Gear ratio for steam engine

[bogstandard]

I am just building a few twin cylinder oscillators and was wondering as a rough guestimate what gear ratio would be required to drop the speed down for use with a paddler. I am asking this because the design of the engine makes it a fairly easy task to drop it to the horizontal position and put in a layshaft with a reduced speed output driven by gears from the main crankshaft.

[Eddy Matthews]

I'm not up on steam engines, so I don't know what RPM your engine will run at, but you should aim for 140-160 RPM for a sidewheeler and around the 80-100 RPM mark for a sternwheeler - They are no load speeds, which will decrease when the model is in the water...

Hope that helps a little?

[bogstandard]

Many thanks, just the info I was looking for. I will get a tacho on a finished engine and gear down to suit.
I think these will make good paddler engines because they have a long stroke, 10mm bore x 20mm stroke.

[steamboatmodel]

I like the looks of your engine, is it from a published design?
Regards,
Gerald

[bogstandard]

Hi Gerald,
The plans are a free PDF download from here -
http://jpduval.free.fr/Plans_moteurs_vapeur_p1.htm
There are a few others on the page but they are all single acting.
I have deviated from the plans in a few places to make them easier to produce (I am making six of them), there are also a few slight mistakes on the drawing, nothing to stop the engine from running, just makes it a bit awkward to operate. If you make one I can give you a few pointers if you want. To make life easier you really need a rotary table on your miller, but it is not essential, I am just helping a chap to build one over the internet and he only has a lathe and drilling machine, and he is further ahead than me, I still have to make the pistons, rods and baseplates.
This engine as I said earlier can easily be dropped on its back and turned into a horizontal motor.

John

[derekwarner_decoy]

Hi PD's & here 'bogstandard' is an auto translated posting from Anton the French engine biulder where he quotes 'a reduction of a ratio from 6 to 8' - this is the only reference I have found nominating such a reduction ratio for model steam engines.......

[I am to use a 5.5:1 chain drive reduction but with an 3 Cm3 alternate brand engine] - Derek
<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<

The engine “Quartz” is a product news generation of workshops ANTÓN.
Of simple design and use, this engine is particularly advised
for initiation with the propulsion vapor.
It is a piston valve engine with rotary reverser of walk, which allows walk before/back, the stop and the idle with only one servo of radio order.

This engine, in its horizontal version, is particularly adapted to the propulsion of paddle boats (side or back). The installation of the engine will be done with a reduction of a ratio from 6 to 8 (cratée belt or pinion).

This engine will be used in boats of 5à 10kgrs, with wheels of Ø100 with 150 Misters.

Model QUARTZ Characteristics horizontal engine
Race: 8 mm
Boring: 9 mm
Cubic capacity/turn: 2 Cm3
Pressure of use: 1,5 to 3 bars
Weight of the engine: 470 grs

[bogstandard]

Many thanks for the info, I will have to wait to see how fast it turns on 35psi (it is a long stroke engine so should run a lot slower than the normal square engines) before I can calculate the correct gear ratios for it.
Because I am only converting one of these engines I don't want to buy in special gears, and the ones I have in stock might mean I have to 'double up' the gears, the only way is to suck it and see, and see if it has enough power in reserve to drive a gear train.

[derekwarner_decoy]

Hi PD's ...sometimes I get a little   here 'bogstandard' , but your oversquare 10X20 twin engine will simply consume twice the steam of a square 10X10 twin... so the speed will be relative to the available steam input

Feeding six HUNGRY cubic centimeters with steam @ 3 Bar will be a challange   :rant  :boom

We welcome you to our PD group...... - Derek from Australia

[bogstandard]

Thanks for that decoy, I will suck it and see, but haven't had any probs with my previous long stroke engines. By the way 35psi is top end, I usually run at about 20 - 25psi, no need for any more.

John

[steamboatmodel]

Thanks John,
I am the Librarian for my local model engineering scociety and one of the steam guys in the model boat club, thus an always being asked for simple designs for people to start with.
Regards,
Gerald

[Bill Hudson]

Eddie posted this e-bay listed engine on the e-bay forum.  Check it out.  It is very similar to your engine.  It appears they are using a belt drive off teh main shaft to drive a larger pulley and shaft.  

http://cgi.ebay.co.uk/Steam-Motor-and-Gear-Box-New-and-unused_W0QQitemZ330102396208QQcategoryZ14737QQrdZ1QQcmdZViewItem

Bill

[Eddy Matthews]

I noticed you said there may be some of these engines available for sale on the Mayhem forum John....

I could well be interested in one if they are! Please let me know... Via a PM if you don't want to discuss money in a public forum.

[mjt60a]

....The installation of the engine will be done with a reduction of a ratio from 6 to 8....

I wonder, does that mean 'a reduction of between 6:1 and 8:1' (depending on the prop/paddles used on your model) I wouldn't think it means a ratio of 6:8 would it?

[sandy_ACS]

 

Hi PD's,

Been keeping an eye on you lot.....not sure your safe on your own....    :music ....

Bill....the engine shown on e-bay is an SVS built engine and is based on the 'SNIPE' marine engine.....it is known as a short shaft engine and has 4:1 reduction gearing.
I actually manufacture a geared version of my 'ASP' engine (similar size to the Snipe) for the same purpose...GARDEN RAILWAY'S ...see attached pictures.

I was approached by a Garden Rail manufacturer about this, since the SVS engines are no longer in production and I modified my ASP engine to suit....it uses a 16 tooth crankshaft gear with a 64 tooth output shaft gear, giving a reduction of 4:1...this is then increased on the loco by a further 1.5:1 or 2:1 (depending upon loco) giving a final reduction of between 6:1 and 8:1.

My ASP engine normally has a stroke of 3/8" (and was quite high reving at around 1200 - 1400 rpm on 35psi, off load) however, this proved to be a little to fast for the purpose and was further modified to give 7/16" stroke to slow the engine a little(this gives around 1000 rpm off load)....it now performs pefectly...giving a good balance between steam used (Derek's point) and torque generated.

I have considered offering this engine for paddler use, however, the extremely high cost of the required gears (the 16 tooth crankshaft is a double ended pinion in stainless steel, with the output gear being 64 tooth gear pinned onto a stainless shaft) made the cost a little on the high side for general production.

Bogstandard.....your engine would lend it's self to a similar gearing mod. and would prove more than adequate for the task....I would suggest 3:1 or 4:1 gearing for the engine with any further reduction being made via external gearing (chain, belt or gears) in the model of choice, this will give a more flexible method of installation.

A suitable boiler would be about 3" dia centre flue.....the loco shown in the pictures has a 2 1/4" dia main barrel with a vertical stub in the cab area ( tee shaped boiler) and gives a good 30 minutes running time. Keep up the good work....looks great so far.

Hope this is of some help.

Best Regards.

Sandy. :vacat  :computer

[bogstandard]

Sandy,
Many thanks for your interest, that has given me renewed hope of converting it to a horizontal engine. I have hundreds of the same gears that give exactly 4-1 ratio (just need a bit of boss machining), just mount the smaller gear where the flywheel is and the larger one can go on the top of the now horizontal standard. I was contemplating having to build a multiple gear train ,no problem in that, but friction comes into the equation with a vengeance on a small motor.

John