Experiment in subtle weight balance in a steam loco

[mmagliaro]

It's not just about the weight.  It's about balance.  And this little experiment sure proved it to me.

In the course of testing my W-5 2-8-2, I made a surprising observation I thought I would share with the group.

The engine, with the GHQ boiler on it and some added lead, is now up to 124.8g (it started as about 110g with the GHQ boiler
alone).

It can pull 55 40' cars up my 1.7% grade.  I have no idea how many more it can pull on level track.

In the course of continuing the work (I have not posted the most recent work to the W-5 thread yet)
I added the smokebox front, compressors, and some other parts that added about 5g of weight to the nose.

After that, it would slip out on the hill with the same 55 cars.  It could not pull the hill anymore.  Surprised, I taped
8g of weight on the cab roof, and it could then pull the hill again.

In fact, I found that if I added 6g, 4g, even 2g of weight on the roof, it could pull the hill, but if I removed those last 2g, it
again slipped to a complete stop (wheels spinning, no forward progress).

So in a 124.8g engine, 2g is the difference between pulling this train or not.  That's under 2% of the total weight.
I would have thought that surely one would have to add about 5g before you would see any measurable difference in
the performance.

More importantly, this proved that adding more weight actually made the engine pull less (because it shifted the weight a little
too much to the front, and the traction tire driver is on the rear).  Naturally, I'll be squiggling a few grams of weight up into the cab somewhere to correct for this.    Although it might not be necessary because there are a more pewter parts to be added to this boiler and some of them are along the middle and rear.

[Chris333]

55 cars      At least there is no slinky effect with the caboose coupled to the locomotive pilot. 

[up1950s]

So is it not possible to just remove some weight from the nose or section forward of the c/g and then even though the loco is physically lighter c/g has now been moved closer to the TT , and as such TE is better . I can't see this happening .

What would be helpful is track scales 1/4 inch wide and one per each rail to measure weight on driver halves .

The adjustments on that to correct to zero on both sides is the tricky part .

Could be that one side of the TT driver is bearing more weight than the other . 

EDIT
Then there is the effects of drawbar pull and grade angle .

[ednadolski]

2g seems like a pretty tiny difference. Seems what you really want is a sprung/equalized frame, but I've never heard of that on an N scale model.

Function sanding pipes would be really neat (with scale sand of course!)


Ed

[peteski]

Function sanding pipes would be really neat (with scale sand of course!)

Sand is a good insulator. There goes the electrical pickup.... 

 

[victor miranda]

if you want to understand more
try the same thing to a minitrix 0-6-0
to tell my result... I found short of tipping the 0-6-0,
more weight, anywhere, got more cars moved.

I have found balance can make a surprising difference.
a b-mann Lt. MTN was my instructor for the above balancing act.
where the weight was placed, made a LOT of performance issues change.

it is quite the puzzle.

victor

[ednadolski]

Sand is a good insulator. There goes the electrical pickup.... 

 

If you can have scale sand, then scale live steam should be easy 

Ed

[mmagliaro]

Yes, I could remove some weight from the front, and probably correct the problem that way.
But but but... REMOVE WEIGHT??? Are you mad???   

No, I would rather ADD weight to correct the problem.   If I can get it balanced again with more overall weight,
I think that will always be better.

Oh, and there ARE sprung, quasi-equalized frames in N Scale.  A lot of the Key/Samhongsa engines are built that way.
Some people say the spings are so stiff they don't do any good, but those can be replaced with lighter ones, and the
springs in the PRR H10 I used to have seemed to work well.   There are also some semi-sprung set-ups like the
Kato GS4, and a few engines I've built where I spring-loaded rear drivers.

Right now, I'm finishing up a repair, but I will get back to the W-5 and fix up the weight issue before I post the next installment.

FYI  124.8 grams is just about the same weight as one of the old Kato F3/F7 "bricks" that can pull
your back teeth out.   When you get a steam loco up to that weight territory, wonderful things start to happen
(like pulling 55 cars).

[OldEastRR]

Can't wait to see your video of the W-5 pulling 55 cars around your new layout. 

[mmagliaro]

Can't wait to see your video of the W-5 pulling 55 cars around your new layout. 

I've been holding off on the next installment post until I could get the new wheel into the trailing truck, and then
fix this weight balance thing so the "shake-down" video would be fairly representative of what it will really do.
I have to wait until I get all the "heavy" appliances onto the boiler so I know the weight won't be changing much.

I did correct this problem.  Some thin sheet lead fit in under the cab, and then there's this big honkin' air tank along the right
side right over drivers 1 and 2.   Pulled 55 again.  I still have to push it to the limit to see what it can do on a flat...
just because  (my layout looks ridiculous with anything over a 20 car train; it's the *principle* of the thing!)

But I have to put on the stack and the Elesco feedwater tank over the smokebox front,
and some pumps and smaller metal things along the sides at the rear, so hopefully all that will balance out.

THEN... you'll see it run!

[Mike C]

I have found balance can make a surprising difference.
a b-mann Lt. MTN was my instructor for the above balancing act.
where the weight was placed, made a LOT of performance issues change.

it is quite the puzzle.

victor

  So Victor where did you put the weight ?  Love my Lt. Mtn. but wish it pulled better.....

[victor miranda]

  So Victor where did you put the weight ?  Love my Lt. Mtn. but wish it pulled better.....

while not exactly why I said what I did...

to get a b-mann LIGHT mountain to PULL,
you have to get the traction tires on the rails.
Among the better ways to do that is to superglue a shim (a layer of paper)
into the bearing pocket over the driver with the traction tire
one has to do all the followup work.   like make a little space on the bottom cover
to allow the plate to be screwed down.
Add a stick of lead to the front deck that looks like a tool box.
Those two will get you into the ball park.

You may find the front driver lifts off the rails under heavy load.
this is a problem in curves mostly.
 a little more weight to the front will help....
and at some point it will not help.

for the loco I was ...trying to fix... The difference was a surprisingly few grams, as Max pointed out.
you may have better luck then I did.

the lt mtn was variable, you may need to get it to sit evenly
or stand flat on the rails first.  I had a couple that were rt front driver and left rear driver
on the rails and the others in between not really on rail.

fun stuff.

victor

[Mr Z]

I had a similar balance problem in and old Bachmann 0-6-0. This was before the split frame design. This engine was extremely tail heavy. I was trying to move the balancing point closer to the center driver. I could add weight but I would end up with a huge block on the front pilot.

What I ended up doing was take a 1/4" drill and drilling a hole in the frame under the cab. This remove enough weight to move the Center of Gravity forward. It pulled much better after that.

Martin Z

[Mike C]

Ahhh ! Thank you Victor !

[Lemosteam]

Speaking of wieghts, this guy got my Minitirx K4 up to 129g total weight (including tender).  The traction tire is on the front driver so all the mass is directly above it: