OO gauge GWR Mogul and Prairie

[Mallard60022]

15 minutes ago, melmerby said:

Once again we get the variations. Mine won't pull anything like that, it's just too weak.

Apologies, wasn't sort of boasting; it is far better with 8. Min radius on the end curves is 28", long and very gentle curves are absolutely flat and I selected the Coaches carefully for free running. All modern Baccy or Hornby Mk1s. All I've done is adapt the tender Loco connection slightly as it was feeble and unplugged far too easily! I suspect that the addition of Lamps hasn't increased the pulling ability

P

[Miss Prism]

However light the spring pressure is on the pony trucks, that spring pressure will detract from the vertical force being applied by the drivers. The usual adage here is that ponys should be sprung/weighted sufficient only for good trackholding.

 

For Prairies, it is desirable the ponys exert a similar force, to keep the effect on the main wheelbase symmetrical.

 

If the coil spring on a pony truck is a short one, the length of travel between zero force and maximum force will also be small. The integration of non-adjustable short-travel coil springs into an RTR chassis is therefore problematic, because the required/desired tolerances become too small. Long-travel coil springs are therefore more suitable, but of course require more vertical real-estate, and the distance tolerancing is not significantly easier. I can guarantee you Dapol hasn't got a clue about any of this, and left the engineering to China, who probably scratched their heads and did as best they could under the circumstances of whatever the design brief was.

 

If I had one of these things, I'd rip out the coil springs and substitute leaf springs - they are far more controllable.

 

 

Edited December 6, 2021 by Miss Prism

[Ian Hargrave]

26 minutes ago, Miss Prism said:

However light the spring pressure is on the pony trucks, that spring pressure will detract from the vertical force being applied by the drivers. The usual adage here is that ponys should be sprung/weighted sufficient only for good trackholding.

 

For Prairies, it is desirable the ponys exert a similar force, to keep the effect on the main wheelbase symmetrical.

 

If the coil spring on a pony truck is a short one, the length of travel between zero force and maximum force will also be small. The integration of non-adjustable short-travel coil springs into an RTR chassis is therefore problematic, because the required/desired tolerances become too small. Long-travel coil springs are therefore more suitable, but of course require more vertical real-estate, and the distance tolerancing is not significantly easier. I can guarantee you Dapol hasn't got a clue about any of this, and left the engineering to China, who probably scratched their heads and did as best they could under the circumstances of whatever the design brief was.

 

If I had one of these things, I'd rip out the coil springs and substitute leaf springs - they are far more controllable.

 

 

 

 

Thanks for this.But it isn’t exactly reassuring in terms of Dapol’s being hands off in engineering design .Perceived wisdom atm indicates the springs as the primary cause of stalling. Not encouraging as I have neither the dexterity nor eyesight for achieving a fix.Have you any other ideas of what might be responsible for the issue ?

[Miss Prism]

10 minutes ago, Ian Hargrave said:

Have you any other ideas of what might be responsible for the issue ?

 

I'd want to know more about the nature of the springing on any of the drivers. Is it a short-travel coil spring acting on a saddle over the middle axle? I'd also want to know more about the sideplay on all the drivers, and how the pickups are arranged and perform at the extremes of that sideplay, which is a notorious common problem with intermittent pickup problems.

 

Edited December 6, 2021 by Miss Prism

[outatime]

I also received my Dapol Large Praire a couple of days ago. Yesterday i finally had the time to test it and mine also stalled at slow speeds, even on my perfectly clean and straight piece of test track. At first i suspected the pickups, but even after adjusting them, the loco didn't run any better.

The Loco has a sprung middle axle which usually is a good idea for better pickup. But in this case, the axle can only move upwards but not downwards. Just hold a ruler or any other piece of straight material on the wheels and you will see that the middle axle ist not moving up as it should.

Finally, i modified the keeper plate, so that the middle axle can also move downwards and is therefore properly pressed against the rails.

After this modification, the loco ist running perfectly fine without stalling even when crawling very slowly.

