Big Ben Bricks XL drivers derailing on switches?

[Phil B]

I’m battling an issue with switches right now ... my Hogwarts Express MOD derails on them. At first I thought it had to do with the pilot truck, but after resolving a small issue where the drive rod touched the pilot wheels ever so slightly at the maximum extend of the switch curve, I’m left with random derailing where the XL Big Ben Bricks drivers (FBF) jump the track on a regular R40 switch. Before I debug this further and descend into insanity, is this perhaps a common issue with XL drivers and R40 switches? 

[ALCO]

What direction are you going through the switch? How far apart are the flanged drivers? Are the flanges hitting the guide rails?

[M_slug357]

@Phil B 

Are the drivers powered or pushed?

Did you quarter (offset) the connecting rods?

Are the switches 9V or plastic?

Is your engine centered on the driving wheels or on the leading&trailing truck(s)?

[Phil B]

38 minutes ago, ALCO said:

What direction are you going through the switch? How far apart are the flanged drivers? Are the flanges hitting the guide rails?

From the single track side to the branch track. Going straight is not a problem. The flanged drivers are separated only by the blind driver, and pretty close at that. See this thread for pictures: 

I think the reason for derailment might indeed be the flanges hitting the guide rails.

4 minutes ago, M_slug357 said:

@Phil B 

Are the drivers powered or pushed?

Did you quarter (offset) the connecting rods?

Are the switches 9V or plastic?

Is your engine centered on the driving wheels or on the leading&trailing truck(s)?

Pushed.

Yes.

Plastic.

Not sure what you mean here but the driving wheels are rigid, the leading truck swivels (2 axis).

[Commander Wolf]

Probably just that the rigid wheelbase is too long to take R40 switches cleanly. In my experience doing a rigid F-B-F wheelbase with XLs (single X) is already pushing it. 

[Phil B]

7 hours ago, Commander Wolf said:

Probably just that the rigid wheelbase is too long to take R40 switches cleanly. In my experience doing a rigid F-B-F wheelbase with XLs (single X) is already pushing it. 

That's what I have - a rigid FBF XL wheel base. There is some play on the wheels because the cross-axle holes are not a tight fit on most of the drivers, allowing them to slide on the axle pins. But if derailment on R40 switches are common with this setup, I will not spend hours trying to debug the issue, but rather accept it for what it is and run my Hogwarts Express on my main line only.

[zephyr1934]

A couple of thoughts,

1. make a dummy car to replace the tender so that you can slowly push the engine through a switch and watch where things bind up. If you can't reproduce it moving slowly then you know speed is also a factor
2. The problem could be the wheelbase between the flanged drivers or it could be the pilot or trailing truck reaching the limit of its swing.
3. If the wheelbase is binding, you MIGHT be able to make it work B-F-F but that also runs the risk of looking odd and not fitting your current clearance
4. At some point lego changed the design of the guard rails on the plastic switches, if you have a mix of old and new switches you could check to see if you have two different types, it might work on one but not the other
5. One of my steam engines does not like the standard switches, but I found that it would run through them just fine if I added a couple of extra "guard rails" in the form of a 2x2 round tile on top of a 2x2 round plate on top of one of the unballasted ties. With the new 1/4 round tiles or triangle 2x2 tiles you can now make longer guard rails too.

[Phil B]

2 hours ago, zephyr1934 said:

A couple of thoughts,

1. make a dummy car to replace the tender so that you can slowly push the engine through a switch and watch where things bind up. If you can't reproduce it moving slowly then you know speed is also a factor
2. The problem could be the wheelbase between the flanged drivers or it could be the pilot or trailing truck reaching the limit of its swing.
3. If the wheelbase is binding, you MIGHT be able to make it work B-F-F but that also runs the risk of looking odd and not fitting your current clearance
4. At some point lego changed the design of the guard rails on the plastic switches, if you have a mix of old and new switches you could check to see if you have two different types, it might work on one but not the other
5. One of my steam engines does not like the standard switches, but I found that it would run through them just fine if I added a couple of extra "guard rails" in the form of a 2x2 round tile on top of a 2x2 round plate on top of one of the unballasted ties. With the new 1/4 round tiles or triangle 2x2 tiles you can now make longer guard rails too.

Those are good suggestions, thank you - will try them out over the weekend. Unfortunately I cannot switch to BFF because the flanges would hit each other. I might try LEGO's Large drivers to see if the issue goes away (my design is compatible with both LEGO Large drivers and Big Ben XL drivers).

In an earlier push-only test on a left-hand switch I did not have these derailment issues, but on a powered run through a right-hand switch they happen every time. Maybe this is related to your points 1 or 4 ... Will check and report back.

Edited March 13, 2020 by Phil B
Clarified the right hand switch statement

[coaster]

You're probably catching the flanges of the XLs on the inside guard rail.  This is the nature of the bigger trains; they simply can't handle the R40 switches.  Since you can't switch to B-F-F, you would likely need to articulate the rear flange. You could even try a B-B-F arrangement, though then you'd probably be all over the place.

[Thai bricks]

Can you increase the gauge of the drivers, or are you on the limit?

[SavaTheAggie]

Are you entering the switch by directly exiting a curve?  I have to separate my curves from switches by at least 1 straight track.

--Tony