I got to thinking. Do my larger HO locos actually have more power to pull and is this just a function of greater weight? I am thinking particularly within a brand, as I assume that the same motors are used for most medium sized 4 axle and 6 axle diesels within a brand (I am writing about all my generally older locos made about the same time period…not new locos with perhaps the latest motoring)
All my locos (except switchers) are equipped with the same NCE D13 decoder (not top of the line, I know.)
So, for some reason, I think that my P2k SD60 is more powerful than my P2k GP30s.
And my P2k E8s seem more powerful than the F units.
And my Spectrum SD-45s and Dash 8s seem more powerful than the Spectrum GP-30s etc.
Or is this just an illusion?
When I get more track added to the layout to build a train over 25 cars, maybe I can do some testing.
12 wheels have more contact area with the rail head than 8 wheels, though weight does play a big factor in our models. More weight, more pulling power. (to an extent)
To properly test the engine you will need an ammeter and the specifications of the motor (s). Assuming the gearing is the same and both have the same motor installed, then the weight on each wheel would be the deciding factor. The ammeter helps to ensure you don’t overload the motor. Just because an engine can pull 50 cars up a 2% grade doesn’t mean it’s not destroying the motor.
My personal experience with my own fleet is that my engines run out of traction before they run out of power. If my train is too heavy it sits there and spins the wheels at the speed it wishes it was going. Slight down pressure on the engine enables it to move on.
Therefor I would guess that the bigger and thus heavier engines will indeed pull more.
A locos weight is definitely a deciding factor in how many cars it can drag but just because it can pull a heavy load without slipping doesn’t mean much. I have a 25 unit train being pulled by 2 SDP40F’s (1 Athearn chassis and 1 Proto 2000 E6 chassis) and a midtrain helper GP40 slipped in about 12 cars back. One SDP40F could pull all the cars on it’s own but it puts a strain on the motor. Same goes for my Proto 2000 PA1. It’s very heavy and will coast for 6 to 10 feet if the power is suddenly cut and it can pull an immense load, even heavier than the SDP40F’s can pull together. I fried a motor doing that.
I’d say it’s a function of weight, eliminating extenuating circumstances such as traction tires.
In your case, the P2K GP30 was reviewed in the April 1999 MR, and the SD60 was reviewed in the October 2000 MR. The GP30 weighed 16 ounces, had a drawbar pull of 3.9 ounces, full speed free current of 0.20 amps, slipping current of 0.37 amps, and a stall current of 0.74 amps.
The SD60 weighed 25 ounces, had a drawbar pull of 6.7 ounces, full speed free current of 0.29 amps, slipping current of 0.58 amps, and a stall current of 0.76 amps.
I don’t know if the motors in the two units were the same, but looking at the pictures in the review they both appeared similar. Since the stall currents are close, I’d guess that both motors are the same.
You’re going to need a lot more track to test these engines. According to the review, the GP30 will pull about 50 free rolling cars on a level track, while the SD60 should pull about 93.
Thanks all who responded. That’s interesting. I haven’t done much magazine readng since getting back into HO 3 years ago. I didn’t know such reviews were done.
Now I hadn’t thought about gearing. But I think that all my P2k are geared the same as they are the same age.
I don’t have space for 93 cars. However, I do have a big hill that is a good pull test. I don’t purposely set up wheel spinning tests, though. They just happen when I try to take a train over with a single loco.
A related question: I have two P2k Heritage 0-8-0s. But one has rubber tires. I don’t like the idea and would like to take them off. But I have never asked if the drivers are sized differently with a model with rubber tires and if it would be wrong to remove the tires.
I would say weight has the most effect on pulling power along with the number of powered wheels and type of material the wheels are made of. Most engines will slip before any damage occurs to the motor, if they are in stock form and have not had any weight added to them.
My thought for testing pulling power would be using a pen scale like an ‘American Weight Penscale’ and use it to test an engines (actual on track) pulling power in grams or ounces. This would give an accurate difference for each engine you have. I plan on having a test track (spur) that will have this scale at the end. It would be mounted horizontally with a coupler on the scale pulling end so an engine could just pull up, couple up, reverse direction and run the pulling test. The max pull measured at just before wheel slip would be the amount pulling power that engine has.
