Any Suggestions?

I was very excited to get my second RDC as I have been wanting to run a pair since they first came out, But I'm disappointed in the performance of them when hooked together. On our layout, we have 4 S bends. Each one of these units will negotiate these bends with ease. No problem. However, when coupled together, it is a disaster. At the mid point of each S bend, when the turn begins to go the other way, the lead RDC, throws the trailing one off the tracks. At first we thought it was a problem with the tracks or perhaps the RDC's themselves, but when we ran them at dead slow speed over these S bends, we noticed that as the rear of the lead unit swung out on the reverse curve, the front of the trailing RDC was forced off the track. After careful examination we found the reason for this appeared to be in the couplers themselves. Looking directly at it from on top, we noticed that the couplers of both units did not swing far enough to allow for the change in direction on these bends. Being body mount couplers this addresses this issue. There just is not enough swing of the mechanism of either coupler to function as real units. We tried turning the RDC's end to end but the result was always the same. The lead unit throws the trailing one off the track on all 4 S bends. Now when we run these on normal curves of 15, or 30 degrees, there is no problem. But on curves of 45 degrees, there is also a tendency for the lead unit to throw the rear unit off the track. This doesn't always happen, just in certain spots which tells us that we have a problem with our track in that area. When we run these units coupled together on a standard oval, they cruise along with no problems at all and look pretty damned impressive to be sure. Since 3 of these S bends are on a main line, we are disppointed that we can't run the RDC's together on it. Instead we have to put them on a secondary, less used line that comprises normal curves.
If anyone has any suggestions on how we might remedy this problem, please tell me. Keep in mind that our tracks on two of these S bends are fixed and are now part of our layout and it would be a monumental task to tear them out and rebuild. Can anyone help us solve this problem. Had these couplers been truck mounted, there would have been sufficient swing to allow for the shift in direction of the curves.
One more thing, this problem doesn't occur with any of our other engines or cars with truck mounted couplers. Only the pieces with the body mounted couplers can't seem to handle these S bends.

 

One solution is, to make permenent connection between the two units via removing the couplers and installing a tow bar. Move the pivot points inward as much as possible. Another, but less elegant way to make a flexible connection between the units is to install a flat bar with a long slot at the front of one unit, a bar with a vertical pin to the other, so the pin can freely move sideways at turns.

 

Pardon me if I am asking a question you have thought of since day 1.
Do your S-curves have a straightaway at least the length of your longest car between the curve that goes one direction and the curve that goes the other? (recommended)---
OR does a curve (especially one or minimum radius tightness) one direction run immediately into an equally tight curve the other direction? (can cause trouble)

 

Hi Ken:
No none of our S bends have any straight pieces between them. They go from left to immediate right or vice-versa. 2 of them are 45 degree turns and the third is 30 degree turns. Perhaps that's the reason we are having the problems. Too late to change things now.

 

Well that was one thing we considered but after reading what you have here, none of us are that mechanically inclined enough to be able to do any of this. I'm really surprised though that AZL never considered this possibility or did testing on the prototypes to remedy this situation. Oh well. They will stay on the oval. It may be a short line, but at least they work together there.

 

You should not blame AZL for not testing their engines onpooly planned tracks. I know you guys are just starting out, but there some very very very basic rules to laying track, and rule number 1 is, never ever ever put up S curves. (Yes there are exceptions to this rule.)
This is basic railroading and pretty much can be found if one does even a bit of research. This is same in Z as well as N,TT,HO,O,S,and G scales.

I do not own one piece of AZL anything,(yet) , but, I see a pattern here, and it is to blame the company,for things going wrong, that can be fixed or prevented by doing some basic research.

 

I disagree with you. I have run these types of S bends on both HO and N scale layouts in the past and never had a problem with engines or cars going off the tracks in this manner. But it is all acedemic at least for two of these curves as the modules that they are part of are finished now and we are not about to rip them apart and redesign them just to accommodate these RDC's Nope! They will stay on the regular, lesser run oval of our layout. But the straight piece between the S bends will be incorporated in future trackwork.

 

Quick question. In your past experience, were you using body-mount couplers, or truck mount? Truck mount will rarely have trouble on an S-curve, while body mount will operate much like a prototype and derail. It's basically physics. There's only so much room for that coupler to travel. Something has to give, and in your case, that something is the trailing unit.

Note that I learned this the hard way with an N-scale Metroliner set. I thought "hey, I bet this would look really good with body-mount couplers!" Well, it did. And it looked really bad lying on its side next to the track that just flipped it. :tb-wacky:

P.S.- And now that I think of it, I'll be putting in a drawbar to fix it so I can finally run it again after all these years.

