What back to back setting do you use?

Model and prototype rolling stock, locos, multiple units etc.
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Martin Wynne
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Re: What back to back setting do you use?

Postby Martin Wynne » Sun Dec 17, 2017 3:22 pm

Julian Roberts wrote:Exactly Martin. And looking at my question this way it's obvious the maximum in S4 will be 18.25 (the prototype CG in 4mm scale) and minimum will be the Check Span 17.67 plus similar clearance, so 17.75. So the slot is 0.5. So in S4 there should be 0.1 margin of error as against 0.2 in P4.

Of course this is all making it seem so easy. But everyone loves the idea it should be very difficult.

Hi Julian,

Bear in mind though that those figures apply if and only if the wheels in use and the rail in use produce an effective flange width of 0.4mm.

The standards assume that will be the case. My guess is that quite often it isn't. Production wheels will vary, and we know there has been a wide variation in rail profile over the years. Reporting the result of locos built 10 years ago running on a layout built 15 years ago simply isn't going to provide reliable information for someone building S4 now with newly sourced material.

regards,

Martin.
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Julian Roberts
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Re: What back to back setting do you use?

Postby Julian Roberts » Sun Dec 17, 2017 9:14 pm

Well your qualification there which I assume applies equally to P4 seems to me a good reason to avoid the maximum setting.

Anyway you confirm what I postulated earlier, that S4 may indeed be much less fiercesomely demanding than is thought. A margin of error (or window of opportunity as I prefer to think of it) 17.75 -17.85 is more than we are thinking here is our far too lax official 0.8 window (17.67 - 75)

Far more than the official S4 standard of 17.87 - 17.89 which is a nonsense on several counts as laboriously discussed on the P4S4 pros and cons thread.

And interestingly, at the minimum setting, exactly the same maximum running clearance of the real thing at maximum flange wear (scaled down)...if I have that correctly worked out.

I'm not going to change myself as I don't have any problems getting good running in P4 (though will candidly say I do lots of work on all stock to make it adequate so don't have a lot of it - I would never consider a vehicle without suspension as being up to scratch) and I don't think the minute visual improvement would be worth the effort, let alone the non interoperability on excellent P4 layouts. But if I was starting out and was only interested in my own layout I would be quite confident it is entirely possible.

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Julian Roberts
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Re: What back to back setting do you use?

Postby Julian Roberts » Sun Dec 17, 2017 10:17 pm

Tim - thanks. Really liked your flying buttresses info, that has always fascinated me. Your approach sounds excellent.

Noel I have had absolutely none of the problems you fear with my six locos in regular P4 exhibition employment which are all made along these lines. Some people similarly predict horrifying problems with the high ratios that all employ - 80:1 or 108:1 to get smooth low speed running and adequate top speed (on the layouts they are designed for) of 30ish mph. None of these fears materialize.

Yes Paul of course there's the issue you mention, frequently mentioned. The only way to tease it out is direct tests at an event. But people seem more concerned about how much pull they have haha than whether they stay on track.

Why are we so obsessed with pulling long trains? Someone said to me a train shouldn't ever be longer than one third of the visible part of the layout or it just looks wrong, so probably that restricts most people's trains to far less than the longer trains both passenger and goods, of yesteryear, and of today.

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Will L
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Re: What back to back setting do you use?

Postby Will L » Sun Dec 17, 2017 11:22 pm

Le Corbusier wrote:
Enigma wrote:Regarding weight = pull, didn't a Class 37 diesel win the Deputy Chairman's Cup once (including the 'pull test') and weighed practically nothing? It was quite a few years ago so can't remember all the details. Owned by Robin (?! - High Peak layout?).


Thinking about this might this not be (like I think on the prototype) something to do with wheel size and number. I always understood that the more wheels and the smaller these wheels were the greater the traction? Hence the 9fs. I always understood that the greater performance of diesel and electric had as much to do with the gearing allowing much smaller wheels to be used and the drive allowing more of them to be powered than on a steam engine? If so, the class 37 should have more pulling power without the need for excessive weight? Could be wrong of course both in my understanding and because such things don't scale down.

Sorry guys, but weight on the drivers is the prime determinant of the pulling power of any loco. The way it is distributed across multiple drivers will have an effect on how efficiently a loco will use its weight (I.e. locos with the same weight can behave differently) but only within a limits which is set by the only other relevant factor, the coefficient of friction between wheel and rail, (hence traction tyres of some early very light plastic RTR offerings).

