Peco Bullhead Points: in the flesh

[The Stationmaster]

9 hours ago, St Enodoc said:

Your dinner must have taken a long time to cook...

I understand it can be quite difficult to get domestic staff nowadays.

 

PS I had to go out and dig up part of our dinner yesterday evening - fresh boiled spuds are delectable with salad

 

But even if his dinner took a long time (or was burnt to a cinder) thanks to PMP for carrying out such an exhaustive test.

[34theletterbetweenB&D]

11 hours ago, PMP said:

So, bored this evening whilst din dins was on the go, and with unrestricted access to the man cave, I tried one or two items out across a set of three CD75 bullhead turnouts. The configuration is 3 x right hand, one pair set as a crossover. So with one failure due to short wheelbase not bridging the frog, (the Hornby 0-4-0 Peckett), it was time to rummage through the cellar to see what worked. To ensure I got a reasonable sample I made sure that the locomotives ran through all three points in both directions slowly. The the model was turned 180 degrees and then repeated ...

 

That's around 70 different types from all major manufacturers that work through these points with no shorting or stalling...

With all respect for the effort you made Paul, this is insufficient.  The problem is the inevitable variation in all manufactured product, and the uncharacterised sensitivity of your test.

 

(I have been there many times in my career, where 'field' have made a mod to a product without engineering authority approval, and then subsequently had problems with functionality in customer use.

 

Field: "But we tested it before we did it, and it worked."

 

Engineering authority answer: "It may have done so for the sets of components you had available, but you have no idea where those components are within the specified acceptable variance, nor whether your test was sufficiently well designed to be sensitive to the full range of specified customer use".

 

I was regularly deeply unpopular with 'field' for bringing this message of joy. Usually because what went with it was "And your cost saving scheme based on this mod will not result in the bonus you are happily anticipating: that will be stopped to teach you the path of righteousness".)

 

On my test track installation - which is subject to all the caveats mentioned above regarding not knowing where the point samples I have lie within the product variaince - the current working estimate is a short occurrence of 1 in 500 passes incidence for the most sensitive vehicles, speed variable, worse at high speed.

 

So not a serious problem, but not one I want, and I am going to fix it by making the points equivalent Peco's electrofrog, which is proven problem free.

[Nile]

12 hours ago, PMP said:

So, bored this evening whilst din dins was on the go, and with unrestricted access to the man cave, I tried one or two items out across a set of three CD75 bullhead turnouts. The configuration is 3 x right hand, one pair set as a crossover. So with one failure due to short wheelbase not bridging the frog, (the Hornby 0-4-0 Peckett), it was time to rummage through the cellar to see what worked. To ensure I got a reasonable sample I made sure that the locomotives ran through all three points in both directions slowly. The the model was turned 180 degrees and then repeated. A couple of these weren’t tested this evening as they have already ‘left the building’. Some of them (57xx’s surprise surprise, and 08’s, DMU’s), are multiples that have worked through this test piece recently whilst checking the viability of the track plan.

 

Hi Paul, did you wire up the frogs or leave them dead?

According to this post:

the problem only occurs when they are 'live'. Or have I misunderstood Chamby?

[PMP]

14 minutes ago, 34theletterbetweenB&D said:

With all respect for the effort you made Paul, this is insufficient.  The problem is the inevitable variation in all manufactured product, and the uncharacterised sensitivity of your test.

 

Paul, I too have a partial engineering (not qualified) aviation background. I’m more than aware that the tests I’ve done are not exhaustive. If you want to get to the bottom of this ‘issue’ the floor is open for you to provide the data with your own testing. Over to you on that one.

 

 

[PMP]

2 minutes ago, Nile said:

 

Hi Paul, did you wire up the frogs or leave them dead?

According to this post:

the problem only occurs when they are 'live'. Or have I misunderstood Chamby?

Fresh from the packet, not wired. 

[34theletterbetweenB&D]

1 minute ago, PMP said:

Paul, I too have a partial engineering (not qualified) aviation background. I’m more than aware that the tests I’ve done are not exhaustive. If you want to get to the bottom of this ‘issue’ the floor is open for you to provide the data with your own testing. Over to you on that one.

All I can report at present is that with the points installed as live crossing, and as Peco supply them; with my assortment of largely BR(ER) appropriate steam and diesel models and stock, both RTR OO and kit built:

 

Estimated 1 in 500 incidence of a short for the passage of the most sensitive vehicles, high (scale) speed is the worst condition for the problem. (I haven't looked at the potential stall problem at all, no short wheelbase four wheel traction on the layout roster, so no need to test.)

 

 It's taken much of the time since these points first went on sale to accrue this much data; both identifying the most sensitive vehicles and then sufficient running passes. I am somewhat fanatical about reliability and fault elimination, and that's enough data for me: I am going to modify to a proven trouble free configuration.

