Rabs

It's finally coming together: All but two boards assembled and ready. I like this shot - I can finally start to get an idea of what the view down the line is going to be like. The last couple of boards are cut and ready to glue together. Then I'll have to find somewhere with enough space to set it all up because it won't fit in the workshop!

Thanks for sharing this. I actually spent some time experimenting with diamagnetic materials at the nanoscience centre in Cambridge a few years ago so I'm familiar with it. I'm afraid that I have to disagree on this one. Bismuth has a lower diamagnetic coefficient than pyrolytic carbon, it's harder to form into a sheet and it has significantly more friction on most plastics and metals. The ideal thickness is ~0.8mm, which is too thin to cast in a mould because the surface tension of molten bismuth means that a minimum wetting thickness is about 3mm. Rolling a sheet would be possible but I don't have the tools to do this at home. Alternatively, if I can find a suitable flux then I could cause it to wet onto a sheet of another metal. I may come back to look at this if it proves necessary but for now I'm going to see how far I can get with carbon. Thanks for the help!

I've been experimenting with a variety of different materials. Bismuth (highly diamagnetic) is available in pellet form on ebay quite cheap but I've not been able to form into a flat sheet because I can't find a flux that will work with it. Plain graphite sheet is cheap and available from RS but only very weakly diamagnetic (that's what this video shows). I suspect that most of the benefit is from reduced friction rather than any significant diamagnetic levitation. Finally Panasonic do a pyrolytic carbon sheet branded as PGS sheet, available from most electronics distributors like RS and Farnell. I've ordered some to try with but it's not arrived yet. It's quite expensive (£15 for a 10cmx10cm sheet) but it should be strongly diamagnetic and roads in N are only small. In fact I don't think that the diamagnetic layer is really necessary, but it does help to reduce the current needed. I think that the ideal spacing for the traces will be approximately the same as the diameter of the magnets used. You're absolutely right about connecting the coils in banks so that each line doesn't need to be independently switched - I plan to do something along these lines. I was planning to do turning by having two magnets of opposite polarity at either end of the vehicle, so that they can be separately controlled. The wheels on that lorry don't rotate, in fact they aren't even touching the surface but are riding a fraction of a mm above.

Yesterday I tested the first electrical and track connections between boards. Electrically everything works well and there is no wobble as the loco crosses the join. One bit in the middle of the right hand board that needs smoothing out but that's not an issue for now. Now that's all checked it's time to get on with tracklaying on all the other modules!

I'm not dead but sadly I have had almost no time to work on Bath since March. This afternoon, however, I had a chance to have a little play with something that I've been thinking about for a while. A few months ago I came across this: And I thought that the same idea could be applied for moving road vehicles in scales too small for on-board motors. It would also be significantly cheaper than things like the Faller car system. On doing some digging I came across this: http://spritesmods.com/?art=magnmicrobots (the next button is fairly inconspicuous at the bottom, but it gets interesting about 3 pages in) So how hard can it be? I tried a similar basic test, but with a diamagnetic carbon layer over the PCB. Simple 1D motion with a 2mm vehicle works quite well: I'm going to design a PCB made which can do 2D motion and drive the vehicle around corners. Also, with electronic control of switching between traces I will be able to make the motion nice and smooth by using something similar to stepper motor microstepping.

I would have thought that a couple of spots of epoxy would do the trick. Enough to hold it but not so much that I can't break it off later. That's what I'm planning to do with mine.

Another thought, looking at your photoshop pic. Is there an opportunity for you to use this for this year's RMWeb challenge? Seeing that 'enormous' chain in front of shot got me thinking.

In my opinion your design change is an improvement - not a compromise! I love the idea of getting a view inside the works. The Farthing layouts are among my favourites and I can see that, with your new design, you could use some of the same tricks to make a really interesting model.

Almost finished gluing up the three new modules now. Here is the skew bridge module with the 3d printed bridge tacked in place. The pier doesn't quite fit below the bridge at the moment, so that will need adjusting. Next step with this module is to add the point motors and the wagon shunting apparatus (see post 108) and check all of that before laying track.