On the prototype the weight on each wheel was strictly limited by the civil engineers who build the track. So as trains and loco's got heavier they developed more driving axles so they could apply more adhesive weight to the job. As weight and material strength really don't scale, we don't have the same problem and can load axles out of all proportion. So a single driver, with a well balanced depleted uranium boiler would be capable of pulling really remarkable loads.

To get max aheasion you want an even weight distribution across all the driver axles, not always easy to achieve on a steam loco's rigid chassis, although in a model CSBs make it a lot easier, (Ok Andy, as will equalization and well designed compensation). On modern bogie mounted locos it is very very much easier to get equal weight distribution.

As for the the deputy chairman cup, as I remember this, they were interested in how efficiently a loco used its weight, so the load pulling award went to the loco that used its weight most efficiently (pulled more grams of train per gram of loco weight), not the loco that pulled the most. So a light loco could win over a heavy one even though it couldn't shift as much, and as explained above a modern image bogied loco had distinct advantages.

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Le Corbusier
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Re: What back to back setting do you use?

Postby Le Corbusier » Sun Dec 17, 2017 11:38 pm

Will L wrote:
Le Corbusier wrote:
Enigma wrote:Regarding weight = pull, didn't a Class 37 diesel win the Deputy Chairman's Cup once (including the 'pull test') and weighed practically nothing? It was quite a few years ago so can't remember all the details. Owned by Robin (?! - High Peak layout?).


Thinking about this might this not be (like I think on the prototype) something to do with wheel size and number. I always understood that the more wheels and the smaller these wheels were the greater the traction? Hence the 9fs. I always understood that the greater performance of diesel and electric had as much to do with the gearing allowing much smaller wheels to be used and the drive allowing more of them to be powered than on a steam engine? If so, the class 37 should have more pulling power without the need for excessive weight? Could be wrong of course both in my understanding and because such things don't scale down.

Sorry guys, but weight on the drivers is the prime determinant of the pulling power of any loco. The way it is distributed across multiple drivers will have an effect on how efficiently a loco will use its weight (I.e. locos with the same weight can behave differently) but only within a limits which is set by the only other relevant factor, the coefficient of friction between wheel and rail, (hence traction tyres of some early very light plastic RTR offerings).

On the prototype the weight on each wheel was strictly limited by the civil engineers who build the track. So as trains and loco's got heavier they developed more driving axles so they could apply more adhesive weight to the job. As weight and material strength really don't scale, we don't have the same problem and can load axles out of all proportion. So a single driver, with a well balanced depleted uranium boiler would be capable of pulling really remarkable loads.

To get max aheasion you want an even weight distribution across all the driver axles, not always easy to achieve on a steam loco's rigid chassis, although in a model CSBs make it a lot easier, (Ok Andy, as will equalization and well designed compensation). On modern bogie mounted locos it is very very much easier to get equal weight distribution.

As for the the deputy chairman cup, as I remember this, they were interested in how efficiently a loco used its weight, so the load pulling award went to the loco that used its weight most efficiently (pulled more grams of train per gram of loco weight), not the loco that pulled the most. So a light loco could win over a heavy one even though it couldn't shift as much, and as explained above a modern image bogied loco had distinct advantages.


Hi Will,

I understand the point about the weight.

But I thought that there were two other factors going on. Firstly as you mention, friction. I understood that increasing the number of either coupled or powered wheels meant that you had more friction and so could use more of the power? Secondly, I thought that the issue with larger wheels was the tendency to slip as the rotation at the circumference meant that it was far too easy to put too much power on. The introduction of gearing meant that you could use small wheels and still achieve high running speeds. So a diesel could actually put much more power down on to the track because it had more points of contact and the wheel circumference was small and so the gradual application of power was more easily controlled (again aided by the gearing). Presumably the fantastic torque characteristics of an electric motor at low revs further helps with all of this (true to a lesser extent with diesel)
Tim Lee

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Paul Townsend
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Re: What back to back setting do you use?

Postby Paul Townsend » Mon Dec 18, 2017 6:33 am

Le Corbusier wrote:
Out of interest Paul ... what does your L-shape gauge measure?


Which one ? :)

The ex S4 Socy Stores blue painted one is 17.76mm
Another of forgotten origin which has shorter legs is 17.72mm
My original Studiolith jobby is hiding somewhere so width unknown
I also have 2 that measure 27.00mm :D
Last edited by Paul Townsend on Tue Dec 19, 2017 6:06 am, edited 1 time in total.

