Bachmann/Mainline Pony/Bogie springs

[Bob O]

Hi all

Being a lazy kinda guy I thought I would ask first and try and see what others think. I have been kinda puzzled why Bachmann/Mainline locos haul about 2 coaches less than the equivalent weight Hornby locos.

Mates at club suggest the dissimilar method of bogie/pony springs.  

 

[Alan Higgi]

Bachmann Jubilee Drake - poor traction

[34theletterbetweenB&D]

Three factors, but the carrying wheel springing is the more significant in most cases.

 

Hornby rarely spring carrying wheels, whereas Bachmann inevitably do. Bachmann product introduced before about 2006 tended to be well and truly oversprung on carrying wheels, sometimes over a third of the loco weight (A1 pacific). Not only is that weight lifted off the driven wheels, it is transferred to often draggy wheelsets which immediately absorb a lot of the potential traction. I have been cutting Bach coil springs down ever since their split chassis product was introduced. Once Hornby started making worthwhile product, all these spring off cuts became useful for equipping their bogie equipped product. (A3, A4, Britannia, Castle; the diagrams often show a spring on a bogie pivot post ideal for the purpose, but in a dozen purchases spread across these types, nary a one have I seen...)

 

Hornby's driven wheel tyres have a slightly better coefficient of friction on nickel silver rail, mean circa 0.15, against Bachmann at circa 0.14.

 

Hornby though fit pretty draggy wiper pick ups on tenders, and these eat into the traction. Typically not too badly when new, but after a year or so of operation the drag kicks in with a vengeance. I have had Hornby tender locos near stopped light engine by their tenders.

 

So if you took a couple of 4-6-2 or 2-6-4T types of similar all up weight from each range, the Hornby would typically be much the better tractively as supplied.

 

Modify, modify, modify...

[Bob O]

The Ivatt "pig" 4mt 43049 has me baffled. Played about with spring, added 30g to cab to balance it but it stil hauls 28 wagons max! A Hornby 8f (10g less) hauls 34.

[34theletterbetweenB&D]

 

...Hornby's driven wheel tyres have a slightly better coefficient of friction on nickel silver rail, mean circa 0.15, against Bachmann at circa 0.14...

Bob,

 

This is the likely explanation, all other factors being equal. Compare a group of Bachmann and Hornby loco pairs, the pairing for the same weight on the driven wheels, and the Hornby locos will on average exert more drawbar force; averaging about 7% more on the data I have collected. There is a lot of variation between specimens from both makers, and confounding factors, such that this not immediately obvious without some careful testing; the variance in performance is significant, even between two notionally identical chassis from the same maker. The variance on both makes is similar to the average difference, so the result you have, circa 20% better haulage from the Hornby falls well within the expected range.

 

So much for what I have learned, modify, modify, modify is the practical solution.

 

Let's face it, 34 wagons is a pathetic load for an 8F to max out with.

 

Are the wagons free rolling? They should roll away on a 1% or 1 in 100 gradient, as a basic standard. (Requires metal wheel tyres and pinpoint bearings.)

 

Weight in the loco.

 

Bachmann Ivatt 4MT; replace all the fitted ballast with lead. If decoder fitting, rearrange internally to hardwire so decoder is in smokebox and the void over the coupled wheels is filled with lead. (It is inept model design to put the light and bulky socket and decoder in a position where ballast for traction needs to go. IMNSVHO.)

 

Hornby 8F; here we have a real problem in that the inept design for plastic bodied modelling lies with Stanier's team! The real answer in model form is a cast metal body to get the weight in. Lots of cutting to do to both chassis and bodywork to get the weight up by adding lead, a real PITA on this design. (Compare to the dimensionally similar properly parallel boilered 8Fs O1 and WD, which can easily be made to weigh 450g, these then pull as well as an 8F should.)

[Alan Higgi]

Based on what 34theletterbetweenB&D said on the black 5 I got my 8f up to 320g. Good for 46 kit built wagons. ( I reckon every 4.5g weight added is worth an extra wagon) but the "flying pig" is a weird one to do. I have not touched mine yet!

