In writing the material that appears as part 1
, I found that I was including a lot of material which related to my rationale for doing what I did. The result was long, even by my standards. As I wanted there to be at least a fighting chance that some people would read to the end, I extracted a lot of the rationale stuff. This omission is already leading to comments. It is given here now, along with details of another application and, in the spirit of the best day time reality TV shows, ultimately, what happens under the J10 loco. Using Rim scraper pick-ups
I’m personally not a great fan of live chassis locos. If they work for you, that's fine, and I suspect the 2mm brigade probably have little choice. Personally I think it easier to sort out unexplained short circuits if there are
bits of your loco that ought to be electrically dead. I’ve found rim scrapers work for me, so I plan to stick with them. Proponents of split chassis, American pick-ups and the like are very welcome to explain their preferences, how can I put this, somewhere else.Use of PB wire on steel rimmed wheels
I use phosphor bronze (PB) spring wire, usually 29 swg (about 0.35mm) because it combines good electrical conductivity with being relatively hard and wear resistant. I know it has been said that you shouldn’t be using PB on steel rims, and that we should prefer brass, nickel silver or such novelties as fitting little pads of gold at the business end of the pick-up.
While there is a whiff of truth in the idea that unlike metals can react,
- PB isn't notably different in this respect than brass or nickel silver
- The erosion effect requires the presence of an electrolyte, say salty water!
I tend not to run my pick-ups under water, salty or not, and despite having run PB pick-ups on steel wheels for a good few years now, I have seen no sign of any reaction.
If you want to know more, see this article on Wikipedia
which, as I read it says that, were there was any truth in this idea, gold would be worse than PB.Removable Pick-ups
I like my pick-ups to be removable. Like many people I started off sticking copper clad strips to various parts of the anatomy of my chassis and soldering the pick-ups there to. But since I worked out that life was simpler if I could drop out the wheels without disassembling them, it became clear it was better if you could remove the pick-ups as well. Pick-up style
I always like my pick-ups to act on the running surface of the wheels, so that is only one part of the wheel I need keep clean. Putting this together with a preference for not putting my pick-ups where they are vulnerable to damage, i.e. hanging around underneath the chassis, has led to me favouring top wipers. These are particularly suited to fitting to tenders, and, in search of the maximum electrical track contact, I always fit pick-ups to tenders.Use or top wiper pick-ups with CSB’s
We had to come back to CSB, but you don’t need to be all that clever to realise there are implicit contradictions in employing top wiper pick-ups on a CSB chassis. Having gone to all the trouble of accurately working out the fulcrum points for one set of springs, it does seem a trifle perverse to then stick on what are effectively an extra set. In my defence this has not been done without some soul searching, and I do take the following precautions so as not to upset the balance of my CSB calculations.
1. I ensure that the pick-ups are all the same length so that their contribution to each wheel set is roughly equal. Which is why in the example in part 1, each pick up is fitted the same distance from each axle, and 11mm was the longest pick-up length I could easily apply to all 6 wheels.
2. I ensure the pick-ups are as soft as possible, so the contribution of the pick-ups is negligible compared to the CSBs themselves.
As best as I can measure them, and its not easy, the pick-ups fitted to the J10 tender each apply a pressure of 2 to 3 grams at the CSB static deflection point, so the body will seem to the CSB’s to be 18 grams lighter than it actually is. Given that I’m expecting the all up weight of the tender to be in the region of 150 grams, the spread sheet tells me this is the equivalent to a change of 0.2 of a thou in the CSB wire size. I think I can live with that.Other applications - The C12
The picture below shows the set of pick-ups fitted to the driving wheels of the C12 which featured in the CSBs and the Single Bogie
Again top wipers fitted to a CSB chassis. This time they could be made even longer, so long in fact that keeping them on the wheel treads still proved problematic. As a result they are bent to hook over the wheel flange. These little bends are tricky to get right, which is why I don't use them if I don't need to. Note the use of the bus bar to carry the electrical circuit past the gear box and down to the rather different pick-ups fitted to the bogie. These have already been described in the thread referenced above.
Like the J10 tender, the feed to the motor connects to a two pin plug mounted on the pick-up PCB pad were you can't see it in this view. This is another consistent feature of my pickup design. Connecting your motor like that makes ensuring your locos don’t go the wrong way simple, and will make life much easier should I ever wish to go DCC.And finally, so what about the pick-ups on the J10 loco?
On this occasion, it wasn’t practical to fit top wipers on the loco, which features a cast white metal footplate and hence no space to hide clever stuff between there and the wheel tops. In fact it wasn’t at all clear how best to fit pick-ups to the front axle at all, without un-prototypical appendages being clearly visible between the frames under the boiler. Ok, yes that space should be full of valve gear slide bars and other similar stuff, but just because there is an absence of stuff that should be there, that is no excuse for displaying all sorts of stuff which shouldn’t be. Given that there was going to be 6 wheel pick-up on the tender, the decision was taken to forgo pick-ups on the leading axle. There follows the view from below.
The pick-ups are on the second and third driving axles. They are fitted below the frames and rub on the edge of the wheel flanges which is close enough to the running surface. They are arranged so as not to deprive the CSBs of any of the loco weight. The construction style should now be familiar, but in this case the bus bar ends and the spring wound section of the pick-up are mounted vertically. Also note the bus bars carrying the pick-up circuit to the flexible connection to the tender, masquerading as the water pipes, which you can see, and the two pin socket which connects to the motor and which is mounted above the PCB plate, which you can’t.
I think that's enough from me for now