Flexi Chassis an Appreciation

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Le Corbusier
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Re: Flexi Chassis an Appreciation

Postby Le Corbusier » Fri Dec 01, 2017 7:03 pm

Andy,

I asked because I think different people are often better at different things ... some swear by one solution whilst others swear by a different one ... yet both seem to work! The wider the range of options to try and play with the better as far as I'm concerned.

I still find the debate and discussions fascinating ..... learning all the time :thumb
Tim Lee

Proto87stores

Re: Flexi Chassis an Appreciation

Postby Proto87stores » Sat Dec 02, 2017 5:19 pm

Flymo748 wrote:Hi Andy,

To comment on this, in an observational way, and to neither defend or attack any suspension system or layout.

At Warley, I sat with Richard Oldfield at the Mostyn workbench whilst he went through the coach which had just derailed. We had a good conversation whilst checking over every aspect of the vehicle.

SNIP

At the end of all of that, the coach was put back onto a spare road in the fiddle yard and propelled by a push at quite some speed through a turnout. Where it was rock steady. The conclusion? We didn't have a clue what caused it to fall off.

It might have been something from one of the adjacent coaches which pushed it off, and kept itself on the rails. It might have been a coincidence of movement and rail joint. At the end of the day, we couldn't find it and the coach went back into service where as far as I know it performed faultlessly for the rest of the weekend.

So the moral of the tale is that sometimes, just occasionally, these things "just happen", on models as in real life...

Cheers
Flymo
[edited for typo]


Thanks very much for the follow up! Hopefully the cause will be discovered eventually. Problems you can re-create are the easiest to find and fix. Others, not so much.

Andy

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Noel
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Re: Flexi Chassis an Appreciation

Postby Noel » Sun Dec 03, 2017 2:01 pm

jjnewitt wrote:I think the joggle in the axleguads was as much to do with the fact that the springs (at 4") were wider than the steel solebars. Otherwise I can't really see any reason why they couldn't have had the same dimension between solebars for both steel and wooden underframe stock.


Iron or steel solebars are narrower than wooden ones, I suggest. It appears that a decision was made to maintain the overall width of the chassis frame measured over the outside of the solebars, which implied a slightly greater width between the inside verticals. Why this was done, I don't know. The joggle is then present to maintain the relationship between axle and axleguards. The inside "V" on either-side brakes is similarly joggled, to permit use of standard brakegear, I presume.
Noel

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grovenor-2685
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Re: Flexi Chassis an Appreciation

Postby grovenor-2685 » Sun Dec 03, 2017 2:28 pm

It appears that a decision was made to maintain the overall width of the chassis frame measured over the outside of the solebars,

I suggest that the primary issue is to keep the springs centered over the axleboxes (6'6" centres) and then the spring supports on the solebar centered over the springs. This would not usually result in keeping the dimension over the outside of the solebars the same, but then there is no reason to do that.
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Re: Flexi Chassis an Appreciation

Postby jjnewitt » Sun Dec 03, 2017 3:33 pm

Noel wrote:Iron or steel solebars are narrower than wooden ones, I suggest. It appears that a decision was made to maintain the overall width of the chassis frame measured over the outside of the solebars, which implied a slightly greater width between the inside verticals. Why this was done, I don't know. The joggle is then present to maintain the relationship between axle and axleguards. The inside "V" on either-side brakes is similarly joggled, to permit use of standard brakegear, I presume.


grovenor-2685 wrote:I suggest that the primary issue is to keep the springs centered over the axleboxes (6'6" centres) and then the spring supports on the solebar centered over the springs. This would not usually result in keeping the dimension over the outside of the solebars the same, but then there is no reason to do that.


I think I'm inclinded to agree with Keith and they would want to keep the spring centre and journal centres the same. The distance over the solebar faces was not the same, indeed it couldn't be as the width of steel solebars varied anyway, even for the same depth. Width of solebars could vary between (at least) 3 1/16" and 3 5/8" depending on the chassis in question. Wooden solebars seem to have generally been 12" x 5".

Justin

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Will L
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Re: Flexi Chassis an Appreciation

Postby Will L » Wed Dec 06, 2017 1:31 am

proto87stores wrote:
Will L wrote:
Proto87stores wrote:
Will L wrote:
The point about all that moving metal applies here too I think.

No. If I use the inside frames as the moving beams, it’s the same metal

It was also the rocking frames on each axle I had in mind Andy.

Experience has also shown that you concerns about getting the spring rate right are not bourn out in practice.
.