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Julian Roberts
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Re: What back to back setting do you use?

Postby Julian Roberts » Mon Dec 18, 2017 7:31 am

Will L wrote:As for the the deputy chairman cup, as I remember this, they were interested in how efficiently a loco used its weight, so the load pulling award went to the loco that used its weight most efficiently (pulled more grams of train per gram of loco weight), not the loco that pulled the most. So a light loco could win over a heavy one even though it couldn't shift as much, and as explained above a modern image bogied loco had distinct advantages.


Interesting Will. The cup predates my membership of the Society maybe; I didn't know that. It must be one of the reasons for the contemporary seeming distaste for something nice and chunky that will stay on the rails and pull something simply by virtue of its own avoirdupois.

Paul Townsend wrote:The ex S4 Socy Stores blue painted one is 17.97mm
Another of forgotten origin which has shorter legs is 17.92mm
My original Studiolith jobby is hiding somewhere so width unknown
I also have 2 that measure 27.00mm :D


You must get really interesting running qualities with that lot! ;)

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Le Corbusier
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Re: What back to back setting do you use?

Postby Le Corbusier » Mon Dec 18, 2017 7:57 am

Paul Townsend wrote:
Le Corbusier wrote:
Out of interest Paul ... what does your L-shape gauge measure?


Which one ? :)

The ex S4 Socy Stores blue painted one is 17.97mm
Another of forgotten origin which has shorter legs is 17.92mm
My original Studiolith jobby is hiding somewhere so width unknown
I also have 2 that measure 27.00mm :D


Sorry Paul .... it was Enigma (aka Paul Gittins) I was asking the question of.

Tim
Tim Lee

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Noel
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Re: What back to back setting do you use?

Postby Noel » Mon Dec 18, 2017 12:25 pm

Julian Roberts wrote:Noel I have had absolutely none of the problems you fear with my six locos in regular P4 exhibition employment which are all made along these lines.


I wasn't fearing problems particularly, just pointing out that your original generalisation is subject to some qualification in that there is always a limit to what you can get into a model engine, especially a relatively small one. Only a vanishingly small number of layouts can ever need model locos capable of starting with the sort of loads that even a relatively small real steam engine could move.
Regards
Noel

Philip Hall
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Re: What back to back setting do you use?

Postby Philip Hall » Mon Dec 18, 2017 3:45 pm

Julian Roberts wrote:
Why are we so obsessed with pulling long trains? Someone said to me a train shouldn't ever be longer than one third of the visible part of the layout or it just looks wrong...


When deciding about the new layout the sudden unexpected availability of a bit more space gave me the chance to build something a bit more ambitious than the one horse branch line I had before. And because it was going to be permanent, it would be easier to maintain the alignments. So I was able to think about having (up to) eight or nine carriage trains and thirty wagons, not all the time, just when I felt like it. Not least because I wanted to join the fortunate band of us lot who do have the space to swish a big engine and a decent train around at a fair lick, reinforcing and proving that such things are not just the preserve of 00 and EM.

I actually think that a long train through a shorter scene is not too out of place, but my ratio of length to train for the total scene, not between (say) bridges, would be twice the train length minimum.

Philip

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Le Corbusier
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Re: What back to back setting do you use?

Postby Le Corbusier » Mon Dec 18, 2017 4:05 pm

Philip Hall wrote: Not least because I wanted to join the fortunate band of us lot who do have the space to swish a big engine and a decent train around at a fair lick, reinforcing and proving that such things are not just the preserve of 00 and EM.
Philip


Now that is something I would like to see a clip of .... if just to stick one in the eye of the 00 brigade :thumb
Tim Lee

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Re: What back to back setting do you use?

Postby Enigma » Mon Dec 18, 2017 4:35 pm

Le Corbusier wrote:
Paul Townsend wrote:
Le Corbusier wrote:
Out of interest Paul ... what does your L-shape gauge measure?


Which one ? :)

The ex S4 Socy Stores blue painted one is 17.97mm
Another of forgotten origin which has shorter legs is 17.92mm
My original Studiolith jobby is hiding somewhere so width unknown
I also have 2 that measure 27.00mm :D


Sorry Paul .... it was Enigma (aka Paul Gittins) I was asking the question of.

Tim


I realised that! ;) Just haven't had the time to reply over the weekend.

