Locos need a nudge

[regme]

Hi

 

Every now and then I have to give my locos a nudge to get them going on my time saver layout.  There is no specific spot that this happens, the track has been cleaned.

 

I have been using the standard Hornby Controller R8250, I'm have thinking this might the issue, but I didn't want to right it off just yet.  I thought about putting in extra power feeds.

 

So if there are any ideas.

 

Cheers

[PatB]

As a first step make sure that the loco wheels are clean. Not just the treads but the backs and flanges too, especially where any pickups make contact with them. Make sure the pickups are clean too.

 

Make sure your track is absolutely flat and level. Unless a loco is sprung or compensated any dips or lumps will leave it with only three wheels in contact with the rails. If one happens to be on a dead spot the loco will stall.

 

Extra power feeds certainly won't hurt. No such thing as too many IMHO.

 

Better controllers can give better starting and slow running but if the juice just isn't getting to the motor it won't help. Proprietary controllers tend to be expensive but building your own can be fun, satisfying and cheap, with many excellent designs available on the net, including here on RMWeb.

[DCB]

Talking low power wall wart DC here.   

 

Clean track helps, however it is the gauge corner, not the rail top, which needs to be clean, as most OO/HO  wheels are coned like the prototype whereas unlike the prototype the rails are not inclined inwards so they make contact only on the corner  The gauge corner is the inner edges of the rails.  I run a Peco track cleaning rubber along the inside of each individual rail angled down at around 45 degrees.  the inside corner of point blades frogs etc need cleaning 

 

You don't say which locos need a nudge.  Some locos with traction tyres like the Hornby Railroad 0-6-0 chassis and Hornby 14XX seem to need a nudge every now and again as the centre axle wheels with traction tyres don't pick up current and the other wheels don't have enough suspension travel to take enough weight to make contact if the the centre wheels stop on a hump.   This is much worse if new traction tyres ave been fitted.

 

Leaving these aside, better still selling them, the older Hornby chassis with under size flangeless centre wheels should be fine as long as the wheels are clean. Really clean and that means the back of the wheels where the pick ups rub, and the pick ups themselves need to be clean.

This is much more important on modern chassis with less pick up tension and far more pickups, 10 as against 2.  Often one or more pickups simply don't do anything and cleaning them without damaging them is difficult.

 

I find the heavier the axle load on the pick up axles the more tolerant locos are to dirty track my old Grafar 94XX with a modified Hornby chassis splashes happily along rain soaked track outside where Bachmann 57XX and the like stop dead.

 

The P 9000 wall wart doesn't deliver enough power to damage fishplates and point tags but extra feeds are a good idea, I like one every six railjoints or so, droppers are too much aggro for me on low power DC though pretty much essential with high power DCC.

 

Some old direct worm drive locos tend to not restart without reversing slightly, this is not a pick up issue obviously but gear meshing and its probably best to sell the loco or you will end up like me in spending hours shimming gear wheels instead of running trains.

[regme]

Thanks for that, the locos I have are the Atlas C424 phase 1,  I'll get onto more cleaning.

 

As for building my own controller, that sounds like a plan, hopefully I can find some step by step instructions, rather than just a circuit diagram.  I'm not electrical engineer.

 

Cheers

[PatB]

Thanks for that, the locos I have are the Atlas C424 phase 1,  I'll get onto more cleaning.

 

As for building my own controller, that sounds like a plan, hopefully I can find some step by step instructions, rather than just a circuit diagram.  I'm not electrical engineer.

 

Cheers

 

I've seen at least one step-by-step photo guide to building a simple transistor controller. I think it was on the Instructables website but my memory could be playing tricks. How well the particular unit performed I don't know, but it worked on the same principles as many other successful designs so it should have been OK. Basically, if you can solder a dropper wire to a rail you can build a DC controller that will work at least as well as one you can buy, for significantly less money. Start with a simple one (the instructables unit had maybe half a dozen separate components) and, if the results are encouraging, the sky's the limit in terms of sophistication.