 

 

It is worth adding that overall I assess the large rad BH point as a welcome advance, the one piece closure rail is superior to the previous 'loose heel' arrangement. But Peco could improve it for my purposes at least, by reverting to the 'electrofrog' design; fortunately this is a simple modification for this owner to perform.

[PMP]

53 minutes ago, 34theletterbetweenB&D said:

 

Estimated 1 in 500 incidence of a short for the passage of the most sensitive vehicles, high (scale) speed is the worst condition for the problem. (I haven't looked at the potential stall problem at all, no short wheelbase four wheel traction on the layout roster, so no need to test.)

 

I think there’s 74? types in my list. At four passes that’s 296 events with no occurrence in straight Unwired DC. There are far more unrecorded events. During lockdown I’ve had these up with isolated sections to test the new layout. This meant ‘playing trains’ with predominantly Bachmann 1st gen DMUS, new 24, 08 B&H, HJ 35’s. Also running ‘whatever’ as it took me, GW outline panniers , 45xx and Jinty’s. None failed. I’m confident that there’s likely more than 500 passes with DMU 108/105//DLW, Bach 08 And NG24 just as a result of playing trains over this past couple of months. It’s only a three point Futers style terminus, so every move passes through at least one point.

Just to try them I added these two thus morning.

They work too. Added to original list with Hornby CL71. I’m certain the MR/ Rapido 16xx works too, but I’ve not had that personally to test, so it’s not on the list.

 

It would be helpful if contributors listed their problem locomotives, then we could compare and contrast.

Edited June 28, 2020 by PMP
Add pics

[34theletterbetweenB&D]

3 minutes ago, PMP said:

...It’s only a three point Futers style terminus.

And there's the key difference in my opinion. Mine are for part of the ECML, and the fast trains go at scale for 60mph+. It's the fast passes where the problem I observe occurs: slow speeds, no shorts.

[PMP]

I would have thought low speed would accentuate a problem, giving whatever is shorting a far better chance of making the required contact than a fast pass. Why would increased speed highlight the problem over low speed?

 

NB all my points are fixed together using the Peco bullhead specific metal rail joiners/fishplates 

[Godders]

The speed in itself would not affect the electrical contact. The speed of anything compared to the speed of electricity is very low. I would suggest that it is more to do with the mechanical characteristics of the trains, perhaps wheels "crabbing" i.e. the wheel not parallel to the track. Probably won't occur in long wheelbases, 6 coupled for example. Possibly another case of BtoB too small.

[34theletterbetweenB&D]

Absolutely, the model's speed component is insignificant relative to the contact required for a short, because the electric moves at near C.

 

The observed evidence I have is that shorts occur when the models move at higher speeds, so that's when contact must be occurring.

 

It would need a high speed camera to prove what I surmise to be the cause: rod coupled wheels 'moving about' due to the drive forces. They don't solely rotate on the axle, but also variably move laterally, and the attitude of the coupled chassis varies too while in motion. Sum all that jumble of movements, and once in a while a tyre gets into a position where it contacts the rail it isn't running on at the crossing, and there's the short.

 

I have already - largely on aesthetic grounds - eliminated inadvisable constructions. One such group, Hornby's two pivot pony truck and Bachmann's 'radial' truck, which can present the truck wheelset skewed which effectively reduces back to back. Also limiting sideplay* to that required for the layout minimum radius, and replacement of wheelsets with tyres of the unconed/steamrollerish persuasion.

 

*A very specific example corrected well before the BH points appeared, primarily because of trackholding deficiency. Of the four Hornby Brush 2 (30/31) chassis I now have, three had excessive side play of the bogie end wheelsets, because the brass strips in which the axle ends run were splayed outwards as viewed in plan, and this was sufficient that the axle ends began to disengage from the axle hole they should have been running in.

 

 

[PMP]

20 minutes ago, Godders said:

I would suggest that it is more to do with the mechanical characteristics of the trains, perhaps wheels "crabbing" i.e. the wheel not parallel to the track.

On that basis the Hj railcars (tested) and the Brit/Clan would likely be prime contenders, with maybe the LMS twins in for good measure. The Railcars have little lateral movement and no swivel. Not just my few trials but it’s not reported here or on HJ threads that these are giving problems. The 1/500 event has me head scratching too. If I think about running my layout at an exhibition, 8 hour day, and assuming one movement per minute across a point, that’s 480 movements. Again assuming I’m running a potential susceptible model, that’s less than one event per day, if everything aligns. I accept it may occur more frequently, but PJ’s given an estimated 1/500. Due to the vagaries of exhibition running, I’d expect at least a few (five to ten OTTOMH), varied failures per day with a well set up exhibition layout and team. 

