Gordon H

Yes, it simplifies matters, but is not impossible to achieve. On my layout the third rail is used to power interior unit lighting and the sliding doors on my Class 508.

So, the Ontrack and Morley controllers are variable voltage, just like Crosland said. The Variable resistance type of controller will obviously give a high off-load voltage because that is the nature of their design, as described by Kevinlms. What type do you claim gives a 'variable wattage' output? Please provide a circuit diagram for such a device (if you have one). A single pot controller with reverse is not that difficult to arrange if you know how.

Hardly requires a diagram of any sort. The description itself is quite sufficient.

The criminals may well take up amputation as an alternative method of getting what they want...

There is no reason why you cannot control two servos with a single switch. The original statement was ill-informed. However, using a 'Y' Servo cable would not be advisable because it assumes the required throw would be exactly the same for both servos - and in the same direction. Much better to use two separate servo control channels controlled by a single switch. This would allow the two points to be individually set up for end stops, including which way round they work.

Perhaps you could post a link for this?

A similar thought along those lines occurred to me the very first time I saw a real B/W pan on 86244 in Willeseden yard back in the mid-80's, basically "if the model manufacturer's can't make cross-arms, what chance have they got of making one of those?" This was, of course, an era when Lima thought it OK to fit their 87's with diamond frame pans - or 'spring donors' as we would refer to them, being the only parts of it worth keeping.

Having scratchbuilt several of these myself over the past 30 years or so, I eventually found them somewhat simpler to build - or at least rather less time consuming - than the Cross-arm version which involved the fabrication of considerably more parts, which by the nature of the design needed to be sufficiently consistent, accurate and repeatable. With the B/W there is, by and large, only one of everything that matters whereas the Cross-arm needed four of most things.

For smaller items I usually draw using Sketchup in 1000x size, and then export the STL in metres. Always seems to work for me. Sketchup does not work properly with curves or circles of 0.5mm radius or less anyway, so the 1000x original overcomes this limitation, and is a convenient figure to work with as well.

This is how standard types of circuit breaker always work, especially simple thermal ones. If you look at their data sheets, you will find a graph of trip current versus time. By and large, the current rating given is that which the device will pass continuously. Slight excursions above it will take a long time to trip, large excursions will trip much quicker. For DCC protection you need something much quicker acting than anything of this sort, and this inevitably means a further piece of electronics that can do the job quickly and accurately by intelligent monitoring of the current flow.

Actually, the sound sample mentioned previously was from a 321 recorded at Gidea Park - not even a 315 as the obvious choice, but I can't remember why not! Anyway, my suggestion was to encourage people to model their OHLE to whatever standard they feel comfortable with . Can't see anything wrong with that. Working tap changers on a Class 90? Don't think so...

As one who favours the working pan aspect as the main point of OHLE modelling, I would suggest that for an electric loco it has rather more importance than almost anything else. Otherwise, you might as well stick to modelling diesels. One compromise that the manufacturers probably wouldn't consider is to supply the models with no pan at all. It would make the models cheaper at a stroke, those that don't really want the perceived hassle of OHLE can run it as-is, and those that want to model OHLE can do it to their chosen level of accuracy and operation by adding to the model themselves, as has been necessary in the past. Just a thought.

First job would be to inspect the pantograph to see if conversion to P4 is worth pursuing...

The '628 doesn't need an external oscillator either. If a device fits the requirement and its price is acceptable, I see no need to look elsewhere just to be 'fashionable'.

Looking at the pictures, it seems you haven't glazed the unit yet. Just wondering what your approach to that will be?

You could also try making the doors open as the thin brass sides would lend themselves to this rather better than my resin version where the sliding doors had to be kept flat rather than curved at the bottom.

Yes, it is sprung. In this instance the springing method was an experiment to try out a simple wire spring, which can be seen at a slight angle inside the base, bearing on the underside of the lower arm. The piece of wire towards the rear of the base running across it, but underneath, can be slid forward to depress the spring wire to lower the pan when necessary. Previous versions used actual tension springs, mainly donated by Lima diamond frame pans and cut to suit.

No need to imagine - I managed to do it over 30 years ago, as described earlier. The only compromise I had to make was to keep the trailing link and aerofoils at a fixed angle relative to the upper arm. It worked then, and there's no reason why it wouldn't work now with a little effort on the part of the manufacturers. Here is a picture here of one I made for a Dapol Pendolino a few years ago, before I got round to adding the aerofoils: http://www.rmweb.co.uk/community/index.php?/topic/13471-brecknell-willis-pantographs/&do=findComment&comment=120781

There are no laws of physics to overcome. If there were, the real thing wouldn't work either.

It really has to be the 'third choice, especially as the first two options have been tried in the past and found to be sadly lacking. Thus we already know (more or less) what the reaction would be to those appearing yet again. Every other aspect of RTR has seen major progression over the last several years, so surely it is time to push forwards with expectations on this aspect too.