I will soon remove the keeper plate again for a photo, but at first i had to test that the modification worked.

I didn't inspect the rear pony truck at all because it was moving freely in every direction, so this was not the fault with my loco.

[Ian Hargrave]

16 minutes ago, Miss Prism said:

 

I'd want to know more about the nature of the springing on any of the drivers. Is it a short-travel coil spring acting on a saddle over the middle axle? I'd also want to know more about the sideplay on all the drivers, and how the pickups are arranged and perform at the extremes of that sideplay, which is a notorious common problem with intermittent pickup problems.

 

Interesting. My Rails Dapol Terrier which obviously devoid of trailing axles also suffers the identical failure and stalls on pointwork

[Miss Prism]

10 minutes ago, outatime said:

Finally, i modified the keeper plate, so that the middle axle can also move downwards and is therefore properly pressed against the rails. After this modification, the loco is running perfectly fine without stalling even when crawling very slowly.

 

Ah, some proper engineering. Excellent.

[Ian Hargrave]

15 minutes ago, outatime said:

I also received my Dapol Large Praire a couple of days ago. Yesterday i finally had the time to test it and mine also stalled at slow speeds, even on my perfectly clean and straight piece of test track. At first i suspected the pickups, but even after adjusting them, the loco didn't run any better.

The Loco has a sprung middle axle which usually is a good idea for better pickup. But in this case, the axle can only move upwards but not downwards. Just hold a ruler or any other piece of straight material on the wheels and you will see that the middle axle ist not moving up as it should.

Finally, i modified the keeper plate, so that the middle axle can also move downwards and is therefore properly pressed against the rails.

After this modification, the loco ist running perfectly fine without stalling even when crawling very slowly.

I will soon remove the keeper plate again for a photo, but at first i had to test that the modification worked.

I didn't inspect the rear pony truck at all because it was moving freely in every direction, so this was not the fault with my loco.

Yes.I’d wondered what part the keeper plate had played in this.So that’s an easy fix.

Edited December 6, 2021 by Ian Hargrave
Adding text

[Harlequin]

15 minutes ago, outatime said:

I also received my Dapol Large Praire a couple of days ago. Yesterday i finally had the time to test it and mine also stalled at slow speeds, even on my perfectly clean and straight piece of test track. At first i suspected the pickups, but even after adjusting them, the loco didn't run any better.

The Loco has a sprung middle axle which usually is a good idea for better pickup. But in this case, the axle can only move upwards but not downwards. Just hold a ruler or any other piece of straight material on the wheels and you will see that the middle axle ist not moving up as it should.

Finally, i modified the keeper plate, so that the middle axle can also move downwards and is therefore properly pressed against the rails.

After this modification, the loco ist running perfectly fine without stalling even when crawling very slowly.

I will soon remove the keeper plate again for a photo, but at first i had to test that the modification worked.

I didn't inspect the rear pony truck at all because it was moving freely in every direction, so this was not the fault with my loco.

It sounds like a generally good idea but it doesn't seem to add up...

 

If just modifying the travel of the centre axle fixes your pickup problems then the implication is that the outer axles have little or no pickup. If that's the case then there's something more seriously wrong somewhere.

 

Your experience seems to be slightly different than most people with the stalling problem and some of us don't see any stalling at all.

 

[Ian Hargrave]

10 minutes ago, Harlequin said:

It sounds like a generally good idea but it doesn't seem to add up...

 

If just modifying the travel of the centre axle fixes your pickup problems then the implication is that the outer axles have little or no pickup. If that's the case then there's something more seriously wrong somewhere.

 

Your experience seems to be slightly different than most people with the stalling problem and some of us don't see any stalling at all.

 

 
Might it depend on the tightness or otherwise of the keeper plate.

[outatime]

10 minutes ago, Harlequin said:

It sounds like a generally good idea but it doesn't seem to add up...

