Trouble with power pickup (DCC loco)

[Chrissaf]

Has the loco been run in?. Ideally just a circle of track will do or a rolling road and run the loco at medium speed for half hour in each direction also turn it round and run the other way. ...HB

[Chrissaf]

I don't have a solution for you, but I just want to commend you for the level of detail in your question. Something we see far too little of.

[Going Spare]

The generic 0-6-0 chassis was used for this model and all the wheels therefore have plastic centres with metal treads.  Are the pick-up wipers making good contact with the metal tread?

Could the fault be caused by a fractured wire making intermittent contact within its sleeve?

GS

[2e0dtoeric]

Short wheel-base loco's always have trouble with plastic 'frog' points.

Try getting right down close to the point, and run the loco over it DEAD slow. See just where it stops.

Maybe there is some debris or plastic sprue in the gap between the rail and guide-rail, that is lifting the loco wheels ever so slightly, thus breaking contact.

Ensure that the whole of the point is dead flat. Some of them have a slight hunch-back - a result of the manufacturing process, and extra track pins can solve it.

[Derek 19B]

Hi macman44,

I would be concerned at the 15 ohm resistance in the loco ( I would only expect 8 - 10 ohms on a 100 meter run of alarm cable. Check your base line on the meter is it zero (always before testing anything) if you still get 15 ohms I would be heating up the solder joints just till they go liquid , it sounds like a bad joint at 15 ohms

derek19b

[macman44]

Wow, what a great response.  My thanks to everyone who took the time to offer suggestions.

 

Let me offer some additional comments and clarifications.

 

I haven't done a very extensive 'run in' of the locomotive, as I don't yet have a loop of track in my layout, but when I get a chance I will take it to my model railway club layout for some running time.  Now I have cleaned it up somewhat it may run well enough to do that if I run it fast enough.

 

In terms of whether the pickups are making good contact with the wheels, I removed the motor/pickup assembly from the chassis, and observed that the pickups for the front and rear wheels spring out by almost half an inch, so no matter how much sideways play exists in the wheels they are always going to be in contact.  And the pickups are nicely positioned  on the back of the outer edge of the wheels, which is the metallic tread.

 

The resistance measurements I previously reported were between the power leads to the decoder and the wheels.  I again removed the motor/pickups from the chassis, and measured the resistance from the pickup points to the power lead to the decoder, and got the expected zero ohms in all cases.  So those previous R values truly represent the resistance from the wheels to the pickups - where I would expect to see low consistent values if all were working correctly.

 

I looked carefully at the turnouts where stalling occurs, and there is no sign of foreign nubs or particles;  I also placed a steel rule across them and they are flat and level.  In any case, other locomotives (e.g. a 4-6-2 Tank) traverse them without any problem.  Most of my turnouts are electrofrog - it's only the slips and crossings that have plastic - so I think the stalling there is only a symptom of the main problem.   And I am getting hesitations and stalling on straight track if it isn't super-clean.

 

And another symptom I just noticed is that the loco does not pass enough short-circuit current from one wheel to another to trip the auto-reversing modules on reverse loops and live frogs.  Likely high resistance again.

 

However, I did notice something I hadn't seen before.  The centre driving wheels do not seem to be in contact with the track, even on straight and level sections.  With the loco on the track, I can move the centre axle slightly from side to side using the normal built-in play, and there is no noticeable rubbing with the track.  It is difficult to see this by eye, even placing a steel ruler across the treads of the 3 drivers, but it is defintely there.  I conclude that the centre wheels are not contributing to power pickup, thus providing only two pickup wheels on each side.

Further to that, I looked carefully at where the loco stopped when run at low speed through a crossing.  One front or rear wheel (never the centre one) always stops on a plastic frog or a short unpowered section of track, thus leaving only one wheel to collect power.  Pressing down on the  end of the chassis with the 'good' wheel does not encourage the loco to move, but gently moving the chassis sideways (using the play in the front or rear axle) will sometimes provide enough power pickup to allow the loco to move.  Remembering that there is always pickup contact on these wheels (if poor), it appears that the pickup needs a little jiggle or additional pressure to get going.

 

So where does this leave me?

First, I have to find a way to get those centre wheels into contact with the track, to get 3-wheel pickup on each side.  But I have no idea how to set about it.  Thoughts?

