Minor Quibble with BLI steam

[mike_lawyer]

I have noticed recently on my BLI steamers that they usually design their steam locos with the rear driver being a traction tire driver, but only powered by siderods and not geared.  On my two BLI M1s, I noticed the same thing that Spookshow identified on his review of these locos - because the traction tire driver is spun only by siderods, a slight eccentricity develops, creating intermittent contact with the rails.

In comparison, the Kato Mikado is a very simple design, with the rearmost traction tire driver driven by gears only and not connected to the siderods.  In my experience, that is a superior design as it maintains even contact between the traction tire and the rails.

I am not sure why BLI makes locomotives with this design, it is more complex having multiple drivers driven by siderods only, and it decreases the utility of the traction tire driver.

Anyone have similar experiences?

[nkalanaga]

Not having much experience with steam models, I may be wrong, but it seems that putting the traction tires on a geared axle would be more efficient.

[mike_lawyer]

What is interesting is that there are places on my layout where my BLI M1s will spin wheels in place at startup and will not move.  Clearly, there must be some minor track dips or something at those locations.  My Kato Mikados have absolutely no problems starting a train at those locations.

What appears to happen is the M1 traction tires don't quite make contact with the rails at those points, I suspect due to the eccentricity of the TT driver spun only by the siderods.

[Mark5]

I agree that having the tt driver not geared seems ... dumb.

That said, my BLI steamers are great runners (so far).

Mark

[mike_lawyer]

I will be curious to see if there are any changes made in the new run of PRR M1s due this fall.

[nscaler711]

Do they even need to have a traction tire? I see more problems with tt's than I do solutions normally...
In Z most locomotives have a traction tire on one wheel per truck, and I have just bought an axle to remove the individual wheels with them and don't see that much of a tractive effort loss.
I wonder if on the BLI's you could get an axle and replace that wheel then you wouldn't see a pick up issue anymore. I'll be honest I don't know much about steamers, but if the geared axle isn't on the main crank rod (whatever wheel that has the big counterweight) couldn't the traction tired wheels be moved to that position?

I also don't have a M1, but I do have their Big Boy and it doesn't have them.
The two Kato Steamers (Big Boy, C62) I have, have the traction tires on the geared axle.
I have a couple more but the rest have geared drivers, MP and Micro Ace...
Hopefully the ATSF Northern wont have this problem.

[mike_lawyer]

My suspicion, and this is wholly conjecture, is that BLI ported over the design of the M1 from the HO model.  Their HO models seemingly use the "traction driver driven by siderods only" design.  I think you can probably get away with that design more readily in HO, as there is more weight on the rails to begin with.

In my experience, N scale steam locos definitely need traction tires.  There just is not enough weight on the rails to generate realistic traction without them.

Kato steamers typically have the traction tire on the rearmost driver, and it typically is driven only by gears and not connected to the siderods.  In my experience, this is a superior design to the BLI "siderods only" approach to traction tire drivers.  With "siderods only", there can be intermittent contact with the rails if there is a slight eccentricity due to siderod action.

[mmagliaro]

The traction tire should go on a geared driver.  Putting it on a rod-driven driver puts load on the crankpins and crank holes, and tends to induce a side-to-side pushing as the rods shove to and fro on each side of the engine.  In real life, when you watch video of a steam locomotive coming straight at you, you can sometimes see this nosing back and forth on the rails.  But we can do without that in our models, thank you.
AND... as you are noticing, it can have a detrimental effect on traction. A geared driver is inherently forced downward by the force of the worm or idler gear against the axle gear of the driver.  A rod driven driver won't have that "bias".  It can float up, down, forward, backward while rotating.

[mike_lawyer]

Max, totally agree.  It's a real head scratcher why manufacturers put traction tires on drivers that are only spun by siderods.

[peteski]

Well, I can think of couple of reasons.

The designers probably think it is easier for the modeler to replace the TT when it is on the last driver ans only 2 crank pins have to be removed, and the tire is easily accessible being the last driver.  Mechanically, it is likely simpler to design the mechanism to have other than the last driver driven by gears.

Also lets face it, Kato engineers always seem to be cleverer than other designers when it comes to mechanisms.  Seems that other  desingers don't  put much thought into maximizing serviceability and wheel adhesion.

Both Mikado, and the 4-8-4 chassis (and of course Japanese prototype steam models) utilize very clever and innovative design, no duplicated by most  other designers.

While the 4-8-4 is not as friendly for TT replacements as Mikado, their design clearly indicates that thought was made to maximize adhesion.  It is done by having only 2 axles supporting most of the locos weight (one of them is the TT driver) while the other drivers are either sprung, or have extra vertical play so they don't really support the locos weight. They are pretty much cosmetic.  The Kato Big Boy also uses similarly designed engines.

I recall when the the Morning Daylight set and GS-4 came out, Kato touted that the steam loco can pull the entire consist.  Back then being familiar with other N scale large steamers of the day I was very skeptical. But the GS-4 did live up to the promise.

However I did observe that the Athearn Big Boy and Challenger utilize some of the Kato's design features.  Each engine has drivers which are cosmetic, and others which support the loco's weight (and one of those is gear driven and has the TT).  I discovered this once I full took both of those locos apart and I was quite impressed.

[mike_lawyer]

Yep, Kato really designs their locos the right way.  They typically run like a Swiss watch and pull really well.

Another problem with the "siderods only" approach to traction tire drivers is when you add weight to a loco, that will put more stress on the siderods.  In contrast, I have had no issues with adding weight to locos with geared traction tire drivers.

[Maletrain]

It seems to me that it would be easiest to replace the traction tires if they were on the rearmost drivers, driven by gears, and not attached at all to the side rods. 

[peteski]

It seems to me that it would be easiest to replace the traction tires if they were on the rearmost drivers, driven by gears, and not attached at all to the side rods.

That's Kato Mikado.  What's funny is that originally the model did not have traction tire (but the design was still the same).  Seems like the traction tire was somewhat (like Bob Ross used to say) a happy little accident.  But Kato's steam loco mechanism design is still hard to beat.

[mike_lawyer]

Love Kato steamers, I just wish they would make a few more generic USRA designs.  A proportionally correct 2-10-2 (unlike Con Cor) would be really nice for kitbashes and such.