 

If just modifying the travel of the centre axle fixes your pickup problems then the implication is that the outer axles have little or no pickup. If that's the case then there's something more seriously wrong somewhere.

 

Your experience seems to be slightly different than most people with the stalling problem and some of us don't see any stalling at all.

 

 

The problem is that if the middle axle is only able to move upwards it means that it is not touching the rails most of the time, just if it was not sprung at all and just as ridgid as the other two driving axles. The rails are never perfectly even and in this case you are left with only three contact points with the rails, for example the last axle and one side of the first (assumed that the rails are not even). Then if only a little dirt on the tracks comes into the equation, the loco will stall. With the sprung axle now working properly, the number of contact points increases from 3 to 5 even in the worst case.

[melmerby]

The Hornby one has a rigid driver wheelbase.

 

If you go very slowly (much slower than in the above video, it will stall on a Peco code 75 Electrofrog large diamond crossing.

Why? Because there is a position where both outer wheels are on plastic and the plastic is very slightly higher than the rail = no contact for centre wheel and loco stops

Reducing the plastic a smidgen (precision engineering term) gets around this quirk.

 

[outatime]

Here are two photos showing the modifications to the keeper plate.

Now that i've had the loco in my hands again, i can confirm that there is an issue with the rear pony truck as well.

The wheel cannot move upwards at all even if the loco is on even track. So it is possible that the pony truck lifts the rear driving wheel in some cases and this reduces the number of contact points to only one axle, the first driving axle.

So some work has to be done there as well.

 

Edited October 6, 2023 by outatime
pictures reuploaded

[Harlequin]

26 minutes ago, outatime said:

 

The problem is that if the middle axle is only able to move upwards it means that it is not touching the rails most of the time, just if it was not sprung at all and just as ridgid as the other two driving axles. The rails are never perfectly even and in this case you are left with only three contact points with the rails, for example the last axle and one side of the first (assumed that the rails are not even). Then if only a little dirt on the tracks comes into the equation, the loco will stall. With the sprung axle now working properly, the number of contact points increases from 3 to 5 even in the worst case.

Yes, that makes perfect sense if the track has dirty spots, as it generally would have, but what confused me was that you had previously said: "on my perfectly clean and straight piece of test track".

 

Anyhow, it's a good modification!

 

Edited December 6, 2021 by Harlequin

[outatime]

On 06/12/2021 at 17:18, Harlequin said:

Yes, that makes perfect sense if the track has dirty spots, as it generally would have, but what confused me was that you had previously said: "on my perfectly clean and straight piece of test track".

 

Anyhow, it's a good modification!

 

Well, sorry, probably it still wasn't clean enough after a few wipes with isopropyl alcohol. 

I just had a look at the rear pony truck and after the use of a small needle file the axle can now move upwards and is still sprung.

A softening of the springs is still a good option, they feel quite strong but not strong enough to lift the loco.

 

 

Edited October 6, 2023 by outatime
pictures reuploaded

[boxbrownie]

4 hours ago, melmerby said:

Why does it need any compensation?

It should run as an 0-6-0 with the trucks having no effect on the weight distribution, a driving wheel shouldn't drop into those gaps.

The vast majority of my tank locos with leading or trailing wheels have no springing at all and dont do it.

 

Edit

Those that have springing have just enough the keep the wheels on the track, they shouldn't be compensating for poor weight distribution on a 2-6-2

I wasn’t suggesting they were, hopefully they aren’t compensating for the balance of the model those springs “should” be there just to keep the pony wheels firmly on the track, does the pony sub chassis actually bear upon the main chassis when it’s running? That would sort of explain the springs…..but obviously not at the rate they are set, they need to be just firm enough to keep the pony wheels on the track, most models seem to do fine with just the weight of the truck but then they are usually metal.

[rembrow]

39 minutes ago, outatime said:

Well, sorry, probably it still wasn't clean enough after a few wipes with isopropyl alcohol. 

I just had a look at the rear pony truck and after the use of a small needle file the axle can now move upwards and is still sprung.