[34theletterbetweenB&D]

_{... the "flying pig" is a weird one to do. I have not touched mine yet!}

 

_{Well, not least of my reasons for generally preferring Bachmann over Hornby is that the screw together construction of the bodies and chassis makes modification for greater weight easier. Where it is unscrewing and breaking the odd cemented join on a Bachmann, all too often the equivalent process on a Hornby involves cutting both metal and plastic.}

 

_{The Flying pig will come apart enabling the cast mazak ballast to come out. Substituting with solid lead makes a big difference, thanks to the much higher density of this material. Very worthwhile as this is such a characterful model, one of the nicest items in their catalogue.}

[Alan Higgi]

Thanks for the inspiration Mr Hatfield.Ok I will bite the bullet! How heavy did you get yours? I think quite a bit needs to go in the cab too for balance? Any tips?

[34theletterbetweenB&D]

Mine are made up to 375g if memory serves (off base at the moment). Most of the added weight is in the boiler/smokebox. One piece of code 7 sheet (about 30g) shaped to fit up under the cab roof above the window line to help balance, where it is completely out of sight. It does balance slightly forward of the centre coupled wheelset, but hey we cannot get it perfect every time.

[Bob O]

Bob,

 

This is the likely explanation, all other factors being equal. Compare a group of Bachmann and Hornby loco pairs, the pairing for the same weight on the driven wheels, and the Hornby locos will on average exert more drawbar force; averaging about 7% more on the data I have collected. There is a lot of variation between specimens from both makers, and confounding factors, such that this not immediately obvious without some careful testing; the variance in performance is significant, even between two notionally identical chassis from the same maker. The variance on both makes is similar to the average difference, so the result you have, circa 20% better haulage from the Hornby falls well within the expected range.

 

So much for what I have learned, modify, modify, modify is the practical solution.

 

Let's face it, 34 wagons is a pathetic load for an 8F to max out with.

 

Are the wagons free rolling? They should roll away on a 1% or 1 in 100 gradient, as a basic standard. (Requires metal wheel tyres and pinpoint bearings.)

 

Weight in the loco.

 

Bachmann Ivatt 4MT; replace all the fitted ballast with lead. If decoder fitting, rearrange internally to hardwire so decoder is in smokebox and the void over the coupled wheels is filled with lead. (It is inept model design to put the light and bulky socket and decoder in a position where ballast for traction needs to go. IMNSVHO.)

 

Hornby 8F; here we have a real problem in that the inept design for plastic bodied modelling lies with Stanier's team! The real answer in model form is a cast metal body to get the weight in. Lots of cutting to do to both chassis and bodywork to get the weight up by adding lead, a real PITA on this design. (Compare to the dimensionally similar properly parallel boilered 8Fs O1 and WD, which can easily be made to weigh 450g, these then pull as well as an 8F should.)

Thanks

 

34 wagons is near to OK. My max load is 36 as the layout is not huge. I am sure you are correct in that the problem is the plating on the wheels as the wagons are all quite free running. So more weight I guess!

[Bob O]

I've found by using silicone grease on wagons that don't have pinpoint axle bearing helps, example 72XX @ 240g will tow 64 wagons with slight slip only at starting.

The 72xx is an exceptional hauler.A borrowed one hauled 45 wagons on my layout. The weight of wagons is a factor. Some Bachmann ones are only about 26g. However most of mine wirh loads etc are 36. Some of the kit built loaded 21t coal wagons are 40g. Back to the 72xx. It must be the finish on the wheels and the fact that 8 wheels give more bite than 6?

[34theletterbetweenB&D]

It's all down to the finish on the wheels and the weight bearing on those driven wheels. Once you have four driven wheels in a rigid model chassis, adding more is no help for traction. Anyone who doubts this, get a look at a H-D 8F, functionally it is a 2-4-0 as the second and third driven axle are flangeless and undersize and thus clear of the rail. Made up to the same weight an all flanged 2-8-0 pulls no better in model form. (There is a proviso to this; the weight bearing on the coupled wheels needs to be centred at the midpoint of the driven wheelbase. This is typically easier to achieve on models as wheelbase gets longer.)

 

The prototype is different. There the significant limit on the weight that can be placed on any single axle necessitates adding more axles proportional to the all-up weight of the loco.  In general extra driven wheels reads as more adhesion, for any given maximum permitted axle loading.

[Alan Higgi]

The Ivatt "pig" 4mt 43049 has me baffled. Played about with spring, added 30g to cab to balance it but it stil hauls 28 wagons max! A Hornby 8f (10g less) hauls 34.

Hi Bob

 

As I have been on nights this week I played about with the flying pig. Got the weight up to 320g - 42 wagons. I never match 34theletterbetweenB&D but his tip on extra in the cab roof was a revelation.

