Bob Nelson
chuck,
We're ALL confused! Your observation is correct; so is lionelsoni's.
Paul needs to get back in here and answer the outstanding questions or I don't see how we can possibly make any progress. Yes?
But later Paul posted:
"I've been studying how the 2-8-0 engine goes over the switch track, and YES it's the pilot trucks that seem to be the culprit. they appear to ride up on the switch mechanism. The other thing I noticed is that all the engines that take the switch tracks easily have 4 pilot trucks [sic], not two!! So Im woundering if it's because that engine only has two pilot trucks [sic]instead of four like the other engines."
(Surely he meant "4-wheel pilot trucks" and "two-wheel pilot trucks".)
Chuck,
You quoted one of Paul's (hummingbird) posts, but here's a more recent one. Confusion reigns, and I for one would appreciate it if Paul would jump back in and clear it up. None of the rest of us has access, so it's up to him.
I've been studying how the 2-8-0 engine goes over the switch track, and YES it's the pilot trucks that seem to be the culprit. they appear to ride up on the switch mechanism. The other thing I noticed is that all the engines that take the switch tracks easily have 4 pilot trucks, not two!! So Im woundering if it's because that engine only has two pilot trucks instead of four like the other engines.
Paul
All my engines go through the switch tracks just fine except my newest loco, the 4-8-0, about 1/2 the time it derails,
The engine that derails is a 4-8-0.
He did list only 4-whatevers in his first post; but I also took the later post to be a correction to that.
Here is an analysis that I did some time ago:
The proper location for the pivot of a two-wheel pilot truck can be computed from a knowledge of the wheelbase length of the driving wheels w and the distance d of the pilot wheels from the center of the wheelbase.
The pilot truck's tongue length is d-p. The square of the radius to the pivot is
2 2r + (d-p)
The square of the radius to the wheelbase center is
2 2 2 2 2r + (d-p) - p = r + d - 2dp
And the square of the track radius is
2 2 2 2r + d - 2dp - (w/2) = r
Solving for p,
2p = d/2 - w /8d
The bottom line here is that the pivot's distance from the middle of the drivers should be about halfway to the pilot wheels. The last term says that it should be a little closer to the drivers, but not much. For example, if the drivers' wheelbase w is 2 3/4 inches and the distance d between the middle of the drivers and the pilot wheels is 4 inches (as for my 2026), the second term is less than a quarter inch. So any pivot close to halfway should probably work well.
Notice the satisfying result that the correct pivot location does not depend on the radius of the curve.
rogruth,
Please re-read humming bird's post of 2/1/2008 @ 1:32 pm. There has been some confusion from the beginning. As I understand it, the locos with four pilot wheels are taking the switch fine, but his newest one, an MTH with only two pilot wheels derails about half the time. Perhaps he can clarify this when he answers the other questions that remain. Then maybe someone can add to what's been said.
lionelsoni,
Bob,
Spent the afternoon with my-son-the-engineer going over this issue and your response. Now understand your analysis and corrective action. (Try not to let it go to your head but the consensus locally is that your analysis of the geometry is quite good, and your solution very useful, in some cases.) Unfortunately, I have only one locomotive that has both a two-wheel pilot truck and a cross-member (spacer) that could be used to drill-and-tap a new pivot point -- if I were having the problem.
We concluded that we really need to know for certain whether "humming bird's" loco is derailing on the the inside of the curve (oversteer) or the outside of the curve (understeer) or both, or what?
So, 'Humming bird," if you are reading, please describe precisely what these derailments look like. As the pilot wheels enter the curved portion of the switch do they tend to keep going straight and climb the longer rail of the curve -- the one on the outside of the curve; or rather do they turn too sharply and climb the shorter rail; that is, the one on the inside of the curve? Another way of expressing this is: when a derailment occurs, which of the pilot wheels shorts against the center rail? Looking forward from the point of view of the engineer, is it the right or the left front pilot wheel that ends up jammed against the center rail? And whatever it does, does it do the same thing virtually every time it derails?
That's not quite it. What I did was to attach a small steel strap to the pilot truck with machine screws to extend the tongue by 3/4 inch. Then I drilled and tapped the front cross-member of the motor for a new pivot--just a machine screw through a spacer. This kept the pilot wheels in their original position. I bent the original pivot on the sheet-metal plate to get it out of the way. For a completely reversible fix, I think I would just manufacture a new plate with the extended pivot (and a gentler arc on the front, concentric with the new pivot) and replace the old plate with it.
If the geometry is perfectly correct, the wheel treads and flanges should be parallel to the rails; so the wheels should roll through the turnout on the rails. It's like steering a wheelbarrow, where you have to walk outside the curved path that you want the wheel to follow. If you walk too close to the path, the wheelbarrow doesn't turn sharply enough and leaves the path to the outside. If you walk too far outside the path, the wheelbarrow turns too sharply and leaves the path to the inside. Because the locomotive's pivot is in front of the drivers, the pivot will always be to the outside of the path. But the way Lionel designed the locomotive, it is too far in front of the drivers and therefore too far outside the path, swinging the tongue of the truck too far to the outside and steering it, like the wheelbarrow, off the path to the inside.
