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The Nth Degree

Fox Walker 0-6-0ST 2mm scale

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I'm going to use this opportunity to give this a go. I've been planning it for a while but, before I launch into a working model, I'm going to build a scale static model using as many of the techniques (but not materials) I will use on the working version.

 

I've never built anything before, beside a few Airfix kits, so this is going to be a STEEP learning curve - I have to learn to work in metal and to solder, and to confine everything to 2mm standards for my proposed micro layout.

 

I don't know what material I'm going to build it from yet. I've been looking around the house for suitable donor items but have not been successful. I have seen a set of cookie cutters that have been keeping a corner of a kitchen drawer occupied for a few years. I don't think they'll be missed...

 

Here is the drawing I made from an amalgam of prototypes. No photographs exist of the exact prototype ("John Owen" of W&CR) before it was upgraded by GWR. I have used a couple book descriptions to make this drawing.

post-11337-0-13932200-1331916142.jpg

 

And here is a basic list of parts to get me started on the raw shell. As you can see, a lot of shape forming is required on the saddle and smokebox. I will probably make a former of both using my drawings to get the exact shape I need.

post-11337-0-15690300-1331916310_thumb.jpg

 

I'm not a member of the 2mm SA yet (?) so will have to wait for the 7mm driving wheels and other detail components until I hear something, or ask a nice member to get them for me...

Edited by The Nth Degree

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Best of luck Nth - I look forward to seeing the model come together.

 

I'm not a member of the 2mm SA yet (?) so will have to wait for the 7mm driving wheels and other detail components until I hear something

 

Go for it, membership will be the most useful £20 you could ever spend for a project like this. :)

 

Thanks,

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I found a photo of what is claimed to be John Owen, as GWR 1385, but before rebuilding, in Part 3 of the RCTS Locos of the Great Western - Absorbed Engines, and I am afraid it is rather different from your drawing. Using this picture, and the much clearer views of the later incarnations on the "Steam" website http://www.steampict...nt/4039615.html et al, I have very crudely sketched the original and later forms.

post-189-0-78212500-1332104538.jpg post-189-0-95172900-1332104550.jpg

Original version, with long tank and flat cab front and back

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Go for it, membership will be the most useful £20 you could ever spend for a project like this. https://www.rmweb.co.uk/community/uploads/emoticons/default_smile3.gif

Good luck, I would second the comment above and join the 2mm FSA.

 

Thanks both, I have actually sent my application in a few weeks ago but have yet to hear anything. I've also emailed what I think is the membership address but no reply from there either. There is a remote chance that I will be able to attend Ally Pally show on Sunday so will join then to make sure the paperwork has been received. The post round here is not the most reliable, as I have found out before!

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I found a photo of what is claimed to be John Owen, as GWR 1385, but before rebuilding, in Part 3 of the RCTS Locos of the Great Western - Absorbed Engines, and I am afraid it is rather different from your drawing.

 

Nick, thank you for bringing that to my attention. I have that volume and had completely forgot that 'John Owen' is included in its original state, as taken over, on plate C161 and the rebuild on plate C162, as you have drawn. My version was based solely on descriptions in the text and the description from another book I have. Obviously, I've missed out quite a bit of detail from the engine but the cab is, as you say, quite different. The boiler also sits lower on the footplate and is the same length but about 8" smaller diameter.

 

This really is an exercise of my abilities rather than a definitive example of the prototype at this stage, but I absolutely take your point. I will redraw it (which will probably make it easier to build!) and start with a card or paper version to check primary reference points before committing to anything more difficult to work in and rectify.

 

Once again, thanks for taking the time for the drawings and letting me know.

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Thanks both, I have actually sent my application in a few weeks ago but have yet to hear anything. I've also emailed what I think is the membership address but no reply from there either. There is a remote chance that I will be able to attend Ally Pally show on Sunday so will join then to make sure the paperwork has been received. The post round here is not the most reliable, as I have found out before!

 

Maybe I will see you on Sunday then. (I'll be on the stand at least half of the day)

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I'm also going to be on the stand on Sunday, so look forward to seeing you there if you manage to make it.

 

A few thoughts on the design concept:

  1. I would expect weight (lack of) to be a problem with such a small model - one possible approach is to make the chassis from solid brass (subject to an insulating gap needed for split chassis electrics). Alternatively pour molten lead into all possible crevices - not "liquid lead", consisting of small lead balls, which is only about half as dense due to air gaps.
  2. I think the 2mm shops will be busy stocktaking at present, so probably won't welcome any orders. From my last order, they currently appear to be out of stock for some of the muffs you will need (depending on which gears you use), also for the PCB spacer based on the website stock status.
  3. If your stepper motor plans don't work out, then the Nigel Lawton micromotor is probably small enough to fit into the boiler, though it is high-revving and would want fairly high gearing. Alternatively it should be possible to use a larger motor in the cab, though that would be a bit obvious with such an open cab design.
  4. When your membership finally comes through, you can download from the Members section of the website the "Building an 0-6-0" booklet. Though it is based on a 30 year old article, and some of its ideas are outdated, you might find some parts fit your concept better than the "conventional" approach.

