Top wipers

[David B]

I have a problem with pick ups. I am building this 4-4-2T which was designed (a) for OO and is now P4 and (b) to take plunger pickups which I am not happy with and anyway, they won't fit now. I cannot get to the tyres very easily underneath because of spring detail which is part of the frames and I am reluctant to cut off. I had thought of rim wipers which would rub the rims in the area between the two drivers. I think this might work but could be subject to wear. One of the brake blocks would also be very close.

So, it has been suggested I look at top wipers which can be concealed by the tanks and certainly appeal to me. However, how to go about mounting them? Soldering to the frames could be a problem as well because I blackened the chassis (and have had to paint). Not sure I would do the blackening again, but it has been done now, so I must live with it.

Suggestions appreciated.

David

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[nigelcliffe]

There looks to be enough space to slide a piece of thin PCB material between the motor case and the frames.

This could then be shaped to clear anything inside the frames (axles, spring hangers, etc), and gapped just above the frames.
The wipers (or brackets to carry wipers) can be soldered to the copper above the gap line.

The copper material inside the frames can be fixed with an adhesive.


PCB is available as thin as 0.3mm double sided. I'm fairly sure that Eileen's keeps it in around 0.5mm.
Almost all PCB available these days is fibreglass based, so don't use your best saw or files to shape it (or they won't be your best for much longer!).


- Nigel

[Will L]

So, it has been suggested I look at top wipers which can be concealed by the tanks

Certainly looks like the easiest solution. Top wipers are nicely out the way of accidental damage, and run on the bit of the wheel you need to keep clean anyway. In fact I can't see why you would put pickups anywhere else given the choice.

However, how to go about mounting them? Soldering to the frames could be a problem ..

Sorry, but why should you want to solder them onto the frames? You have a nice flat place behind the motor with a screw coming up through it. A pad of copper clad held down by that screw should be an ideal attachment point for some pickups, which would then removable for maintenance painting etc. It will depend on what space you have inside the body of course, but on a 4-4-2 I suspect you have plenty. Once the copper clad pad is in place, use rigid brass wire to run from there to the point above the wheel where you want to attach the pickups. Then make the pickup proper from thin phosphor bronze wire. Use a sufficient length to be springy enough not to act like brakes and follow any movement in the wheels.

On the Loco Suspension, fitting CSBs thread in the next few weeks, I shall be doing the pickups in this style for the J10, for both tender and loco. I will be explaining how, at considerable length knowing me, and it is all just as applicable to none CSB chassis.

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To be going on with this is a repeat of a photo from that thread, which should give you an idea of what I mean. This is a tender chassis but the same ideas work on a loco. Don't be put off by the fancy coiled springs, they aren't mandatory, but top wipes on a CSB chassis do need to be very softly sprung.

[David B]

Thank you, Will. The screw through the lead goes straight a nut under the cab floor but I take the point. The picture, too, is very helpful - worth a thousand words? It's a lovely, clear piece of work.

I had in mind soldering the copper clad to the frames and scoring an electrical break. My mind set is on soldering wherever I can as I don't have much success with glue (bits keep falling off) and I was never in to Meccano, so don't think nuts & bolts. My education was clearly lacking in essentials!

David

[martin goodall]

I notice that Will's current collectors bear on the tyre tread. Could this cause any sort of problem with arcing, pitting, or dirt build-up? In order to avoid any risk of this, I have always arranged the current collectors so that they make contact with the edge of the tyre flange (from behind).

I am not saying Will's way of doing it is wrong; I simply wonder whether it might cause any problems. I would be interested in any comments from Will or others. (Sorry, if this is the wrong thread - Will may prefer to delay responding until he deals with current collection in his J10 write-up.)

[David Knight]

A few comments if I may based on my own experiences with the J72 build. Top pickups are a useful thing and can be well concealed but with CSBs you have to be careful of how much force is applied or otherwise you either; (a) add brakes, (b) negate the effects of the CSB or (c) get lousy pickup. In answer to Martin's question I use a modified stylus type of pickup shape and it helps keep the treads clear of 'crud'. Periodic maintenance is required but would be anyway. An attachment will illustrate my chosen method.

