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Author Topic: Locos derailing with coaches  (Read 586 times)

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Offline chicky365

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Locos derailing with coaches
« on: July 10, 2019, 08:14:37 AM »
Hi all,
I have installed a fairly tight curve, although  as I was having problems I replaced it with set track, so I think it is about 12" rather than 9" (so not the minimum radius). I am finding that whilst locos can get around the curve on their own, as soon as they are pulling coaches, they either get stuck and need a nudge or they derail.

It looks like the coach connection is forcing the bogies to go at a different angle to the corner, so as soon as one wheel pops off the rail, as soon as they get to the next straight section/point, off they go. The main culprit is a Dapol class 33 which has quite a short wheelbase.

I had the same issue with flexitrack which is why I replaced it with set track, but its made no difference and Im short of space to make the curve any larger.

Any ideas?

Offline Bealman

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Re: Locos derailing with coaches
« Reply #1 on: July 10, 2019, 08:18:15 AM »
Is it loco bogie or the coach bogie that derails?
Vision over visibility. Bono, U2.

Offline chicky365

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Re: Locos derailing with coaches
« Reply #2 on: July 10, 2019, 08:19:57 AM »
the loco.

the coaches were, but I replaced the small coach wheels with larger ones and that has helped.

Offline Bealman

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Re: Locos derailing with coaches
« Reply #3 on: July 10, 2019, 08:24:19 AM »
Larger flanges will help on tight curves, but are the loco couplings on the bogie, or in a NEM socket on the body?

I am unfamiliar with a Dapol Class 33, unfortunately.
« Last Edit: July 10, 2019, 08:36:33 AM by Bealman »
Vision over visibility. Bono, U2.

Offline njee20

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Re: Locos derailing with coaches
« Reply #4 on: July 10, 2019, 08:27:43 AM »
Not quite sure I understand your terminology - do you mean the buffers are making contact between the loco and coach and that’s lifting the loco off the track? Unusual for it to be that way around given how much heavier the loco is.

If the buffers are making contact on curves then you may be able to put longer shank couplers on. That’s a bit odd on a 12” radius corner though.

Offline chicky365

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Re: Locos derailing with coaches
« Reply #5 on: July 10, 2019, 08:37:25 AM »
I cannot see exactly what is happening but the loco is not touching the coaches via the buffer. They are connected via standard Farish/Dapol factory fitted NEM? connectors. It looks like as the coach goes around the corner, the NEM connector/coach is pulling the whole wheel/bogie section around sharper than the rails will allow.

I can only think it is this as the loco is ok when not connected to a coach, so it definitely something due to a coach being connected to it, although there is about 1cm space between the loco and the coach (due to the connector) so they are not colliding.

The loco couplings are on the bogie

Offline Bealman

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Re: Locos derailing with coaches
« Reply #6 on: July 10, 2019, 08:41:22 AM »
One coach only, or a rake?

A rake in a tight curve can cause problems. Because of it's mass, it prefers to take a straight line across the curve.
Vision over visibility. Bono, U2.

Offline chicky365

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Re: Locos derailing with coaches
« Reply #7 on: July 10, 2019, 08:43:03 AM »
Probably more of a rake but only 3 coaches max. I thought using set track would solve the issue but do you think I need to try and increase the radius?

Offline ntpntpntp

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Re: Locos derailing with coaches
« Reply #8 on: July 10, 2019, 08:44:42 AM »
Hmm.... a bogie diesel loco such as a 33 should be able to handle 12" radius (and indeed 9" radius) with no problem at all, and of course you say the loco travels round the curve fine by itself.

So this sounds more like the coupling between loco and first coach is too short and you're getting buffer locking, but on the other hand your latest reply says it's not the buffers? I have seen occasional problems where a coupling hook itself is not completely horizontal and catches on the underside of buffers in tighter curves. 
Is it always in the same place on the curve? 
What coaches are they?
What happens when you're pulling something different such as a 4 wheel wagon behind the loco?

Can you post  photos from above and from the side, of the loco and coach on the curve at the point things start to derail?
Nick.   2016 celebrating the 20th anniversary of "Königshafen" exhibition layout!

Offline chicky365

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Re: Locos derailing with coaches
« Reply #9 on: July 10, 2019, 08:48:13 AM »
I will double check the buffers tonight in case I have missed something. If that does not shed any light then I will take some photos

The coaches are Graham Farish and I think the connector is on the bogie rather than the coach body. I will also try with some wagons so I can come back with some correct information.

thanks

Online railsquid

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Re: Locos derailing with coaches
« Reply #10 on: July 10, 2019, 09:28:02 AM »
Is there any unevenness in the track which might be contributing to the wheels jumping off?
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Offline Bealman

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Re: Locos derailing with coaches
« Reply #11 on: July 10, 2019, 09:29:51 AM »
I thought that as soon as I saw the post.

Good point.
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Offline Newportnobby

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Re: Locos derailing with coaches
« Reply #12 on: July 10, 2019, 01:24:13 PM »
Is there any unevenness in the track which might be contributing to the wheels jumping off?

As only one curve composed of set track pieces is mentioned in the OP I'd venture a join is not correct thus causing a 'step' the loco will pass over OK but lighter coaches will derail/catch on :hmmm: :hmmm:

Offline njee20

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Re: Locos derailing with coaches
« Reply #13 on: July 10, 2019, 02:16:13 PM »
Seems unlikely given it was a problem with flex track too.

Is it one particular coach? Have you turned the loco round, and turned the offending coach round, as well as trying a different coach? If it still happens with all of those permutations then it's a track issue (or board or underlay or whatever), if that fixes it you can narrow down the offending item.

A stiff coupler can cause these problems, more common on Dapol coaches where you've got the coupler mounted on a kinematic cam, rather than on the bogie.

Offline Newportnobby

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Re: Locos derailing with coaches
« Reply #14 on: July 10, 2019, 03:53:45 PM »
Seems unlikely given it was a problem with flex track too.


Possibly but we don't know if there was a join in the flexitrack.
Easiest way to find out is to run a finger along the top of the rail through the curve and if blood results then it's a poor join >:D ;)

 

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