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Reply to "MTH Premier "O" Scale 3 & 4 Truck Shay Steam Locomotives Announced"

@H1000 posted:

Now the big question, do these really need O-72 curves? The first run production back in 1997 would run on O-42.

Owning a few shays myself, sort of a loaded question (not intentionally). Since the drive shaft runs down one side, depending on if that is inside the curve or outside of the curve (which direction the engine is facing) determines if the driveshaft shorten or lengthen in the telescoping portion as it rounds the curve. As such, there are limits on how far they can compress or expand before the shaft just pops out or binds. While a designer or manufacturer could modify the design and the universals and where and how these telescoping shafts are and max length and collapsed length, they I would think you stray from being scale.

Now imagine your track plan - either a simple oval, or something that invokes curves in both directions or S curves.

That radically changes what might get by and what flat out doesn't work. Depending on engine direction to allow you to user a smaller than "recommended" diameter works one way, but not the other.

Again, say you moved the pivot points of the trucks further down the engine making longer shafts and thus longer telescoping section- OK, but then that changes the details and "scale".

https://ogrforum.ogaugerr.com/topic/49297155953251505

Picture from that topic by @VALE40

Bottom line- like so many trains, specifying a larger "required" curve to cover all scenarios to handle those "what if" situations VS, telling the customer a minimum diameter it will run on, but then that only applies one direction to a simple oval and the instant you stray and add curves in the other direction (or turn the engine around forcing drive shaft inside the loop/curve VS outside) it won't work.

Ultimately, this is why a Heisler or a Climax with a driveshaft down the center changes this entire aspect of what works and doesn't, compared to a Shay with the driveshaft down one side.

Last edited by Vernon Barry

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