 

You know, the more I get involved with Z scale, the more I find the word compromise popping up. I spent 40 years in the manufacturing sector, and the presidents, vice presidents, CEO's boards of directors, engineers, lab techs and managers from all departments of the three companies I have worked for would never accept compromise as a means to an end. I guess what I learned from them makes if difficult to accept compromise in order to keep to the prototype and still make it work. But if I want to continue operating in this scale, compromise has to be part of the equation. If any of my former co-workers heard me say that, I'd be hung out to dry.
By the way, if the piece where the coupler comes out of is called the pilot, then does that make the same piece at the other end the co-pilot?

 

As far as I can remember, they were all truck mounted couplers. I can't remember ever having an engine or car with a body mounted coupler. Of course that was many, many years ago. Frankly, I never really thought much about it back then. Interesting!

 

Ouch! Hehe. OK, at least you still have a good sense of humor about it. If you think Z-scale is tough, try T! Nevertheless, there has to be a break point where the manufacturer says "We've got a great looking model that will satisfy 80-90% of our target market and do almost everything it can, while still being affordable enough for people to actually buy it in enough quantities for us to be able to sell it and make a profit." There are some companies and individuals out there making amazingly accurate stuff, and the price tag shows it, too.

 

The thing is, in contrast to manufacturing, everything to do with model railroading is a compromise. For starters, it's physically impossible to make a 100% accurate scale model, so compromises must be made to reach a satisfying result. Perfectly scaled handrails, for instance, would make a model locomotive too delicate to handle without damage, so a compromise dimension is chosen that's strong enough to be handled but slender enough to look acceptable. Wheels with scale flanges could never stay on the rails, so a compromise is made between appearance and functionality. Functional scale couplers are totally out of the question—in Z scale, they're the size of a pinhead; even when they're made as small as practical, they're many times larger than those in real life.

The real world is enormous. Even in Z scale, some features are simply too large to model; so we compromise by using selective compression to achieve a design that will fit our space. At the other end of the size spectrum, many smaller features are simply too tiny to model at all, so we compromise by leaving some of them out.

Model track poses some of the biggest challenges of all, principally because we work with curve radii that are many, many times sharper than those in the real world. We do this out of necessity in order to fit layouts in our space. However, it creates massive problems for manufacturers, who have to figure out how to make long-wheelbase rolling stock operate on outrageously sharp curves. Some manage to find clever ways of making then negotiate the curves, but they're still left with other problems: do they mount the couplers so they work better, or look better? This is a compromise with no single perfect solution, and indeed in some circumstances it's a problem that's virtually impossible to solve. The fact that modelers will place two very sharp curves back-to-back, forming an S-turn, compounds the problem still further. Some rolling stock simply will not operate well on sharp curves, let alone S-turns, and to expect it to do so is unfair.

So as modelers we must all be prepared to make and accept many compromises. There is simply no alternative. And the smaller the scale, the more of them we must make.

 

I know you're right Dave and it has been a tremendous learning curve for me and my fellow association members. But for me, such compromises are hard to accept when you've been schooled in the principal that compromise is not an option. We have learned also, that as you say, some cars don't function well on sharp curves. But we have also learned that sometimes, these cars can be jockeyed around and put in different positions in the train makeup and the problem is overcome. That being said, we have also found that when we have a difficult car, we religate it to a line with fewer or more gentler curves, or at some point in the future, to a static display in an industrial complex or siding. We have spent many an hour testing our 100 + freight cars in various positions and we continue to do so to see which ones will work perfectly. Since our cars are a mix of AZL, MTL and others, it has been a challenge to say the least. Especially when coupling AZL and MTL cars together. There are potential problems there. The single most annoying thing we have encountered is the fact that the couplers on all of these cars regardless of who is making them, are far too week to be able to handle the stress of 20+ car trains going up a grade of 2%. Even with heavier cars in the lead, there is still unplanned uncoupling. They just let go and we lose have the train. We have thought about trying to design some kind of wire clip to fit over both couplers to keep them from pulling apart, but so far, nothing we have thought of will work, especially when it comes to taking them apart. We have found that we have to plan our trains very carefully so that we can get the right balance to avoid this problem. But even with that, we still get the unwanted and very frustrating uncoupling on an upgrade.
Not to put too fine a point on it, but we have had the same problem mixing AZL and MTL engines together. For example, when we mate an AZL SD75 with an MTL GP9 or 35, the AZL engine couplers droop causing the MTL couplers to either ride up, or pull apart because there is not enough of the AZL coupler to hang on to. We like to mix and match engines since it more closely resembles the real thing and it looks impressive. But these uncoupling problems make it so frustrating and infuriating sometimes, that the end doesn't justify the means and we segregate them into separate trains on separate lines. These are compromises I particularly don't like making. But as far as I can see, we have no other options except changing out AZL couplers to MTL and that is just too much of a pain in the butt. I did this once, changing two of my AZL engines to MTL couplers and it took almost all day to do and produced limited results. I just can't seem to win. Perhaps one day, someone will design and manufacture a coupler that will work for both and be strong enough that unwanted uncoupling won't happen regardless of how long or heavy the train may be. Until then we compromise. Oh how I hate that word.

