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:D COOL model! Love it, gotta get one.

 I'm sure your premise that "by gearing both wheels there's less stress on the drive wheels than if only one was geared, and you reduce the chances of breaking a gear tooth" is correct, and that 4 wheels driving would give superior traction on slippery metal rails than only two.

All these parts would have been cast-iron, and though iron is 'strong', it's somewhat brittle. It wasn't until the mid 1800s that the Bessemer process ushered in the age of industrial steel. Cast-iron's brittleness would surely have been a factor in designing those gears to try to avoid breaking. B)

Thanks for weighing in, Bill. B)

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It is possible that they saw a day when it would have to turn a corner, and made the right two wheels the drive wheels. The other two could be freewheeling, reducing any stress and slippage during cornering, caused by the difference in wheel rpms. Although the brittle metal explanation makes perfect sense as well. 

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   Another option could have been given the Common Drive Gear was mounted to the Boiler/Firebox "Tank" it could have been a way to reduce/eliminate flex of the Common Gear's shaft.

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Your guy's guesses are as good as anyones!

Here is some interesting info on this locomotive, courtesy of wikipedia...

In 1802, (Richard) Trevithick built one of his high-pressure steam engines to drive a hammer at the Pen-y-Darren Ironworks in Merthyr Tydfil, Mid Glamorgan . With the assistance of Rees Jones, an employee of the iron works and under the supervision of Samuel Homfray, the proprietor, he mounted the engine on wheels and turned it into a locomotive. In 1803, Trevithick sold the patents for his locomotives to Samuel Homfray.

Homfray was so impressed with Trevithick's locomotive that he made a bet with another ironmaster, Richard Crawshay, for 500 guineas that Trevithick's steam locomotive could haul ten tons of iron along the Merthyr Tydfil Tramroad from Penydarren (51°45′03″N 3°22′33″W) to Abercynon (51°38′44″N 3°19′27″W), a distance of 9.75 miles (16 km). Amid great interest from the public, on 21 February 1804 it successfully carried 10 tons of iron, 5 wagons and 70 men the full distance in 4 hours and 5 minutes, an average speed of approximately 2.4 mph (3.9 km/h).[16] As well as Homfray, Crawshay and the passengers, other witnesses included Mr. Giddy, a respected patron of Trevithick and an 'engineer from the Government'.[17] The engineer from the government was probably a safety inspector and particularly interested in the boiler's ability to withstand high steam pressures.

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To heck with all of this engineering jargon. Somebody get the pilot a better box to stand on.

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So at 2% inflation since 1803, that £500 bet in 1803 would be $39,558 today.

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Well, I have to admit I didn't "do the math,"... but I'll take your word for it! :D

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I forgot to mention...typical Harry looks-like-museum-quality work. Always inspiring. :)

Thank you.

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That's a great model, Harry -- I built the Airfix one as a sort of "Steampunk" display model in lots of different metallics a couple of years ago. Interestingly, I think both Airfix and Minicraft have got this a bit wrong. As people have pointed out, you couldn't safely drive or stoke the thing the way the kits are configured.

The replica on Youtube is clearly driven from the other end

And there's a replica in the Swansea Museum that also makes much more sense:

 You could probably swap the endplates of the boiler on the Airfix kit easily enough, but switching the piston, conrod and frame assembly might be harder...

bestest,

M.

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indeed it does. Fascinating.

Makes you wonder what the "original" source of info was for each one. They can't all be right, since they are rather different!

"we carried ten tons of iron in five wagons, and seventy men riding on them the whole of the journey... the engine, while working, went nearly five miles an hour; there was no water put into the boiler from the time we started until our journey's end... the coal consumed was two hundredweight".

So clearly, the fire was stokeable as they ran on. Equally clearly, there's at least an image or two from which the kit tooling guys worked, which is reasonably detailed in the fine detail, but not so clear in the "big picture!".

bestest,

M.

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It's a muddled picture. From what I've been able to find, this locomotive was based on Trevithick's previous 1802 Coalbrookdale locomotive, which was very similar in appearance and function, but the Pen-y-Darren had several differences. Apparently no drawings of the Pen-y-Darren exist... so it's anybody's guess as to which configuration is correct (front-mounted piston rods and guide bars or rear-mounted). Obviously, operating recreations have been made in both configurations, but I guess there's no way for sure to know which is correct.

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Thanks or sharing his unique build with us Harry.Also thanks for posting the videos of these very and unique full size working replica machines.If we find them facinating today I can't imagine the intrest in them that early in the 1800's when the only alternatives were animal powered.Great choice of subject matter and superb executution!

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Perfect work on an interesting model!

I love such peculiar and even educational topics. Ask people who built the first locomotive and 99 per cent of those who have any idea will answer: "Stevenson, of course!"

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