Second, it looks like my earlier comment about the pickup material being  rather flimsy and unable to exert much pressure might be a contributing factor.  I suppose I could bend them beyond the half inch they are already, but I am a bit reluctant to distort them too much, and I have to be careful about possible short-circuits to the metal chassis.  I wondered whether there is such a thing as a conducting lubricant I can sparingly smear on the back of the wheels to inprove conductivity?  I have to get over that intermittent (but frequent) 15 ohm conductivity.

Thirdly, a period of runnng in might help settle things down.

 

I'll keep at it, but this is proving to be more work than it ought to be.

 

Paul.

[96RAF]

Two things....

1. you mention the centre wheels sometimes dont touch the track. Some of these six wheel chassis had sprung rear drivers and the instructions speak to adjusting the spring rate to get the ride correct.

2. I have a Bachmann Jinty and the moulded springs under the chassis were lifting the wheels off track over certain frogs. A rub with a file reduced these in height to improve clearance.

Rob

[2e0dtoeric]

Macman put - The resistance measurements I previously reported were between the power leads to the decoder and the wheels.

Did you unplug the decoder before measuring? Or did you inadvertently measure the impedance of the decoder input?

[macman44]

Unfortunately there is no sign of any adjustment or springing in any of the wheels on this locomotive.  The wheels have steel axles which ride in bronze (?) bushes which locate firmly in cavities machined on the underside of the cast metal chassis, then being held in place by a plastic moulding which also represents the underside of the loco.  The only ways I can see to get the centre wheels closer to the rails would be to deepen the cavities for the front or rear wheels (seems impossible without machine tools set up for this), or to slightly pad the cavity for the centre wheels (how?) so that they 'stick out' from the chassis a little (and possibly file away the plastic retainer to make space for this).

 

Am I expecting too much from a basic locomotive that has no adjustment and is relying on accurate alignment of the wheels to reliably pick up power?  Or should I be contacting Hornby and see if they have any suggestions?  Always keeping in mind that I still haven't solved the high resistance wheel pickup problem on the other wheels, and until I do this engine won't run on my layout at all.

 

On the subject of high pickup resistance, I seem to remember a product that Peco used to sell years ago called Electrolube.  It was supposed to improve sliding contacts such as these.  Peco don't seem to carry it anymore, but it does still exist, and I wondered whether it would be worth trying to get some to see if it would help.  Or perhaps there are other similar  (and better?) products out there.

 

And to answer 2e0dtoeric's valid question, no I didn't unplug the decoder but I didn't need to, since all my measurements were confined to a single lead facing outwards from the decoder towards the wheels on that side, without measuring through the decoder itself.  The reference to the decoder was simply to identify where I connected one of the ohm-meter probes.

 

Paul.

[The son of Triangman]

What was the loco's performance like before decoder fitting?

 

Admin please could you move this thread to the DCC section? We seem to be getting a lot of DCC related threads in the main forum of late.

[Chrissaf]

The OP stated the model number as R3121X the X denotes that the decoder was Hornby factory fitted.

.

Thread moved as requested.

[Chrissaf]

I have just bought a Class J2 0-6-0 tank locomotive (Hornby R 3121X), and am having difficulty getting reliable power pickup from the track.  I am looking for  suggestions as how to improve it.  The loco often stalls when traversing turnouts and crossings with short unpowered sections (e.g. frogs), and will hesitate or even stall on straight track that has even a trace of dirt or grease.  As confirmation of this behaviour, restistance measurements with an ohm-meter between the track feed to the decoder and each driving wheel in turn reveals values between 2 ohms and 15 ohms or more with a lot of 'dither' (i.e. the resistance varies within a range whilst the loco is fully quiescent).  So it's the wheel pickups that are the problem.

My other locomotives run fine through the same track sections.

The engine has pickups on all 6 driving wheels with a welded (phosphor bronze?) pickup assembly on each side, which is in good condition.  There is plenty of springiness in the pickup arms, and there is no doubt that they are fully in contact with the backs of the wheels at all times.  However, the pickup material is very lightweight, and it is doubtful whether it is exerting much pressure on the wheels.

I have thoroughly removed all traces of tarnish from the pickup points with 600-grit emery paper, and have cleaned the pickups and wheels with iso-propyl alcohol (no dirt was present, however).  Everything is sqeaky-clean.  It still doesn't run well.

