# Swapping axles on RDC-3 trucks



## JackM (Jul 29, 2008)

I'll admit I'm a bit late to the dance with this question.

I finally got around to putting the RDC-3, which I bought last year, on the layout. To my dismay it derails at exactly the same spot as the RDC-1 that I bought five years ago. Exactly the same spot.

The cure I applied to the RDC-1 was that controversial remedy of rotating the motor blocks 180 degrees. The -1 hasn't been run in over a year, but I recall that the rotate remedy did the job. It was something of a pain to do because I had to splice in a few inches of wire on each lead to allow the trucks enough freedom of movement. (The rubber tires were removed long ago. The tireless wheels seem to run just fine without the rubber.)

I don't remember how that discussion played out because I had no intention of buying an RDC-3 _back then_, and now I can't find any trace of it remaining on MLS. At the risk of dredging up an old discussion, was there any concensus about rotating the engine blocks on the RDC-3?

JackM


----------



## Greg Elmassian (Jan 3, 2008)

no .... ;-)


----------



## JackM (Jul 29, 2008)

Greg - I'll see your  and raise you a .

The RDC-1 has been off-layout for a long time, so my plan is to put it back on and see how it performs around the curve that has "that" problem. If it stays on the track as I expect, I'll do the deed and reverse trucks on the -3 as well.

Stay tuned, or whatever.

JackM


----------



## Paul Burch (Jan 2, 2008)

Sounds more like the problem is with the track and not the RDC's.


----------



## JackM (Jul 29, 2008)

Possible - except that nothing ever derails at that spot except the RDC-3. The track is smooth, even (side-to-side), over 12' radius. It seems to be an example of "if it ain't broke....".

JackM


----------



## Greg Elmassian (Jan 3, 2008)

I learned early on to not blame the rolling stock first, but look at the track.

The RDC is one of the longest locos ever made, in terms of wheelbase.

The trucks often do not flex enough. Put a level on your track both ways, I bet a dozen donuts that you have a cross level problem.

If you removed the traction tires, did you replace with "solid" wheels, ones without the groove for the traction tire.

Greg


----------



## JackM (Jul 29, 2008)

Aw geez, I didn't mean to start up this question again; just looking for an answer.

My ol' RDC-1 is in a few pieces in the basement right now, awaiting a new decoder installation. Unfortunately, we're enjoying a spate of "Goldielocks" weather (not too hot, not too cool) but I'll try to get both RDCs running and do some comparison road tests. I'll try to report back in a day or two and see what I learn.

JackM


----------



## DKRickman (Mar 25, 2008)

> Aw geez, I didn't mean to start up this question again; just looking for an answer.


You got an answer, you just don't like the answer you got. It kind of reminds me of the joke about the guy who goes to the doctor and says that whenever he touches his elbow or either knee, his finger hurts, and could he have arthritis? The Dr. says, "No, I think you have a broken finger."

You asked for advice from people who (presumably) have more experience than yourself, and the answer came back "look at your track." You may not want to bother with your track, which is your business, but don't complain that you got the same answer as you did last time.

In my experience, derailments at a fixed location are ALWAYS a sign of an issue with the track at that location. The only semi-exception is when a piece of equipment is simply not suited to the layout (too long, too rigid, whatever) - but even that I would consider a track issue, since it's the track which enforces the limitation. So if you've found a work-around involving modifying your equipment, all you've done is to force the equipment to adapt to less than ideal track. The next time you put something similar on the layout, the problem will almost certainly come back (as it has done here). The solution is to fix the track, not the rolling stock.

Now, if wire length is what's limiting the truck swing, you might consider just splicing some wire in but NOT rotating the truck, and seeing if that's the problem.


----------



## JackM (Jul 29, 2008)

Sorry if you thought I was complaining, I was just asking since I couldn't find the old discussion anywhere. And since this is called a "forum", I thought we could talk about it a bit.

Like I said, I'll try to find time to get my RDC-1 back on the road and do some comparison tests alongside the RDC-3. (I don't mean alongside literally.)

