Calculating the scale speed of OO gauge models

[The Johnster]

15 minutes ago, melmerby said:

The Nautical mile has nothing to do with the imperial mile (apart from the name), being a subdivision of the circumference of the earth being 1 minute (sic) of latitude along a line of longitude.

It is now defined as exactly 1852 metres

Something else I’ve learned today!

[Reorte]

5 minutes ago, The Johnster said:

This seems to be one of those polarising subjects where entrenched opinions are wont to clash.  I have a suspicion that much support for Imperial units is rooted in a longing for the Imperial past, storms in channel Continent isolated, British is best sort of thing.  I use Imperial because I’m used to it, it’s my comfort zone, but accept that metric is the superior system. 
 

This sort of prejudice probably goes back to the horrors of the French Revolution and the subsequent Napoleonic wars; there was still a residual element of Boney as a boogie man when I was at school in the 60s.  He was no saint, but no Hitler either, though my history teachers seemed to consider them as on a par.  Still an element of thinking that anything as European as the Metric system was fundamentally capital B Bad, and an assault on some sort of mythical British dammit Carruthers way of life.  One sees the same thing with identity cards, a very sensible and rational idea that would be political suicide here. 

 

Probably more just a reluctance to change something that the majority of people using it don't have much of a problem with. And what's wrong with having bits of national character and individuality? Doesn't necessarily have to mean "foreign is bad" (although often gets painted as such). Personally speaking I find that often those little details and variations are what makes the world an interesting place, and I happen to value that more than an increase in functionality once I'm happy with the level of functionality (just my personal view of course).

 

It's subjective to say ID cards are sensible and rational... Not that being subjective is a problem in itself of course - you can rationally say objectively what is but when  you start talking about value, good or bad, it starts becoming subjective. And subjective, intangible things often get dismissed out of hand yet are absolutely crucial about how we view the world and our relationship with it. That is, I think, why we end up with clashing entrenched opinions, because of the way it all boils down to subjectivity - neither side can offer the other something it'll regard as an improvement, because to that other side it isn't.

[Michael Hodgson]

5 hours ago, Philou said:

 

Just as an aside, when I worked in labs at the Polytechnic, we had to make a freezing mixture (to be used to cool another experiment at negative temperatures) using rock salt and water and I got my mix down to -45°C - proud of that or what!

 

Cheers,

 

Philip

 

 

Ah yes.

Hear no Evil, See no Evil and Speak no Evil.  The famous three brass monkeys. 

[Dungrange]

Being born in the year that Britain went metric, it's what I was taught at school and am therefore familiar with.  I always think of temperature in Celsius (although Kelvin is the SI temperature unit).  I always think of weight in grams and kilograms and I think of volume in litres and millilitres.  I would never think of using imperial units of measurement for temperature, weight or volume and don't see imperial units as superior to the metric system: I generally view imperial units as an outdated legacy that will die out eventually.  However, when it comes to distance, I do find an 'inch' to be a useful unit, so whilst I still tend to measure things in millimetres when sawing timber, I also more often than not think in feet and inches when planning model railway layouts.  In my mind, the layout that I am building will be 15 foot long: it just seems more useful than saying it will be 4577 mm (yes the layout is actually 5 mm longer than 15 foot).  

 

Therefore, whilst some imperial units will probably die out within the next few decades, some will likely survive longer than others and I think feet and inches will be around for longer than most imperial measurements.

[Pete the Elaner]

1 hour ago, melmerby said:

A gallon (imperial not US!) of water weighs 10lbs

Therefore 4000 galls weighs 40000lbs. To convert to tons 40000/2240 which is about 18 tons, just as easy.

Mind you that is one of the few imperial measurements that are easy!

 

Sorry but dividing something by 2240 is not as easy as moving a decimal point & I really did do the conversion & calculation in about a second.

& what if you needed to be accurate? With imperial, you would need to do long division. By the time you'll have finished that, you would be well behind.

 

& I see we have more weird scale-ups:

16 oz in 1lb, 14lb in 1 stone. 160 stones in a ton to make 2240lbs?

Base 14? 

I am sure units of 14 & 160 have their history but they are simply poor to use.

A gallon is 10lbs. This seems to be why a UK pint is a cocked-up measurement: US pint is 1lb, not a 1¼lb as it is in the UK, which makes the US gallon 8lbs.