 

 

 

[Il Grifone]

Friction between surfaces is proportional to the applied pressure. Hence eight wheels will pull no better than six (or less) for the same total mass. The weight of the wagon (within limits) only really enters the equation when gradients are involved.

 

 

My Dublo 8F will pull around 18 HD wagons plus her heavy die-cast tender, which equates to around 60 pin point bearing wagons. She seems unduly prone to slip however.

[Alan Higgi]

Friction between surfaces is proportional to the applied pressure. Hence eight wheels will pull no better than six (or less) for the same total mass. The weight of the wagon (within limits) only really enters the equation when gradients are involved.

 

 

My Dublo 8F will pull around 18 HD wagons plus her heavy die-cast tender, which equates to around 60 pin point bearing wagons. She seems unduly prone to slip however.

As I recall the Dublo 8f weighed a pound (454g)

[Alan Higgi]

 

 

34theletterbetweenB&D, on 30 May 2013 - 22:29, said:

 

Hornby's driven wheel tyres have a slightly better coefficient of friction on nickel silver rail, mean circa 0.15, against Bachmann at circa 0.14.

Modify, modify, modify...

 

You are not on your own putting the blame on Bachmann wheels; enclosed is a report from a wheel conversion. A normaly wheeled PT @ around 210g moves 5 coaches/23 wagons before slipping! Bachmann Class 8750 'Pannier Tank' conversion pack - Ultrascale ...

www.ultrascale.com/sites/default/files/reviews/review01.pdf‎

 

"That said, I exaggerate not when I say that I found

the tractive performance astonishing. On the dead level S4 'Green Street', with seven

Bachmann Mk1s, a rapid application of full voltage causes a slip for roughly the length

of the loco, followed by brisk acceleration to a scale 60 mph or so.

 

On the test rig it showed a peak pull of 55 grams before slipping at an average around

52 grams, which at an overall weight of 214 grams, gives drawbar pull figures either

side of 25% of the tractive weight. Few Deputy Chairman's Cup entries have achieved

this figure, even less with round and true wheels. Better still, as the prototype weights

varied by a few tons up to just under 50 tons, it fits with my preferred 1 gram of pull per

ton of prototype tractive weight theory - exceeding it slightly, even.

 

What makes this design so effective? Well, I would put it this way - if one accepts the

premise that a rigid six-coupled chassis has in fact only three wheels in contact with

the track most of the time, it follows that if the centre axle of a similar chassis is sprung

with enough 'rock', then it will have five wheels in contact most of the time, except when

it has six. Now, if the spring rate of the middle axle is carefully chosen, so that the

effective weight on each axle is nearly identical, then the most efficient pull for a given

tractive weight will be realised."

[34theletterbetweenB&D]

Rather think his stock is too draggy though. My ordinary but well run in OO Bachmann mk1s take just under 2g force to break out from rest on level track, bit over 1g force to keep rolling. A regular Bach pannier as supplied with its ordinary OO wheelsets delivers about 30g force on nickel silver rail, and thus will reliably start past a dozen of their mk1s on level track, with no wheel slip.

 

Good rule for rolling stock: ideally should roll away from rest when on a 1 in 100, at a minimum should keep rolling once started on this gradient. Like an idiot I sold several sets of the Trix Commonwealth pattern bogies, only retaining one pair by accident. The polymer used, in combination with pinpoint steel axles and a hard metal tyre, enables the vehicle to roll away on gradients of less than 1 in 250. Love to see this polymer available for bearings.

[Alan Higgi]

Rather think his stock is too draggy though. My ordinary but well run in OO Bachmann mk1s take just under 2g force to break out from rest on level track, bit over 1g force to keep rolling. A regular Bach pannier as supplied with its ordinary OO wheelsets delivers about 30g force on nickel silver rail, and thus will reliably start past a dozen of their mk1s on level track, with no wheel slip.

 

Good rule for rolling stock: ideally should roll away from rest when on a 1 in 100, at a minimum should keep rolling once started on this gradient. Like an idiot I sold several sets of the Trix Commonwealth pattern bogies, only retaining one pair by accident. The polymer used, in combination with pinpoint steel axles and a hard metal tyre, enables the vehicle to roll away on gradients of less than 1 in 250. Love to see this polymer available for bearings.