But to your considered opinion. I notice that my USAT SD70MAC has, for lack of a better expression, floppy wheels on the outermost (front and back) axles. Likewise my A/C SD45. I must wonder, and this is actually more of a rhetorical question, why the manufacturers of (probably) 80% of all our rolling stock (A/C & USA) feel this approach to be a good idea. Perhaps they're trying to design units that can best handle normal variations which might be expected to be found in normal layouts. If so, then rotating the RDC engine blocks 180 degrees could be considered to be following the examples of the manufacturers. 

Sometimes, a "work-around" is really just good design practice.

JackM

Come to think of it, what is the reason all road locomotives back in the age of steam had small wheels in front of the drive wheels? Were they to help guide the drivers to handle the normal variations of the track?


----------



## Doug C (Jan 14, 2008)

Track was the issue with our rdc-3 !

Sure everything else ran thru location without derail but rdc did derail ! RDC had also previously (club weekend event) ran fine no derails on 'loose' track laid on top of cobblestone flooring. 

The RDC3 on home railway hi-lited a bad spot with adverse side-to-side levelling issues !! Ran trouble-free with fix to roadbed !

doug c


----------



## Greg Elmassian (Jan 3, 2008)

Not really sure to make of the response of the OP... "Ah Jeeze, all I want is an answer"... you have some of the most helpful and experienced people around.

If you want an explicit answer to turning the trucks... it's a band aid in my opinion and the poor trackwork will still be there to cause problems. Maybe swapping the trucks will help a bit, maybe enough to make it stop derailing every time. It's not advice I would be proud to give... solve the problem, not the symptoms.

Then the complaint is about not being able to talk about things?

So again, all I can take from this is you want to discuss the merits of floppy axles on the outboard axles of the loco.

OK. 

But do you want a simplistic discussion, like "just give me the answer" or do you really want to discuss it and go into years of experience, the dynamics of "floppy axles" combined with the suspension (or lack of) on the various motor blocks, along with all the other factors that go into the complete dynamics of all these different motor blocks? 

I'm game.

What I won't do is give you a bullshit response, or bad advice... 

There's really no simple answer about the loco trucks... there IS on the trackwork, make it flat, smooth, and everything you have will most likely run much better.

Regards, Greg


----------



## eheading (Jan 5, 2008)

Well, I have always been a fan of the floppy axles being on the outer axles on Aristo engines, particularly the two axle ones. I couldn't agree more that the real issue is probably track warp, but with the floppy axles outboard, the engine becomes much more tolerant of variations in track, which on my railroad of poor trackwork means I have to deal with the issue much less often. For me it is just an issue of how often I want to deal with the trackwork.

To each his own poison. As I said above, I know the real issue is trackwork, but I just find I have to tweak my track much less when I have a more tolerant engine!!

Ed


----------



## JackM (Jul 29, 2008)

Greg - You misunderstood the jeez: "Aw geez, I didn't mean to start up this question again"
But thank you for your advice regarding trackwork. Although, yes, I thought maybe a few bits about both sides of the question might've made for an enjoyable and enlightening discussion.

Mr. RIckman - I regret my offense but I do think there might be some validity to my comparison with the SD45 and SD70 models.

Doug C - Thanks for your input. My track is on loose stone and, being in Upstate New York, every spring brings new problems. 

Ed - I hate re-railing my SD70MAC. Seems I get one axle on and another falls off. But once on, I love driving it, it really feels solid.

JackM

No, really. Why do steam locos have the smaller lead wheels?


----------



## DKRickman (Mar 25, 2008)

> Mr. RIckman - I regret my offense but I do think there might be some validity to my comparison with the SD45 and SD70 models.


No worries, you haven't offended me. It takes a lot more than that! As for the floppy axles, I can't claim familiarity with the design, but the idea of some kind of suspension is definitely a good one. Note though that, especially for a 2-axle truck, the axle must be able to move vertically only - any side to side play would allow the whole truck to rotate and cause more derailments than it would solve. If you really want to solve the problem using good engineering, look into 3-point suspensions for railroad cars. You'll need to have all the axles on the car able to move within carefully constrained limits, which will take a lot of rebuilding, but you'll have the most flexible and reliable RDC around.