 

You are doing a good job of convincing me further that imperial is a badly conceived jumble of measurements.

[Reorte]

19 minutes ago, Dungrange said:

Being born in the year that Britain went metric, it's what I was taught at school and am therefore familiar with.  I always think of temperature in Celsius (although Kelvin is the SI temperature unit).  I always think of weight in grams and kilograms and I think of volume in litres and millilitres.  I would never think of using imperial units of measurement for temperature, weight or volume and don't see imperial units as superior to the metric system: I generally view imperial units as an outdated legacy that will die out eventually.  However, when it comes to distance, I do find an 'inch' to be a useful unit, so whilst I still tend to measure things in millimetres when sawing timber, I also more often than not think in feet and inches when planning model railway layouts.  In my mind, the layout that I am building will be 15 foot long: it just seems more useful than saying it will be 4577 mm (yes the layout is actually 5 mm longer than 15 foot). 

To be devil's advocate if you were doing it from scratch in metric wouldn't your layout more likely to be planned to be 5 m long, and some random-seeming number of feet?

 

Agree that the inch and foot is a useful size though, and that's one of the key reasons imperial has lingered on (it's telling that Farenheit has dropped out of favour faster than most others). The interval of 1000 in metric is rather on the large side for many applications, and the centi- prefixes rarely used, the deci- ones even less often (can't think of any other than decibels, even though quite often the decimetre might be handy). Intervals of 100 might've been a better standard, keeping most figures encountered in two digits.

[Reorte]

13 minutes ago, Pete the Elaner said:

I am sure units of 14 & 160 have their history but they are simply poor to use.

14's a poor one but 160 I don't think's too bad, other than being somewhat on the large size.

 

I'd be inclined to go base 12 if starting completely from scratch, i.e. could discard the effort of learning to count in a different system. With only three factors 1, 2 and 5, and fifths not being a particularly commonly encountered fraction base 10 is a little clunky, whereas base 12 has 2, 3, 4, and 6, giving convenient divisions of halves, quarters and thirds (and sixths and twelfths, not that they're all that handy).

[Philou]

1 hour ago, The Johnster said:

This sort of prejudice probably goes back to the horrors of the French Revolution and the subsequent Napoleonic wars

 

Well, the conversion to the metre was started BEFORE the French Revolution and Boney. It was an attempt to standardise measures in France as the peuple were getting restless at being ripped-off. There was the pinte, the pouce (thumb) and the livre (pound), but depending which town you went, they all differed AND if you were buying and selling grain for example, the pinte for buying was bigger than the pinte for selling, the difference being 'ker-ching' - PROFIT!

 

There is a book 'Measuring the Earth' that I can't find at the mo', in which two Surveyors Royal were sent out to do exactly that - measure the Earth - well the distance between the North Pole and the Equator along the 0° meridian and the 1/1 000 000 measure of that distance would be the metre. They set out long before the Revolution started and finished well after it was all over having been arrested as spies and the like in between times.

 

The nub of it was they didn't have to go all the way to the North Pole nor the Equator, but measured France from about Boulogne to the Med following a meridian (the 0° Meridian as we know it wasn't established until the 1920s - my French great-Grandfather was involved in that) and allowing for pesky mountains and rivers getting in way, they did it. I don't recall the exact measure they came up with but is was slightly bigger than the French yard (une latte IIRC - from which we have our lath and is also the Welsh word for a yard). Anyhow, the measures were erroneous due to wear in the instrument they used - the instrument was very finally calibrated but the mechanical gubbins weren't up to the job being mainly in brass.

 

The revolutionary government of the day decided to NOT go metric and put it on the back burner until Napoleon took it up. Unfortunately, the 'standard' metric length in platinum was a fudge and isn't the 1/1 000 000 distance that it was intended to be. Over the years ALL the physical weights have changed due to loss of surface atoms and changes in gravitational influences and hence they're now based on atomic wavelength measurements.

 

HEY!!! Wake up at the back!! I'm nearly done. Just to finish off, over here, you can still go into a shop and ask for a demi-livre of butter (250g).

 

And the imperial measures - and inch being the length of the king's thumb twixt knuckle and first joint, shoe measurements being based on lengths of barley corn and the Avoirdupois (literally 'have-some-weight') was based on the weight of a particular seed (IIRC came via the Greeks).