 

If you want to give it a go it's worth tracking down Roger Amos' Practical Electronics for Railway Modellers, which leads the reader through various projects, starting from very basic principles. It also includes several controller designs from ultra-simple to very fancy indeed.

[regme]

I have found this

 

 

I was going to use a laptop power suppy 18.5V 3.5A to run it.

 

The other one was this

 

However the power supply required is a full wave rectified AC supply at 16 V DC.  I'm not sure on what I actual need as searching on this gave alot of different results.  I do have an old controller that has an 16V AC output but I don't know if it's a full wave rectified AC supply, or how to tell.

[Jeff Smith]

I would steer clear of any track cleaner rubber as they tend to leave deposits on the rails and can prevent satisfactory point blade contact. The best way of cleaning track and wheels is isopropyl alcohol and a piece of cotton (old handkerchief etc).

 

Also I wouldn't get too hung up on it being a controller problem. As one poster noted, uncompensated OO/HO locos are often running with only three wheels in track contact, even bogie type locos, it only takes tiny piece of grit or fluff to insulate that one wheel on one side to cut the voltage.

[PatB]

I have found this

 

 

I was going to use a laptop power suppy 18.5V 3.5A to run it.

 

The other one was this

 

However the power supply required is a full wave rectified AC supply at 16 V DC.  I'm not sure on what I actual need as searching on this gave alot of different results.  I do have an old controller that has an 16V AC output but I don't know if it's a full wave rectified AC supply, or how to tell.

 

The Fig 3.3 one should be fine run from a laptop PSU. I don't recognise the other. However, I can't see anything in it that should not work also with the laptop supply, even though it won't give a full-wave rectified voltage.

 

The 16V AC output on your old controller will not be appropriate. The output from these terminals will vary from +16V to -16V at a frequency of 50 Hz (that is, 50 times per second). At best, the controller won't work. At worst it'll cook the transistors. Full-wave rectified AC means that this +- voltage has been fed through a rectifier (normally made up of a network of diodes, which each pas current in only one direction) to give a voltage which varies from 0V to +16V at a frequency of 100Hz (that is, 100 times per second). In other words, the -16V valleys in the output have been reversed in order to become extra +16V peaks.

 

I'm not sure why the second circuit specifies this. Such a power supply does have some advantages in getting and keeping small motors moving at low speeds but I can't see anything there that requires it. It is, however, simpler to obtain from a supply like your old controller's 16V ac output than would be a smooth voltage.

 

All that said, I still heartily recommend Roger Amos' books (TBH those  diagrams look like they may have come from one of them) because he explains the basics much better than I am able to.

 

I would also concur with David and Jeff. Don't get too hung up on controllers at this stage. Cover the basics, get current pick up properly sorted and then, if you still wan't better performance and are interested in learning a new set of skills, break out the soldering iron.

[robert17649]

I concur with all the above ,some form of springing or compensation resolves a lot of running problems .

 

Peter Denny used loads of weight, I have three or four small locos using black beetles or Tenshodo bogies and they all go well as long as the wheels are cleaned meticulously as is track, isopropyl alcohol is really good if a bit toxic, all of them have as much weight as I can cram in, however, even if in sprung this is a great help.

 

Good luck with your running.

[regme]

Those diagrams come from "Complete Book of Model Railway Electronics" - Roger Amos, I'll have a look for "Practical Electronics for Railway Modellers" as well.

 

Thanks for the advice, as they say you have to learn something new every day.

 

Also what was meant by "Unless a loco is sprung or compensated" does that involve some sort of modification to the locos to allow them to pick up the current better?

 

Cheers

[Jeff Smith]

To further my comments above, I have two 0-4-2 locos running on code 70 16.5mm track. The first is a RTR On30 Porter, it has pick-up only on the four main drivers and the trailing wheels are just along for the ride with no pick-up and no weight bearing. This loco is quite good at speed but can stall on the points even though they have live frogs. It sometimes needs a nudge even on plain track.

 

In contrast my Peco white metal bodied GVT 0-4-2 with compensated Branchlines chassis performs much better. The leading drivers are rigid and with pick-ups. The rear drivers also have pick-ups but are pivoted on a beam to the trailing wheels. Although the trailing wheels have no pick-ups they bear weight and ensure that the rear drivers are always firmly on the rails. This arrangement, together with the greater weight helps with the better performance over the Porter.

