TurboTrain help...

[nscaler711]

Technically speaking, but if you put 29" wheels in one truck and put 33" in another in the same car you would be able to see the difference... Maybe not initially as its rolling by, but when it is stopped, definitely.


But if you bump the wheels up to 33" you will have better clearance and the wheels won't look misplaced.
If you do go that route consider making all of the wheels 33" having multiple sized wheels on a consist that is supposed to be one size is noticeable.


For instance Maxi IVs use 33" (maybe 36" ) wheels in 100 ton trucks at the end and 38" wheels in 125 ton trucks for the intermediate sections. That also applies to other Maxi stacks and Thrall sets as well.
Now I can tell in my Walthers Thrall sets as thats what I tried to replicate. Granted I had to substitute 38" wheels for 36" and used two different BLMA trucks; 70t and 100t respectively.  Also Kato does have 38" wheels in their Maxi stacks as well as 125t trucks so they got that right.
 
But my point is (in my sometimes incoherent rambling) wheels are noticeable. To some of us anyway...  (I like to think of myself as a Defect Detector. Not a rivet counter... There are too many of those to count.  )

[narrowminded]

Hi guys,

OK - NEW PROBLEM!

The factory fought me when I tried to have prototypical 30" diameter wheels on the Turbo. But they grudgingly put them on.

Now they have illustrated the problem. See the image attached.

The gears are basically touching the rails. They will certainly hit crossings and frogs. The factory wants to increase the wheel diameter to 36". To make the train look correct, it means we need to increase all the wheels to 36".

Would that be considered acceptable in N scale? I'm not keen on increasing the wheel diameter, but I'm not seeing any way out of this.

Your input would be appreciated.

Thanks,

Jason

Is that graphic showing the new 36" wheel clearance or the original 30" wheel clearance.  I ask because IF it's the 30" shown they are saying it has .012" clearance.  While close, that should be enough.  If that's the clearance WITH the 36".... well the gear or the wheel's got to change.

Edit add:  Just looked closer and those must be 12 tooth/ .3 mod  final drive gears which would mean the clearance they pictured is for the 30" wheel.  But why then jump to 36"?  If this is the case 32" would get the clearance up to .017" (.43) and 33" would get up to .020" (.5).  How much clearance do they want? 

While it's closer than you might want to throw out there for general consumption (crappy track work), I have run as little as .008" (.2) clearance*  and had no trouble with switches.  32" or 33" might be visually close enough but all of the way to 36" does become visually noticeable to those with a good eye and familiar with the original and seems to be excessive. 

*14 tooth .3 mod w/ 33" wheels

[rapidotrains]

Food for thought. Thanks, guys.

I will find a Z-scale engine and have a look.

-Jason

[bobdobbs]

I spend alot of money upgrading to 36" wheels, I notice the diff, keep the 30".

[Point353]

OK - NEW PROBLEM!
The factory fought me when I tried to have prototypical 30" diameter wheels on the Turbo. But they grudgingly put them on.
The gears are basically touching the rails. They will certainly hit crossings and frogs. The factory wants to increase the wheel diameter to 36". To make the train look correct, it means we need to increase all the wheels to 36".
Would that be considered acceptable in N scale? I'm not keen on increasing the wheel diameter, but I'm not seeing any way out of this.
Your input would be appreciated.

Judging by some prototype photos,
http://www.railpictures.ca/wp-content/uploads/2014/11/Turbo-Final-1280x855.jpg
https://upload.wikimedia.org/wikipedia/commons/2/2f/United_Aircraft_TurboTrain_at_Transpo_'72.jpg
the wheels are not that conspicuously visible.
IMO, assuming that your model will have good fidelity to the prototype and that the wheels will be blackened/weathered, 36" wheels should be acceptable.
OTOH, if your model is going to be closer in appearance to that from Bachmann, then the wheels need to be the exact correct size.
http://www.trainweb.org/fredatsf/Amtrak-TurboTrain_files/image013.gif

[u18b]

"Nobody will notice the difference....."

It's been said many times.



 

[Lemosteam]

Man, those things really give new meaning to "bloody nose scheme."

@eric220 , I'm waiting for your paint ideas for a 5 Stripe set on the Transcontinental PRR...   

[Lemosteam]

Hi guys,

OK - NEW PROBLEM!

The factory fought me when I tried to have prototypical 30" diameter wheels on the Turbo. But they grudgingly put them on.

Now they have illustrated the problem. See the image attached.

The gears are basically touching the rails. They will certainly hit crossings and frogs. The factory wants to increase the wheel diameter to 36". To make the train look correct, it means we need to increase all the wheels to 36".

Would that be considered acceptable in N scale? I'm not keen on increasing the wheel diameter, but I'm not seeing any way out of this.

Your input would be appreciated.

Thanks,

Jason

@rapidotrains ,

Since the power transfer of a involute tooth spur gear is transferred to the next tooth just before the first tooth no longer contacts its mating tooth, reducing the OD of the axle gear should have absolutely no ill effect on the gear set.  See below the red points of contact exist at the same time.



After you look at your mesh there may be some OD reduction available:

[ Guests cannot view attachments ]

If you are tooling new gears for these axles anyway that is what I would look into.

[u18b]

John.
Great illustration.  Thanks for posting.

The tentative observation I have is.....

What you have show in a snapshot of something new.
At present, you have clearly show that you could remove material.

But assuming the amount you indicated were removed....... over time, those edges will wear a bit.
I would think there might be a danger of eventually cogging without the extra material.

[Lemosteam]

John.
Great illustration.  Thanks for posting.

The tentative observation I have is.....

What you have show in a snapshot of something new.
At present, you have clearly show that you could remove material.

But assuming the amount you indicated were removed....... over time, those edges will wear a bit.
I would think there might be a danger of eventually cogging without the extra material.

Yes, this is entirely dependent on their design. 

But maybe all they really need is a hair.  With a smaller ID, the tooth is also stronger at the tip than it was before.

It should never cog because the next tooth is in contact ans is being driven through. That is unless there is too much clearance, or backlash- that's when you get perceptible noise and skipping teeth.

[narrowminded]

@rapidotrains ,

Since the power transfer of a involute tooth spur gear is transferred to the next tooth just before the first tooth no longer contacts its mating tooth, reducing the OD of the axle gear should have absolutely no ill effect on the gear set.  See below the red points of contact exist at the same time.



After you look at your mesh there may be some OD reduction available:
(Attachment Link)

If you are tooling new gears for these axles anyway that is what I would look into.

At a glance and in a largely blown up graphic it looks good BUT.... what you'll find when you get some real world dimensions is that the addendum and dedendum (resulting in that clearance) are already optimized in the standard and that dimension, even abusing the standard, doesn't have much more than a couple of thousandths room in these small gears.  Simply put, it won't get you much at all.

Another reality, at least in my observation and opinion, is that the mod .3 gear size is chosen for its robust sizing (relative) affording generous tolerance for these services and manufacturing methods.  While a finer tooth gear might have the necessary strength it also becomes much more dependent on exact tolerances.  Simply viewed, if an .008" tooth engagement would be sufficient for the service but adding all stacked tolerances consumes four of that, pretty soon you've got a problem.  A coarser tooth that has, say .015" engagement could afford a sloppy fit, as much as .007", without giving up the needed strength.  So a finer tooth ups the tolerance requirement exponentially and while it seems like a change as suggested might be an out, in the real world much more than a couple of thousandths on the diameter (.001" radial clearance) will cause trouble.  And going to a smaller mod caries some other considerations as well but not for here.