 

All-in-all, all of it is a right dog's breakfast!

 

(But metric is simpler to use but less flexible - consider: 10 is divisible by 2, 5 and 10, whereas 12 is divisible by 2, 3, 4, (6), and 12)

 

Oh, and the kids over here do not 'do' their 12 times table either that I consider pretty important.

 

Cheers,

 

Philip

 

 

 

 

[Dungrange]

1 minute ago, Reorte said:

To be devil's advocate if you were doing it from scratch in metric wouldn't your layout more likely to be planned to be 5 m long, and some random-seeming number of feet?

 

It would indeed, but then I ordered baseboard kits from Tim Horn and his standard ones are 610 mm, 915 mm and 1220 mm!  I had to get custom built curved boards for the corners, which is the reason that the layout is slightly longer than 15 feet, but although I specified the dimensions in millimetres, starting with a baseboard width of 610 mm was never going to give me a round number in millimetres.  Five metres would never have fitted the space available, but I suppose if I'd rejected the standard boards and got them all custom sizes, then I could have designed a layout that is 4.6 m long.  However, that would have cost more for no real gain.

 

It could also be that many items of 4mm rolling stock on my layout are near enough a foot long: Class 60 or Class 66 locomotive, Mark 3 coaches or various large bogie wagons.  A Class 158 unit is almost exactly two foot long and a Class 170 almost exactly three foot long.  It's almost as though one foot could be considered a standard unit length for a lot of my rolling stock.

 

 

[Philou]

..................... and before I forget as it was mentioned above, plywood sheets can be bought over here in 1220 widths (4 foot) and can be 2.4 (8 foot) or 2.5m in length. French plasterboard is BA13 (13mm) but measures out at 12.5mm (1/2 inch!)

[AndrueC]

3 hours ago, Reorte said:

For all the supposed complexity of the Imperial system most people who seem to complain strongly about it appear simply to not be used to it. It's generally easy working with whatever you're used to; quite often you don't change which set of Imperial units you use (e.g. inches to miles) so it doesn't really matter how many of one go in to the other. Funny how metric's advocates never seem to get worked up about 60 seconds in a minute, 60 minutes in an hour, 24 hours in a day, 7 days in a week, differing number of days in a month...

My main objection to imperial is that it's unsuitable for a modern global economy. There's too many units which are inconsistent in different jurisdictions. Ordering a 20 gallon tank from America needs care lest you don't get what you want. But I can order a 20 litre tank from anywhere in the world and I know exactly what I'm going to get.

 

Then there's the 'ounce'. How many types of ounce does the world really need?

 

And the multiple units is just confusing. Inches, feet, yards, miles..it's pointless complication. The metric system has only one unit for almost everything. Also everything is defined in terms of everything else. This means when doing a calculation you can simplify the units like you would any other expression.

 

I always thought it said a lot that when Mythbusters was doing a skit on something that involved acceleration or force they did it in metric. The rest of the time of course being American it was always imperial. I remember the skit they did about cooling beer in sand and that was completely ruined for me because I had no idea what temperature they were trying to get the beer to. Mind you it didn't help that I'm a wine and whisky drinker so don't really give a damn what temperature beer should be cooled to 

[AndrueC]

3 hours ago, Il Grifone said:

IMHO the imperial system became obsolete the moment the metric system was invented. (Perhaps if it had not been French?)

I'm not sure you can call it 'French'.

 

https://en.wikipedia.org/wiki/Metre_Convention

 

"The Metre Convention (French: Convention du Mètre), also known as the Treaty of the Metre,[1] is an international treaty that was signed in Paris on 20 May 1875 by representatives of 17 nations (Argentina, Austria-Hungary, Belgium, Brazil, Denmark, France, Germany, Italy, Peru, Portugal, Russia, Spain, Sweden and Norway, Switzerland, Ottoman Empire, United States of America, and Venezuela)."

 

And although we weren't signatories to that:

 

"British scientists, philosophers and engineers have been at the forefront of the development of metrication – in 1861 a committee of the British Association for Advancement of Science (BAAS), including William Thomson (later Lord Kelvin), James Clerk Maxwell and Joule among its members, defined various electrical units in terms of metric rather than imperial units, and in the 1870s Johnson, Matthey & Co manufactured the international prototype metre and kilogram."