I know that the original skew bridge that you are modelling was replaced in the late c.19th (1887?) - at about the same time as the mixed gauge track was removed. Are you modelling the mixed or broad-only period? It should be a lovely model when you're done. Are your laser cut structures card, plastic or wood (or a mix)?

Hi bgman, Great to have you along! I got very confused by your first post - I was thinking to myself "but..but, I haven't built that bit yet - where is that model from?". I'm very interested, please feel free to add as many photos of your work or anything interesting that you've learnt in your research as you like to this thread. I can't quite work out on your first photo - is that the station building roof folded back or are you modelling the original Brunel over-all roof over the tracks? I don't see why you would need to remake anything - it looks like a great start. It's a pretty tricky shape to do and I think that you have captured it very nicely. Funny you should mention the skew bridge. I've not had time to do much modelling since Christmas but as it happens I'm just preparing to assemble that module (see post 1 - it's the left most of the scenic modules): In the second picture you can see the four cutouts for the point servo motors. These will use the 'rotating wire in tube' method I tested in post 118. That way there won't be anything visible under the skew bridge except for some 2mm tubes. There are quire a few pipes slung under the bridge so I'm hoping that these tubes will blend in nicely. Once I've got this module varnished and glued I'll pose the 3d printed bridge sections, that I made right back at the beginning of the project, in place. You can expect more regular updates for the next few weeks at least.

Or even a bit less: http://www.ebay.co.uk/itm/CNC-3020T-ROUTER-ENGRAVER-ENGRAVING-DRILLING-AND-MILLING-MACHINE-/321169610171?pt=UK_BOI_Metalworking_Milling_Welding_Metalworking_Supplies_ET&hash=item4ac73355bb I know someone who has one of these and is very happy with it. Noisy and messy by comparison though. Definitely less 'home' friendly than a robotic craft cutter.

Out of interest Missy, may I ask how much a sheet of parts like that costs and how big the sheet is? I've not had any etching done before but am interested to try (although I might do it at home!)

You're going to need some 7mm scale boats for that view I think! Could be a good one for this year's challenge.

I did, I've sent an enquiry to RM to see what happened to them but it looks like I'll have to reprint, which will have to happen after I get some more resin. Sorry about that.

They look great - looking forward to seeing the paint go on. What livery will you be doing them in?

Well, that's them trying to be confusing with their brand name! Silicon is a hard, brittle semiconductor (computer chips and all that). Silicone is a polymer which is based around a silicon chain (most polymers - aka 'plastics' - have a carbon based chain). Loosely speaking: silicon is to silicone what graphite (or diamond) is to polythene and other plastics. So to call a silicone polymer 'SILICON" is very misleading! Silicones vary widely, some can tolerate up to 300C+ and some will fall over at about 100C. If it were me I'd give it a go, but I'd definitely take precautions when running it, particularly for the first time (face shield, overalls, etc.)

One thing I would be concerned about with wood (from an outside point of view with no experience) is long term warping or moisture induced swelling (e.g. when soaking the ballast with glue). Can anyone who has used this before comment on it's long term stability vs. plastic or soldered track? Is it fine so long as you do something to protect the wood?

But if you offset the magnets the traverser will just position itself so that the horizontal forces are equal and opposite, with no net force on the traverser - so it doesn't make any difference. You're still sitting at a position with no net force,. Ineither case there will only be a horizontal force when the magnets underneath move. If there was a residual horizontal force then the traverser would move until there was not - Newton's 1st law.

I agree, it is fantastic. I've been looking through your blog to find a description of your method for ballasting, painting & weathering the track but coudn't find it. Can you point us to the right place?

And today on "When railways go wrong": The cat that thinks it's a ground signal. How a red collar and head tilting brought mayhem to shunting operations.

Looks good! Brass will be ok for the rods - only ferrous metals are magnetic. If it were me I'd consider some thin plasticard strip down the long edges to hide the sandwich layer effect.

If you find that the magnets are too much and affect the locos then you could use magnets below and just strips of iron or non-stainless steel on the traverser.

Slow progress at the moment but the wiring for the first module is nearly done - just a couple more connections and I should be able to get something moving!

I haven't even got that far - and I've had the bits longer than either of you!