Is there any literature on developing plans for a model from scratch?

As per the thread title really.

I have debated making some live steam models for a while, but with a history of working on heritage steam it doesn't really excite me...  Nevertheless I have the itch to build something which isn't a sub-assembly or component, but is complete in and of itself.

I'm currently coming to the end of the design phase for a Horizontal Boring Mill which I originally envisioned being a ⅜ scaled working model of a TOS W100A but due to cost constraints and the practicalities of making a functional machine tool, will be entirely it's own thing.

Once I move on to building it, I will have the headspace to start designing something else, and I'm drawn to making a model of a Vicker Vigor / VR180 (for the uninitiated: a very strange, and unreasonably fast 1950's bulldozer made with spare parts from WW2 era tanks).

It strikes me that the inherent ergonomic and operability issues with scaling something like that down are much the same issues that everyone who builds model trains for 5" or 7¼" gauge face in terms of needing a to create human scale seating and controls, whilst maintaining the aesthetics of the model.

My thoughts so far are that it should be small and light enough to fit on a standard plant trailer, use standard rubber tracks from a widely used model of mini/midi excavator, and use a standard diesel-hydraulic power-pack in the 45hp-80hp region which is well supported (probably Yanmar/Kubota).

Those constraints give me a starting point, but I can't really design off that alone, without giving consideration to where I will sit and how to arrange the controls given that's going to impact how I package the hydraulics and gearbox (if I choose to go direct drive), which will in turn dictate the power transmission to the final drive.

Which gets me back to, has anyone written articles or a book on how to work through these design challenges in a sensible order to prevent me from finding myself in an endless cycle of designing and re-designing things?

Edited By Jelly on 05/03/2023 21:57:27

Which CAD program have you been using for your design work?

I default to Solid Edge CE, but have the option to use Siemens NX, AutoCAD or Fusion360 if it's called for.

Do any of them have the ability to change the rest of the design if you change the size or location of a part?

As you constraints are already a compromise from a full scale replica by quite along way have have a bit more choice about how you will drive it.

Most tracked scale models I have seen tend to be made to a smaller scale and if not radio controlled then it's a case a knocking them into gear and walking along side.

In the larger scales its a case of doing like many of the traction engine drivers do an arranging a seat that hangs off the back which would be more practical than a separate driving truck being towed behind. Also depends on the state of your back and how far you can reach forwards. Radio control would still be an option just like you see a Hiab o stump grinder being controlled but less fun than being able to rid eon it.

I can see where you're going with that, One way or another all of them have that functionality, and SE is probably amongst the better options for it too.

No foolproof but definitely worth the time investment to set up, the parametric relationships between parts during initial design.

I've only been doing CAD for 8 weeks but I'm getting there

At sea oversight plans were called "General Arrangement of..."

I don't think a book would help you. Being a designer all my working life in a few different fields you start with what you know, ie your power unit as you seem to know what you want to use, and work out from there. Use photographs to give you the exterior outline ideas then work out what goes in between. Design is all about working things out to give you an end result, the mathematics of scale is all part of it. You start with a sketch or series of sketches outlining what you want and work in from there. The cad system you are using is just a tool to create working drawings so the system you use doesn't matter so long as you are confident in it. The drawing time can be a long process, especially if you are only working on it a couple of hours here and there.

I guess I have already compromised on having a true scale model by wanting it to be somewhat functional, as modelling the engine to scale would result in a power pack with really weird characteristics that would (probably) not develop the required torque; (not to mention the amount of pattern-making required to replicate that RR inline six block).

If I'm willing to fully sacrifice how true to life it is in terms of mechanicals a bit further and go for the approach of producing a functional visual replica, then it would allow me to use a hydraulic drive system, which gives back a lot of space for the operator and controls.

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When I began idly thinking of this, I was considering 6" or 4" scale, and having worked through some numbers, it seems like 6" scale would be sort of do-able and should result in a trailer-able sub 3 tonne "model" with enough room to have the operator inside the track footprint.

4" scale would actually fit within the bed and GVW of my pickup (just) but would need to be RC to avoid the risk of legs being in the pinch zone of the blade hydraulics; and wouldn't really have the weight required to put it's tractive effort down and actually doze anything other than loose sand/aggregate, which would be sort of a shame.

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If I do go down the hydrostatic power route, the next logical step is to go looking for a donor vehicle to lift motors, final drive and control valves from so I know the dimensions of key parts which I wouldn't be building in-house.

Looking more at the material which is out there about the Vigor, I am beginning to suspect there might be merit in deciding to make my own tracks rather than use COTS rubber ones, as the christie type suspension flexes far more than any modern track system... But I can sense how thankless and expensive a task that would be from several years away!

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I do suspect I sound completely nuts even by ME standards.

Not really nuts I've seen quite a few, the Germans tend to make Lanz ones, the Italians small tracked Fiats and the popular one in the US is the Holt 75, though not a dozer it's still tracked. though these tend to be a bit smaller at 2-3ft long.

Nice Fiat 55L build photos on this site and the finished model

I suppose a tracked Bobcat would be a good donor machine and make it outline or stand off scale rather than a full replica. Watch where you can use all steel tracks, may beed rubber inserts at the least but making your own is quite common at least in teh smaller sizes.