HTH

David

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[Tim V]

To make use of the truck wheels, you could de-insulate the rear truck wheel to one side and the pony to the other side. By putting an insulated pivot, and a fine wire you could increase the number of pick up wheels, without any wipers causing drag on the small wheels.

[Philip Hall]

I agree with Martin about pickups bearing on a tread, and always arrange them, as he does, to bear on the edge of the flange. This is, I find, the cleanest place, and if you clean wheels with the simple dodge of cleaning fluid on a piece of kitchen towel spread over the track, it cleans the pickup point as well.

Pickups underneath bearing on the edge of the flange can usually be fitted in, even if there are springs and brakes in the way. I always use 0.3mm brass wire rather than phosphor bronze as Mike Sharman warned me donkeys years ago against using PB with steel wheels, and I put a few little coils in it as Will has done. Often I put a couple of thicker wire busbars the length of the chassis which gives lots of choice about where to solder the pickups.

Sorry our computer won't submit pictures at the moment so I hope it's reasonably clear.

Philip

[Tim V]

I've not heard of this brass wire versus PB before?

[Will L]

I notice that Will's current collectors bear on the tyre tread. Could this cause any sort of problem with arcing, pitting, or dirt build-up?

Exactly why should that happen any more on the tyre tread, rather than anywhere else? Experience says, not a problem.

I agree with Martin about pickups bearing on a tread, and always arrange them, as he does, to bear on the edge of the flange. This is, I find, the cleanest place..

Why cleaner than the tread? Don't understand why that should be, the tread is the bit I'm going to spend most effort on keeping clean, particularly as I'm relying on rolling contact with the rail rather than scraping contact with the pickup..

I always use 0.3mm brass wire rather than phosphor bronze as Mike Sharman warned me donkeys years ago against using PB with steel wheels ...

I personal haven't seen any sign of any harmful interaction between steel tyres and PB pickups and, as plenty of folk do use PB, I would have though we would have seen the horror stories by now. If your talking Galvanic Comparability here, as I read the tables, brass is slightly less compatible with steel than PB. Any real metallurgist in the house?

Will

[Will L]

...I had in mind soldering the copper clad to the frames and scoring an electrical break. My mind set is on soldering wherever I can as I don't have much success with glue (bits keep falling off) and I was never in to Meccano, so don't think nuts & bolts. My education was clearly lacking in essentials!

Perhaps not, I found that increasing modelling experience produced a progression from glues, through solder to the use of the bolt. Sounds to me that you are already part way down the same road.

Will

[David B]

This is developing into an interesting business. Keep going, chaps, as I am sure it will be of interest & use to others.

Martin - please carry on. Philip - is the suggestion that PB, with any arcing or heat, will react adversely with steel?

I had thought that the wire operating on the tyre face might serve the dual purpose of current collection and cleaning, whilst agreeing with David about routine maintenance. Might a smaller contact area on the rim induce greater wear on the wire?

Tim - you have highlighted another thing that was going through my mind. Further pickup points would be highly desirable and I had thought of the bogie but rejected the idea because any wire connection would have to be very flexible and I couldn't think of any such material. The pony truck is a more sensible proposition.

I have now laid my hands on the copper clad and regretted it! I got frostbite. The thermometer was still at -9C at 09.00 and I didn't have gloves.

Thanks, chaps, for the contributions.

David

[martin goodall]

As regards the wire used for pick-ups, Mike Sharman has always advised that phosphor-bronze wire or strip should not be used to collect current from steel tyres. He reckons that there is some sort of chemical, or electro-chemical, reaction between the two metals. But I have no idea whether there is any scientific basis for this theory.

There is also a theory (again, without any scientific basis of which I am aware), that you should not use the same metal for the pick-ups as you use for the wheels. Thus you should not use steel wire to collect current from steel wheels, nor nickel-silver wire to collect current from nickel-silver wheels. This may well be yet another 'urban myth' - I have no means of knowing.

