Kadee Sprung Trucks

[5050]

It's none of them.

[highpeak]

While I don't doubt that Andy's theory is perfectly correct, I am struggling a bit with the idea that a truck design that supposedly has better track-holding abilities is derailing when a less sophisticated design is staying on the track. Surely if the track was that bad everything would end up in the dirt?
 

One potential issue with the Kadee trucks that might have a bearing on 5050's problem is "side frame toe out, which can actually lead to derailment." (Source: Kadee patent application for two-part truck frame, US patent 7434518. The patent mostly laments the assembly difficulties with the sprung trucks before describing the two-part truck, but it does include a comment about the toe out problem being inherent in the sprung truck design.)

 

The side frames are able to move out of parallel because of play between the frame and the bolster, the movement isn't very much at all, but perhaps the resulting extra side play in one axle might be a factor in the derailment? I'm not 100% convinced of this because there can be plenty of side play in a rigid truck (which the Reboxx wheels offer a remedy for because they have a range of axle lengths), but it might be that if the frames go out of true, the side play might become just a bit too much for that track configuration and as Andy mentioned, allow a wheel that is "freer to rise" in the first place to rise right off the rail.

[Andy Reichert]

Derailment problem solving without some very specific description of what is happening and exactly where on a turnout, tends to quickly become just guesswork. Also we don't know what locomotive types the layout is limited to. So I'm reluctant to offer any deeper speculation without more input. (but happy to, if I receive it)

 

I will agree that while Kadee trucks perform well on uneven height track, they can certainly find more problems on dimensionally "bad" track than some rigid trucks might. Where "bad" includes sideways misaligned rail joints, raised, dropped,  or too thick point blade ends and overly wide or narrow gauging.

 

The good and bad news about rigid trucks is that they are rigid.  That can result in very uneven weight distribution over the four wheels, if one leading wheel is pushed up hard by a sudden track fault. I.e the pushed up wheel could have almost four times the normal weight pushing it back down,  if the whole truck lifts along with it and stays perfectly rigid. That would defintely help keep that wheel from climbing the rail, compared to a Kadee riding the same fault. That's even more likely to help if the car is barrelling downhill and then leans hard on the outer wheel as it is forced into a tight turn by sharply curved swtch points.

 

I also thought I saw "narrow wheels" mentioned. Rigid trucks are far better at getting any code 88 wheels to travel more reliably over NMRA frogs. The rigid truck often supports the wheel that otherwise would drop into the too wide frog gap. (but hides their fundamental misfit problem)

 

IMHO, the best of all worlds is to test and fix the trackwork thoroughly first, then never have to worry about some specific type of car or loco turning up later and having issues. Apart from running the NMRA gauges over every inch, having a specially rigid (and true) car or long 4 wheeler and testing to see if it rocks or clicks anywhere can be very "educational".

 

Andy

[5050]

What has locomotive types got to do with it?  I don't have any problems with locos even 6-wheel truck ones like SD45's etc. (and Consolidations and Mallets).  I explained in my first post what and where the problem point was and that only Kadee trucked vehicles had difficulties.  My track is well laid, smooth joints, no kinks etc etc. and was well tested prior to ballasting and scenicking.  My years of P4 modelling have ensured that.

 

Using the Sherlock Holmes principle, having discounted all else, the problem must be the sprung trucks for whatever reason.  I'm not really bothered what that reason is.  Rigid trucks have solved the problem.

 

However, I have thought that the Kadee trucks allow a lot of sideplay in the axle bearings, more than rigid trucks.  This and the corresponding lack of 'stiffness' in the body of the truck as a whole could easily allow wheels to ride up on the flange root and over the outside rail.

 

Not a lot more to say I reckon.

 

Mind you, I reckoned that a week ago.................................

[Andy Reichert]

I'm sorry 5050,  but I still can't speculate about your results, without knowing more about your track situation specifics. All I picked up so far is that you have an 18" radius Peco  curved point at the bottom of a down grade. Locos of course are much heavier than box cars, hence my wondering. (even with a longer wheel base length)  if they also worked OK.

 

I don't like to draw general conclusions from single case examples. I would however express substantial doubt over your own conclusion by posting this (.gif) video clip.

 

 

The box/reefer cars shown are unmodified, standard commercial 36 ft MDC kits, with NO extra weight added. (They weigh approx 3 oz each).

 

 

They are fitted with Kadee sprung trucks and 33" Proto:87 wheelsets, same 26 mm axle length as regular HO. The two cars are linked by standard, body mounted, Kadee couplers. The track curve radius however is an extremely tight 8", which combined with the high running speeds, stresses the trackholding reliability to almost it's furthest limits.

 

Now if I follow your reasoning, the video example above can't be possible, especially since P87 flanges are less than half the depth of HO ones. You are claiming that the "free to rise" wheels have "extended sideplay" and that combination should climb over the railhead  easily the instant they hit the curve. 

 

There are of course at least two differences here. Those are that there is no relative grade between the straights and curves, and no Peco turnout.