The end linking bars of small rocking loco frames would just be tiny, maybe just flat hook in etched beams. No need to duplicate the complex rocking W iron scheme. I only duplicated the "shadow" w irons on the wagon chassis to save the usual more thorough lengthy design time and effort of creating smaller alternative linking methods. Twin holes around the same bearing seemed to be a no-brainer for what I'd hoped was just a rapid evaluation. There's actually no need for them to be w iron shaped, or as big.

Given that the only significant components in a small 0-4-0 chassis are the frames around which everything else is built/attached, making them mobile may present a few issues, though I'm sure you would be up to the challenge. My real concern with the driven axle was not finding an appropriate motor/gear set, it was more to do with how one would combine the drive and the axle equalisation pivot on the same axle.
As to the claimed working success of current methods, I can only point to just the latest report of track holding problems on this forum. E.g. Multiple derailments on one of the newest, team-built, well run in, major P4 layouts, Mostyn, at it's latest exhibition outing. And we know Mostyn's trackwork isn't something that is continually being changed :? But more to the point, the Mostyn spokesperson, in responding, seemed to think of that as a normal good performance. E.g nothing needs fixing. Is that the same "not borne out in practice" criteria you are using?

You really shouldn't read too much into one "things fell off when I watched it" type comment. The railway (big or small) hasn't been invented yet which doesn't suffer the occasional derailment. Anybody who says theirs is otherwise is quietly excusing the ones that happened to then, probably, lets be charitable, because they try to understand and fix any derailment, making such events rare. Mostyn isn't really my cup of tea, and its organising group may not be that given to being charitable either, but there is a lot of it and it generally runs very well. But it is almost all modern bogie locos and stock, presumably mostly RTR conversions(?), 4 wheel wagons are rare. CSB fitted locos and sprung 4 wheelers won't be a significant part of there manifest, so in terms of this conversation, there is little practice there to be born out or otherwise.
Even after 15 years or so, this is forum is notable for the number of topics still relating to trying out yet more ways to build sprung or compensated chassis successfully. That doesn't make sense if there is no problem

You know better than that. Much P4 stock is hand crafted and the success or failure of a particular approach (i.e. whether there is a problem) is as much or more down to the abilities and knowledge of the builder than to the characteristics of the method.

In practice I think that the Bill Bedford style sprung 4 wheel chassis has now reach the level were most people, who actualy want to go beyond a rigid chassis, would accept that it is the best thing since pinpoint axles and the right way to go. There are plenty of other suppliers producing examples, and lots of practical experience on many layouts to show it works.

A multi axle steam loco chassis is a much more complex problem and much more subject to variable need as well as variable ability. With many 4mm scale modellers not accepting there is any need for suspension and many more content to go with wheel substitution in RTR chassis, it is only those of us who want faultless electrical pick up and/or chose to go with a scale flange, who start to belive that the need for suspension is real. So it is a minority pastime for people who like building things for themselves and I suspect in that company you are always going to get a range of opinions and methods. I would like to think that there is evidence that use of CSB is becoming increasingly common among people who have actually tried to build one, not necessarily because the results are so much better than a fully compensated (no rigid axle) loco, but because its easier to do.


I have considerable respect for your ideas and methods (I arranged things so you could contribute to this thread remember) and it is certainly true you do as much as anybody to make effective methods accessible to the less skilled builder. None the less your practical experience of Steam Loco Chassis construction would seem limited. I look forward to seeing your fully equalised N7 and then we'll be able to judge whether the method has advantages or not.

Proto87Stores

Re: Flexi Chassis an Appreciation

Postby Proto87Stores » Thu Dec 07, 2017 6:27 pm

Hi Will,

Thanks for the thoughtful response.

I think you'll find that on an 0-4-0 you don't need to position the transverse beams over the end wheel bearings. They still have to pivot in the same horizonta plane as the side beam pivots, and be symmetrical about them, but otherwise can be inwards or outwards of the axles.

Almost at the buffer beams will give good clearance for the transmission, but outwards will magnify any fore/aft tipping caused by the track. Inwards will of course reduce the tipping effect of the track, but give you much less room for the motor, etc.

I have long noticed that hand-crafted is a big part of the Society direction, philosophy and pool of excellence, but that doesn't mean the various digests couldn't give more and more substantiated guidance on methods that are close to infallible in many more circumstances, and have much more commonality of parts across different modelling problems. If un-adjusted single spring and pin points is good for 4 wheel wagons, why do you need spread-sheets for CSB's and plain journals instead for locomotives? They are both just track guided vehicles.

While I am comfortable with the basic functionality of "Bill's" sprung 4 wheel wagon approach, my early 1960's teen experience makes me think that pin point bearings and and per wheel springing arrived pretty much simultaneously when I managed to afford a couple of Peco's then brand new "wonderful wagons". I don't see any particular difference in the current technology from that. Just music wire instead of nylon for springs.