Can anyone suggest anything that I haven't tried, to cure this problem?  I don't have the opportunity to return it to the vendor, since it was bought at a train show 'as-is', and is clearly an item that has been sitting around for a while on a dealer's shelf, although obviously unused.

Thanks,

Paul.

[macman44]

This really isn't a DCC issue, since the power pickup problem is occurring independently of the decoder, and before it gets involved.  If there were no decoder, I would be having the same issues with getting this loco to run.  That's why I originally put it into the general discussion forum, without the title originally identifying that it is a DCC loco.

[Howbi]

Hi Paul, just tested my J50 from the Digital Mixed Goods set.........the resistance from each wheel to the decoder connection was 0.2 / 0.3.......have a look at the phosphor bronze pickup strips along each side.  There is one section which has an insulating coating to protect it from touching the chassis ( ringed in red). Would be worth checking also condition of the solder joint on the strip......HB

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[macman44]

Thanks, HB.   Good to know what sort of R value I need to get to.

 

Anyway, I think I have finally got to the bottom of it.  The inside of the wheels, although having the appearance of polished steel and coming up clean with alcohol cleaning, apparently was coated in a very thin, very hard, uniform, very difficult to see, and somewhat insulating coating of some kind.  Maybe some oxide of the metal the wheels are made of, I don't know, and I don't know how it got there.  It proved difficult to remove, and I had to take the wheels out of the chassis and sand the insides extensively with 600-grit emery paper.  The result is a bright but scratched finish which now picks up power reasonably well, and has a pick-up resistance comarable to HB's.  I don't think I got all of the coating, and I am concerned that the roughter surface will attract dirt over time, so I would appreciate thoughts as to how I can polish up these inside surfaces, and prevent deterioration again.

 

And I still have the issue that the centre wheels really don't contact the track well, thus negating their contribution to the power collection.  Thoughts on dealing with this would also be appreciated - no springs or adjustments provided.

[Howbi]

Your problem with the centre wheels not touching the track is very odd.......as far as I can see the three axles run in their bearing grooves in exactly the same plane in the chassis casting.......have you tried to measure the wheel diameters to prove the centre wheels are correct?.........HB

[96RAF]

I wonder if a previous owner has sprayed a coat of lacquer onto the loco and oversprayed the inside of the wheels by mistake, in which case a rub with thinners/IPA would have been kinder than a rub with abrasive paper. Too late now as the damage is done and will have to be lived with, likely as needing more regular cleaning.

Rob

[macman44]

Your problem with the centre wheels not touching the track is very odd.......as far as I can see the three axles run in their bearing grooves in exactly the same plane in the chassis casting.......have you tried to measure the wheel diameters to prove the centre wheels are correct?.........HB

Good thought.  I went and measured the diameters, and they are all the same to within 3/100 of a mm.  It isn't possible to detect the non-touching visually, but you can feel the lack of friction with the track as you move the centre whels sideways; I have also confirmed that there is no continuity when measured with an ohm-meter.  But following up on that train of thought, I placed a steel ruler across the centre-lines of the axles, and the centre one is certainly out of line (away from the track) by almost 1 mm relative to the front & rear (hard to be precise, but it's definitely there).

Could there possibly be a slightly mis-cast/mis-machined chassis block?  I have had a mis-cast part before in a different Hornby loco that had to be replaced.  How can I be certain about it?  If so, what are my options for fixing it or getting it replaced?

Paul.

[macman44]

I wonder if a previous owner has sprayed a coat of lacquer onto the loco and oversprayed the inside of the wheels by mistake, in which case a rub with thinners/IPA would have been kinder than a rub with abrasive paper. Too late now as the damage is done and will have to be lived with, likely as needing more regular cleaning.

Rob

The first thing I tried after a visual inspection was to scrub with iso-propyl alcohol.  The cleaning cloth came up very clean, and it made no difference to performance.  And I believe that I am the first owner other than the dealer upons whose shelf this locomotive has probably sat for quite a while.

And having fixed the bronze contact problem, I find that the wheel flanges/tyres seem to have the same problem (intermittent contact with the track), and I am open to suggestions about what to try short of going the abrasives route again.

Paul.