 

I'm not arguing to be awkward or critical. I just have so much confidence (backed by evidence as above) of the completely satisfactory trackholding of Kadee trucks, vs possibly undiscovered track problems. And I don't want anyone to be mis-informed.

 

Andy

[5050]

Like a dog with a bone.....................

[F-UnitMad]

That video clip is very interesting & I don't want to sound cynical, but there's no turnouts on the board; i.e. no breaks in the rails.... it's at a turnout that 5050 has had problems....

[Andy Reichert]

Cynicism is perfectly proper. That's why I reacted to the tossed out public conclusion that there was suddenly something wrong with all Kadee's equalization after approximately 40 years of successful mass use.

 

BTW There are rail joints approximately every 4" on that board. Both even and staggered. Photo's on request.

OTOH, a properly designed and built turnout has no rail breaks, or excessive side ways angles, or shallow rail head slopes, that wheels at anticipated speeds can detect and fail on. Apart from a possibly more forceful direction change, (here speed and car weight matters), it should be just like any other place on the trackwork.

That's the whole point of a turnout. Entering or crossing one below it's maximum allowed speed isn't intended to be either a dangerous mechanical shock or a mechanical risk. If the wheels derail at the same place every time and only at that place, then the turnout isn't looking to the wheels like the rest of the problem-free parts of the track. There are no standard compliant wheel designs that can't handle turnouts. (How would they know? - think about it). But there can the occasional faulty for some reason turnouts that can't handle properly weighted compliant wheels.

As to speculation about increased or reduced side play. Note I said the P:87 wheelset axles were the same length as the axles they replaced. That would make any sideplay between the wheels and side frames exactly the same after as before.

HO wheels have greater side play (due to smaller BB) vs. their running rails gauge than do P:87 wheels. But that occurs regardless of truck design. However, if the rail head has a properly near vertical running edge, and the cross section of the wheel flange at rail head height is the usual "narrow eliptical" shape, it's difficult to see what side play can have to do with rail climbing, unless the gauge itself is seriously wider at that location.

 

Andy

 

 

[F-UnitMad]

It might just be me, but I didn't get the impression at the start of this thread that the intention was simply to trash Kadee sprung trucks, denounce them or dismiss 40-odd years of experience..? Just ask why something was happening that really should not.

 

I like sprung trucks myself - in O Scale - after all, my trackwork looks like this...

 

 

... but I found that, although Atlas trucks can be made 'better' by removing a part of them across the bolster, when they are the type with rotating bearing caps, they are better left rigid, as the long axles bind too easily and create too much drag if the trucks can flex too much.

[Andy Reichert]

If the axle can move from side to side, and has pin points, then as it sashays from side to side, the wheel centre is moving up and down with respect to the axle box in the truck frames, which reduces the effect of the springing, and who knows what is happening - that was the point, not all variables had been eliminated, and denouncing the Kadee trucks may not have been appropriate.

 

It was a posting in support of your position, but feel free to simply dismiss the comment, rather than using an open-ended question to further explore the thinking. I might be wrong in my thinking, but at least it won't be me that looks like an idiot...

 

Sorry if I came across as too defensive in my thinking. I actually wasn't sure which way to interpret your original post. The point I was trying to make was that I thought I could eliminate side slop as an additional varaible to be considered, because the same length axles should exhibit the same up/down behviour, including any too short poinpoint "de-centering" within the axle box caused by sideways movement.

 

The concept of a bogie with sloppy wheels problematically "twisting" so the wheels are unstably approaching the rails diagonally instead of parallel is a commonly suggested idea on many US elists. And often proposed as a justification for over-narrowing the gauge at the frogs on turnouts. The maths doesn't hold up, but few proposers dig that deep before posting and it always sounds good to the general audience. So I am rather over-sensitized to thinking I'm seeing it and I apologize for my over-reaction.

 

 

 

 

Just in case not everyone is familiar with the particularly US ubiquitous  pivoting sideframe truck design, it's the norm for the prototype. And the freight oriented prototype here has far bumpier and uneven track than the UK as a norm. And of course much lower speed limits generally as a result. But that track situation does require a greater practical vertical wheel movement that you would normally find in a UK vehicle, or which could be handled ad well by simple springing.

 

Note there are no separately sprung axleboxes in hornblocks, nor any rigid connection beam across the side frame ends to make the sidefames into a rigid unit. So the wheels are primarily 100% equalized by the pivoting sideframes to handle the uneveness, while just the connection from the sideframes as a whole to the bolsters has any actual springing.

 

Andy

 

PS I'm just now in the process of bringing my demo track into complete operation after about 5 years of not quite finished neglect and roadbed developed uneveness caused by all those annual humidity cycles . And right away I'm finding that my few rigid test trucks are failing, while the equalized trucks are riding with no problems over the same sections of unevened track.

 

Andy

[F-UnitMad]

. And the freight oriented prototype here has far bumpier and uneven track than the UK as a norm....

We know - it's one of those things we love about US Shortlines in particular (& it drives some US-resident members here to distraction, as of course it's not all like that )