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[mogogear]

I have thought on this and asked elsewhere and nothing definitive. I may have over-thought or under thought on moderately easy ways to achieve this.

Possibly helpful details:

I also would prefer contra-rotating props.

I have a torpedo Boat destroyer under construction. I will be using a Graham Twin for the engine a sufficient horizontal boiler both now in hand....

She is 50" x 8"... and prop size is yet under determined but leaning on 2" - 3 or 4 blade

some gear reduction is desired...looking at about 3:1 ( currently- as testing will prove out what I need)

I have seen Dumas Adapt-a-drive- but as they are made for bolting electric motors I am a little confused on how to transmit the drive to the output side..

I have also seen a dual output unit from Battlers Connection   http://www.battlersconnection.com/html/gearboxes.html but it is a bit narrow and not flexible to adapt.( nice unit though)

Any links, drawings advise is etc is greatly appreciated....

[tonyH]

Hi Mo, sorry that it's me again

I had a twin screw gunboat using a gearbox that was made by Saito for steam engines. It had 4 gears, all the same size, in a line across of which the two in the centre were from the input shaft and an idler gear (which allowed you to get the contra-rotation) and the two on the outside were for the drive to the prop shafts.
As I mentioned, all the gears were the same size because although you have plenty of torque with steam, the revs are not great enough to justify a reduction.
The props on Ambrakia were about 3 inch.

The only (minor) problem is that you have to have a double joint in the shaft from the engine to the gearbox to allow for the offset.

With the width that you have in, I presume, the USS Cushing you could get away with 4 cogs of about 1 inch diameter which could carry the load.

Just lay out 4 coins of the same size on the table and you'll see how it works.

Tony

[mogogear]

Tony

Thank you for jumping in..I have taken a closer look at some shots of the Dumas frame and gears--I now do see that the drive gears to carry through the frame so a coupler can be added if inline withe crank on the engine or a pinion gear added to be driven by a gear of fthe crank ( I assume that is what you meant by "double joint"?)

           engine
               l
               l
             ---- -----
                    l
                    l
     ----- ----- ------ -----
       l                   l
      ~                 ~

Hope that makes some kind of sense

[derekwarner]

Mo .......I am sure that a proprietary gearbox is designed for the same application but for an IC engine which would naturally be totally suitable for a steam prime mover

Remember to build your own gearbox even with straight cut spur gears........you must take thrust into consideration as a resultant of each prop....then magnified into each of the four intermediate shafts ...etc...Derek

[mogogear]

As a novice- Thanks for the reminder of that-- thrust bearing / washers will be included and not forgotten!! Do any "off the shelf" dual output gearboxes come to mind ( IC intended)?

[tonyH]

Hi Mo,

The double joint is using 2 couplers on the shaft from the engine to the gearbox so you make a dog-leg to allow for the fact that the input shaft of the gearbox is not in the centre. The Saito gearbox I had was simply two sheets of steel with the pinions sandwiched between and held on the shafts with grub screws - no bearings at all. When I bought it it was a bit tight but I just gave it a good run-in with an electric motor and with a load of oil and after that it was fine.It would be simple to make if you have access to a pillar drill and just clamp the two sides together so they match.
I've attached a rough sketch of the system which may or may not appear!

Tony

PS I forgot to put in the need for two further couplers between the gearbox and the prop shafts.

[mogogear]

Thanks Tony....To compensate for most of the off-set- I could also have the idler gear on one side placed above the pinion/drive gear and the driven/output gear. This would minimize the offset so much as a simple weight would eliminate any listing..

I see I am going to need to download a simple sketch program.....



BTW --here is a quick shot of the foam hull- lots of sanding to go-- this is with about 4 hours of work ...



The boiler--Boiler is 7.5" x 3.5" with a 1.5" burner tube ( 6 x 3/8")cross tubes--mated to a Graham twin





Back to the Shop--gears==shop---gears-- thanks!!