The performance of the Peco WW's was however relevant to my current thinking in that they seemed so light, that they would bounce from, and sail away down the track at high speed, if merely bumped during shunting. If you tried to weight them significantly for more normal inertia, the pin point bearings would become much higher friction. That's also a common trait for current plastic RTR models.

I don't have much experience of conversions using custom fitted metal bearing cups and steel axle points, but the relatively high extra cost of adding the low-volume manufactured bearings should be compared with the recent low prices and advantages of imported miniature ball bearings. They easily allow a five-fold increase in weighting and inertia, while barely affecting the rolling friction. And the common fault of bearing misalignment due to a lack of hand-crafting skill, is now a thing of the past.

Once you have vehicles with fine flanges and working suspension that are noticeably heavy when trying to hand lift them off the track, you find that it's just as difficult to get them to derail due to some sudden height change in the track that they are passing over, or bad handling. The wheels are almost "glued" to rails by the much greater weight, and derailments now only occur to due to actually faulty track.

Even for traditional Flexichas loco designs, the crude high friction ideas of resting beams on the centres or ends of running axles, is transformed by using ball bearings in those situations.

So my vote for the best thing since pin point axles is ball bearings and high inertia. And it's really only Equalization/Flexichas that easily and simply give working suspension that optimizes the necessary weight independent use of both.

Andy

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Will L
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Re: Flexi Chassis an Appreciation

Postby Will L » Fri Dec 08, 2017 12:30 am

Proto87Stores wrote:I think you'll find that on an 0-4-0 you don't need to position the transverse beams over the end wheel bearings. They still have to pivot in the same horizontal plane as the side beam pivots, and be symmetrical about them, but otherwise can be inwards or outwards of the axles.

Almost at the buffer beams will give good clearance for the transmission, but outwards will magnify any fore/aft tipping caused by the track. Inwards will of course reduce the tipping effect of the track, but give you much less room for the motor, etc.

Agreed. I await with interest how you combine drive system and the pivot.
--- If un-adjusted single spring and pin points is good for 4 wheel wagons, why do you need spread-sheets for CSB's and plain journals instead for locomotives? They are both just track guided vehicles.
Because
1. Outside frame 4 wheel wagons suit pin point bearings where as inside frame Loco's don't.
2. As you rightly went on to say, getting sufficient weight on each wagon axle is important to achieve reliable running. Most people are using 50gm/2ounces per 4 wheel wagon, which means the size of wire needed is known and comes with the kit.
3. The CSB spread sheets came about because of the need to work out where the fixed fulcrum points must go.
4. For a 4 wheeled inside bearing loco this is actually trivial as they just need to be symmetrical. The only real use for the spread sheets is to get the wire size right first time.
5. For locos with 3 or more driven axles, fulcrum placement isn't intuitive, hence the need for the spread sheet. Also there are many possible right answers which take different wire sizes to achieve the same effect.

While I am comfortable with the basic functionality of "Bill's" sprung 4 wheel wagon approach, my early 1960's teen experience makes me think that pin point bearings and and per wheel springing arrived pretty much simultaneously when I managed to afford a couple of Peco's then brand new "wonderful wagons". I don't see any particular difference in the current technology from that. Just music wire instead of nylon for springs.
That's right Peco got their first, but the plastic spring didn't age well, and, as you pointed out, they didn't use metal on metal pinpoint bearings, and they didn't weigh enough.
...I don't have much experience of conversions using custom fitted metal bearing cups and steel axle points, but the relatively high extra cost of adding the low-volume manufactured bearings should be compared with the recent low prices and advantages of imported miniature ball bearings. They easily allow a five-fold increase in weighting and inertia, while barely affecting the rolling friction. And the common fault of bearing misalignment due to a lack of hand-crafting skill, is now a thing of the past.
As a P4 modeller, who is inevitably going to replace the wheel sets, the additional cost of the metal pin point bearing is trivial, and the performance of metal on metal pinpoints is pretty dam good. Even ignoring the issue Keith picked up about the space available for ball bearings on an outside frame wagon, I'm not sure that the degree of improvement they will produce over pinpoints will be enough to make the change attractive.
... Even for traditional Flexichas loco designs, the crude high friction ideas of resting beams on the centres or ends of running axles, is transformed by using ball bearings in those situations.
I must admit I have wondered about using ball bearings were we currently have plain inside bearings. Fitting ball bearing axle blocks in our current horn block assemblies might be worth thinking about, but the 1/8" axles we use would make these significantly bigger than the current generation of plain bearings. This isn't desirable as these components can already take up rather more space in our chassis than I would like. Reducing the axle size would help, but we would need the co-operation of the wheel suppliers for that one, which might prove hard to come by.