 

I think that's maybe where my real dislike of the imperial system comes from. We've known it was a better system for over a hundred years (arguably two hundred years) yet it still hangs around like a bad smell. It's gradually fading and should be largely gone I think within twenty to thirty years (thankfully pretty much gone from industry now).

 

Railway modelling might remain a hold-out (in this country at least) simply because it's an 'older man's' game. But when you've got whipper snappers like me (54, lol) who prefer metric beginning to join in then I think its days are numbered.

Edited April 19, 2021 by AndrueC

[Reorte]

49 minutes ago, Dungrange said:

A Class 158 unit is almost exactly two foot long and a Class 170 almost exactly three foot long.  It's almost as though one foot could be considered a standard unit length for a lot of my rolling stock.

 

That's interesting in its own right, I'd never really perceived the significant difference in length of units!

[melmerby]

1 hour ago, Pete the Elaner said:

 

Sorry but dividing something by 2240 is not as easy as moving a decimal point & I really did do the conversion & calculation in about a second.

& what if you needed to be accurate? With imperial, you would need to do long division. By the time you'll have finished that, you would be well behind.

 

 

4.54 litres per gallon? Hardly moving the decimal point no easier than dividing by 2000 and knocking off 10% and yes I can do it mentally in probaly less than a minute.

Edited April 19, 2021 by melmerby

[Michael Hodgson]

2 hours ago, AndrueC said:

Ordering a 20 gallon tank from America needs care lest you don't get what you want. 

 

The Texans  are well known for their exaggeration. 

You can only get 9 gallons in a ten gallon hat.

[Michael Hodgson]

1 hour ago, melmerby said:

4.54 litres per gallon? 

 

Extremely convenient when I was driving in Germany and the litre/gallon rate was the same as the deutschmark/sterling exchange rate , as it meant their prices could be compared directly to ours.

[Dungrange]

1 hour ago, Reorte said:

That's interesting in its own right, I'd never really perceived the significant difference in length of units!

 

Well a Mark 3 body shell is 23 m long (75' 6"), which is close enough to 76' to give a one foot long scale model.  In the case of a Class 158 unit, the prototype has a car length of 23.21m (76' 2"), so when scaling that at 1:76.2 it comes out at almost exactly a foot long.  I know that 0.2 feet and 2" is not the same thing, but it's as near as makes no difference.  The Class 158 is a two car unit, so the model is two feet.  A real Class 156 is only a few inches shorter, so a little closer to two Mark 3 coaches, but still as near as damn it a two foot long model.  Most of the second generation DMUs use a similar length body shell. 

 

Locomotives are a bit shorter, but both a Class 60 and Class 66 are around 70' in reality, so scale to about 11" in model form, but if I think of that as needing a one foot length of siding, then it will fit.

 

Of course if I modelled the railway in the early Victorian era, I could get a three coach train on a foot of track!!  Scale speed would be much slower as well.

[Colin_McLeod]

What's wrong with the hundredweight furlong fortnight system?   

[Il Grifone]

3 hours ago, AndrueC said:

I'm not sure you can call it 'French'.

 

https://en.wikipedia.org/wiki/Metre_Convention

 

"The Metre Convention (French: Convention du Mètre), also known as the Treaty of the Metre,[1] is an international treaty that was signed in Paris on 20 May 1875 by representatives of 17 nations (Argentina, Austria-Hungary, Belgium, Brazil, Denmark, France, Germany, Italy, Peru, Portugal, Russia, Spain, Sweden and Norway, Switzerland, Ottoman Empire, United States of America, and Venezuela)."

 

And although we weren't signatories to that:

 

"British scientists, philosophers and engineers have been at the forefront of the development of metrication – in 1861 a committee of the British Association for Advancement of Science (BAAS), including William Thomson (later Lord Kelvin), James Clerk Maxwell and Joule among its members, defined various electrical units in terms of metric rather than imperial units, and in the 1870s Johnson, Matthey & Co manufactured the international prototype metre and kilogram."

 

I think that's maybe where my real dislike of the imperial system comes from. We've known it was a better system for over a hundred years (arguably two hundred years) yet it still hangs around like a bad smell. It's gradually fading and should be largely gone I think within twenty to thirty years (thankfully pretty much gone from industry now).