A softening of the springs is still a good option, they feel quite strong but not strong enough to lift the loco.

 

I've made the same modification to the axle slots of the rear pony and I'm now getting a couple of mm of lift of the truck, without the driving wheels lifting. I have reinstalled the springs, reduced in length, which ensure the axle stays on the track, but with less pressure than originally. I extended the axle slot gradually, as there is not much room between the wheel tread and the underside of the cab floor  so I wanted to avoid the wheel tread scrapping the floor. As posted last night, the loco has been tested on a makeshift incline, reverse first, and the driving wheels are not lifting from the track.

[Chuffer Davies]

6 hours ago, melmerby said:

Why does it need any compensation?

It should run as an 0-6-0 with the trucks having no effect on the weight distribution, a driving wheel shouldn't drop into those gaps.

The vast majority of my tank locos with leading or trailing wheels have no springing at all and don't do it.

 

Edit

Those that have springing have just enough the keep the wheels on the track, they shouldn't be compensating for poor weight distribution on a 2-6-2

Hi Melmerby,

There is no reason to think that Dapol have sprung the pony truck to compensate for poor weight distribution.  It is more likely that this mechanism was intended to provide better track holding of the pony truck when a train is attached to the integrated coupling.  

 

The weighting of model locomotives is always a compromise.  Too little and the tractive ability of the model will be severely compromised, too much on the wrong places can make the model unstable but stability should not be an issue with the Prairie.  

 

You have stated (not unreasonably) that the vast majority of your tank locos have no springing and don't do it (wheels dropping on to the gap of a point frog).  At the same time you have also remarked that where a loco passes over a plastic frog with a raised rail head it is prone to stalling.  Dapol's attempt to address your 2nd problem is the reason why their Prairie behaves differently and drops into the frog of a universal point.  The reason a rigid chassis is unlikely to exhibit a wheel dropping in the frog is because the middle axle supports the chassis whilst an outer wheel traverses the gap.  By springing the middle axle Dapol have improved significantly the current collection of the Prairie (5 wheels minimum in contact with the track at any given time instead of 3) through uneven track work, but as a direct result the centre axle can no longer support the weight of the loco as an outer wheel traverses the gap in the frog and instead that wheel now follows the contours of the frog rather than flying across it.   This is therefore a feature of the design but definitely not a fault as you had suggested.

 

Regards,

Frank

[Miss Prism]

There is no excuse for bits of plastic to be higher than the metal rail surface in any item of point and crossing work.

 

Unfit for purpose, plain and simple.

 

[melmerby]

3 hours ago, Miss Prism said:

There is no excuse for bits of plastic to be higher than the metal rail surface in any item of point and crossing work.

 

Unfit for purpose, plain and simple.

 

Well, they would be better if the check rails were actually rails, rather than bits of plastic, then there would never be a problem.

I only noticed it when I tried to see how slow my Hornby 5101 would go through pointwork.

Only on the slowest setting on the controller did it stop (that was very slow) anymore and inertia carried it through.

 

A quick scrape of the plastic, cured the problem.

[tomparryharry]

18 hours ago, melmerby said:

Once again we get the variations. Mine won't pull anything like that, it's just too weak.

Imitating real life, I'm afraid. That's why we have big locomotives, and little locomotives. Putting a class 3 loco on a class 6-7 load will end in tears. 

 

Of course, it's the manufacturers fault......

 

Now, I'm not having a pop at anyone at all; not in the slightest. But, the manufacturers make realistic models, which are required  to run unrealistic loads. 

 

Of course, it's the manufacturers fault..... Lesson one in a QC situation. Is the product fit for its intended  purpose? 

 

regardless of manufacturers, the required standards are usually quality, realism and fidelity to the product concerned. 

 

Of course, it's the manufacturers fault.... Naughty manufacturers!

 

Cheers,

Ian.