Edited By JasonB on 06/03/2023 11:21:06

Edited By JasonB on 06/03/2023 11:22:48

I have about a decade of design experience building and modifying chemical plants (with a smattering of toolmaking and architectural joinery thrown in because my career history is a little odd), but the constraints there are generally very different to a mechanical product like a tiny plant machine... There's no analytical method for developing a comfortable control layout or making greasing points easily accessible and so on.

I think you're probably right that nothing I take from a book is going to replicate just working through the design process systematically, and it's very clear that the constraints I have developed:

• off the shelf power pack,
• accommodates the operator on the machine,
• doesn't weigh more than 2800kg,
• is actually capable of working as a (tiny) bulldozer,

completely over-ride any considerations of accurately producing a scale model, so it becomes more about aesthetic design of the visible components.

It's more the 6" scale and functional elements that make me wonder if I'm coming unspun...

A larger skidsteer (even non-tracked) could be a viable donor machine, I think I need to go have a chat with my local second-hand plant dealer about giving me a call if they get suitably sized non-runners in before they start parting them out.

Thanks so much Jelly for solving a mystery of mine. In the early 60s when I was about 4 or 5 I had a remote control blue plastic bulldozer. I think it was second hand but even at that age I could appreciate it as a lovely bit of kit and my first introduction to electro-mechanics. Although it was designed to run off those big block 4.5V screwed terminal Eveready batteries, my father converted it to run off the mains, so I had endless hours of fun with it. As I was able to adjust the voltage to something much higher than the battery would have provided the tractor was able to do some real work !

I had never forgotten that toy and in recent times wondered what it was. All I could recall from the depths of my mind was the name 'Vidor'. I decided this must be the well known battery company who must have sold the toy as a marketing opportunity. As soon as I read your reference to 'Vickers Vigor' I knew this was the name of the model I had. A google search has thrown up lots of images for me that have really stirred my memories of its construction and detailing.

I'm so pleased I read your post now !

Gerry

Design is the most difficult part of engineering because all options are open. Materials, technologies, shape, size, ergonomics, appearance, cost, strength, performance, and a host of other decisions like is it going to be bolted, soldered, brazed, welded, glued. riveted or clipped together!

I see the design process as eliminating options to get to the goal. The starting point is defining the purpose, because that eliminates many alternatives. If the purpose is to hammer in nails, don't make the striker out of cheesium, true from toffee hammers to nail-guns.

The purpose is usually a long list of Requirements, divided into mandatory and desirables. Important to get the requirement correct at the ouset because the cost of fixing mistakes multiplies by 10 at each stage.

In theory design should be "top down" rather than "bottom up". The idea is to get the big picture correct before tackling details and not letting trivia steer the design. Top down favours team work because parts of the design can be farmed out. Most modern design is multidisciplinary teamwork. Barnes Wallis, b1887, d1979, said he felt lucky to have started at a time when it was still possible for an individual to design an entire aircraft. Not how the Wellington was designed: in 1932 Barnes Wallis led a large team who implemented his 'big picture' vision, and he didn't have much input into complicated sub-systems like the radio installation, or what Rolls-Royce did with the engines.

In practice, a singleton or small team, can benefit from a "Middle out" approach. Details may have to be solved first, and perhaps the requirement has expensive low-value features, or the design process revealed a too-good-to-miss opportunity. The trick is maintaining control: all too easy for projects to drift off course, or lose touch reality. Top down is best practice, but it pays not to be too purist!

Design being hard work liable to go wrong, designers should reuse standard components and designs as much as possible. Modellers are in the happy position of being guided by the prototype. LBSC didn'tt have to derive the shape of his locos, or tackle much from first principles. He didn't have to invent the multi-tube boiler, injector, regulator, pressure gauge or valve-gear from scratch. "All" he had to do was scale full-size designs down in a way allowing them to be assembled a small workshop, and then add the "words and music" enabling an amateur to build one. Not trivial and LBSC designs include many modifications to get reasonable performance out of his engines, including a giant perched on the tender to reach the controls!

As full-size and model design principles are so similar, there are plenty of books. I favour those written before about 1960 because they tend to be less academic, but many have been updated, helpful for things like FEA. Shigley's Mechanical Engineering, 8th Edition (2006) .

I don't know of any books on model design. I have one with a promising title, but it's actually about models for testing full size designs. Interesting, but not model engineering as we know it.

In Jelly's case, I suppose the first requirement to nail down is whether or not he wants to ride on the model.

• If riding-on the design problem is carrying the driver's weight, with a certain degree of comfort, so he can see where he's going, and positioning the controls so they can be operated properly. Is the driver a slim, agile, 12 year old, or a creaky left-handed 6' 5" pensioner who has eaten too much cake? The controls can probably copy the original layout, tweaked and extended to improve access.
• If remote controlled, all the driver on-board problems disappear, to be replaced by other issues. Radio Control is a possibility, but servos have to arranged to drive the model's controls safely. Working controls whilst walking alongside with a stick is a simpler form of remote control, but introduces other issues, like a model that moves faster than the driver!
• Computer control is a possibility. The model runs to a program, but senses obstacles and stops if necessary. Could be combined with a remote "dead-man's hand" where the operator can stop and start the machine manually, and the machine stops if the signal is lost.