David

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Thanks David. I reckon I'll need some sort of machine workshop to carry this out properly. I've thought about milling the whole frame section out of solid (split) material, leaving a cut-out for a gearbox on the front axle. The axels themselves would be solid perspex (or similar) with pick-ups on the bushes/bearings of all axles. The motor and electronics would be mounted inside the boiler tube, while the saddle would be filled with solid material (probably a brass shell filled with lead). The combine weight of the solid chassis and the lead saddle would be ample to pull a 4-coach train or 6 wagons.

 

To insulate the frame section from the bodywork, I would have to make the footplate from a non-conductive material (perspex?) and attach the bodywork to this. I don't really know what the traditional way of making chassis' is so I'm using Steve-Logic®. It's a bit like common sense but has no basis on experience...

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Perhaps I am misunderstanding you, but your proposal to use "solid perspex axles" suggests that you might be missing the usual concept for split-chassis in 2mm. The usual method, for which components are readily available from the 2mm shops (subject to intermittent out-of-stock problems with particular sizes), is to use metal "half axles" (actually slightly less than half-length) which are integral parts of metal wheels, inserting two such half-axles into opposite ends of a non-conducting muff (plastic of some sort, I presume).

 

The rest of your proposal sounds sensible to me - but as I am still part-way through my first locomotive builds don't regard me as an expert.

 

David

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Hello David, no you didn't misunderstand, that is exactly what I meant. From my point of view, and taking a completely fresh approach, I don't understand why I'd have to use absolutely massive plastic muffs when I could use a narrower diameter non-conducting axle and take up less room in an already cramped chassis. As long as the conductivity between the wheels and the bearings is sufficient to carry and transfer the current to the split-frame, that would be all I need to produce a solid chassis, leaving sufficient space for a cog to turn on the front axle. I'll try to draw a plan of what I'm trying to say later tonight but it makes sense to me.

 

I don't have the benefit (or hindrance?...) of existing designs or theories so I'm doing what I think is good and sound logic to save as much space as possible in this tiny space. However, I am ready and willing to be corrected if I'm wrong!

 

Regarding the stepper motor, as long as I can get as many micro-steps (8 would do but 16 would be better) as I could within a processor that's small and cheap enough I would completely avoid the need of any reduction gearbox at all, relying on precision control and increased torque (generally) from stepper motors. This route would unavoidably be DCC but I could live with that (DCC because the processor/controller would need a constant supply).

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Split frame chassis is intended to simplify pickup, using contact between the half-axle and bearing. I don't think that contact between wheel and bearing would be reliable, so you would probably have to add some form of "wiper" from the chassis to the wheel. Try both approaches and see which one works best for you.

 

One possibility that might be worth investigating, though I am rather sceptical whether it would work, is use of aluminium for axles - this is conductive in its "raw" state, and insulating when "anodised". Unfortunately I think it is only a surface treatment, but perhaps you could anodise the surface of one half of the axle - thus half the axle would be "live" and provide simple current pickup, halving the requirement for wipers. There is some mention of anodised 2mm axles here in the context of "dropin" wheelsets for diesels.

 

The stepper motor sounds like an attractive approach, and I hope that you can get it to work. I can see that elimination of the gear train would avoid the rather substantial power loss that usually generates, but would there be enough torque from the stepper motor? In a conventional gear train, you start with a high rpm/low torque input from the motor and arrive at a lower rpm/higher torque output at the wheels...

 

David

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Updated plans, thanks for the reminder Nick. This time they should come out as 1:1 scale drawings (as a reference, the loco is 42mm between buffer beams). Excuse the garish colour coding - purely for my reference.

 

And thanks for the info David, very interesting! Had no idea anodising would effect electrical conductivity. Stepper motors use PWM so the full current is sent to the motor in very short bursts. This, combined with up to 200 steps per revolution, makes them very controllable and have a much higher torque than a conventional motor of the same size.

post-11337-0-63613300-1332291868.jpg

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Nth Degree,

I have no experience of anodised axles as such, but in my other hobby (Radio Controlled Car Racing), some of the parts in my car have a Tri-nitride coating to reduce friction - typically though this coating does get worn away, although it's ok where it passes through a plastic bushing in the shock absorbers for example but on the hinge pins for the (carbon fibre) wishbones the coating does get worn off (probably by minute particles of grit between the surfaces, and possibly because carbon fibre is significantly harder (and rougher) than plastic.

 

Obviously an axle will be a rotating part in a hole, so I would expect some degree of wear (even in an oiled bearing) leading eventually to a short.