[Ian Hargrave]

You’ve just taken a stroll into a minefield here,@tomparryharry.The performance in terms of haulage power is determined by track conditions and min/max curve radius plus any gradient that might be there. Then you must consider what both these locos were capable of on the day.Both could and did punch above their weight.Both handled express passenger turns such as for the mogul Summer Saturday extras to the West Country and Prairies regular turns between Gloucester and Cheltenham on Paddington turns or from Pontypool Road the Swansea portion of a North to West express. Throw in the performance of the stock used  on your layout and its free running or otherwise capabilities and it’s a difficult balancing act. I don’t think it’s at all unreasonable for the design and development of a model to factor in such variables to be reasonably prototypical but again depending on the size of your layout I.e.what looks right in your eyes.  Thus for the sake of a hypothetical scenario,I would expect a Prairie to handle 5 Hornby Colletts/Hawksworths and between 5&7 of the same for a Mogul without over taxing them. Bachmann Mk 1 is another matter .

[JST]

38 minutes ago, tomparryharry said:

Imitating real life, I'm afraid. That's why we have big locomotives, and little locomotives. Putting a class 3 loco on a class 6-7 load will end in tears. 

 

Of course, it's the manufacturers fault......

 

Now, I'm not having a pop at anyone at all; not in the slightest. But, the manufacturers make realistic models, which are required  to run unrealistic loads. 

 

Of course, it's the manufacturers fault..... Lesson one in a QC situation. Is the product fit for its intended  purpose? 

 

regardless of manufacturers, the required standards are usually quality, realism and fidelity to the product concerned. 

 

Of course, it's the manufacturers fault.... Naughty manufacturers!

 

Cheers,

Ian.

 

Can’t argue with that but I would add a “requirement” and that is uniformity & consistency of product. It seems that this is where the industry as a whole is falling down. One person has a perfect example of a model and the next one gets a dog. This must be a QC issue. There is a problem for manufactures here in a much as if a high profile reviewer gets sent a duffer they will call it out. The Hornby large prairie is just one example of this.

[tomparryharry]

24 minutes ago, Ian Hargrave said:

You’ve just taken a stroll into a minefield here,@tomparryharry.The performance in terms of haulage power is determined by track conditions and min/max curve radius plus any gradient that might be there. Then you must consider what both these locos were capable of on the day.Both could and did punch above their weight.Both handled express passenger turns such as for the mogul Summer Saturday extras to the West Country and Prairies regular turns between Gloucester and Cheltenham on Paddington turns or from Pontypool Road the Swansea portion of a North to West express. Throw in the performance of the stock used  on your layout and its free running or otherwise capabilities and it’s a difficult balancing act. I don’t think it’s at all unreasonable for the design and development of a model to factor in such variables to be reasonably prototypical but again depending on the size of your layout I.e.what looks right in your eyes.  Thus for the sake of a hypothetical scenario,I would expect a Prairie to handle 5 Hornby Colletts/Hawksworths and between 5&7 of the same for a Mogul without over taxing them. Bachmann Mk 1 is another matter .

 

In so many words, you've summed up & expanded my post; nice! 

 

Example: Llantrisant would turn out 1471 on the Penygraig auto. In the worst weather, the 14xx was often replaced by a pannier.  

[spamcan61]

32 minutes ago, JST said:

 

Can’t argue with that but I would add a “requirement” and that is uniformity & consistency of product. It seems that this is where the industry as a whole is falling down. One person has a perfect example of a model and the next one gets a dog. This must be a QC issue. There is a problem for manufactures here in a much as if a high profile reviewer gets sent a duffer they will call it out. The Hornby large prairie is just one example of this.

The trouble is, toy trains are manufactured in small volumes and there's an awful lot of hand assembly involved, generally by a third party on the other side of the planet.  So there's no business justification to spend extra  time and money re-engineering the product to make it easier to ensure consistent 'quality'* . 'Design Clever' is as near as we got, and presumably didn't go well as Hornby don't shout about it any more. So I don't think anything is going to change significantly. 

 

* For whatever definition of  'quality' is relevant to particular buyers.