query re: locomotive weights

I've found the NMRA recommendations for weight of rolling stock - in the case of N scale, 1/2 oz plus 0.15 oz per inch of car length. I was thinking I had seen something about recommended weight of locomotives as well, but I can't seem to find that now. Anyone know? I'm interested in N scale.

The recommended weight is as heavy as you can make it without risking a motor-stall and burn-out. ;-)

Not that there's much room in an N scale loco to pack in the lead. They tend to be cunningly machined blocks of metal with plastic slip-covers. Even so, they don't weigh much. For this reason, traction tires are very common on N-scale locos.

Fact is, that a smaller scale loco, say an 0-6-0T, will pull about as many wagons (a dozen or so) and carriages (two or three) as their prototypes. The larger locos won't.

What you didn't ask about, but it's relevant: The length of a train is calculated in terms of the gradients it will encounter on its scheduled run. Gradients have an surprisingly severe effect on the hauling ability of a locomotive. Eg, a loco that could haul, say, 30 or so vehicles on the level will be assigned about a dozen if it must tackle a lengthy 1:100 hill. If hills are short, then momentum will carry the train up them, in that case longer trains can be marshalled.

HTH Wolf K.

N scale weighting has a very simple formula: "make your loco as heavy as is possible." You can't overweight an N gauge loco. Extra weight has 3 main advantages:

- better traction current collection.

- smoother running through greater momentum.

- better tractive effort.

Rolling stock weight then becomes a balancing act between the length of train able to be pulled and trackability. (abilty to stay on the track.

Greg.P. NZ

For HO the method of determining weight to add is to run the loco against a stop block, apply 12 volts to the rails, add weight in small increments until the loco stalls and then back off the weight until the drivers begin to turn again. Even in HO, smaller locos are difficult to weight to that level as there is usually insufficient space for the weight. Rubber tyred locos make horrible noises when subjected to such treatment.

Locos like 4-6-0s need the weight over the drivers. Adding weight in unbalanced areas such as the smokebox can actually reduce tractive effort as the weight gets transfered onto the leading bogie.

Greg.P.

All locos need the weight *centered* over the drivers, and this includes diesels.

If it's a steam engine you pick the loco up by the center drivers if it has an uneven number of drivers, such as a 4-6-0; or you pick it up

*between* the center two sets of drivers if there are an even number of drivers, such as on a 4-8-2. In either case the loco should balance fore-and-aft at that point, and if it doesn't, then weight should be added to the lighter end of the loco until it *does*.

In the case of a diesel you balance the loco halfway between the trucks if it doesn't balance there already. (Most -but not all- do this right out of the box.)

There are no "unbalanced areas" on locos, just unbalanced locos. If your steam loco should be tail-heavy -and balance aft of the center drivers- it's perfectly okay to add weight to the smokebox until you get the center of gravity (CG) moved forward to where it belongs: directly over the center of the driver sets. But if the loco sits nose-heavy, then you have a choice of either removing some weight from the nose -not usually a good idea- or adding it to the rear end until the loco's CG sits -once more- centered over the driver sets.

Steam locos with too-heavy boiler weights seem to be quite common, and rather then remove weight that's needed to provide traction I've poured the cab roofs full of lo-temp metal on many a brass loco, and been inventive in finding other ways of adding even more rear-end weight in extreme cases such as my Fuji S.P. E-23 4-4-0 -which would actually tip forwards a bit on the front drivers if you chopped the throttle suddenly.

Now it no longer tips forward, and will pull about three more cars than it did before. Similar results can be expected from any loco after the CG has been centered over the drivers.

~Pete

There is an interesting series of articles in the last two issues of Model Railroad News magazine, about the effect of drawbar height on locomotive pulling power. If the drawbar is higher than the center line of the drive axles it tends to lift up the front of the locomotive and reduce traction.

An interesting read.

Now that *is* interesting! It's something I'd never heard of before, but I can see how it would work.

It should work in the opposite way too: if the drawbar height was significantly lower than the center line of the driver axles it should tend to lift the rear drivers a bit. But in either case, the effect would be magnified by a drawbar the was mounted quite closely behind the rear drivers, and the farther the drawbar was spaced back from them the lesser would be the effect.

You learn something every day! Thanx, Melvin!

~Pete

Ok, ok, a slight misuse of language :-) As I generally model small locos I sometimes use part of the tender frame resting on the loco rear beam. The forward bogie of the tender is loose vertically so all the tender weight forward of the rear axle (three axle tender) rests on the loco frame.

Greg.P.

The original Norris locomotives (4-2-0) used a similar effect to gain tractive effort. Near maximum effort the loco (slightly) pivoted around the driving wheel point of contact with the rails which lifted the front of the loco off the front bogie and put the full weight of the loco on the drivers. The same thing happens with larger leading bogie locos if the driving wheel suspension is equalized.

Greg.P.

Mike Sharman was doing this on models of early locomotives like Cramptons which really needed it, in the 1950s.

He wrote a book describing a compensation technique he called Flexichas, and recommended this technique for locomotives where adhesion weight was a problem.

You got me! ;-) I've been a fan of Mike Sharman ever since he published some of his techniques in the 60s-70s. My models tend to be from the end of the eighteenth century rather than the beginning but the same techniques work. I tend to favour heavier construction than the etched brass frames common in UK kits and most of my compensation is based around milled blocks of brass rather than flimsy sheet. (etched detail overlay) I tried and rejected Sharman's gearing system with pinion reduction before worm gearing - I tend to used worm on the motor shaft and spur reduction between the worm gear and driven axle(s) Spur gears at motor speed are too noisy for my liking.

Greg.P.

I never heard of recommended weight for N scale locos. As it was mentioned earlier in this thread, there is no way you can make N scale loco too heavy (even if using depleted Uranium as ballast)! Weight in a loco improves its pulling ability and power pickup.

Peteski

Thanks for the note. I sure thought I had seen that. Power does not seem to be an issue - I can generally spin the wheels on a moderately steep incline. I was disappointed with the pulling of a Kato F7 and after reading about Bullfrog Snot, decided I'd try a similar approach. I masked off all but one pair of wheels and applied spray Plasti Dip in several light coats (while the loco was running upside down) and allowed to dry. Made a huge difference and the price was very reasonable.

True, but there's more than one advantage to weighting your locos with depleted uranium.

Just for starters, you don't have to wire them for headlights; and the glow makes them easy to find in the dark.

~Pete

I wonder what part of 'depleted' it is that you don't understand.

I wonder what part of "humor" you don't understand.

Oh wait! It's all of it.

About as much as you don't understand of 'nonsense'.

How depleted is "depleted"? Not sufficiently active to run a nuclear reactor, but nothing one would want in the neighbourhood, let alone one's own basement or spare room.

Greg.P.

I once read an article about a 2mm finescale model of Ashburton - and the builder had a 517 (predecessor of the GWR 14xx class) 0-4-2 tank with a footplate machined from tungsten.