 

Railway modelling might remain a hold-out (in this country at least) simply because it's an 'older man's' game. But when you've got whipper snappers like me (54, lol) who prefer metric beginning to join in then I think its days are numbered.

 

It was invented well before then.

https://en.wikipedia.org/wiki/Metric_system

 

The spellings metre and litre give a clue. Americans spell them meter and liter, but the USA is the last stronghold of the imperial system (or at least their version of it).

Britain was to have converted to the metric system by 1975, but a change of government  got in the way despite our joining the (then) Common Market in the meantime. Our modelling scales (or most of them anyway) remain a mixture of metric and imperial. (Hornby Dublo started as 5/32" to the foot, but 5/32" is near enough to 4mm for the standards of the system....)

[Reorte]

33 minutes ago, Il Grifone said:

Our modelling scales (or most of them anyway) remain a mixture of metric and imperial. (Hornby Dublo started as 5/32" to the foot, but 5/32" is near enough to 4mm for the standards of the system....)

 

A mixture usually sounds irritating on the surface but if you want to model in metric it's not a bad idea when so much of the prototype was designed in imperial.

[meil]

Before you start down the road of scale speed you first have to define what you mean by "Scale Speed".

 

If you mean that a model traversing a scale mile in 2 minutes will be defined as travelling at a scale 30mph then that is one definition but it will not have any of the dynamic characteristics of a full size train travelling at 30mph. To have the dynamic aspects of a full size train at 30 mph you would need the model to travel at about 8 times the speed of the full size.

 

The issue is that you can't scale time and time is part of velocity and acceleration.

[DCB]

Scale speed the ratio of the scale, say 1:76  for OO, applied to dstance so should  a 1:76 scale loco cover 1/76th of  mile in one minute it is doing as scale mile a mnute or 60 OO scale miles per hour.

It is also the rotational speed of things like steam locomotive driving wheels, or the tempo of wheels over rail joints.    Unless it is Hornby O gauge all these are likely to be the same plus minus  about 10%.

I found years ago that timing trains from one place to another is fine,  if you are on the train. but actually

It's much easier to time the train passing a fixed point .

I did a chart  years ago, it works for all scales from 12" to 1 foot to  Z gauge,  just start the stopwatch as the front of the first coach passes the fixed point and stop it after a sutable number of coaches or wagons have passed.  Then consult the chart.  I have timed HSTs from the other side of the Exe from Exmouth, and loads of trains at exhibitions,  Ah Exhibitions, We had them pre covid.

[DCB]

On 19/04/2021 at 23:05, DavidCBroad said:

 

 

Edited November 10, 2023 by DCB

[Dungrange]

1 hour ago, meil said:

The issue is that you can't scale time and time is part of velocity and acceleration.

 

But that's not really an issue.  You apply a scaling factor to each unit separately and they don't need to be the same.  In the metric system, we measure distance in metres and time in seconds.  Velocity is therefore measured in metres per second.  If you have a 1:76.2 scale model, that means that the linear dimensions have been scaled by 1:76.2, but as you point out, time cannot be scaled: one second in the real world equals one second in the model.

 

We therefore have a model speed of 1 metre / second * 76.2 metres / metre * 1 second / second = a scale speed of 76.2 metres per second.  The same logic applies for acceleration.  One of my lecturers at university used to insist that every factor was written with it's units, including factors that were unity.

 

The issue is when you want to start looking at properties like inertia, which is measured in Kilogram metres squared.  The linear distance is scaled at 1:76.2, so area is scaled at 1: (76.2)^2, which is 1:5806.44.  The question is of course mass isn't scaled in the same way as the linear dimensions, because the model is made of different materials, with different densities and in any case it is only a model with an electric motor in it rather than a miniature diesel engine or steam pipes.  Whilst you could devise a ratio between model weight and the weight of the prototype, this won't be consistent across the model, with different ratios for each locomotive, coach, wagon etc.  So yes, if you want to start looking at the dynamics of inertia and momentum then it will get complicated, but a simple scale speed is relatively straightforward.

Edited April 19, 2021 by Dungrange

[frobisher]

9 hours ago, meil said:

The issue is that you can't scale time and time is part of velocity and acceleration.

 

Er nope. Time isn't the issue, gravity is...