Adding Weight to Dummy B Unit

Model Railroader General Discussion (Model Railroader)
1

I have a BLI Blueline F7ABBA consist (HO scale) with two powered A units, one at the front and one at the rear, with two unpowered dummy B units sandwiched in between the A units.

Each A unit measures 6.25 inches in length and weighs 17 ounces.

Each B unit measures 6.25 inches in length and weighs 5.25 ounces.

I want to add more weight to each dummy B unit. The question is, how much weight?

The NMRA standard suggests that the current weight is adequate, but my experience with this consist tells me that I need more weight on the B units.

Should I add as much as 10 to 11 ounces to match the weight of the A units?

Any thoughts?

Rich

2

LION did it with Atheran units. Him first got rid of plastic wheel sets on the B unit, replacing them with metal wheels from old A units., him then used printers slugs to add weight.

Betcha cannot find many printer’s slugs anymore.

ROAR

3

I use sheet lead that I cut from lead roof vents. I start with four ounces extra weight and work up from there. That will bring each B unit up to 9.25 ounces which should be enough to stop them derailing. Any extra weight subtracts from how much your locos can pull. I have very few dummy locos. The vast majority of my F3B’s are powered thus rendering the weight problem academic.

4

Get a handful of pennies, and put a few in with tacky glue. Keep adding them until you get it right. You won’t need as much weight as a powered engine, and the incremental approach will get you the results you want without going overboard.

I’m putting together a couple of Tichy boxcars right now. They each came with two big 1/2 inch hex nuts. That’s another option for weights.

5

My inclination is to meet halfway and add 6 ounces of weight, bringing the dummy B units up to 11 ounces.

Bringing them up to 17 ounces to match the weight of the A units seems unnecessary, but I just don’t know.

Rich

6

“Until you get it right”. I am not sure how to define or determine that.

The derailments are infrequent and not always in the same spots. The A units never derail.

Rich

7

Like he said, until it seems right. Add some weight, run the locos a while. If it’s not enough add more and run them again. Keep it up until they behave themselves.

8

Well, I was just putting my 2 cents in. If that’s not enough, try 4 cents.

Since you’re running an ABBA consist and you’ve been asking about speed matching, have you tried running the consist the other way to see if one direction or the other is causing more problems? I’m thinking that you’ve got some places where the couplers are going into compression, possibly because the lead engine stalls on a dead spot and the rear engine keeps pushing. As another experiment, try running AABB instead.

I can’t speak for everyone, but 90% of the derailments on my layout (other than operator error) are caused by trackwork.

9

Let me tackle the last issue first. At this stage, while not bullet proof, the track work is pretty good. That is not to say that it is perfect, but most derailments are turnout related or lighter cars like these dummy B units. I just am convinced that I need more weight.

As far as speed matching goes, there are two different sets of ABBA units in play. The speed matching issue relates to a set of Athearn Genesis ABBA units, all of which are powered. Separate issue. The ABBA consist with the weighting issue is a set of BLI Blueline ABBA units in which the A units are powered and the B units are dummy unpowered units.

I understand what you are saying about adding weight until you get it right, Mr. B., and I appreciate the advice. I guess that I will just have to experiment. At this point, I am hoping for someone to evaluate the issue of whether adding as much as 11 ounces seems like too much or whether adding as few as 6 ounces seems about right, or just leave the B units as is.

Rich

10

Rich,

On a similar note, I weight all my steam loco tenders to something between 5 and 10 oz depending on size, it makes a big difference in tracking with no real effect on pulling power.

I would think your 10-11 oz target is just right and will make the locos track correctly.

On a related note, I am amazed that some of these companies are still making/sellng dummy locos in this age of low current motors and mass produced similar drive lines under diesel models. In fact I specificly avoided several BLI/PCM and Proto offerings because of dummy units - OR - found them so cheap I bought extras and powered the B units in the case of my first run Proto PA1’s.

I did away with all dummy units several decades ago - if it looks like loco, it is a loco. I run lots of three and four unit lashups, incuding a set of PCM F3’s that had to be rewired from their original “lashed up” design which allowed the use of only one decoder for each AB set.

Power is one of those things subject to the old Victorian era rule - Some is good, more is better, too much is still not enough!

Sheldon

11

Sheldon, thanks. I am inclined to go with that 10-11 oz target, so I appreciate the encouragement.