My well-used venerable example (stamped P4 BB) appears to measure 17.70+ (ie - nearer to 17.00 than to 17.50 - but measured on a cold day). This is using a good (Mitutoyo) set of vernier calipers so seems to be narrower than several gauges mentioned. I also use examples of early track, pointwork etc. gauges and the two together (with rail taken from an equally venerable heavy duty cardboard tube that I purchased full a long time ago so could be original Studiolith?) work fine for me.

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Le Corbusier
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Re: What back to back setting do you use?

Postby Le Corbusier » Mon Dec 18, 2017 4:49 pm

Enigma wrote:...appears to measure 17.70+ (ie - nearer to 17.00 than to 17.50 - but measured on a cold day).

Isn't 17.70 over 17.50 ? .. do you mean nearer to 17.70 than 17.75 ?
Tim Lee

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Re: What back to back setting do you use?

Postby Enigma » Mon Dec 18, 2017 10:39 pm

Le Corbusier wrote:
Enigma wrote:...appears to measure 17.70+ (ie - nearer to 17.00 than to 17.50 - but measured on a cold day).

Isn't 17.70 over 17.50 ? .. do you mean nearer to 17.70 than 17.75 ?


Sorry!! Finger slippage :oops: Should have typed '17.00+' - which now (hopefully!) makes sense of the following statement.

BTW, I've found the cardboard tube for the rail and it was actually from the Scalefour Society Stores, 80metres quantity which cost £1.20 to post. Along with an address of 'The Chase, Enfield', this should date it. All my layouts have been built from this rail - and I still have around 10 - 12 metres left.

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Le Corbusier
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Re: What back to back setting do you use?

Postby Le Corbusier » Mon Dec 18, 2017 11:22 pm

Enigma wrote:
Le Corbusier wrote:
Enigma wrote:...appears to measure 17.70+ (ie - nearer to 17.00 than to 17.50 - but measured on a cold day).

Isn't 17.70 over 17.50 ? .. do you mean nearer to 17.70 than 17.75 ?


Sorry!! Finger slippage :oops: Should have typed '17.00+' - which now (hopefully!) makes sense of the following statement.

BTW, I've found the cardboard tube for the rail and it was actually from the Scalefour Society Stores, 80metres quantity which cost £1.20 to post. Along with an address of 'The Chase, Enfield', this should date it. All my layouts have been built from this rail - and I still have around 10 - 12 metres left.

sorry ... totally confused now :? The digest states P4 b-to-b range is 17.67 - 17.75. So if you are nearer to 17.00 than 17.50 :?:
Tim Lee

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Paul Townsend
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Re: What back to back setting do you use?

Postby Paul Townsend » Tue Dec 19, 2017 6:09 am

Julian Roberts wrote:
Paul Townsend wrote:The ex S4 Socy Stores blue painted one is 17.97mm
Another of forgotten origin which has shorter legs is 17.92mm
My original Studiolith jobby is hiding somewhere so width unknown
I also have 2 that measure 27.00mm :D


You must get really interesting running qualities with that lot! ;)


Where on earth did those ridiculous figures come from?
Mega-typos?? Typed at 06:00 with no coffee and careless proof reading...sorry for disseminating rubbish

I have edited my original post but can't edit it where used in quoted replies.
The figures were meant to be:

The ex S4 Socy Stores blue painted one is 17.76mm so a smidgeon over size
Another of forgotten origin which has shorter legs is 17.72mm
My original Studiolith jobby is hiding somewhere so width unknown
I also have 2 that measure 27.00mm

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Julian Roberts
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Re: What back to back setting do you use?

Postby Julian Roberts » Tue Dec 19, 2017 9:10 am

I know this may not be seen as the point of the thread. But regarding my contention that axle loading is more significant to staying on the track than minute variations of BB, I came across this in Iain Rice Chassis Construction

Capture Rice axle loading 1.JPG

Capture Rice axle loading 2.JPG
You do not have the required permissions to view the files attached to this post.

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Re: What back to back setting do you use?

Postby Enigma » Tue Dec 19, 2017 4:43 pm

Le Corbusier wrote:
Enigma wrote:
Le Corbusier wrote:
Enigma wrote:...appears to measure 17.70+ (ie - nearer to 17.00 than to 17.50 - but measured on a cold day).

Isn't 17.70 over 17.50 ? .. do you mean nearer to 17.70 than 17.75 ?


Sorry!! Finger slippage :oops: Should have typed '17.00+' - which now (hopefully!) makes sense of the following statement.

