Engines > Your Own Design

Chris's New Steering Engine

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crueby:
Hi all,
With the Ohio Crane model complete and some improvements done on the mill and the shop cleaned up, its time to start in on a new engine. This time it will be another steering engine. These steam engines were used on ships right through WW-II when they were replaced with hydraulic and electric driven equivalents. They take input from a steering wheel, and use that to control a valve which runs the engine forward or reverse until the rudder position matches where the steering wheel was turned to - the original power steering! The feedback mechanism in them works a lot like a rodaio-control servo does, just using mechanical linkages rather than electronics and sensors. They were invented in the 1800s, and went through many different designs though most worked on the same principals. They were needed when ships got so large that the rudders were too big to turn and hold by hand againts wave/motion pressures.

Here is the model I built a couple years ago, its based on the original engine that Michael owns, from a German paddle steamer:

And here is the design for my new one:

It functions in the same basic way, with a number of differences. The other one has a set of clutches and a second steering wheel to allow for manual steering (with more gear reduction) in the case of loss of the steam engines or steam supply. It has a rudder indicator built in to the main shaft, and uses a set of crank arms and linkages to get the control input down to the control valve. The cylinders use spool valves, switched by the control valve between center admission and end admission to control the direction of rotation.

On the new design, based on the style used by Navy torpedo boats and others, is a simpler design. In these engines, the manual steering backup and the rudder indicator were done outside the steering engine. It uses a direct linkage from the control shafts to the control valve, eliminating the cranks and links (which is good for the model, less motion loss in all those connections). Also, I have changed from the spool valves to the 4-port valves and double layer D valves as used in steam shovel slew/crowd engines. These valves are simpler to make and get good seals on at model scale. Other than those changes, the function of the feedback mechanism is the same.

The model will be built with 1" bore/1" stroke cylinders, and will sit on a 6" x 6" base.

The feedback and control valve setup on steering engines is pretty clever. Here is a diagram of the main shafts:

The steering wheel at the left end turns an inner shaft that runs about halfway down the length, to where the threaded section is. There is an outer shaft that spins seperately - the center of that shaft, between the two bronze bearings just left of center in the diagram, holds the worm wheel that is turned back and forth by the engine. That shaft also turns the grey piece in the center, with long flats cut into it. Those flats turn the bronze colored control nut.

So, when the steersman turns the steering wheel, that turns the threaded section, causing the control nut to move in or out - the control nut is kept from spinning by the flats mentioned above. The control nut moves the valve rod at the right end - this rod is concentric with the steering input shaft but is seperate from it. When the valve rod moves, it pushes/pulls the D valve in the control valve, sending steam down one pipe and taking exhaust from another, those pipes lead to the 4-port valves on the cylinders, making the engine start to spin. As the engine spins, a worm gear on the crankshaft turns the worm wheel mounted on the outer shaft (see the picture above this diagram to see those gears). As the worm wheel turns the outer shaft, that turns the control nut via the flats. That turning of the control nut re-centers it, which pulls the control valve closed again. Quite clever! As the outer shaft turns, that also turns the chain sprocket, moving the chain that leads to the rudder. You can see a video of the action here, on the first steering engine model:
http://www.youtube.com/watch?v=pKp-J9aGXiA

Thats where this build will go with the new design. This morning the shop elves went up to the bandsaw, and cut me the kit of parts for the cylinders, end caps, crosshead guides, and the base plate. The cylinders/guides are being made from 1-5/8" brass roundbar, all taken from a 4' length I picked up at Yarde Metals Drop Zone, where they sell offcuts from their commercial supply at a very good price. The whole bar cost me about $100, and this model is only using a fraction of it.

Then I spent some time on the lathe, getting the end caps trimmed to thickness, and the other bars trued up on the ends. The cylinder/crosshead bars are all about 1/2" over finished length, to give me room to chuck them up. The outer ends you see will be the mating surfaces at the piston rod gland end, to ensure the bores are square to the mating ends. The other ends will be trimmed off after all shaping is done. The outer ends of the cylinders get the end caps, which are less critical to alignment. First I cut the outer profile on the cylinders, and drilled a starter hole down the bore:

Likewise with the crosshead guides. The left end of the guides, up by the chuck, will be the ends towards the crankshaft. Those ends have a smaller flange than the other ends, since they do not need a bolting flange.

Next will be to rough out the bores close to the final ID, final cutting will be done later when the bolt circles are drilled in. The cylinders need flats cut on the outsides to silver solder on the steam chest bases and the floor mount blocks. The final boring will get done after those steps are done, in case there is any movement from the silver soldering and milling steps.
 :cheers:

redhouseluv:
wow - a new start already Chris, and moved from trains to ships! It looks like another great challenge, I never realised that was how the steering mechanism worked.

tghs:
he'll be done with it Sunday afternoon.. :cheers:

crueby:

--- Quote from: tghs on May 03, 2025, 05:53:41 PM ---he'll be done with it Sunday afternoon.. :cheers:

--- End quote ---
Don't  exaggerate. Monday morning!    :lolb:

cnr6400:
Maybe we should start a pool like they do for when kids are born. My guess is Tuesday afternoon at 2:35.  :Lol:

Just joking Chris, looks like a great start on the steering engine version 2.  :cheers:

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