[kiwimodeller]

Mo, just thinking aloud more than anything for what it is worth -
1) Not sure that I agree with Derek about thrust. Surely prop thrust should be taken by a thrust washer on the propshaft tube, not on the engine or gearbox. I can see a need for good bearings or bushes to reduce friction in the box but I see no need for thrust washers/bearings.
2) If it is possible to mount the engine a little off centre could you not fit one gear direct on the crank? The Graham can be set up to drive from the other end to the flywheel. This would elimate a primary driveshaft and tidy up and shorten up the installation.
3) It would be interesting to have some discussion about the prop size relationship. What do you think the two 2" props you are considering using equate to in a single prop? I feel, based only on my experience with a Graham single which easily turns a 2.25" prop with 2.5" pitch, that the twin engine must be capable of turning a 3'' single prop so then we need to equate that to the size of twin props. If you do use a reduction I would think that 2" props might be too small. I believe it is essential to load the engine up rather than let it rev if you do not want it to be hungry on steam consumption.
Hope all this rambling is of some help. Cheers, Ian.

[Circlip]

To cook your own, start with the propshaft centres (Centers) drawn on a sheet of paper with a horizontal line between them. The gears on these shafts must be the same size as each other. The gear on the motor output shaft can be a smaller diameter to allow the engine to be brought back central in plan view but would be higher or lower in end view. as long as the intermediate or coupling gear between the engine and the second shaft is the same as the one on the engine, both the propshafts will rotate at the same speed as each other but in opposite directions.

  A good source for reasonable gears are the cordless drills with a mechanical reversing mechanisms. Some of these have metal gears about 6mm (1/4") thick. 

  (Baracketed translations for American markets) 

  Regards  Ian.

[tonyH]

Hi Mo, you could certainly modify the gear layout as drawn.

I've got to go with Kiwi Ian about the need for thrust washers and the prop size question. Especially if you follow what Circlip Ian mentioned about having a smaller gear on the motor output shaft which would reduce the revs at the prop end.
I can see one problem of having the first gear on the output shaft of the motor if you need to adjust the gear clearance for any reason.

A great start with the hull former - it shows off the lines well.

Have you deepened the hull atall? You mentioned that you had widened it to get some more stability but it looks from the photo that you've deepened it as well so that could have a bearing on the prop size it could carry.

No stress in this hobby is there?

Tony

[mogogear]

Many good words to chew on - thank you to all for your input.

The prop size considerations are as of yet still to be researched ( like everything in boats and steam etc) I am planning on not having a gear reduction and the drawings and gears I am sourcing will all be the same size- so 1:1...

I will make ( if you use my drawing as an example ) two of the gears sits in slotted apertures for lash adjustment. The top idler gear will have a  Up / down adjustment and the output shaft on the far side from the idler will have a side / to side adjustment. This hopefully this will allow to fine tune load and noise.

As for hull height-- here is a rough drawing that I did to plan out cutting the foam prior to bonding and shaping and general placement. My boiler alone is 10" from end to end, the engine is 4" , I will use a disposable canister fuel tank ( another 4") plus room for coupling and gearbox-- usable length I have currently in the "engine room" is 23" -25"




 It is deeper than scale mostly due to the clearances needed for a boiler - the 3.5" boiler diameter along with room for fittings coupled with a need for lower COG for the boiler drove me to add room down in the hull.

I am sure I will learn so much from this "exercise" 

Cheers fellows- thank you again for ideas input or wake-up calls!!

[derekwarner]

mmmmm sorry ... .....not trying to confuse   ...please look at my mudmap

a. with the prop turning clockwise...each blade is biting into the water so the resultant thrust is outboard
b. with the prop turning counter clockwise...each blade is biting into the water so the resultant thrust is inboard

An example of this is with motor vehicle dash heater/cooler fans or windscreen motors........they are designed for rotation in one direction only  & have a single ball [bearing] between the armature shaft & the motor endcap housing

When run in the designed direction the EMF produced thrust is taken smoothly between the ball & the housing ...when reversed....the EMF produces  float & dither in the armature shaft as the resultant thrust is not constrained  .......most commercial stern tubes have simple parallel bushes, however these cannot constrain thrust

Over the years I have used a single row conventional ZZ ball bearing in the prop shaft drive....& whilst not designed specifically as a thrust bearing adequately cope with the force units of thrust we are talking about

I would be interested to understand how others cope with this thrust element....... .....Derek

[mogogear]

Consider me in the class room and taking notes of what I am sure will be a interesting discussion

 

[derekwarner]

mo....we are all in the class room & sitting @ the student desks.... ...it's all a learning curve  ........but sometimes I am fearful....... about the teacher...... .....

Nick @ Mohanan used ZZ stainless ball races in the big end of his engines, JMC from France do the same in their smaller engines.........Anton from France appear to use bronze bushings......