I just picked up a second pannier on Ebay. This one weighs 283g! It's older than the first one so I guess it's a similar position to Bachmann 2251 Class - 

[Bob O]

Hi Alan

Yes after a nice long hol I got back to the pig and tweaked it, Kinda halfway house in that its now 314g and 38 wagons but you might find that second pannier is a split chassis and not long for this world!

[Bob O]

It's all down to the finish on the wheels and the weight bearing on those driven wheels. Once you have four driven wheels in a rigid model chassis, adding more is no help for traction. Anyone who doubts this, get a look at a H-D 8F, functionally it is a 2-4-0 as the second and third driven axle are flangeless and undersize and thus clear of the rail. Made up to the same weight an all flanged 2-8-0 pulls no better in model form. (There is a proviso to this; the weight bearing on the coupled wheels needs to be centred at the midpoint of the driven wheelbase. This is typically easier to achieve on models as wheelbase gets longer.)

 

The prototype is different. There the significant limit on the weight that can be placed on any single axle necessitates adding more axles proportional to the all-up weight of the loco.  In general extra driven wheels reads as more adhesion, for any given maximum permitted axle loading.

Hi 34theletterbetweenB&D

 

What is your take on the Hornby Black 5?--------------------as it as a sprung rear driver it is 4-4-0plus

[34theletterbetweenB&D]

Never had a Hornby Black 5 of my own to play with! (The Hornby model has so far failed to inspire a purchase. When seen alongside the choice of other suitable 'useful medium power mixed traffic engines' we now have in RTR like the B1, K3, Ivatt 4MT, BR std5, it has consistently failed to make the cut.)

 

The problem with RTR 4-6-0s in model form, especially with a Belpaire type taper boiler, is getting enough weight in the right place. The manufacturer will have been seduced by the cuboid Belpaire space to make a wastefully bulky motor and gear train installation right where the weight should go. I would be thinking about fitting a pretty stiff spring to the rear axle, and making sure it has a little downward travel below the plane of the two fixed axles; filling the cab with lead up to the window line and in the roof above the windows, to balance whatever weight can be got in forward.

[Il Grifone]

An old dodge is to let the tender lean on the locomotive (the leading axles are lightly sprung or in a separate 'bogie'), or alternatively cantilever a weight from the rear of the locomotive and hide it inside the tender. I hesitate to suggest powering the tender in addition to the loco.

 

RE Hornby's Black Five, IMHO any attempt to spring any axle other than the centre one(s) is doomed to failure. Even if all are sprung, the outer axles need tougher springs.

 

I don't understand the comment on 'proper' parallel boilers. I thought everyone knew that all the best locomotives have taper boilers and Belpaire fireboxes! (see below)

[34theletterbetweenB&D]

Well, any competent engineering survey will reveal that the Belpaire firebox and excessive tapering were unnecessary affectations. Perfectly successful steam locos were built in the UK and all around the world without these features, and out-performed those with, by no small margin. That's on first cost, fuel and water consumption while delivering superior power performance, and repair cost.

 

For modelling purposes, 'roomy' is very handy too...

[Alan Higgi]

Never had a Hornby Black 5 of my own to play with! (The Hornby model has so far failed to inspire a purchase. When seen alongside the choice of other suitable 'useful medium power mixed traffic engines' we now have in RTR like the B1, K3, Ivatt 4MT, BR std5, it has consistently failed to make the cut.)

 

The problem with RTR 4-6-0s in model form, especially with a Belpaire type taper boiler, is getting enough weight in the right place. The manufacturer will have been seduced by the cuboid Belpaire space to make a wastefully bulky motor and gear train installation right where the weight should go. I would be thinking about fitting a pretty stiff spring to the rear axle, and making sure it has a little downward travel below the plane of the two fixed axles; filling the cab with lead up to the window line and in the roof above the windows, to balance whatever weight can be got in forward.

Hi

 

Based on earlier comments from your good self I weighted up Black 5 #1 to 290g. 3 tap washers in the smokebox (to space) then 4 foreign coins weighing 20g and the rest in the cab. “sun roof” closed to allow a pb lump below. Black 5 #2 is 330g – nothing in the smokebox but replace the DCC “thingy” with a 35g lump of lead. Over the centre axle you can fit a half tube of lead (16g) and a bit in the cab to balance. I used a Masterpiece crew plus a loco inspector as this gang weigh 9g so I left the “sun roof” open. Both locos have Brassmasters and Comet bits added and look super.

 

[Bob O]

Hi Alan,

 

How about adding weight to the Hornby 8f? Any tips?