 

This of course does not help solve problems with RTR locos but just illustrates the point about why some basically rigid chassis locos stall occasionally!

[tamperman36]

It may also be a good idea to check and clean the commutator on the motor. If there are carbon deposits on the copper contact parts this could cause the motor problems when trying to set off, it would also require more power. The cleaner the commutator the easier it will be to get running.

[NCB]

Thanks for that, the locos I have are the Atlas C424 phase 1,  I'll get onto more cleaning.

 

As for building my own controller, that sounds like a plan, hopefully I can find some step by step instructions, rather than just a circuit diagram.  I'm not electrical engineer.

 

Cheers

 

Surprised at an Atlas C424 having problems. Atlas diesels are normally very good runners these days (the original ones were variable). I think the bogies are flexible enough to ensure good rail contact.

 

Is this on pristine track, or has the track been painted/weathered? The latter can dramatically effect reliability. If this is the case, ensure that there's no paint on either the rail top or the inside of the rail head. If in doubt, scrape off, or run some fine wet-and-dry, or polish with a fibreglass pen, or all three. If that's OK, try cleaning the track before each session; I use meths and a cotton bud.

 

If you think the track's OK, check all pickups are in contact with the wheels, as suggested above.

 

If still no joy, think of a new controller. I find the Gaugemaster Combi a relatively inexpensive but reliable option.

[PatB]

 

Also what was meant by "Unless a loco is sprung or compensated" does that involve some sort of modification to the locos to allow them to pick up the current better?

 

Cheers

 

A rigid loco (or, in the case of diesels, substitute "bogie" for "loco")has two or more axles whose position is fixed in relation to both each other and the loco chassis itself. If one wheel goes over a bump that wheel will lift and, because there is no movement between axle and chassis, the whole side of the loco will be lifted. Because the loco chassis is also rigid, at least one other wheel must lift off the track. Think of a chair with one leg sitting on a bump in the floor. A wheel that is not in contact with the rail can play no part in picking up current.

 

To avoid this, it is possible to introduce suspension. On the prototype and on some sophisticated models this involves introducing springs between the axles and the loco chassis. If one wheel goes over a bump, the spring between the chassis and that end of the axle compresses and all the other wheels stay in contact with the track. On our models that means that they can continue to pick up current. Compensation is a method to achieve this result, generally without the use of springs. At its simplest, on an 0-4-0 loco or a four wheeled bogie, one axle is held rigidly to the chassis whilst the other is permitted a limited amount of sideways rock. This allows any one wheel to rise over a bump or fall into a hollow whilst not lifting any of the other wheels off the rails.

 

In practice, diesels tend to be less in need of some form of suspension because, as long as they have pickups on both bogies, the inherent flexibility between the two bogies tends to keep enough wheels down over a sufficient length of track to ensure that at least one wheel on each side is collecting current as it should.

 

However, this is getting quite some way from how to make r-t-r locos work as they should. given clean track and wheels, and pickups operating as designed, most r-t-r locos should start from rest unaided  every time.

[Jeff Smith]

To further my comments above, I have two 0-4-2 locos running on code 70 16.5mm track. The first is a RTR On30 Porter, it has pick-up only on the four main drivers and the trailing wheels are just along for the ride with no pick-up and no weight bearing. This loco is quite good at speed but can stall on the points even though they have live frogs. It sometimes needs a nudge even on plain track.

 

In contrast my Peco white metal bodied GVT 0-4-2 with compensated Branchlines chassis performs much better. The leading drivers are rigid and with pick-ups. The rear drivers also have pick-ups but are pivoted on a beam to the trailing wheels. Although the trailing wheels have no pick-ups they bear weight and ensure that the rear drivers are always firmly on the rails. This arrangement, together with the greater weight helps with the better performance over the Porter.

 

This of course does not help solve problems with RTR locos but just illustrates the point about why some basically rigid chassis locos stall occasionally!

