7th Street Shops- Ma and Pa Balance Post 28

 

Gem Models HO Maryland & Pennsylvania 28 (4-6-0) constructed 6 Dec. 1962, Tokyo Japan

In the past few posts I have discussed the tools, principles and a bit of the history about the balance of model steam locomotives. Hopefully, the reader has a better understanding of the importance of balance.

Model Railroading offers satisfaction from the simplest amusement of watching the wheels go 'round 'n' 'round to delving into the complexity of game play that we play called, "operation". It all hinges on one definitive feature - animation. At 7th Street Shops miniature locomotives are FIRST machines and then models; because, they must move. All of the rest of it doesn't really matter if they don't move. 

HOW they move is important to how they meet our expectations. Maybe the point isn't clear; if they don't meet our expectations, even mobility becomes frustrating and meaningless; and that will overshadow the enjoyment of our game. Watching the wheels go 'round 'n' 'round is much more enjoyable when a respectable train comes along with them. Pulling is important and balance of an engine is key to that function.

Without boiler weight engine is heavy to front

So. Let's do it.

In the photo (left) the open pole motor was replaced some years ago by a motor similar to the Can motor shown. The original motor weighs 1.5oz and the Can weighs 1oz with a 1/4oz flywheel attached. The engine (that part of a locomotive that generates the power to move) weighs 6.9oz without the boiler weight (seen on the scale). The overall balance of the model is rather heavy to the front as seen by the beam drop. The 2 axle pony truck, still in place, has very little weight to contribute to this. Note how far back the operational center of the driver coupling is on Ten-Wheeler types. Despite the long front end the weight still needs to bear evenly on each of the drivers. This certainly contributes to the type's tendency to be front heavy.

In this case, the three driver axles are spaced evenly apart; that makes it easier to see that the engine is on the beam's rocking axis. The model's relative center of balance is substantially ahead of the coupling's mid point. It took an extra ounce on the cab roof to balance the engine (below right).

Adding 1 oz to the cab roof balances the engine

Without any  added weight in or on the engine the locomotive struggled to pull even5 ounces up the 2 percent grade. 

This is a good place to point out that the engine pulls not just the weight of the train but that of the tender as well. This tender weighs 3.25oz. In action it contributes nothing to the pulling efficiency of the engine and plays no part in balance other than pull-down along with the rest of the train. Generally, there is no advantage to an over weighted tender in terms of electrical pick up; clean the truck tires (don't forget the bolsters pads either) and the track and electricity will flow to even a lightweight tender! However, as a light car at the front of the train it needs to have some weight so that the load does not pull it off of the track. The 3.25oz of this tender is just about right. If you remove weight and find that the tender derails when the locomotive is pulling, add back weight a little at a time until the problem is resolved. Any more is waste and robs the engine of pulling capacity.

Unweighted engine could not pull 15oz up 2%

 

I added 0.5oz to the cab roof. It took 1oz to balance the engine but I don't want perfect balance. To counter pull-down I left 0.5oz to the front. I still did not add any weight into the boiler. With this simple addition the locomotive pulls 10oz up the grade though with some slipping.

To establish the Tractive Effort of a locomotives I run the model as slow as it will go so that I can detect wheel slip. The "tonnage" is then defined at the greatest load before the wheels start to slip at slowest speed above stalling. Of course, slight undulations in the track may cause an occasional slip. If the model does stall bump up the voltage until it moves again - without slipping.

I finally installed the original boiler weight back into the engine and increased the cab weight to 1.75oz. The train weight was increased incrementally until it was over 22oz and the wheels started to slip more severely. At this point I was confident of a coarse of action that I'd wanted to do for this model.

I don't need a lot out of this or any of the Moore & Moore Lines motive power. The Ten Wheeler will probably never be expected to haul more than two or three smaller wooden passenger cars that only weigh 5 or 6oz each.

5/8" brass tube with turned brass caps

The M&ML cannot handle long trains and its longest (and only) passing track has just 33" of train capacity. The ruling grade on the M&ML is 2%. 

With these considerations I built a custom boiler weight that is greater in diameter yet shorter in length than the original. I was willing to give up a little weight in order to make room for electronics inside the boiler. It is a trademark of 7th Street Shops DCC installs that rarely are there more than 3 break away wires between the tender and the engine. Sometimes there are none.

The original boiler weight wasted a lot of room inside. It is less than 1/2" in diameter yet 1 3/4" long. Even so, it weighs 1.6oz - it is solid brass. The new weight is a 5/8" O.D. brass tube 1.2" long with turned end caps. It weights 1.25oz filled with buckshot. It fits the target location better and leaves plenty of room in the smoke box for a current storage device or even a small speaker plus the components for the headlamp.

The advantages of using buckshot in a tube is a degree of flexibility to fit the desired location and other components and considerations. An added plus is that there are no unsightly chunks of metal visible from track side. The trade-offs seem worth it.

I also added a smaller tube positioned inside the 5/8" tube to accept the saddle screw. The screw is long enough to pin the weight in place. The alignment of this "pocket" is marked on the end of the weight to aid in positioning the weight during assembly.

The mark indicates where the hole for the boiler screw is aligned

I gave up 3/10ths of an ounce in the boiler and a corresponding amount in the cab. The overall weight of the engine is now more than it was after the motor was replaced. But it is 3/4oz less than the greatest amount with the original boiler weight as I described above. So now how will this model perform with its newest configuration?

I'll tell you about it next time.