BTW, I've found the cardboard tube for the rail and it was actually from the Scalefour Society Stores, 80metres quantity which cost £1.20 to post. Along with an address of 'The Chase, Enfield', this should date it. All my layouts have been built from this rail - and I still have around 10 - 12 metres left.

sorry ... totally confused now :? The digest states P4 b-to-b range is 17.67 - 17.75. So if you are nearer to 17.00 than 17.50 :?:


Oh dear, dear, dear me!! It must be something about the name :oops: :roll: I amended the wrong figures so please totally ignore all I've written before and work from the following which (I hope!) is now correct.

My b-2-b gauge measures 17.50mm (cold) which is narrower than many of the figures quoted as being 'correct'. I have just re-measured it to make sure.

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Paul Townsend
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Re: What back to back setting do you use?

Postby Paul Townsend » Tue Dec 19, 2017 5:40 pm

Apparently, most Pauls type garbage at the first go......with the possible exception of Paul Willis.

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Paul Willis
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Re: What back to back setting do you use?

Postby Paul Willis » Wed Dec 20, 2017 5:51 am

Paul Townsend wrote:Apparently, most Pauls type garbage at the first go......with the possible exception of Paul Willis.


Oh I don't know... But I do try and keep that for work!

Cheers
Flymo

PS - I've not had the spare time to write up very much at all in 2017. Modelling has occasionally taken place, and one day the stories may be told...
Beware of Trains - occasional modelling in progress!
www.5522models.co.uk

Enigma
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Re: What back to back setting do you use?

Postby Enigma » Wed Dec 20, 2017 1:36 pm

Paul Townsend wrote:Apparently, most Pauls type garbage at the first go......with the possible exception of Paul Willis.


Well, here's a bit more (you might think!)

I checked my b-2-b gauge again this morning as I am using it to fit some driving wheels to my current project. Guess what - it measured 17.70mm!!!!!!!!!! Is it made of rubber? Is it extremely sensitive to temperature variations? Am I going round the bend? Should I go the Specsavers?

In fact, I went there a couple of weeks ago and all seemed generally OK so that's not the problem!

wibble wibble wibble.......................... :? :cry:

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Le Corbusier
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Re: What back to back setting do you use?

Postby Le Corbusier » Wed Dec 20, 2017 2:23 pm

Enigma wrote:
Paul Townsend wrote:Apparently, most Pauls type garbage at the first go......with the possible exception of Paul Willis.


Well, here's a bit more (you might think!)

I checked my b-2-b gauge again this morning as I am using it to fit some driving wheels to my current project. Guess what - it measured 17.70mm!!!!!!!!!! Is it made of rubber? Is it extremely sensitive to temperature variations? Am I going round the bend? Should I go the Specsavers?

In fact, I went there a couple of weeks ago and all seemed generally OK so that's not the problem!

wibble wibble wibble.......................... :? :cry:


It was only a curiosity question in passing ;) Lets just say ... whatever the dim it works for you :D
Tim Lee

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Julian Roberts
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Re: What back to back setting do you use?

Postby Julian Roberts » Wed Dec 20, 2017 7:48 pm

Pleased to report the loco referred to earlier that derailed in the video is now much improved. This is the link: 20171209 132745

Measures taken
1. Ease out BB to 17.75
2. Replace front springs with next thicker grade wire.
3. Add weight to the front.

The loco instead of not once taking the turnout without derailing in the forward direction, now fails to derail at all doing the identical move. Specialists may be interested to know the centre of gravity is now between middle and rear driver. Where it was previously is not known.
Last edited by Julian Roberts on Wed Dec 20, 2017 11:15 pm, edited 1 time in total.

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Le Corbusier
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Re: What back to back setting do you use?

Postby Le Corbusier » Wed Dec 20, 2017 9:11 pm

Julian Roberts wrote:Pleased to report the loco referred to earlier that derailed in the video is now much improved. This is the link: 20171209 132745

Measures taken
1. Ease out BB to 17.75
2. Replace front springs with next thicker grade wire.
3. Add weight to the front.

The loco instead of once taking the turnout without derailing in the forward direction, now fails to derail at all doing the identical move. Specialists may be interested to know the centre of gravity is now between middle and rear driver. Where it was previously is not known.


Julian,

What is the springing?

If you added weight to the front and this places the C of G between the middle and rear driver, wouldn't that imply that the previous C of G would have been even further back?

Tim
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Julian Roberts
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Re: What back to back setting do you use?

Postby Julian Roberts » Wed Dec 20, 2017 11:16 pm

Edited previous post

Tim yes it must have been even further back!

Individual guitar type wire springs for each wheel


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