 

I should have mentioned that my two locos above are both DCC.  DCC should in theory be less susceptible to poor track contact as there is constant 18V A/C or thereabouts whereas starting a DC loco will probably be in the order of 3V or less so any high resistance in the actual wheel/track contact, ie with dirty track, will be more noticeable.  However once a wheel has actually lifted from the track, even by a few thou, actual voltage doesn't matter.  Stay-alive type DCC decoders may help with the momentary loss of track contact but mine are only standard factory fitted Bachmann or Digitrax so I have no experience on this.

 

Your Atlas loco may have pick-up on all eight wheels but some bogie locos had two wheels on one side insulated and the two on the other side connected to the motor.  The other bogie would be the opposite way round.  This means only two wheels for each polarity - I have a Lima GWR Deisel Railcar with this arrangement.

[AndyID]

The Fig 3.3 one should be fine run from a laptop PSU. I don't recognise the other.

 

 

Both circuits are really just emitter followers. The advantage of the one in Figure 4.1 is that it only drops the voltage from the input pot by one base-emitter junction.

 

BTW, both circuits need some sort of over-current protection. A 21 watt car turn signal bulb is one way to do it.

[kevinlms]

 

 

BTW, both circuits need some sort of over-current protection. A 21 watt car turn signal bulb is one way to do it.

Especially since the power source being suggested, is an old laptop power supply. Ones things for sure, that won't be the weakest link!

[DCB]

Using a laptop power supply sounds like a good way to set the railway shed on fire,  I have had several laptop power supplies fail, they always seem to run hot even just running a laptop.  They simply are not intended to run at maximum output for long periods or o cope with short circuits, . You need something with decent overload protection around 1 amp and a 21 watt bulb is still going to allow 30 watts/ 1.75 amps on an 18 volts supply which won't do your fishplates, point blade tags, or locos pickups and internal wiring much good if you get a dead short.  A 10 watt bulb might be a better bet but a proper thermal breaker is a better idea.

[AndyID]

Using a laptop power supply sounds like a good way to set the railway shed on fire,  I have had several laptop power supplies fail, they always seem to run hot even just running a laptop.  They simply are not intended to run at maximum output for long periods or o cope with short circuits, . You need something with decent overload protection around 1 amp and a 21 watt bulb is still going to allow 30 watts/ 1.75 amps on an 18 volts supply which won't do your fishplates, point blade tags, or locos pickups and internal wiring much good if you get a dead short.  A 10 watt bulb might be a better bet but a proper thermal breaker is a better idea.

 

The bulb isn't going to have 18 volts across it. But we probably digress.

[kevinlms]

Using a laptop power supply sounds like a good way to set the railway shed on fire, I have had several laptop power supplies fail, they always seem to run hot even just running a laptop. They simply are not intended to run at maximum output for long periods or o cope with short circuits, . You need something with decent overload protection around 1 amp and a 21 watt bulb is still going to allow 30 watts/ 1.75 amps on an 18 volts supply which won't do your fishplates, point blade tags, or locos pickups and internal wiring much good if you get a dead short. A 10 watt bulb might be a better bet but a proper thermal breaker is a better idea.

I'm no fan of laptop power supplies either, but for different reasons to your logic. Their voltage and current ratings are both too high for modern rtr locomotives. Too much excess power to dissipate in the event of a short circuit, all too common on model railways.

[t-b-g]

One thing I haven't seen mentioned yet is to check for fluff, dust and muck between the pick ups and the wheels and also to make sure that the pick ups are touching the wheels at the full extent of any sideplay.

 

Clean wheels, clean track and clean contact from the pick ups to the wheels solve 99% of cases where locos need a nudge in my experience.

[34theletterbetweenB&D]

100% agreement on the need for clean rail, tread and wiper contact. Don't know what your rolling stock or track set up is, but elimination of sources of dirt really pays off. I would be inclined to suggest elimination of all plastic wheels, traction tyres, plastic point crossings, and minimal lubrication using grease - which 'stays put' - in most locations. It does need a degree of fanaticism to drive the dirt away...