There is a video if it on the Bachmann website, which clearly shows the pan has an external linkage on the lower arm. In that respect it fails at first base as far as I'm concerned.

My association with modelling the PEP derived units all started one Saturday in the very early 80's during a trip to the 'Comp Shop' in New Barnet to buy a few extra 'K' of RAM for my UK101 computer. The contrast between the smooth running of the Class 313 with airbag suspension I rode there from Moorgate and the Class 302's I was used to on the LTS was quite impressive, so I started to look at the possibilities of producing a model of a 314 for use on our forthcoming 'Carstairs' layout. Nothing RTR came even close (to this day!), so I had a go with resin casting. This resulted in the 314 model shown in another thread, produced in 1986 and shown in one of the MRC display cases at IMREX a year later. Moving forwards another 11 years or so, 'GWC1' on here was about to start exhibiting his layout 'Effingham South', based around Southern Region EMU operation. Still having the moulds from the 314, I decided to have a go at producing an original four car 508 to run on the layout. As I had the means and capabilities to try out all sorts of unusual features during the build, it ended up with a lot of things incorporated which (to my knowledge) had never been done before, certainly not in the way I was planning to do it. This was before DCC came to the fore as a controlling medium, so much of what I did at the time could be achieved much more easily nowadays. Memory wire was just becoming commercially available at the time, so I adopted this as the means of operating the sliding doors. Using actual third rail pickups was another desire - after all, the 314 had a working pantograph, so why not? Lights were another obvious item to include, including the door operation indicators, of course. To achieve all this, the obvious solution was to make the floor/chassis of each coach as its own printed circuit board incorporating the circuitry needed for the functions within that coach. Overall control of the unit, including the Infra-Red remote control link, was performed by an Atmel 89C2051 processor. To provide all the connections required between coaches, I devised a 7 pin PCB based rigid coupling, which worked well both electrically and mechanically as the coupling. The windows were produced using clear plastic sheet and some special rub-down transfers I had made for the window frames. Most of the work was done over a period of about 3 months, between Christmas 1997 and Scalefour North 1998 (I think). Frightening to think it was that long ago! The BRM article appeared in the latter part of 1998. The unit hasn't been displayed on the MERG stand for some time now, as we simply don't have space for it with all the demo other kit as well.

A stepper motor will move the exact distance you want it to, simply by the number of steps you give it from the controller - assuming no slippage or missing steps due to mechanical problems. Their limiting factors are the step angular resolution and torque they can provide. A simple continuously rotating servo in this context is little more than a geared down motor. Unless you can contrive a way to count the number of turns it makes, and what its angle is within each turn, you can't really use it as a position servo in the conventional sense. All it can really do is hit endstops. Also bear in mind that the more gears etc. you add to the overall mechanism, the greater the backlash through it all, and consequent inaccuracies at the critical interface, i.e. where the rails are meant to line up consistently and repeatably.

When I started to scratchbuild mine shortly after the real thing first appeared, it was clear that for pivot (1) it would be virtually impossible to provide a linkage to maintain the head angle. Thus all mine have this top arm as a fixed feature, set at a compromise angle relative to the upper arm to look correct at a nominal wire height though the pan head itself is pivoted to allow for variations. The function of (2) cannot be done properly with just a spring. There needs to be a linkage of sorts, replicating the arm and chain that runs up the hollow lower arm on the real thing. For mine I started with simple thread, superglued to the upper arm top surface and wrapped over the (2) knuckle, feeding down through the hollow lower arm and wrapped/glued to the underside of the front base cross member to provide a constant length while it is under tension. With the length set just so, all you need to do is provide a spring between the base assembly and lower arm (3). The linkage thread then does the rest, as its path is offset from the mechanical pivot points and performs the pantograph function. Subsequently I have used actual metal chain rather than thread, soldered in position as before - but this needs care to prevent the solder simply wicking up the very fine chain links and producing a solid 'wire' instead. The only disadvantage of this arrangement is that it cannot prevent the pan 'unwrapping backwards' if the pan head catches on something on the wire while travelling in the conventional 'forwards' direction (i.e. to the left as shown in the diagram), as the chain only operates under tension. However, with properly set up and maintained wires this should not be too much of a problem as the only force the pan head sees should be downwards, whereby it works fine - electrically too, using all metal construction. For me, a 'poseable pantograph' is not a pantograph at all. Might as well not be there if you're not going to use it.

For another historical broadcasting link, construction of 'High Gill' commenced on the day that 'Essex Radio' started. I still have a copy of the 'Corners' programme recorded at the time (1987), and have the section of particular interest as a separate file - for my own viewing, of course. The presenter is now flogging over-50's life insurance on TV.