As far as the dummy B units go, there are a rarity. I bought the set of 4 from FDT a few years back to add to my layout on which I already had the Athearn Genesis F7 ABBA Warbonnets, all powered.

The attraction of the BLI Blueline Warbonnet set, albeit dummy B units, was the fact that they had factory installed sound which my Genesis units do not. And the price for the Blueline consist was irresistable. And, I can break the consist into two AB consists and I still have sound in each one. So, I wasn’t too concerned about the B units being dummies.

Rich

12

My dummy units are “old friends,” holdovers from my teenage years. They are all Athearns, and were powered by rubber-band drives. The frames are quite heavy, so no additional weight was required, even after removing the motors. I run short trains on a flat layout, so power is not a problem. I’ve installed SoundBugs in these, giving me an economical multi-engine sound consist.

13

I am beginning to realize that there is a practical limit as to how much weight I can add.

I have a supply of adhesive steel weights that come in 1/4 ounces pieces. Twelve of them, for example, add up to 3 ounces. I may not be able to fit more than 6 ounces under the shell, bringing the total weight to 11 ounces. So, that is going to have to good enough.

Rich

14

I missed most of the discussion, but that sounds about right. I actually think the easy answer here is, “An unpowered B-unit is actually a freight car…” for weighting purposes. So whatever is close to the NMRA recommended weight per overall length like a piece of rolling stock should work.

15

I respectfully disagree. You typically would not put a freight car between two powered A-units. I’d say an unpowered dummy needs to be a bit heavier in that configuration.

16

Yeah, that is my thinking as well. Two 5 ounce unpowered B units sandwiched between two 17 ounce powered units seems like an accident waiting to happen.

Rich

17

Maybe. I run ~20 car HOn3 freights with the locos split and run in “DPU” mode (well, it’s just DCC, but you get the idea.) This works well and actually is less likely to derail (which is surprisingly rare either way, now that the track has been massaged repeatedly) because there’s less chance to stringline on curves, etc.

I guess I don’t see any real difference between putting one or two units/cars between powered units and putting ten.

This is not say that adding more weight to the B units will not lessen the possibility of derailments, if that’s the problem. It will, but also takes away from the tractive effort. In standard gauge and with MU-ed diesels, not too much of an issue. With HOn3, that would be a bigger deal, except I don’t have any narrowgauge dummies…

18

I wouldn’t solve the problem with weight. I would swap the shells on an A and a B so that the first two units would be powered followed by two dummy units. Yes, this eliminates (or at least makes it harder) to split them into two A-B lash ups but how often would you do that?

19

The more rolling stock running between 2 powered units will have the advantage of greater “coupler” action, One light piece placed between even a good speed matched set can have issues if the lead unit happens to slow even slightly due to variation of track power (sw, separate or distant feeds or power districts)

20

Bob,

I agree that more cars is a cushion, especially when you’re running 714s![:O]

On the other hand, I’d bet if I run one or two cars between the units I’d get the same results.

That said, there’s one or both of speed matching or track issues that must be at the root of Rich’s unhappy F units. The speed matching is obvious, sort of, (I haven’t read Rich’s other thread, but the speed curve is critical, too, in such things), but track sometimes isn’t.

I recently resolved a problem that had me looking at both multiple pieces of motive power/rolling stock and multiple track locations over a 12’ section of dual gauge track around a curve. I got a bunch of smoother running equipment out of it. Didn’t think it was the track at first, but I fixed several issues at several spots, too. Still getting the same results[:(!][U]

And on the standard gauge, too. No excuses![sigh][|(]

Eventually, I found it when the F units started heading off. It was a piece of track that was a spiral transition, both vertical and horizontal curvature, just as finished the curve and went into a facing point turnout. It was mostly a problem in one direction, too, which ended up being another clue. The combination of my pretty well tuned equipment, the third rail, generally good track and a gentle curve allowed cars to derail there, or at least position themselves to derail, then jump the curve anywhere between right there and the next town, 12 feet and 180 degrees away. Some slight settling or further drying of the subroadbed caused just enough of a shift that the problem only slowly started affecting ops.

All the light stuff was like pinballs, they could land almost anywhere. Those heavy ol’ F units – all powered BTW – landed pretty much right where they went off the track. It still took some minor surveying work to get the exact problem in sight. So maybe adding weight will help more closely identify where the track issues are…

Very myster