In the last post, I threw in the phrase "proof of concepts" or however I spelled it that time. What is a proof of concept in this case? At work we model solutions to real world business problems in software and use proofs of concept to see if the conceived solution will meet expectations without being required to implement the whole solution. For this Christmas project, I wanted to try a few things I had either not done or only done to certain levels.
My last project was in HO scale and saw me making an "up and over" double loop that meant I had built my track raised off the plywood base for the first time. The Christmas project requires the track not to have grades (as the HO up and over does) but to be well clear of the solid base to allow the scenery to fall away from the track so that I could do something I had not done before: build a trestle bridge. In a way, each model project is a proof of concept but some things require a small trial run before building a bridge that scales out to many hundreds of feet long.
When modelling, we are trying to represent reality. In software, this means we have to cover all the required business rules while allowing the end user to work in a way that makes sense, is logical and comfortable. In model trains, the aim can differ from scale to scale but overall it is to show railroading in miniature. In the largest scales, this extends to the function, particularly of the locomotives:
- Many large scale diesel-electric locos have an internal combustion engine that drives a generator that powers motors geared to the wheels, just like the prototype.
- Large scale steam locomotives have an operational firebox that heats the water in the boiler that expands to push the cylinders which move the motion to turn the wheels.
Would that modelling was a simple case of putting real world objects in a "reducer", twisting a dial for the desired scale and out pops an exact detail but smaller version of the real thing. Whilst it is frequently possible to obtain smaller versions of the materials or components that make up real world objects (tubing n smaller sizes, thinner plate materials, and so on) certain aspects do not scale. The most noticeable are strength and weight. Some of this comes down to the physics that make it unlikely we will ever have a "reducer" as described above: the space occupied by an atom is largely made up of the electron cloud (not going beyond my high school physics as sub atomic particles are not required to explain the dilemma) which cannot be compressed as its size is dictated by repulsive forces which, as far as I know, cannot be changed.
This is why a model of locomotive 3265 that is 1/160th the size of the real thing it is modelling does not weigh 356kgs while being only 11.4 cms long! In a way, it is good for my bench work and back this is not the case :-) The other aspect of materials important to modelling is that the smaller they are, the less strength they have to the point of failure. This means that a model handrail that is able to withstand general wear and tear will be thicker than it should be in the smaller scales where materials reach their limit and snap or break. Sometimes changing materials allows smaller and thinner representations but even if you used single strand carbon fibre in models, you would still reach a limit, though in this case it is more likely to be one of cost.
So in the smaller scales, certain things will appear fatter or thicker than they would if the model were a simple reduction of the real thing. It was mentioned above that large scale models follow the function as well as the outward form of their prototype. N Scale live steam models are rare and tend to be done to prove a point more than as good way to power such models. Most N scale models, then, are built to look like the real thing rather than be the real thing in miniature.
So to the trestle bridge. What does a real trestle bridge look like and how where they built? The Internet can be your friend here in terms of how others have done it as a model and photos, plans and drawings of the real thing. Most examples on the net I found were larger scale, O or above, so what I ended up doing was the same, only different. The question the proof of concept was to answer here was, "Can I simply build a bridge that is strong enough and looks right just by following the techniques the original bridge builders used?"
The answer seems to be yes, sort of: in the place of bolts and other fasteners I have aquadhere, but otherwise, the proof of concept was built using a suitably reduced printout of the plan labelled "Standard Trestle Bridge, California Central Railway." Templates for the bents (upright bits that go between the ground and the track) seemed to be the key to having the bridge look right every time. Instead of the usual wood block formers, I used pins with the heads trimmed off. Balsa wood from my friendly Riot Arts & Crafts store made up the bents which then had diagonal matchstick braces to space out and separate the bents.
What did I learn from building the proof of concept?
- Templates are your friend (I guess frameworks would be the software equivalent)
- Some things can be built using the same techniques as the real thing, it helps that trestle bridges were meant to be quick and easy to build when you wanted to cross a gap. Strength on the real things was not their...strong point. Speeds over trestle bridges tended to be limited and don't be up there when it's windy!
- Soaking wood in strong cold tea makes it a lovely rich wood colour: darker than balsa or matchsticks really look BUT don't soak glued parts, they come apart :-( That is another reason proofs of concept are good, if they break, less tears are shed and it can be easier to get back to something that works
- Only use as much glue as the joint needs else it runs and splodges everywhere
- All structures are just assemblies of smaller parts, no matter how intricate or complicated they look. Have a go, start small, work up, and eventually you can build the whole thing.
A long post this one and some physics and perhaps philosophy, but now to the pictures; the template I used and the trestle bridge proof of conept
No comments:
Post a Comment