[Colin_McLeod]

A rigid loco (or, in the case of diesels, substitute "bogie" for "loco")has two or more axles whose position is fixed in relation to both each other and the loco chassis itself. If one wheel goes over a bump that wheel will lift and, because there is no movement between axle and chassis, the whole side of the loco will be lifted. Because the loco chassis is also rigid, at least one other wheel must lift off the track. Think of a chair with one leg sitting on a bump in the floor. A wheel that is not in contact with the rail can play no part in picking up current.

 

To avoid this, it is possible to introduce suspension. On the prototype and on some sophisticated models this involves introducing springs between the axles and the loco chassis. If one wheel goes over a bump, the spring between the chassis and that end of the axle compresses and all the other wheels stay in contact with the track. On our models that means that they can continue to pick up current. Compensation is a method to achieve this result, generally without the use of springs. At its simplest, on an 0-4-0 loco or a four wheeled bogie, one axle is held rigidly to the chassis whilst the other is permitted a limited amount of sideways rock. This allows any one wheel to rise over a bump or fall into a hollow whilst not lifting any of the other wheels off the rails.

 

In practice, diesels tend to be less in need of some form of suspension because, as long as they have pickups on both bogies, the inherent flexibility between the two bogies tends to keep enough wheels down over a sufficient length of track to ensure that at least one wheel on each side is collecting current as it should.

 

However, this is getting quite some way from how to make r-t-r locos work as they should. given clean track and wheels, and pickups operating as designed, most r-t-r locos should start from rest unaided  every time.

PatB your post may have been away from r-t-r loco running improvement but, for me, it is a very informative and succinct explanation of compensation. Something I never really "got" until I read your post. Many thanks.

Colin

[kevinlms]

100% agreement on the need for clean rail, tread and wiper contact. Don't know what your rolling stock or track set up is, but elimination of sources of dirt really pays off. I would be inclined to suggest elimination of all plastic wheels, traction tyres, plastic point crossings, and minimal lubrication using grease - which 'stays put' - in most locations. It does need a degree of fanaticism to drive the dirt away...

Agreed, all those you mention are the normal means of preventing build up of dirt. Minute sparks created by loosing power, contribute to dirt on various surfaces. It can be largely eliminated by having as many pick ups as possible. This is where modern RTR locos have a huge advantage (except of course when they only have 4 wheels), as generally they have more pick ups. A long way from old Tri-ang days, where they usually only picked up from 4 wheels, regardless of actual wheels available.

The early Hornby Pacers, were amongst the worst, due to the fact ,that while each of the 2 cars were both powered, only actually picked up from 3 wheels each.

 

Sometimes on RMweb, it is suggested to eliminate problems of shorting on Peco Insulfrog points, that nail varnish or similar, be used to INCREASE the length of the plastic frog - amazing!

[Crosland]

 a 21 watt bulb is still going to allow 30 watts/ 1.75 amps on an 18 volts supply which won't do your fishplates, point blade tags, or locos pickups and internal wiring much good if you get a dead short.  A 10 watt bulb might be a better bet but a proper thermal breaker is a better idea.

 

No.

 

A 21W bulb rated for 18V will dissipate 21W and limit the current to 1.16 A, if there's a dead short with an 18 V supply. No harm will result to anything that was fit for purpose in the first place.

 

A 21W/12V bulb (implying a hot filament resistance of 6.8 ohms) with 18V across it will attempt to dissipate 47 W and will probably blow, if there's a dead short with an 18 V supply. The idea of using a bulb instead of a fuse is that you do not need to replace the bulb after every short.

 

It's simple application of ohms law V=I*R and power = I*V.

 

With a transistor controller some form of fast electronic cutout or current limit is to be preferred over thermal. It's very easy to arrange as part of the base drive to the output transistor. There are lost of circuits available. MERG used to have some on the public part of their website, worth looking there.

 

Laptop supplies have very fast overload protection and would be ideal if it were not for the high output voltages for MR application. A 12 - 15V switch mode supply is preferable except for those circuits that rely on the 100Hz from a rectified but unsmoothed supply.

Edited July 18, 2017 by Crosland