I think we should ask our member Bernhard   the builder of many  open hulled steam boats for an opinion here as to how he contends & constraines thrust.....as he would be a good teacher.....................Derek

[HS93 (RIP)]

Derek why not ask for this to be put in a new post as it is just distacting from the post in hand and that is gearing two props from one motor, it is something that effects every prop driven boat.

Peter

[derekwarner]

Peter - the subject of "1 Steam engine 2 output shafts..best way?" ..essentially requires an understanding of how to accommodate thrust

In OZ..... we are taught to take the blinkers OFF.....& be students & ask questions....... ......so I do not see that I have distracted from the original question

Naturally if the thread owner or a moderator considers I am off line & .... I would be more than happy for my questions or comments to be deleted........Derek

[HS93 (RIP)]

Peter - the subject of "1 Steam engine 2 output shafts..best way?" ..essentially requires an understanding of how to accommodate thrust

In OZ..... we are taught to take the blinkers OFF.....& be students & ask questions....... ......so I do not see that I have distracted from the original question

Naturally if the thread owner or a moderator considers I am off line & .... I would be more than happy for my questions or comments to be deleted........Derek

Is this something that effects most boats with a shaft and propeller  ,if so it needs anew topic

Peter

[Circlip]

Thrust shouldn't be transferred to the gearbox shafts. If pin and disc couplings are used on the output shafts there is no thrust component transmitted back from the prop shafts. The older RipMax ball type couplings had enough "Slack" built into them that allowed the prop shaft some end float so that the thrust was taken on the prop end bearing of the tube. Laziness of alignment has been perpetuated with the Chicane type universal couplings and It aint missile teknowlegy to designing in a sliding element into the drive system (Splined coupling? A La rear wheel drive, car [Full size] propshaft?), just consumes a bit more time to make it

  Seem to be trying to re-invent a method of generating linear movement with a rotary element (?) but in any of the OLD toy boatbuilding books there were various designs of "Thrust Blocks" which used either a "Normal" thrust bearing ie. two hardened grouved washers with a ball element between them or a cone type bearing like a bicycle bottom block.

  It's easy enough to do, just takes a little application of the grey matter and a bit more time. No doubt if required, some aspiring manufacturer can get them on the market so the "Must have it termorrer" brigade will be able to flaunt them.

  A "Proper" thrust block and sliding pin coupling take up LESS space than a red or black plastic wobbler, but you do need to align the ends properly.

  Regards  Ian.

[mogogear]

Ok a starting point has now been reached.......



toss the end connectors for the couplers- disk / pin will be a possible coupler that I do like to use. and now to work on a frame to hold this arrangement with bearings ....This gives me 2.5" between output shafts- which allows me room for 2" x4 blade props( 1 LH and 1 RH) or for you on the other side anti and clockwise..

[Circlip]

God ole Meccano, and by bringing the gears between the frames and encasing and filling with oil, a quieter and safer drive is made. By having bearings out board of the gears, the driveline is NOT overhung.

  Regards  Ian.

[mogogear]

you have read my mind well Ian..a friend in New Zealand who had Meccano parts put this together for me ..I will finish it up shortly!!

[tonyH]

Hi Mo,

Are you sticking with the 1:1 ratio or the layout in the photo which seems to be about 3:1

Tony

[mogogear]

Tony

It will all be a test...I realize I will lose a lot of RPM's with 3:1 but I will do some testing to see if the Graham + 3:1 + 55mm 4 blade props can push the Cushing around and at what speed- who knows

The gearbox was made up by a friend of mine in New Zealand who had the Meccano gears -

[MOG8]

THIS IS MY METHOD, WHICH I HAVE NEVER SEEN ELSEWHERE.
THIS ALLOWS YOU TO HAVE A CENTERED ENGINE.

[mogogear]

Yes- I thought about stacking the two center spur gears but figure the small amount of weight to offset the 1/4" from center line would be easy to overcome---and the engine is hidden under superstructure so it does not scream "out of alignment!!" at me all  day

Here is the prototype arrangement I made up- I now have added flanged sealed ball bearing on each end of all 4 shafts- Reamed all the gears, re tapped the set screws and replaced shafts with precision hardened steel 3/16" rod. I am awaiting my  completion of the hull with fiberglass so I can fit the power plant !!



It now runs smooth and true

Thanks for the drawing Giovanni-- always good to have ideas here for those that follow or my next effort