It is only a matter of time before some bright spark (sorry - an unintended pun) suggests split axles/split frames to eliminate the wires altogether. Actually, I have been mightily impressed when I have seen the performance of locos which collect current in this way, but I have never plucked up the courage to try it. Quite apart from the time and effort involved in devisng the insulation and then shorting out the plastic wheel centres, there is the problem of gearboxes, etc. If your gearbox is virtually touching the hornblocks on either side, how do you ensure that you won't get a dead short if the axlebox which has a different polarity compared with the gearbox touches it when running (or shorts out through the axle, by bridging the insulation)? Added to the complications of CSB, etc. I fear that split axles would be a bridge too far. On the other hand, if someone has tackled these probelms successfully, I would be eager to learn about it and to see the methods used.

[craig_whilding]

There is also a theory (again, without any scientific basis of which I am aware), that you should not use the same metal for the pick-ups as you use for the wheels. Thus you should not use steel wire to collect current from steel wheels, nor nickel-silver wire to collect current from nickel-silver wheels. This may well be yet another 'urban myth' - I have no means of knowing. .

It makes sense to use a softer material for the pickup than your tyre so you wear away the pickup rather than the tyre.

[Philip Hall]

Martin's explanation of Mike Sharman's preferences is just what I remembered from Mike all those years ago on one of Iain Rice's courses at Chagford. I have no idea about the evidence either, but Mike convinced me and I've seen no reason to bother with PB since on anything I build myself that's got steel tyres.

The other side of the coin is that I regularly convert proprietary locos to P4 and EM and most of the time we've got (new) steel wheels and PB strip pickups! And the pickups also bear on the back of the tyre, the worst possible place to keep clean. So far, no problems, but that's only on the test track, time running on the layout is the only real test. It's also true that with a Hornby loco you've got masses of pickup (bogies sometimes, always on the tender wheels) so any problems with oxidizing or suchlike will of course be minimised.

Philip

[Jol Wilkinson]

Like others I too heard (and believed) the theory about PB pickups and steel tyres. So all my locos have been built using either brass wire pickups or PB strip with brass rubbing pads at the tyre contact point.

Going back to David's original posting, I have a LRM Precursor Tank 4-4-2T which is fitted with top acting pickups on the coupled axles. These are PB strip with the brass pads (from etch scrap). The pads bear on the tyre running surface. Despite being the only pickups on this loco, which is simply compensated it will run happily under exhibition conditions on London Road over a weekend, usually only requiring cleaning once.

This is not the only loco that has only two axles fitted with pickups. A LRM 2-4-0 Jumbo has a similar arrangement, but with brass wire pickups acting on the edges of the coupled wheel flanges. This also runs well, neither of these etched kits carries much extra ballast and are both fitted with Sharman Wheels.

Perhaps the action of the pads on the tyre surface with the top acting wipers is partly self cleaning. Locos with wires bearing on the edge of flanges or with pads bearing on the rear of tyres get dirty wheels (on the tyre surface) just as much if not more.

Based on this experience, my preferred system now is PB strip for "springiness" with brass rubbing pads. I recall someone recommending gold wire or strip for the contact pads in the past, but that's a bit too sophisticated for me.

Jol

[martin goodall]

Craig Whilding wrote that it makes sense to use a softer material for the pickup than your tyre so you wear away the pickup rather than the tyre.

I seem to recall hearing somewhere (but this may be yet another 'urban myth') that where a harder and a softer metal rub together, it is the harder metal that gets abraded, not the softer metal. I must say I find that very hard to believe, but would be interested if anyone can shed more light on this theory.

The question which Craig's comment initially raised in my mind is whether or not one should use steel wire to collect current from nickel-silver tyres. And is brass wire tough enough for this job? My instinct has always been to use 'nickel silver' wire in preference to brass (which is brass [i.e. copper and zinc] with added nickel).

Maybe split axles would be worth investigating after all!

[Paul Willis]

Based on this experience, my preferred system now is PB strip for "springiness" with brass rubbing pads. I recall someone recommending gold wire or strip for the contact pads in the past, but that's a bit too sophisticated for me.

I seem to recall that this was an Iain Rice idea, from around the time that he was doing a lot of articles in the old Model Railways - 1983 or so.