 

It's indeed a major contributing factor. Furthermore if your curves are tight. For a further layout, keep in mind what K. Anthony wrote: between 2 opposed curves, always insert a straight section that is at least as long as the longest vehicle to be operated on the layout. And moreover than beeing necessary for operating reasons, it's far more "cosmetic" for eyesight!:ru-rolleyes:

Dom

 

I think a S-bend can operate if radii are broad. That's the case with a R495 turnout matching a R495 curved track for a siding for example. Or two head to head R495 turnouts. Myself I have the same arrangement on my layout and I admit that luckily I've not the least problem (However I'm wondering what will happen when I try the autoracks I've just ordered...). But definitly I should not try any S-bend with tight radii (R225 or lower)....

Dom

 

I carefully read what you're writting above. If I understand, the problem comes from MU'ing AZL coupler equipped engines with MTL coupler equipped engines. Actually I didn't encounter this kind of problem. However, there is a simple solution in my opinion: on my SD70s I removed the front truck mounted couplers. I removed the snowplow mounted AZL coupler box and I swapped it with a MTL coupler box. Very easy to do as the coupler box is screwed on the snowplow assembly. Then I glued the snowplow on the locomotive shell, forward side. So now my SD70s are equipped with AZL couplers aft and MTL couplers forward. Even with that I've no problem running a 3-unit SD70 lashup. But I have to admit my radii are quite broad (35 cm / 14" minimum).

If you have problems matching AZL and MTL couplers you can then operate MU'ed lashups consisting of randomely positionned MTL locos and a pair of back to back SD70s. So all the locos of your consist will be coupled with MTL couplers, except a pair of AZL couplers between SD70's long hoods.

Just my 2 cents,

Dom

 

Funny you should mention about the coupler swap on the AZL engines. I did exactly what you suggested here. It works so long as we run two SD75's back to back and then couple an MTL engine to the head end of the trailing SD75. It's when we connect a GP9 or 35 to the rear of the SD75 where the problem occurs. If you put them both on the track and move them so that they are just touching, then look at both from track level, you can see how the AZL coupler droops down from the truck and when you compare the positioning against the MTL coupler, you can see why they have a tendancy to pull apart. But it's when you couple them and then take up the slack so that there is tension on both, that you really see the difference. The MTL couplers ride almost 2/3's of a coupler height higher. Now when you add additional engines or cars, the added strain forces the MTL coupler to ride up even further and then pull apart. I have tried to remedy this problem by taking off the coupler on the SD's rear truck and repositioning it so that it is bent slightly upward from the truck. But I found that once you take this coupler off, it will not stay when put back on, even in it's original position. I had to very carefully Krazy Glue it back into the slot and socket in the position I wanted it. This met with limited results as I still get the pulling apart when there is too much tension on the MTL coupler. I am convinced though that if both engines ran at the same speed, which they do not, this problem might be lessened if not eliminated all together.
As for your autoracks negotiating your turnouts, we have 8 autoracks of the first run and we don't have a problem with any of them making it through head to head turnouts. The one thing you may have to watch for is the wheels snagging the points of the turnouts. We initially had that problem but after rounding the points slightly, that problem was eliminated. This helps with our engines as well. We had one GP35 that always snagged the points of the turnouts when it was heading into them. It was ok in the opposite direction, and this caused it to either derail or cause a short. So after rounding the points, this Geep makes it through now with no probs.

 

I would agree with you that a 490mm S bend is part of the Marklin design with the turnouts. I would like to suggest that you check out the trucks of you RDCs. When I first ran mine, I had problems derailing on curves. What I found is that the trucks ride in slots inside the body skirt. The trucks can be twisted (particularly when extracting the car from the vacuform tray) so that the tab on the trucks isn't riding in the slot. You might want to check if this might be your issue.

Mark