Of course, there are other forces in play. There is, as you suggest, a centripetal force from the outside rail accelerating the truck toward the center of the curve: The inertia of the truck does indeed act to make it prefer straight motion. But there is also the friction between the wheels and the rail, which makes the wheels want to roll in the direction they are steered, which is over the inside rail. And the flanges counter both of these to try to keep the wheels on the track. The misaligned flanges due to oversteering can also make things worse. The leading edge of a flange, running closer than normal to the rail, can catch on an irregularity in the rail and lift the wheel up, whereupon it can roll over the rail. The angled flange also makes a tighter fit between the rail and a guard rail and may also lift the wheel.
So it's all very complicated. It seems to me that eliminating the oversteer is all to the good and a reasonable thing to try if one is having trouble with derailment to the inside. Otherwise, it is unlikely to cure the problem. That of course is why I asked the question.
lionelsoni
Bob, if I understand your several posts on this subject (dating back to at least 2003) you extended the "tongue" of the front trucks toward the rear, thus pushing the axle-and-wheels farther forward -- because the actual pivot point does not change. One might do this by soldering a metal strip to the tongue and drilling a hole to fit over the existing shaft at the existing pivot-point. Presumably this would re-position the axle of pilot wheels 1/4 to 3/8 of an inch or so forward of the factory position? Is that right so far?
I think you are right, yet both in my experience (and when I try to draw these different configurations) I have a problem with your observation about "over-steer." Just to be sure we are on the same page: whenever I have had these problems it is the pilot wheels that derail (not the drivers) and what they do is to climb the outside rail of the curve, whereupon the inside wheel promptly shorts out against the center rail. That looks to me like "understeer," if I understand the term correctly. To put it another way (as "chuck" suggested above) it looks like the pilot wheels tend to keep going in a straight line (per Newton's first law) and climb the curved rail that is resisting this tendency. Where am I going wrong?
What I have in mind I have mentioned on the forum before: Many if not all Lionel locomotives with 2-wheel pilot trucks have a steering-geometry error that causes them to oversteer, so that the axle is not perpendicular to the rails and the wheels are aimed too far to the inside of the curve and, in my experience, are likely to climb the rail if given the chance.
When I have brought this up before, others have insisted that Lionel could not have made such a mistake and that any problems must be due to improper gauge, rough or unlevel track, insufficient spring pressure on the truck, and so on, and that they cured their derailments by fixing those things. I am sure that getting everything else right helps and can very likely cure a particular derailment problem. That however does not prove that proper steering is unimportant.
I have had a Korean-war 2026 since I was in high school. It derailed so stubbornly that I finally just took the front truck off the locomotive, until a few years ago when I figured out the oversteering problem. Then I lengthened the tongue of the truck to correct the geometry and found that the problem was solved. If that is the problem with your locomotives, the modification can probably be done in a way that is reversible. All that is needed is to move the pivot point farther back on the locomotive frame.
Ken said,
Another thing that everyone is missing here is to make sure the wheels are in gauge.
Not strictly accurate, Ken.
Random thoughts: Lionelsoni needs an answer to his question. He must have something in mind. Two wheel pilot trucks have been going through switches uneventfully for years. It's more than likely that the problem is not 4 wheels vs. 2, but that something is not right with the combination of the naughty loco and that switch. I had a brand new Williams that wouldn't negotiate my 022 switches until I strengthened the spring a bit. Even if otherwise worthless, this post should serve to keep the thread alive....
humming bird
Paul,
A number of things can cause this, including the pilot wheels being slightly out of gauge, or a slight misalignment of the track, or the things that the others have suggested. In my experience (two cases) the problem was solved by putting more downward force from on the front pilot truck, either by stretching the spring or by replacing it with a slightly stronger one. (I prefer the latter solution.)
Unlike a "real" train, the pilot wheels on a toy locomotive do not really support anything. On the contrary, the loco rides almost exclusively on it's drive wheels, and the spring at the pilot simply exerts a downward force to keep them from "climbing" a rail or bouncing off the track. Same at the rear. At least that's my understanding. I have noticed that some of the springs on modern locomotives, regardless of manufacturer, seem more "frail" that postwar Lionel.
Even if the spring is entrapped by a rivet-like shaft it is not necessary to cut anything. One can simply unwind/rewind the spring around its shaft. This preserves the original one in case this solution does not fix the problem.
Some folks have suggested laying a small, thin mirror between the rails, the better to see and diagnose what is going on.
when I have these problems I run the engine and tender without cars through the switch or crossing. Watch the wheels and see which one is popping up, then I run the engine through again and watch the boiler to see if the switch or crossing is out of alignment with the rest of the track.I have found that most engines like the switch and crossing to be level and the track leading into the switch and crossing to be level with the switch or crossing. A little shimming of the track and you should be good to go.
Hi everyone,
I hope your all doing well. Well I just discovered another "mystery of electric trains", I have 4 steam loco's, one is a Lionel 4-4-2, one is an MTH 4-6-2, one is an MTH 4-6-4, and my newest one is an MTH 4-8-0. I have a large 0-42 curve oval, and inside that there's a smaller 031 curve oval, they are connected by lionel switch track (all my track is the old type Lionel). All my engines go through the switch tracks just fine except my newest loco, the 4-8-0, about 1/2 the time it derails, the switches are thrown in the right position, but the 4-8-0 loco still derails when it goes over them!! Since the other loco's take the switch tracks well why does the new 4-8-0 derail?? Could it be that some loco's just don't like switch tracks? Any thought on this will be appriciated.
Our community is FREE to join. To participate you must either login or register for an account.
Get the Classic Toy Trains newsletter delivered to your inbox twice a month