> Why do steam locos have the smaller lead wheels?


They are there to guide the locomotive into curves. But a word of caution - they don't work the way they do on most models - just a truck flopping around out front. They're tied into the suspension of the locomotive in rather interesting and complex ways, and the truck swinging into a curve actually lifts and pulls the engine into the curve. Diesels do not generally need them because they have shorter rigid wheelbases and separate trucks already.


----------



## Totalwrecker (Feb 26, 2009)

DKRickman said:


> No worries, you haven't offended me. It takes a lot more than that! As for the floppy axles, I can't claim familiarity with the design, but the idea of some kind of suspension is definitely a good one. Note though that, especially for a 2-axle truck, the axle must be able to move vertically only - any side to side play would allow the whole truck to rotate and cause more derailments than it would solve. If you really want to solve the problem using good engineering, look into 3-point suspensions for railroad cars. You'll need to have all the axles on the car able to move within carefully constrained limits, which will take a lot of rebuilding, but you'll have the most flexible and reliable RDC around.
> ---------------------------------------------------------
> 3 point car suspension = One truck snug, just rotates, Other truck loose can rock as well as rotate.
> Tighter truck creates 2 lift points over the wheels, loose truck give a single lift spot at kingpin. (screw)
> ...


-----------------------
They also carry some weight, four wheel trucks are generally used for higher speed (passenger) locos. More stability and better tracking.
The wheels behind help carry larger fireboxes, too light for balance compared to the water sections of the boiler, extra wheels allowed for bigger fires and counter balanced the leverage of the extension.

John


----------



## Greg Elmassian (Jan 3, 2008)

I'm happy to have the discussion on "floppy" axles!

On thing is that no matter which orientation of the truck, there are still 2 axles on the loco that are pretty rigidly attached to the really long body.

Some people have added more flexibility between the truck and the body, but now you get the problem that many people encountered when trying to make all axles "floppy" in an Aristo 3 axle truck, the locomotive can list off to one side or another, nothing to return it back upright.

For example, the Aristo design has independent gearboxes with nothing in the basic design to return them to level. Take a truck apart and you will find some pieces of rubber underneath the gearboxes, that, depending on the thickness of the rubber piece, will limit the travel of the gearbox, or even lock it in place.

Over the years, there have been various factory configurations, and most people have indeed found that locking one axle, leaving one completely floppy, and limiting one somewhat works best.

And in deference to mister Headington, indeed the outer axles left completely floppy seems to work best. I don't personally believe that this is because the outer axles are floppy, BUT that the rigid axles inboard makes the shortest rigid wheelbase.

I futzed and futzed, and found that eliminating cross level problems made any modifications to the loco unnecessary. With 40 or 50 locos, fixing the track made the most sense to me, since it affects all rolling stock.

Regards, Greg


----------



## eheading (Jan 5, 2008)

I agree with you about the track, Greg. We each have to do which works best for us. Modifying 50 engines or so would be a little intimidating!!!! For me with just a few engines, when I modify the engines I don't have to do track "maintenance" anywhere near as often, so for me that works.

Regarding the floppy vs. the rigid axle. Short rigid chassis is good, no question. At one point though, I had a serious warp in a spot on my mainline. I had a new RS-3 that kept derailing there. So I laid down on the ground (no mean feat when you're 77!!) and watched the engine at that spot. When the warp appeared the front axle rode right up and over the rail. When I reversed the truck so that the floppy axle was forward, that front axle just rode right with the rail and pulled the rear axle along with it. "Twas a very enlightening moment for me to actually watch the action at the wheel.

Ed


----------



## JackM (Jul 29, 2008)

We seem to be headed toward "whatever works for you" as an answer to my original question.

For Greg, with a gazillion locos, "he may be crazy but he ain't stoopid".
For many of us, "we may be stupid but we ain't crazy".

JackM


----------