[martin_wynne]

These discussions are interesting but don't change the fact that there is a flaw in the Peco design:

 

 

A wheelset which is not set to the maximum possible back-to-back, or is not square on the axle, is liable to contact the end of the metal closure rail in the Peco design as it stands. The closure rails are at fixed opposite polarities, so a short-circuit condition is then inevitable. It is much more likely for wheels running in a facing direction, but not impossible in a trailing direction.

 

This applies to all 00 models of any origin, it is purely a matter of individual circumstance in the way the wheels happen to be running to avoid it (and the sensitivity of the short-circuit protection).

 

To avoid the problem the dead sections at the knuckle need to be much longer, as shown. It is very likely that Peco will make such a modification to the tooling in due course. They may not say so, because that would imply a product recall for the existing turnouts.

 

In the meantime, a smear of epoxy or hard-wearing varnish on the side of the rail will fix the problem.

 

Martin.

[Chamby]

4 hours ago, Nile said:

 

the problem only occurs when they are 'live'. Or have I misunderstood Chamby?

 

Hi Nile.  Shorting occurs more often when the frog is live because there are more opportunities for rails of opposite polarity to be in close proximity.  But shorting can also occur with the frogs in dead mode, for example:

 

On the basis that a picture paints a thousand words...  Yes, I have staged these for photographic expediency, but they demonstrate what happens.  My apologies for the limited macro capability of the iPhone camera used here!

 

 

The photo above shows the 'crabbing' effect of the L1 front pony bridging the gap between rails of opposite polarity just before it reaches the frog.  Note the back of the flange touching the opposite rail, the far side of the insulated rail break.  This short occurred frequently with both of my L1's and is what first drew my attention to the possible issues.  It now doesn't ever happen following the modification, because the electrical rail breaks have been relocated to where the rails are farther apart.  Epoxy insulation on the inside of the rails would also work here.

 

 

Apologies for the poor depth of field in the photo above, which shows a 'Princess Coronation' fitted with the flangeless trailing bogie wheels that enable it to negotiate tighter radii.  You can make out, despite the blurring, that when running on the curved track, the wheel 'hangs out of gauge' and can short across the top of the rails of opposite polarity on the straight road, before encountering the frog.  I have two Princess Coronations and seven A3's with this arrangement, some are fine, others will short intermittently.  It seems to depend on whether the flangeless wheel actually sits on the rail or is suspended above it.  Epoxy on the inside of the rail wouldn't work here, it would need to obscure the top of the rail and that would extend the length of the dead section.  Incidentally, the rear driving wheel also shows just how close the back of its flange is to the straight rail which is an opposite polarity at this location.  As has been said many times, it only needed the rail breaks to be moved a bit farther away from the frog, like in the FB electro frog turnouts, for the problem to disappear.

 

1 hour ago, 34theletterbetweenB&D said:

...The observed evidence I have is that shorts occur when the models move at higher speeds, so that's when contact must be occurring...

 

 

I have observed this too.  The laws of physics suggests it may(?) be something to do with centrifugal force?  At higher speeds and therefore higher inertia, the locomotives wheels are pushed harder against the inside face of the outside rail.  You can imagine with the Coronation above, that the flangeless wheel might 'hang out' farther as the loco travels faster through the curve.  As we all know, drive too fast on too tight a radius, and the centrifugal force will even cause the loco to fall off... on the outside of the curve of course.

 

1 hour ago, PMP said:

...On that basis the Hj railcars (tested) and the Brit/Clan would likely be prime contenders, with maybe the LMS twins in for good measure.... 

 

There appears to be considerable variation between apparently identical models... have a look at your one example, the Clan, do the trailing bogie wheels actually touch the top of the rail?  Some do, some don't.  I notice that you have very few Hornby pacific's on your list and you haven't tried the L1 either.  Trust me, other forum users do know what we're talking about here, because we found out the hard way and I hope that the above photo's communicate at least some of the issues clearly.

 

Phil

 

 

Edit:  Just to clarify, I am still buying and using these points for the scenic sections of my layout, but I do now always make the previously mentioned modifications.  They still represent a relatively straightforward way for a non-trackbuilder to acquire fine-scale bullhead turnouts in OO gauge.

Edited June 28, 2020 by Chamby

[Nile]

Thanks to Martin and Phil for illustrating the issues.

[Jeff Smith]

Just looking at the NMRA wheel standards page for 16.5 mm track, ie HO, there is a note at the top that says "Back-to-Back, B, is derived by knowing B = K-T.  K is the primary controlling dimension."

 

 in other words if the flange, T, is incorrect, setting the BtoB will not necessarily be correct.  T is quoted as being a max of 0,76mm, so no minimum.  If the flanges are undersize setting the correct BtoB could result in the wheel back hitting the opposite polarity rail if the whee-set is hard over onto the stock rail rather than running with the wheel back on the stock rail check rail.

