O gauge steam power train question

I don't think the connecting rods actually rotate the wheels. On my scale williams hudson, there seems to be two moon shapes on the chassis bottom, presumably for gears.

@jhz563 posted:

are the other drive axles typically connected through gearing, or just through the connecting rods?

The Lionel Berkshire, N&W J, 773, and turbines(and their derivatives & reissues) transmit power through the rods.

The 1946 models 726 and 2020/671 do have a drive shaft in the chassis that transmits power to the rear and front set of wheels via spur gear.  In 1947 this was changed to a worm gear set up only driving the rear axle. The power was transmitted through the drive rods. The frame casting was changed drastically for this.

I have a fondness for the 1946 726.  With motor bearing replacement, proper inspection and lube the can be pretty quiet but sound very different than a 1947+ engine. 

Thanks folks.  I am looking to design a lego steam locomotive for O gauge.  In lego terms, O gauge is narrow gauge.  So the usual lego drive train configuration won't fit between the frame members.  I was simply looking at various existing O gauge steam model drive trains for inspiration.

A drivetrain and motor from an On30 Bachmann locomotive might drop right in.

MELGAR

@MR_P posted:

I don't think the connecting rods actually rotate the wheels. On my scale williams hudson, there seems to be two moon shapes on the chassis bottom, presumably for gears.

Au Contraire, most modern O-gauge steam does indeed drive the wheels with the rods and have just one set of drivers linked to the motor.

@MELGAR posted:

A drivetrain and motor from an On30 Bachmann locomotive might drop right in.

MELGAR

I appreciate that sir.  Alas, that's not the idea.  The challenge to myself is to use as many actual lego pieces and techniques as possible. Lego has come a very long way. Here's an article from a couple years ago that will give you some visual idea of what is possible. 

"L" gauge is wider than O.  So power transmission gearing arrangements that have been well established for lego trains just don't work. Fortunately Lego is entirely modular.   So I know it can done,  just requires more creative thought.

Also, you can now get Kadee couplers in Lego compatible mounting boxes.

@gunrunnerjohn posted:

Au Contraire, most modern O-gauge steam does indeed drive the wheels with the rods and have just one set of drivers linked to the motor.

Yup. Most all modern steam locomotives from Lionel and MTH have the motor in the firebox. The motor is connected to a worm shaft which turns a worm wheel on one of the axles. That drive wheel then transmits power to the other drive wheels via the side rods.

@gunrunnerjohn posted:

Au Contraire, most modern O-gauge steam does indeed drive the wheels with the rods and have just one set of drivers linked to the motor.

The Polar Express and related engines, and those thousands & thousands of 0-8-0 PRR Flyer steamers(and other starter sets) would be prime examples.