I can’t say specifically for the engines you have (may be different runs?), but I don’t believe that the GP30 and the SD60 are geared the same. I probably should have included that review information originally. The GP30 top speed was measured as 65 scale mph, and the SD60 as just over 50 scale mph. I seem to recall that there were some complaints about the SD60 being too slow. the review did say that you could get the model up to 63 smph if you increased the motor voltage to 15 volts. I guess they must have tried this, but I didn’t see where they were recommending that anyone else do the same.
I don’t think you can just remove the rubber portion. Typically the rubber ring is contained in some sort of a groove. So you’ll be dealing with a non-flat wheel thread, as well as a difference in diameter due to the removed thickness of the rubber portion. You’re best bet would be to find a set of replacement drivers (check with walthers) to replace the existing traction tire set.
HO locomotives all have enough motor torque to spin the wheels. That makes the tractive effort depend entirely upon the friction forces of wheel on rail. This will be equal to the coefficient of friction times the weight on drivers. Coefficient of friction for metal wheels on brass or nickel silver track is in the order of 0.25, so if all the locomotives weight on its drivers, it’s maximum tractive effort is about one quarter of its weight.
Rubber traction tires have a coefficient of friction about three times that of metal on metal, and so they can pull three times as much.
All wheel drive diesels and steam switchers have all their weight on drivers.
Steamers with pilot and trailing trucks put a small amount of their weight on the un powered pilot and trailing wheels, but that effect is probably too small to detect. All the same, you can squeeze a tiny fraction more tractive effort out of a steamer by removing or weakening the springs that push the pilot and trailing wheels down on the track. Add as much lead as you can to the pilot and trailing truck to replace the lost spring pressure and keep them on the track.
All locomotives will pull more if you add weight.
The electric motors are happy and will not burn out so long as they run cool. They are cool if you can hold the back of your hand on the motor for the count of 10. The motors do not like to be stalled, so you should check that they can still spin the wheels after adding weight, although it is nearly impossible to squeeze enough lead into an HO locomotive to keep the wheels from spinning should the locomotive encounter an obstruction.
Going way, way back to a time when John Page was the MR editor, he once covered the issue rather nicely. IIRC, he titled his editorial, Scale Weighting Your Locomotives.
In brief, he had weighted all of his locos to the max, then discovered that his 0-4-0T could move the longest train he could run - so why did he need a 2-8-0 road engine to pull 12 cars around the basement? He decided to remove weight so that the locos could only pull an appropriate number of cars. The 2-8-0 (his largest steam) could still pull 12 cars, but the little teakettle was de-weighted until it could only move a four car cut, “With a little honest wheelspin if the engineer tried to hurry things…”
My own roster has locos of all sizes, from 0-4-0T to 16-drivered electrics. Except for one 0-4-0T (which is a solid block of lead with a wheel on each corner) my steamers can pull different numbers of cars up the 2.5% grade - pretty much in line with their prototypes on a similar profile. That EH10, however, busts the curve in the opposite direction - it looks big and powerful, but only has four real drivers. Only by filling that end of that carbody with weight was I able to convince it to pull a twenty car train, and it will spin its wheels if the throttle is advanced too quickly!
Chuck (Modeling Central Japan in September, 1964 - with scale-weighted locomotives)
I’ve modified all of my locos with added weight, and, without traction tires (which, in my opinion, should be reserved for toy trains), the best you can expect is a tractive effort of 25% of the loco’s weight. For steam engines, this is usually somewhat lower, due to some of the weight not being on the drivers, plus the losses due to friction in the drive train. It’s very important with steam locos that the weight be balanced at the mid-point of the driver wheelbase, in order that equal pressure be applied to all drivers.
This loco has a large can motor, but was not a particularly good puller as it was back-heavy due to the weight of the motor. I cast a new boiler weight for it, and managed to get the total weight of the loco (excluding the tender) to 32 oz., while still keeping it balanced. It is just below its limit, weight-wise, as it’s still able to slip its drivers on a very heavy train - more weight causes it to stall when attempting to start the same train.
This Athearn U-boat, along with two identical sisters, was ballasted to 33 oz., and was tested at a nearby club layout, showing a drawbar pull of 8.3oz.
They’re nowhere near their stall point, even though there’s no room left for more weight:
I also managed to increase the pulling power of my four Athearn Mikados by bringing the loco weight from the stock 12.5oz. to a more respectable 16.75oz. Even more important was getting that weight balanced, resulting in useful locos able, doubleheaded, to move a 100oz. train up a curving 2.5% grade.
