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Scale Factors for Models

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  #1  
Old 1st February 2021, 11:13
Master Cutler's Avatar
Master Cutler Master Cutler is offline  
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Scale Factors for Models

Following an exchange of emails with a rail fan friend of mine, we got to discussing scale factors for models with regard to time.
Apologies if this has been done to death before, but I can't find any previous posts so if there are any model makers on line, I need to confirm I've got the facts right.

To keep it simple, let's say a locomotive is 100 tonnes and we make a scale model at 1:100.
The weight of the model, if identical materials are used will be;
100 tonnes X 1/100, X 1/100 X1/100 = 0.1 kg
If the loco is 20 m long then the final length will be 20 X1/100 = 0.2 m long

If the full size locomotive travels at 60 mph it will complete 1 mile in 1 minute.
Therefore scale wise should the model speed be 60 X 1/100 mph = 0.6 mph?
So after 1 minute it will travel 0.01 miles which, if my arithmetic stacks up equates to 52.8 feet. Or speed of 52.8 feet per minute. (Sorry for mixing Imperial and Metric).
And now the 64,000 Dollar question, will artificial smoke from the model chimney follow the same rules and look correct if say the model is being filmed in real time?


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Old 1st February 2021, 12:55
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Beeyar Wunby Beeyar Wunby is offline  
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And now the 64,000 Dollar question, will artificial smoke from the model chimney follow the same rules and look correct if say the model is being filmed in real time?
It's unlikely. I've always been fascinated by cinema. So much so that I spent the first half of my working life on 16mm film & video (albeit as a sound specialist rather than optical).

I love the old filmy films (real 35mm acetate) which were shot in the days before CGI. As I'm sure you know, extensive use was made of models for the dramatic 'set pieces'.

And just as you mentioned scaling in your post, so there used to be specific frame rate charts for camera technicians to 'overcrank' camera shutter speeds. The standard shutter speed for movies is 24 fpm, and this was raised significantly for shooting scales models.

Obviously when the film is played back at 24 fpm, the action is slower - but also the movements are more smooth. There is an element of trial & error, so test rolls were shot to hone down the best setting before they blew up the expensive viaduct or sank the 50ft long Titanic model.

Cheers, John
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Old 1st February 2021, 13:31
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Master Cutler Master Cutler is offline  
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Many thanks John, so it's quite a bit more complicated.
Makes sense though.
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Old 1st February 2021, 14:35
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On the plus side though, video editing software is so good and socheap now that it's probably possible to enhance the smoke effect.

Digital rain and snow can be pretty convincing, so maybe there's a treatment for smoke?
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Old 1st February 2021, 14:54
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Another problem would be getting the smoke to exit the chimney in an authentic manner.
On the full size version the smoke from the fire is dragged through the boiler tubes by the action of the cylinders exhausting through the blastpipe. If the model wasn't " live" you would need a variable speed smoke generator to mimic the actions of the full size version.

Cheers John
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Old 1st February 2021, 15:28
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Thanks guys, so it would be, increase shutter speed and synchronise the smoke generation, to get something like the real thing.
The reason my friend and I discussed this was relating to wind tunnel modelling using scale models, but I won't elaborate as I think I understand the problems a bit more now.
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Old 1st February 2021, 17:47
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Thanks guys, so it would be, increase shutter speed and synchronise the smoke generation, to get something like the real thing.
That's it, but being absolutely clear, you....film at a higher frame rate, but play back at the standard rate, to produce a slowed down and smoother image.
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Old 5th February 2021, 03:55
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Cine film and video frame rate does present some interesting oddities.
Especially when combined with shutter speed.
Aircraft propellers appearing to spin backwards, also similar with spoked wagon wheels.
The perception of speed at small scale is one facet of model railroading that can stand out blatantly.
Many old movies featuring scale models tend to be obvious in regard to speed and scenery relationship.
Soot belcher exhaust smoke also giving the game away.
So, most model train prangs were staged during darkness when things are less perceptive.
One that springs to mind was a WW2 era espionage BnW flick that was dubbed Ghost Train (I think).
I mean, if you really looked close enough at the drive in cinema, you could squiz them Star Wars model wires.
Yes, flick FX are a heck of a lot better today with computer wrangling.
I was viewing a DVD yesterday featuring the Brewongle Barn Bahn layout before it was dismembered.
An amigo had asked me to attempt to wrangle it as it refused to spin correctly in his DVD spieler.
The disc was scratched, so I gave it a good clean and then utilized me computer software to burn a copy.
The copy did spin up ok.
While viewing the copy, I was amused by the HO scale model train activity.
You Poms gotta be different and have OO scale.
Oh oh, that Flying Scotsman don't look the same as that Yankee Ho ho K4.
The operators obviously not having much perception of scale speed.
A train would commence to rattle, and then suddenly it would blast off like a saturn v rocket.
Hurtling down the track at warp speed Mr Zulu.
All the ho ho scale cattle face skin pulled back like in early flicks depicting a saturn v blast off.
Yes, OK, the Easy DCC system utilized was NOT the best available, even though them Yanks professed it was.
We suffered numerous hassles with it, especially with visiting locos that were not configured for Easy DCC.
So, I spent a lot of time wrangling CVs to configure locos for it, but then needing to unconfigure them at the end.
If left in that configuration, the owners might experience difficulties on their home layouts, using different DCC control.
Way back in the dim dark past, when we had a model nutter club here, I planted a smoke generator in me soot belcher.
Sleuth brand which I believe are still available today.
The only drama being that to get the element hot enough to burn the oil, yer soot belcher had to do warp speed.
Then the smoke would erupt forth like a maniac fireman was on the footplate.
After one or two laps the oil was expunged and the puff puff stopped.
Yes, it was a gimmick for exhibitions where kids got excited.
The early noise chuff chuffs were VERY basic, also back then.
The modern day DCC sound decoders are a tad better in producing loco noises.
But, all is in the eye of the beholder.
Unless you know the specific 1 is to 1 scale loco and noises created, you can be fooled by the noises offered.
I remember one bloke wanting noise in his 45 class DL541 aussie alco model.
An acquaintance found an el cheapo Yankee sound decoder for an SD45 and jammed it in.
The first time I earwigged this NSWR 45 class, I just stood bewildered gawking at it.
ER UM, you do realize that that ain't quite correct, I suggested.
An SD45 is a 20 cylinder EMD two stroke thing, NOT a 12 cylinder Alco four stroke thing.
E GADs.
YES, you could certainly hear that 45 class approaching on the BBB.
I researched a more suitable decoder for it and they finally swapped it over.
But, model trains are definitely not a kids toy any longer.
The things are outrageous in pricetag, especially when noise is provided.
Playing trains out on the humongous BBB layout was fun, except for the Easy DCC hassles.
Since revamped and shoved into the Black Box museum, I ain't squizzed it since last february.
I spat the dummy on the final working day afore the GRAND OPENING, telling the council that it was NOT ready.
Steve.
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