K by the way is quoted as target = 15,32 +0,05 -0,18.

[Jeff Smith]

I just measured some brand new Hornby wagon wheels at 14,16mm BtoB but the flange is about right at about 0,79mm.

[tender]

Another solution that doesn't involve cutting the switch rails (providing you haven't laid them yet) would be to cut the switch rail bonding wires and feed them to switches on the point motor so that only the active switch blade is live.

Edited June 28, 2020 by tender

[martin_wynne]

1 hour ago, tender said:

Another solution that doesn't involve cutting the switch rails (providing you haven't laid them yet) would be to cut the switch rail bonding wires and feed them to switches on the point motor so that only the active switch blade is live.

 

There is still a tiny risk that a wheel back could be touching the back of the open blade at exactly the same moment that another wheel is shorting at the knuckle. It's such a small risk that Sod's law practically guarantees it will happen.

 

Martin.

[PMP]

5 hours ago, Chamby said:

 

There appears to be considerable variation between apparently identical models... have a look at your one example, the Clan, do the trailing bogie wheels actually touch the top of the rail?  Some do, some don't.  I notice that you have very few Hornby pacific's on your list and you haven't tried the L1 either.  Trust me, other forum users do know what we're talking about here, because we found out the hard way and I hope that the above photo's communicate at least some of the issues clearly.

 

Phil

@ChambyThanks for the images. Re L1 and Pacific’s , I have no L1’s And just the Clan/Brit. For 2-6-4’s the Fairburn and 80xxx are that same arrangement, and the 61xx/42xx both have Hornbys vari length chassis with pony trucks with longitudinal movement. I obviously note they aren’t identical, but share similar characteristics.

 

Re the Clan and Brit. This evening I’ve only been able to try the clan, the tender electrical link failed on the Brit. Once repaired I’ll try it. The Clan and others as you note have the solid rear pony truck and flanged/less wheelsets to go with it. If you tighten the keeper plate fully I note the treads actually lift off the rails by approximately 1mm possibly less.
 

Same criteria as the list, not wired, DC, Peco CD75 bullhead railjoiners to Peco Bullhead Flexi. With the Clan and  a brave pill I can get full speed across the points and stop it before I get wood. I’ve tried it at various speeds and also removed the rear pony axle to see if that had any impact. I adjusted the keeper plate so it allowed vertical travel for both wheelsets, and haven’t been able (yet) to get the model to electrically short. I then took the keeper plate off and ran without that, but wheelsets in. Flangless derailed, flanged ok. B2b set at 14.5mm.

 

ps I don’t think either PJ or Phil are making this up and don’t doubt something is occurring with their equipment. 

 

 

 

@Chambydoes the name Arthur busbridge mean anything to you?

Edited June 28, 2020 by PMP
Add ps bit

[Chamby]

1 hour ago, PMP said:

 

@Chambydoes the name Arthur busbridge mean anything to you?

 

Yes, but I’m struggling re: joining the dots!

[tender]

13 hours ago, martin_wynne said:

 

There is still a tiny risk that a wheel back could be touching the back of the open blade at exactly the same moment that another wheel is shorting at the knuckle. It's such a small risk that Sod's law practically guarantees it will happen.

 

Martin.

 

Does that really matter if the switching arrangement is such that the open blade isn't connected to anything?

[martin_wynne]

58 minutes ago, tender said:

Does that really matter if the switching arrangement is such that the open blade isn't connected to anything?

 

If the back of a (metal) wheel touches the open blade, it will connect it to the stock rail.

 

cheers,

 

Martin.

[Chamby]

@tender‘s proposal would work if the switch blade not in use was electrically isolated when the other route was selected.  There are two potential issues for me with this modification however:

 

Firstly, albeit very unlikely, as @martin_wynne points out, contact could possibly occur at either end of the blade rail, if this happened simultaneously it would cause a short.  This would be dependent on the locomotives wheelbase being just the right length to bridge the staggered shorts, of course - so perhaps a theoretical issue for most.

 

Secondly, the electrics get a bit more complicated and at least two switches will be needed, one for the frog as per usual, and one that switches the frog’s selected polarity to the live blade rail.  Depending on how you have wired the layout, the type of point motor you are using, and whether you want other functions such as signalling operating from the point motor switches, this may be impractical.

 

Has anyone actually tried this yet?

 

 

[tender]

6 minutes ago, Chamby said:

@tender‘s proposal would work if the switch blade not in use was electrically isolated when the other route was selected.  

 

 at least two switches will be needed, one for the frog as per usual, and one that switches the frog’s selected polarity to the live blade rail.  

 

Has anyone actually tried this yet?

 

 

Thats exactly how i envisaged doing it. I use servo motors for the turnouts so doubling up on the switches is not a problem.

 

Haven't tried it yet but will do shortly.