Bachmann 2-8-4 Berkshire/Kanawha in stock at M.B. Klein

[mmagliaro]

Here's some video of my "fixed up" engine (and I use the term loosely, because I am still not really happy with how it runs,
but at least it's a lot better than it was).

https://www.youtube.com/watch?v=MBmFdAS71ig

[peteski]

The side-by-side photo of Bachmann and LL enginer clearly shows how weird the Bachmann drivers look.  One way to decrease the spacing between the drivers is to decrease the flsange height. Seems that LL flanges are smaller than Bachmann.    The thicker tire (and smaller diameter of the spoked area) also makes the Bachmann drivers look odd.  It is one of those things that even without side-by-side comparison to another locomotive, it stilll looks wrong to my eyes.  It is one of those subtle details which makes or breaks the look of a model.  I'm also sure that not everybody sees it that way.

[Mike C]

Here's some video of my "fixed up" engine (and I use the term loosely, because I am still not really happy with how it runs,
but at least it's a lot better than it was).

https://www.youtube.com/watch?v=MBmFdAS71ig

   Looks like it's running pretty good to me . Now that I've seen it running I can't really complain about the way mine runs . I think your's runs a tad better than mine , but it should considering the work you put into it  . Maybe if there is ever a second run they will have the bugs worked out of it .

[victor miranda]

158 posts to this thread...

and in conclusion?

(A quote from a post long ago)

Hi Max,
over this past weekend I was showing off how well the Kato FEF runs.
and showed off the sound in the b-mann berk.

my friend asked why the berk seemed unable to move as slow...
or why the Kato went  slower and without all the hitchy-ness.

I thought about it some...
I decided the single biggest problem is the way b-mann
made the motor/worm/worm-wheel.

Kato uses 2 threads on the worm and the gear reduction is lower.
the worm has far less thrust on it than the b-mann...

dangit.... I do not want to tinker in the Berk for my forseeable future...

never mind

victor




 




 

[mmagliaro]

158 posts to this thread...

and in conclusion?

(A quote from a post long ago)

Hi Max,
over this past weekend I was showing off how well the Kato FEF runs.
and showed off the sound in the b-mann berk.

my friend asked why the berk seemed unable to move as slow...
or why the Kato went  slower and without all the hitchy-ness.

I thought about it some...
I decided the single biggest problem is the way b-mann
made the motor/worm/worm-wheel.

Kato uses 2 threads on the worm and the gear reduction is lower.
the worm has far less thrust on it than the b-mann...

dangit.... I do not want to tinker in the Berk for my forseeable future...

never mind

victor

The worm and motor are certainly part of it.   Are you saying Kato's worm has two teeth contacting the worm wheel
 at any given time, so the pressure on the worm is spread out over 2 teeth instead of 1? 

The worm and motor are part of it, but I really think the demon is in the sloppy rods.
Watching how the rear driver plays catch-up around the circle, I think that
is a big deal.  There is a little bit of rotation where only 3 drivers are actually moving, and then the rod hole on #4 catches up and drags #4 along.  Every once in a while, usually at 1 or 2 specific locations in the rotation, when #4 catches up and has to be tugged along, it is in a bad spot for that to happen.  By that, I mean, for example, that the lefthand rod has been free-running, and #4 isn't turning, and when #4 takes up the slack in the hole, the wheel is in a bad spot for the left side to be pulling it, and it hitches a little until the wheel moves.  If the quartering and the holes were really tight, the wheel would have moved just a little before the lefthand rod had to pull on it, and it would have been able to pull it easily.

If you quarter to try to eliminate that problem in one spot, it just appears at another place in the rotation.  Which
means to me, after a lot of experimentation with it, that there is no one orientation of
the quartering of driver #4 where the problem stops happening.  The crankpin always hunts back and forth in the
rod hole, too much to tolerate.   

It's really just quartering, but with sloppy rods.  It's like the driver goes in and out of quarter all the time, no matter how carefully it is actually quartered.  Taken to the extreme, if the rods were sloppy enough, it would not run at all. 
It would jam.