Considering options, the designer has to watch practicalities. A mechanical engineer able to build a ride-on model, might discount computer control because he doesn't have the necessary skills. The contents of my junk-box often constrain what I do!

CAD is a powerful design tool, not magic, more a "power assist". The designer still has to know what he's doing. CAD build the design as a 'virtual' object, existing realistically inside a computer, by understanding most of the rules that apply to the real object. Saves lots of time by highlighting interferences, impossible configurations, weaknesses, assembly problems, part mismatches, over-weight etc, that are very difficult to see on paper. Sadly CAD is skilled work in it's own right, taking time and effort to learn.

Dave

Jelly

You seem to vaguely know what you want. One system of working would be:

1. Write a specification to cover as much as possible
2. See what others have done. Try to understand their failures and successes. This means talking to people (and not being swept along by their enthusiasm), getting and understanding design details including drawings and so on.
3. Note your capabilities (CADs, workshop tooling etc).
4. Start designing. Take note of everything required (materials and tools). Work out how you are going to make items, what castings to buy etc.
5. Review your progress and, if necessary, return to any of the above steps.

At some point you will stop, fed-up with the above. It may be after a few days but could be months. Ideally you will know what you are going to do including what is needed (tools, material etc).

I suspect I may have answered a different question.

JA

The world of engineering is littered with the beautiful corpses of unfinished projects

So you're the person who's been peeking through my workshop windows!!!

I think most points have been covered but the one I have learnt by bitter experience that means my model steam-wagon is over a decade behind any sensible "schedule" , is that you do need think a long way ahead, of many possible consequences.

Not my strong point! Hence my often re-making or at least altering parts made ten or even twenty years ago, because I could not foresee what would happen if I make this bit that shape rather than the other.

One trap I fell into many times was over complicating parts, leading to messy, un-prototypical things that just wasted steel, electricity and hours of work.

Another was putting assemblies in locations that years later, make it hard to locate others. For example I am trying to design its two-speed transmission cramped by the driving-chain and the engine-case, and driven by a crankshaft I have unwittingly designed and made from solid, a good couple of inches too short..

'

This is where design come is, and I mean design not just drawing.

It does not matter if you use pencil and paper or CAD. Each, the alternative to the other, is valid in its own ways, pros and cons; but still a means to an end, not the end itself. My prototype's 1908 design was drawn using loose tee-squares on elm boards, and I now use both paper sketches and orthographic drawings (but not 3D ones) in TurboCAD.

If you are already skilled in either you have a head start but you still need understand your objective and source information. If like me you have no more than a few old photos of the exterior you have a lot of designing to do. CAD does score there even in 2D, if only by speeding up the drawings and making them easy to modify. It still does not design the thing for you!

'

I have seen no texts on designing miniatures. Lots on the metalworking skills, yes; a few books about materials, gears and the like; little or none on how to design entire machines replicating ones built many years ago.

So, in the absence of original works drawings or at least full service-manuals for the prototype, what you can very usefully do is seek "full-size" general engineering text-books of the prototype's era.

In my case, my oldest book is of 1911 vintage, so pretty well contemporary to my project; but most are of 1930s vintage. Their value is of showing how things were proportioned and joined, bearings were made, parts secured to shafts, etc; in the era of interest.

'

You do as others say need consider how you will drive it, and if you need ride on it, you risk having to compromise its static show appearance, to accommodate you for operating. A tractor or bulldozer, like a traction-engine, has its controls at the back so that you might be able to drive it from a trailer. That video of the Hornsby engine shows a full-size driver on a cantilevered seat is not a very stable combination. A model steam-wagon, or any sort of lorry, has to be large enough for the driver to sit on it; and my thought is to use its fully-planked platform for static display but a special, pierced, one for driving from.

@@@@@

Incidentally I don't know who owns it now (the one named at the end of the video?) but that Hornsby tracked steam-tractor and its wagons, in the video shown by Jason, were built by Steve Baldock, of the Model Steam Road Vehicle Society. He registered it for road running, but as it is tracked he had to take an extension driving-test. He reported that the examiner was so impressed and intrigued by this vehicle - unique in both prototype and model and rare for having wheel-operated steering - that he had a go at driving it himself! A peculiarity not obvious in the video, or has been ironed out by track adjustment, was that it put only the middle four or five treads flat down at once, giving it a strange pitching tendency in motion. The original was built for hauling goods between the harbour and gold-mines inland, in the Yukon; and sprouted a large, enclosed cab for the weather conditions there.

A bit off topic but have you posted anything about this? Sounds very interesting

I haven't because it's still sort evolving and I have some other projects to finish before I start working on it in earnest, which will give me an opportunity to prototype doing some of the more awkward bits.

I'm also still resolving between getting castings made or fabricating certain parts as a design decision as well.

I will probably start a build thread when I get underway in earnest.