Model Railway Forum banner

Another loco stalling on points issue

2067 Views 29 Replies 7 Participants Last post by  Graham Plowman
Apologies for regurgitating this all over again - I have looked at previous posts on the subject, but I wanted to ask a specific question, in relation to a theory about the points design/manufacture, that I couldn't find an answer to.
My layout (controlled by DCC) incorporates Peco insulfrog points. My two locos, a J94 and a class 4575 small Prairie both tend to stall at low speeds at several sets of points, as the central of the larger wheels reach the plastic of the insulfrog.
I thought I had the problem sussed when I tried applying a small weight (about 10 grams) to each loco - at the front of the J94, and the rear of the 4575. (Each loco moving slowly in a forward direction). However the issue returned, despite the weights still being in position, when running in the opposite direction. I'm starting to suspect that the locos are being lifted imperceptibly at the frog which is affecting electrical contact to the driving wheels, and the application of the weights is just enough to keep the wheels in contact at one end.
So, here's the question. Would you think that the base of plastic insulfrog mouldings are not made low enough to the base of the track, to allow the wheel flanges to pass over them unhindered. If this is correct what remedy can be taken?
Thanks for taking the time to read
1 - 20 of 30 Posts
I think you will find the flanges are not contacting the bottom of the crossing moulding, Peco are pretty good at getting their mouldings right. (It takes a very coarse flange such as the old 'pizza cutter' flanges on Lima to foul on the bottom of the moulding.)

You have actually begun to identify the problem by seeing the 'balance' issue. The problem is that the point base has a slight upward bow imparted by the curved rails attempting to straighten - that's an issue Peco haven't corrected. What happens as a result is that the centre coupled wheel is raised slightly on the plastic crossing, and the loco balances with both of the coupled wheels either side out of contact with the rail - and there is no pick up!

If you take one of these points off the layout and sight along the rail top - which should be flat, i.e. horizontal - you will be able to see the upward bow. Comparison to a steel rule as a straightedge will make the slight deviation apparent. It's not gross, but it only needs a tiny airgap between tyre and rail to prevent current collection.

Cure. My preference is to glue down the point on the ply base.I have some steel blocks which sit on top for at least 24 hours as the glue goes off. (I do this on Peco live crossing points too, rail top should be horizontal, on all except intentional gradient transitions.)

Then again with the steel rule straightedge. If there is any hint of a rock across the crossing, use some fine abrasive paper on a small block to bring the plastic crossing down to match the metal rail top. Gently does it, there shouldn't be much to remove and avoid scratching the rail top.
See less See more
I concur with 34C.

There are two solutions:

1) Make sure that your track-bed is flat/level and ensure that your turnouts are firmly attached to it. Some people do this by putting pins through the middle of the turnout. Personally, I prefer to glue it down with weights located on top until the glue dries. My mirror tip will help you look along the tops of your rails: Using a Mirror to Align Track - Model Railways On-Line

2) Having dealt with (1), run a file across the common crossing (the V). You may find that it is slightly raised, in which case, you can file it down level with all the other rails. As 34C indicated, Peco are usually pretty good with this now, although it used to be an issue in the past.

  • Like
Reactions: 1
...My mirror tip will help you look along the tops of your rails: Using a Mirror to Align Track - Model Railways On-Line
Can't believe I forgot to mention this, it's such a good 'detector' for points already laid. Needs to be 'nailed up' somewhere in a 'hint and tips' file!
Thanks 34C and Graham, great advice both.👍. I'll follow both suggestions through, but as I had a minute to spare and steel rule to hand I did a quick check on one, and it does seem there is a slight deviation.
By the way all points were already glued firmly down, using weights, so all good there.
Thanks again
Update - Having checked on the flex of the glued down points (and there was a little in places), I have now done belt and braces, so as well as glue, I've pinned all the points as well. Is there a slight improvement in slow speed running? Well, maybe, but equally could just be because I'm willing it to be better??
I have also used my vernier callipers to confirm that the loco wheel flanges do not interfere with the base of the groove of the plastic frog mouldings. All that's left now is to address the cause of the slightly raised section around the frogs
I think you might have found the shortcoming of using Insulfrog with DCC. The specific design of Insulfrog has the two frog rails extended much closer to the frog than other makes of dead frog point, this is an excellent feature for DC as it gives a lot more metal on the frog, but for DCC it means that you will get a momentary short as the wheel tread touches both of the frog rails (which are at opposite polarity).
  • Like
Reactions: 1
Hi Suzie,
Thanks for your comment, much appreciated. I'm beginning to wonder if I should have installed electro frogs instead 🤔. It is noticeable that my J94, having a short wheelbase between the wheels with the contacts is more problematic than the longer class 4575.
This is typical 'learn as you go'.

Yes, live crossing is superior: 'electrofrog' in old Peco speak, but now we have 'unifrog' from Peco as their new standard, which can be wired for live or dead crossing. (Peco have to offer both options as a great many layouts are still constructed on the basis of using the points for power isolation, a bodge that simply won't go away...)

Suzie is quite right about the potential for DCC shorts on dead crossing points; but you haven't mentioned your DCC system tripping when a loco stalls on a point so that presumably isn't happening at present? Some wheel forms and 'arrangements' found in RTR OO are worse than others for this problem, I can definitely point at Hornby's class 30 and the flangeless wheels in their pacific trailing trucks among current products; there are probably more. (It is possible to modify these dead crossing points to eliminate the problem completely, essentially altering them to live-crossing-alike' but that is for another day...)
See less See more
Another thing to check is that the pick ups are in contact with the wheels at all points in the side to side movement of the axles.
The momentary short is usually not enough to shut down the command station, but is enough to deprive the loco of power.