My best pulling engine from my HO days was a Life-Like F40PH. Yeah, a model of a passenger locomotive. I believe it had only one powered truck but it was so weighted that it could pull the walls off a house. And it had a good running motor if I recall. I used to use it on freight trains, but in those days I took a lot of liberties on my very unrealistic layout.
Agreed, I have an old LL F-7 that you could pull teeth with. A pretty smooth runner for a single power truck. Too bad it has trouble on dead frogs due to the 4 wheel pickup.
A bit off topic but another thing to consider if you want to run longer trains is to check how free turning your train car’s wheels turn, stiff turning wheels will take up a fair bit of any locomotive’s pulling power a lot more than you realize. A truck tuner/hone and replacement metal wheels will free up a lot of the drag from poor rolling train cars. As an example I had an Athearn Mikado (HO scale) that could pull only 8 Athearn blue box cars befrore using the truck tuner could pull 10 cars with no other improvements or modifications.
I recall the old LL F7. Recieved it one christmas early 70’s it would make it all the way to about the late 90’s until the motor finally gave out. The 4 wheel power pickup was definately a negative.
I recently sold my F7 ABBA group off and that particular group was treated as one engine. Together all 4 were able to handle 40+ on any grade.
The BLI’s Heavy Mike in stock form was able to stop with a 16 car train on a 3% and restart the same train with very little wheelslip if consistent attention was paid to the throttle input.
I dont add weight to my engines. But I do expect alot from them.
To do this one puts the engine on the track and block it so that the wheels are spinning/skidding. Add weight watching the amp meter. Stop adding weight when the wheels stop skidding or the current draw exceeds the maximum for the motor according to the specifications. In fact, one should probably stop before the current draw reaches the maximum.
Everyone should take note of this statement by tinman1. Even properly weighted locomotives (as above) can have issues. Back in the mid 1980s when I was a little into pulling power I rigged up an Atlas SD24. Special motor, reworked gears, special decoder, additional pickups. I was able to pull every car the club owned out of the main yard and around the layout (about 90 cars at the time). This involves one long grade of 3%, but mostly 1.5-2%. I thought it was way cool. However the locomotive never ran the same after that. In fact it seemed the opposite. It was sluggish and wouldn’t pull well. Still don’t know why, never figured it out exactly. I assume the motor somehow internally fried itself or magnetic field. But now I think 30 cars is plenty for an HO model of an SD24.
My big puller is still an Athearn BB GP7. It has the really low Urnest<sp?> gearing, a high torque rotating commutator motor, a special decoder, custom drive train, and weight crammed in everywhere I could get it (I even have a lead weights that sit on the walkways). I noticed that under load one of the trucks would tip and do a wheely on the rear axle. So I reworked it and added weight on the truck itself. Top speed is about 20 smph but I
A member here sent me an email yesterday with a link to I think it was youtube with a video of a live steam O scale Allegheny pulling what must have been a 25 meter train, maybe 120 hoppers or more, on an outdoor viaduct-style layout. It ran very nicely, but it spun both engines alternately near the tops of several grades…understandably. I observed to the sender that I would never treat such a precious and expensive item that way unless I were flush with cash and didn’t mind doing a lot of maintenance and maybe even machining to keep the thing running. It was doing a lot of tire scrubbing, and I hate to think of the wear and tear on the valve gear and rods.
So, I agree with TZ, just because you can get your Fiat Spider up to 140 mph doesn’t mean its the smoothest move to do so.
I have two PK2 SD60s and two Athearn SD50s that can easily pull 35-40 cars as a two unit set. The SD60s are too new for my era (1981) and won’t be regulars on my layout. On a long 2% grade three SD units (combination of Athearn BB and PK2) can easily pull my 35-40 car trains. My cars are all very free rolling.
I want to use helper service in my operations, as does the prototype KCS. I am buying old Atheran BB SD40-2 and dummys (when I can find them). I will put sound in the dummy unit and run a three unit set with two powered SD units and a dummy. This will require a set of pwoered SD units to push the train up the grade.
Yeah, if I recall I used to run the 4 wheeled pickup engines with another one so they could be pushed across the spots they lost power on. As they say, what a way to run a railroad.
