High torque low speed engine

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CogMachine

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Hello!

So, I want to start with a little story:

I want to build a steam engine. So I built one. A small model of course for practice, in LEGO and with air. This learned me a lot as I progressed from a completely useless brick that would not turn to a perfectly smooth running little engine. I learned a lot of things from this, for example that the valves should be timed with a 90 degrees turned crank and that the valves themself should never cover both inflow holes at the same time as that would create too much pressure and therefore friction in the valves.

But one problem remained: I like slow running engines so I can hear the distinctive strokes, but I want to have the power to actually drive something with one cylinder. But it was going too fast and had little power.

I experimented and it seems while a heavier flywheel seemed to have some effect its overall weight would power down the engine instead of conserving it because it adds friction (am I wrong here? Please correct me).

Then of course, relating to the flywheel I talked about before, an engine has different torque over its cycle, with a 0 torque on the turning point on the piston crankshaft. So this brought up the question if it is actually possible to have a slow running, but powerful engine.

I therefore experimented again and found that letting it run fast but gearing it up (converting the speed into torque) actually works (and the now fast flywheel seems to only start to even out the torque at a higher speed, not a lower one?), but the gears provide friction again lowering the power output, plus it would make the engine run fast which I don't like!

So, my question is: Is it possible to have a lower speed but high torque single cylinder engine? If yes, what would need to be changed? Would the piston chamber need to be bigger or smaller relating to the pressure? Any changes on the crankshaft? Flywheel improvements?

Also, I guess a double cylinder which is offset at 90 degrees would provide completely equal torque over its whole turn (again, please correct me), but I prefer single cylinder ones, so I would like it to be solvable with them.
 
It all depends on bore and stroke.

Taking a 'square' engine with say a 10mm bore and 10mm stroke, you will end up with a fairly high revving but low torque engine.

Now if you go to say 10mm bore with a 20mm stroke (which is the type I used to build) you end up with a lower revving engine with a lot more torque, ideal for a steam engine going into say a model.boat with a displacement hull turning a fairly large deep angled propellor.

Click on any of the pictures on this site, except for the one with a boiler and you will be able to download the plans for a 10mm bore x 20mm stroke engine. Starting with the single cylinder, and going up should show how they work.

http://jpduval.free.fr/Plans_moteurs_vapeur_p1.htm

The ones I used to make were based around the one at the bottm LH side.

Hope this helps

John
 
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It all depends on bore and stroke.

Taking a 'square' engine with say a 10mm bore and 10mm stroke, you will end up with a fairly high revving but low torque engine.

Now if you go to say 10mm bore with a 20mm stroke (which is the type I used to build) you end up with a lower revving engine with a lot more torque, ideal for a steam engine going into say a model.boat with a displacement hull turning a fairly large deep angled propellor.

Click on any of the pictures on this site, except for the one with a boiler and you will be able to download the plans for a 10mm bore x 20mm stroke engine. Starting with the single cylinder, and going up should show how they work.

http://jpduval.free.fr/Plans_moteurs_vapeur_p1.htm

The ones I used to make were based around the one at the bottm LH side.

Hope this helps

John

Does this also apply on double-acting engines? Also, what exactly is a "stroke" in this context? I know that a bore is the inner diameter of the piston cylinder, but a stroke? Is this the inner length of the piston cylinder?

Also has this any effect on the efficiency? How does it cover the point of 0 torque? Can at that point the flywheel bring it over also at lower speeds (including with power being drawn by machines)?
 
Click on any of the pictures on this site, ...

http://jpduval.free.fr/Plans_moteurs_vapeur_p1.htm

The ones I used to make were based around the one at the bottm LH side.


John

Thanks, I hadn't found that site - I often wonder about plans/pages in French, German etc but not speaking either its ain't easy. Its good to get a recommendation for a wobbler plan from someone who has actually built it.
 
Stroke = Total stroke of the piston, so with the piston at the very top of the bore, measurement from the bottom of the piston to the bottom of the bore equals the stroke.

So with a 10mm height for the piston, then the bore would be 30mm long (plus maybe a tiny bit more for the end cap and gland location).

I always use Google Translate for looking at foreign websites, and yes I have made a few of those twin cylinder engines.

I used to make batches of 6, and on the last photo you can see how it compares to a high speed 'square' engine.

John

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What do you intend to run the engine on? Steam will make it run in a different way to air as you have the expansion of steam which makes a lot of difference.
 
What do you intend to run the engine on? Steam will make it run in a different way to air as you have the expansion of steam which makes a lot of difference.

Well, Steam of course. It should be a normal steam engine that gets its power from heat (aka boiler), nothing fancy.

If you ask what it should be able to run, things like little loom machines, spinning machines, marble lifters, etc. Nothing where it really has to pull strong stuff, but it should still be capable. The slow running is mainly for artistic purposes, the high torque should just be a side effect so it can actually do all that stuff still.

I have also thought about attaching an electricity generator to it, but am not sure if that would need high rpm or can also do with high torque to generate enough power to run some SBCs´(single board computer).
 
I used to make batches of 6, and on the last photo you can see how it compares to a high speed 'square' engine.

John

The image of the one on the mill has overhung cranks both sides. The finished one completes the crankshaft on one side for power take off. Is there a good reason why one shouldn't take power off th flywheel (flat belt) or off a pulley beside the flywheel to a chain, v belt or toothed belt?
BTW, what is the 'high speed square' engine in the last pic?
 
Anatol,

You could have a takeoff almost anywhere, bearing in mind, if you used a flat belt off the flywheel you are in fact gearing up the output, so loading the engine more. There are pictures of my horizontal version which had a geared takeoff instead of the flywheel, designed for a paddle boat. Because of the down gearing to the shaft, it has a very powerful output. With a couple of PSI fed to it, you just couldn't stop the shafts by finger gripping

The engine in the last picture above is in fact a commercially made engine produced a long time ago called 'The Puffin', made by the now closed Cheddar Steam company, it has a 3/8" bore X 3/8" stroke, so a fairly fast engine.

The whole range of Cheddars' models are now being sold (and most probably made) by an Australian business.

Here is the Ebay number for the same engine with a slightly larger bore and stroke - 251733325412

Hope this helps

John

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