It should be possible to rewire the points as if they were live frog, but a bit of a big job after the track has been laid due to the need to fit insulated joiners.
The momentary short is usually not enough to shut down the command station, but is enough to deprive the loco of power.

It should be possible to rewire the points as if they were live frog, but a bit of a big job after the track has been laid due to the need to fit insulated joiners.
Even in my very early DC days, I recognised that this was a problem with dead-frog turnouts, so I treated them like live frogs and fitted IRJ's to the back end of the crossing and power fed from the toe.
Once I discovered live frog turnouts, I have never used anything else since.

Remember that a short in dead or live frog will only occur where two opposing polarities are in close proximity and something like a wide wheel tread or out of gauge wheels can bridge between them.
Best practice is always a good idea to wire so that opposing polarities are never close together or of there is a risk that they could be, that one rail is isolated ie not connected at all.

Wiring live frog turnouts here: Live Frog Wiring - Model Railways On-Line
Graham, thank you for your further explanation and the link, which describes the wiring and alterations needed very clearly. Very helpful.
Update 2 - I have followed the good advice above, and worked through several possibilities as to why I'm still seeing the locos stalling. I've made sure the pick ups are properly in contact with all the wheels in relation to axle side to side movement (thanks Butler-Henderson), and while I was at it, I cleaned the treads, flanges etc to ensure good electrical contact. I'm still not sure if I'm getting a momentary short somehow but the DCC controller does not trip, and I checked to ensure the wheel treads are not shorting at the converging of rails at the frog. Overall, the situation has improved with complete stops being reduced, but I'm still seeing the locos regularly 'stuttering' through the same points each time (although not all interestingly). However when the locos do completely stop it inevitably is when the central coupled wheel is over the plastic of the frog. When this happens, to get the loco moving again it either needs a slight downward pressure on the cab, or funnel, or slight sideways movement across the wheel axles. Of course, there is no such problem if the loco speed is increased.
I'm coming to the conclusion that I need to replace one of the points for an elecrofrog with associated IRJ to prove this cures the issue once and for all, then replace all the others likewise.
See less See more
If you are still getting stuttering and the command station stays stable (ie no cut-out due to short), it would suggest to me that there is a loss of power.
Although you've checked that the pickups are contacting the backs of the wheels, it doesn't necessarily mean that they are making good electrical contact.
If you haven't done so already, may I suggest that you position you loco upside down and connect two wires from the rails to the wheels on one wheel set at a time while power is running. The purpose of this is to check the continuity of each individual wheelset and its pickups. Wobble the wheels a little to see of the motor stops - I highly suspect that you may have some axles which are not fully making contact, in which case, the pickups may need tightening up a bit more.

It could also be an issue of lifting. Since centre driving wheels on a crossing seem to be a common factor, it suggests that there might not be any vertical movement possible in the other wheelsets, although this would be unusual. Having said that, I have filed groves in chassis base plates before to enable a little axle vertical movement for exactly these situations. Be careful with this approach as it can be a case of solving the symptoms (stuttering, which some people mis-identify and end up using stay-alive) rather than the root problem - track which actually is raised - try my mirror technique above to see if the rails are raised.

If that doesn't cure the issue, then yes, electrofrog is the way to go.

See less See more
Graham, thank you for continuing to help, it's much appreciated.
I should have said earlier that I did try your mirror technique which was very helpful, insomuch as it didn't highlight any issues with the points. I will try the two wire technique next, and also check for vertical axle movement. I had already found that the central axle has virtually no side to side play, and had wondered about that, although of course it does stop the possibility of the loco looking off centre in relation to the track.
I was naturally focusing on the track to identify the issues as the two locos I have are brand new, and I thought it unlikely that they would both have similar electrical pick up problems.
I don't know if other newbies experience similar problems, and although frustrating, it is giving me the opportunity to quickly learn various maintenance techniques which otherwise may have taken much longer to pick up.
Thanks again for your help and patience
...I don't know if other newbies experience similar problems...
They certainly do. There are a great many many key pieces of know how, to get the best out of model railway based on two rail electrical pick up.

Happily you appear to have the engineer approach of understand what the evidence is revealing and learn how to systematically rectify. This is an essential because the production of RTR OO product isn't as well engineered as is truly desireable. Every single piece I own has been altered, adjusted or worked on to optimise performance and/or appearance. It does become easier as experience is obtained.
I've now completed the two wire test on both locos and all axles. No problems encountered.
The total vertical axle movement appears to be less than 1mm on front and rear axles, and pretty much nothing on the centre one. This is the case with both locos.
Electro frogs are getting closer 😉
Ooops, I hope I will be corrected on this, but thinking about replacing the insulfrog No. 2 radius points (code 100) with electrofrog equivalents appears to be a non-starter. Having looked on Peco's website it seems that there are no electrofrog points with the same dimensions as the insulfrogs, not only are the overall lengths different but so is the radius and frog angle.
Back to the drawing board 🤔
That's correct. Unfortunately you are using OO 'set track' (made to a 1960's design, and introduced by Triang-Hornby in about 1971, now manufactured by all of Hornby, Bachmann and Peco) which has had no updating to better suit DCC.

Far the better option readily available in the UK is Peco's OO 'Streamline' range which offers a much wider range of live crossing points, which hopefully you can start using in time.
1 - 20 of 30 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.