 

Ian

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Guest Natalie Graham

Are the Peco Insulaxles for bogie wheels still available? They had an insulating coating on them.

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Are the Peco Insulaxles for bogie wheels still available? They had an insulating coating on them.

 

I think they were anodised.

 

Andy

Edited by 2mm Andy

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Looks like a great project!

I don't want to be difficult - but I think you should look again at the Stepper vs. DC motor decision. Stepper motors, size for size are by definition less powerful, and have lower stall torque than DC motors. A switched reluctance motor (such as a small stepper motor) has multiple windings (sometimes known as phases - although this is incorrect terminology but in some designs they happen to be the same thing). In any one position one (or two if half stepping) windings are active. As a result only a fraction of the total volume of the motor is doing useful work at any one time. A brushed DC motor has 1 winding, which is on when the motor is on - so 100% volume of the motor is doing useful work. Therefore, a DC motor will (almost) always outperform an equivalent stepper - even at low speed. The trick is to get one with the right I-V characteristic for your application so that it won't overheat if you want to run it near stall (slow).

Also, there's nothing to stop you from using PWM control of a DC motor - in fact it's by far the most common way of controlling them in the real world, and how DCC systems do it.

Good luck.

 

PS anodising will probably wear off - if you're planning to use it to insulate between two surfaces that are rubbing

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Rabs, firstly, thanks!

 

Secondly, although I'm no expert, my understanding of this technology is that for a given size of motor a stepper motor is more powerful than a conventional DC motor. This is because a stepper driver by nature is PWM, thus provides 100% power at micro intervals and so induces a positive response on each pulse. By contrast, a conventional motor Is unreliable at maintaining speed and control at low power by the nature of their design (they are typically high revving because they are unstable at lower speeds).

 

Of course, I could opt for a PWM-driven DC motor but, in this case, I would need to sacrifice a huge amount of space for a reduction gearbox suitable enough for a small high revving motor of the type that could fit in this loco design.

 

Anyway, all of this aside, I won't be persuing motorising this particular project just yet. I've got someone looking at a micro-stepping driver design for me that would take cues from a DCC controller - they talk the same language so it's just interpreting the intent that's the problem. In fact, the biggest problem is providing enough steps to provide smooth motion and dumping excess heat in a very small form factor.

 

Essentially, there are two conversations happening here; this project and a future one. This particular project is to see if an office-based, chair-warming, pen-pushing absolute beginner who can barely make his own dinner can make something they want but can't buy. This is the first step.

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my other hobby

 

Thanks Ian. Ahh, the memories! I had a Tamiya Scorcher (?) the VW Baja Bug years ago - loved it! Technology has moved on quite some way since then!

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I've had very little time to work on this so far but here is a small update. I printed out a 4mm scale version to test build and can see I'll have to make some edits to the final files already.

 

Bending the boiler/saddle is next.

 

Oh, thought I'd stiffen the paper by glue-laminating it to card. Big mistake - it warped all over. I've straightened it best I can with a kettle.

post-11337-0-44909800-1332530231_thumb.jpg

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This is as far as I'm going to go with the over-sized card model. There are a few adjustments to make then I'll make a 1:1 paper model for a final check. Gratuitous coin shots below.

post-11337-0-56049000-1332542892_thumb.jpg

post-11337-0-48648600-1332542916_thumb.jpg

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Small update on the plans. There's a lot of detail to be added still (brakes, tool boxes, pipe-work, railings, buffers, couplings, not to mention the motion and valve gear) but I will do this mostly off-plan. I will also add some tabs to help fix components onto the footplate. Thanks to Nick who helped with some frame details.

 

I'm quite envious of Wordsell and Natalie who have experience and confidence (and tools!) to jump straight into cutting metal.

post-11337-0-45608500-1332794681.jpg

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Small update on the plans. There's a lot of detail to be added still (brakes, tool boxes, pipe-work, railings, buffers, couplings, not to mention the motion and valve gear) but I will do this mostly off-plan. I will also add some tabs to help fix components onto the footplate. Thanks to Nick who helped with some frame details.

 

I'm quite envious of Wordsell and Natalie who have experience and confidence (and tools!) to jump straight into cutting metal.

Looks a nice project. Don't worry about what the others are doing. You will gain experience and grow more confident as you progress. A very big well done for starting in the first place. My first scratch build was hidden from the world. I would of been very reluctant to start the way you have. Good luck I will follow with interest.

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You're very kind Peter, thank you.

 

I've been studying the photo I have of this prototype tonight and have made quite a few small changes to the plan. I've also discovered that the boxes on the sides were also coal bunkers. They're called cab bunkers and supplemented the small rear bunker. Some industrial locos didn't have a rear bunker at all and relied on these cab bunkers entirely. I didn't know that.

 

When I've finished with these (I'm going to make two for my layout) I would love to make that loco in your profile pic - it is the cutest thing I've ever seen! What is it?

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