By converting it to use one solid rod, I partially alleviated the problem, because the rod can't droop downward
at number 4 anymore.  We get a little more gentle pushing from below the crankpin as the rod comes up, which helps take some of the slop out of #4's motion.  A more precisely-drilled 3-4 rod with very small crankholes may have helped.  I tried that, but the first test rod I made didn't work.  Divining just how far apart those holes should really be isn't easy.

If I wanted to make a months-long project out of this, I suppose I would start with another fresh engine,
pull the motor and everything out except the wheels, and make sure they can all roll with just side rods on them.
My bet is that even like that, you would feel a bind in that driver that can't be completely eliminated by adjusting the quartering.

[victor miranda]

the 'hunting you describe is a lack of fit.
the siderod center-to-center is not the same as the axle center-to-center
or....
the crank throws are not the same length.

those both will never fit even if the quartering is right.
and they will always bind.

the worm reduction is 22 to 1 for the fef
and from a picture 36 to 1 for the berk

22 to one takes more torque to turn in a perfect gearbox...
and the thrust loads on the bearings are lower.

at 36 to 1 the worm is trying far harder to get off the wheel
and putting even more thrust on the bearings (in this case the motor.)

lets call this additive... a little binding will cause the motor a lot more loading in the berk.

fun stuff.

I may well end up carefully measuring cranks and side rods.

victor

[peteski]

The worm and motor are certainly part of it.   Are you saying Kato's worm has two teeth contacting the worm wheel
 at any given time, so the pressure on the worm is spread out over 2 teeth instead of 1? 

The worm in question has 2 spirals instead of a singe one.  But only one tooth of the worm-gear is fully engaged at any given time (just like with a single spiral worm).  But the gear ratio will be different when using single or double spiral worm.

http://en.wikipedia.org/wiki/Worm_drive

[mmagliaro]

Whoa...  !   Kato used a double-start worm in that FEF?  Why would they do that?  To get more angle?
More efficiency?  That sacrifices 1/2 of your gear reduction.

[peteski]

Whoa...  !   Kato used a double-start worm in that FEF?  Why would they do that?  To get more angle?
More efficiency?  That sacrifices 1/2 of your gear reduction.

Yup, they did!   They must have figured out that the very high torque coreless motor will be able to deal with that.

[victor miranda]

if you go by total gear reduction the amount of torque required is the same.
both at close to 40 to 1

the kato worm does not require more torque to turn the wormwheel
... the worm wheel will go at different speeds... so it is not exactly a straight comparison...

the Kato worm generates lower bearing loads for a given amount of torque passing through.
so it does not add to the power consumed...

the bachmann worm is not well designed to handle the loads generated by the worm and wheel...
... think it adds to the problems.
extra torque needed to move past the bind makes the worm load the bearings more.
that ADDS a lot to the motor's torque demand.

it makes a bind more obvious.

victor

[Chris333]

From what I've read the double worm just tranfers torque better. Doubt that makes a difference this small.

[SkipGear]

But a double worm at the same pitch as a single worm, halves the gear reduction.

If it is a finer pitch double worm vs. a coarser pitch single worm yielding the same ratio, yes the double worm will spread the load out more and the pitch angle of the gears will be less making it more efficient. But the same could be said by just going to a finer pitch single worm and then not having as much reduction later in the transmission.

[Cajonpassfan]

Complaints about the driver spacing make no sense. The drivers measure out to within a few percent of scale. The flanges are almost touching. What more could they do? The ...

With apologies to Max for using his picture to illustrate my point, but the drivers are NOT almost touching, and that more than anything contributes to the odd proportions IMHO. In N scale, with our oversized flanges, drivers have to be tightly spaced. I'm willing to put a lot of effort into an engine I want (even though I shouldn't have to), but not if the final result looks off. Too bad, because Bachman steam has come a long way and this is going backwards...
Otto K.

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[Blackout]

Got some mechanical wizards in this thread. This should help me fix mine, or at least make it run better.