It was based around the idea of using bits of gold/gold-plated wire culled from the backs of earrings. These were soldered on to springy wires, in the same way that you are doing with brass pads.

The benefit, of course, is that the gold should not tarnish. Whether that makes a significant difference or not in practice... I suspect that I will NOT be strolling up to Hatton Garden this lunchtime for a length of gold wire just to experiment with!

Flymo

[Joe Newman]

I have followed the discussion about the effects that wipers made of different materials may have on steel wheels with some interest. Metallic corrosion is a very complex subject which was well summed up by an engineer from Lucas Industries saying 'it's all loss and no profit!

Corrosion can occur if two different metals are placed in a liquid that can behave as an electrolyte, i.e can conduct an electric current. Iain Rice referred to one positive effect of this when he described electrolytic cleaning of etched kits in his 1990 book Etched Loco Construction (page 31). To clean the brass etch, it is placed in a solution of sodium carbonate (the electrolyte) in contact with a piece of aluminium. The chemistry of the process is rather complicated but the most reactive metal chemically (aluminium) will dissolve in the sodium carbonate solution, a process that corresponds to it being corroded.

If we now turn to wipers on a steel wheel, unless the wiper is steel, there is the possibility of corrosion - but only if there is some conducting liquid between the wiper and the wheel. Since most of the liquids (e.g. methylated spirits) we use for track cleaning are not conductors of electricity, there should be no corrosion of the tyre.

If there is an electrolyte present, then the more reactive metal will be corroded. In this context, zinc is more reactive than iron and since, as Martin Goodall points out, zinc is present in both brass and nickel silver, the pick up should corrode and not the wheel.

I wonder therefore if the corrosion which has been referred to is due to sparking. Here we could in effect have spark erosion, which is today known as die sinking. And perhaps we should remember that early motors required a much larger current to turn them so the applied voltage would be higher.

I offer these thoughts in the hope that they may help towards a better understanding of what to use for pickups – rather than where to put them which was the original thread!

Joe Newman

[Philip Hall]

Martin Goodall wrote:
My instinct has always been to use 'nickel silver' wire in preference to brass

I have always used 0.3mm brass as it's quite springy and easier to get (until I found some 0.3mm nickel at Eileen's) in 0.3mm than nickel. Nickel seems a bit stiffer so I shall experiment next time around to compare them.

Philip

[grovenor-2685]

I seem to recall hearing somewhere (but this may be yet another 'urban myth') that where a harder and a softer metal rub together, it is the harder metal that gets abraded, not the softer metal. I must say I find that very hard to believe, but would be interested if anyone can shed more light on this theory.

I don't think that would even qualify as 'urban myth' I've certainly not heard it before.
Ever tried filing steel with a brass file?

What was used as the standard bearing surface with steel axles for many years, until roller bearings took over? White metal of course and I've never heard of it abrading the steel axles
Of coures if the lubrication fails and no-one notices the white metal might melt, gives a good bearing for a short while until it all runs out leaving the brass to take the strain at which point things start to get very hot and the axle end eventually shears off. But abraded by the soft metal, no.

Keith

[David B]

It has taken me some time, but I have read and made use of the advice offered, eventually come up with the following. The wire is .35pb and I have attached brass wipers to the ends. I made the holder for the pickups from some scrap, attached it to some very thin copper clad which in turn is epoxyed inside the frames. I don't like the idea of heat near the motor any more than necessary, hence my 'plug 'n' play' system. This makes it easy, if required, to reverse the polarity or replace the motor.

Apart from the obvious cleaning up, replacing the sand pipes and attaching the cab roof, I have to sort out the motor. The current is being picked up well enough, but the little darling will only go in one direction.

The kit is an AF Hammond (Ron Cadman design) from 1986 which I bought a couple of years ago. 4600 was the first of a class intended to replace Metro's on suburban services, but the 2-6-2 prairies proved more capable and versatile. It remained a one-off. I'm quite chuffed with it as a first brass loco. Just got to get it running!

Thank you to all who responded to my request for help. Your contributions have been very helpful, informative and appreciated.

David

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