the total rating of the motor(s) in watts is probably a better indicator of pulling power than the number of motors. Again as with a car, the power:weight ratio of a loco is vital. Our Aristo RDC-3s can pull a surprising amount, and their relatively light weight probably has something to do with that.

Tom’s observation about gearing is trenchant. As with a car, a good gearbox can do great things with an ordinary motor, and vice-versa.

A Dash-9 will start pulling from a standing start at lower amps than any of the USA locos we own. Once they get enough juice, though, four-axle USA Geeps are capable of handling almost, but not quite, as much weight as a Dash-9 up that steep test slope.

These experiments provided hours of fun. For me, seeing what these babies can do is one of the most interesting aspects of the hobby.

#7

I had to look “trenchant” up:

trench·ant –adjective

  1. incisive or keen, as language or a person; caustic; cutting: trenchant wit.
  2. vigorous; effective; energetic: a trenchant policy of political reform.
  3. clearly or sharply defined; clear-cut; distinct.
#8

My Annie can barely pull two of my coaches over my 4% grades on my layout, but my F40 bash with two AC Centercab bricks can pull all 4 over even though it weight slightly less. All of my bashes that use the Centercab bricks are similar, they pull remarkably well. Of course the Annie was to lug its tender as well so that reduces the overall pulling capacity, and its only got 4 wheels touching the rails vs 8 on the bashs, I think that adds a great deal of tractive effort vs the Annnie or any of the steamer types, the more turning metal you can put on the rails, the better.