There is also the question of whether you get significant value from reducing frictional losses on the bearings of the loco driving axles. These axles don't run free being constrained by the motor, so the startling improvements produce by low fiction bearings on othere rolling stock just aren't apparent or available. Nore is it likely that their would be an improvement in loco pulling performance. Any decently built loco chassis should be capable of spinning its wheels once the load exceeds its adhesive capability. The motors we use today do this easily, so reducing the internal fictional losses in the chassis will not produce any change in performance.

proto87stores

Re: Flexi Chassis an Appreciation

Postby proto87stores » Fri Dec 08, 2017 10:09 pm

Will,

Before we get into possible misunderstanding by comparing apples and oranges, I need to let you know my estimated finished weighting for the Airfix model wagon is 160-190 gm, modeled as loaded. Not the 50 gm you mention as being the typical design weight of Bill's chassis. I.e., I am talking about a near 4:1 ratio difference.

The unmade kit weighs around 20 gm and a couple of wagon length sections cut off a 1" x 1/4" steel bar weigh 70 gm each. There appears to be room for adding an additional 1" x 1/8" steel bar section as well.

For comparison with the earlier posted running videos, my out of the box Bachmann MK1's weigh 164 gm. My only, so far, just under floor weighted, Amfleet cars weigh over 300 gm. Eventually I would like to have all my bogie cars weighing a similar x4 ratio of around 600 gm.

I found the Bachmann MK1's (with their factory Pin points) to be extremely free running as is. But the Amfleet Cars weighing nearly double also ran at least as freely, without even cleaning and properly lubricating the bearings from their grease packed, delivery state.

Moving on to actually running and inertia, my greatest concern with lowering friction, is to, as much as possible, eliminate the visible sudden speed changes when a model vehicle, or whole train, starts from rest, and/or brakes to a halt. Subsequently, I also wish (somehow) to see the prototypical very extended slow rolling to a halt of un-powered vehicles.

Just about any model and most toys can easily demonstrate a smooth run by at medium speed. That’s because most model motors and fast moving un-powered cars, can easily overcome reasonable running friction. The problem comes when a small motor has to overcome “stiction”, or the model static friction from rest which is typically several times greater than the moving friction once a running speed is established.

Applying sufficient starting power for initial movement all too easily results in a jerk as the static friction drops. While bemf control nowadays does hide some of the effect, it also causes the opposite issue when a vehicle encounters a natural obstacle that should stop it. For example, a loco slowly approaching a stationary and supposedly heavy train, in order to couple up to it, instead thrusts it into up to matching speed.. Similarly, Stiction often suddenly “kicks in” just as a train is otherwise realistically still slowing to a gradual halt. And instead jerks it to a realistically impossible sudden stop.

All the above “jerking” issues can be significantly improved if the model vehicles involved weigh far more than current practice. Having much greater additional inertia slows down all jerking situations considerably and extends the free rolling momentum. But at the same time friction should be held low, or even reduced, rather than increased.

Andy

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Re: Flexi Chassis an Appreciation

Postby Philip Hall » Fri Dec 08, 2017 10:37 pm

I always thought that Rodney Cooper (Rocar) and Trevor Pott (Churston) along with yours truly built heavy carriages until I read this. I aim for about 180 - 190g for a carriage and I know that Rodney and Trevor often end up with a bit more than this. With this kind of weight the buffers and gangways work properly, and the vehicles roll along nicely and hold the road well. Friends of mine think my vehicles are a bit heavy.

Having built carriages (not many) and converted Hornby ones to P4 and EM (lots) I have to say that I have no idea where this kind of weight could be fitted into a British 4mm carriage unless we started using rare metals. There is little room underneath a Hornby or Bachmann carriage if you are to include a decent amount of underfloor bits and pieces. And it looks odd if some of the obvious bits are missing. I added lead under the seats and in the luggage compartments of the new Hornby Maunsell rebuilds to bring them up to 180g. I would have had to fill up the seating moulding to waist height to get anywhere near 600g, and in that situation would be far too top heavy. A carriage that weighs that much is to my mind impractical, to say nothing of the colossal weight a twelve car rake would come to - over 7 kilos! However free running they may be, what would we have to do to an engine to make it able to pull such a train up anything approaching a reasonable gradient? Maybe an all wheel drive big heavy diesel would manage it, but a lot of us are running steam; some, like me, will have a flat layout, but not all of us do...

Philip
Last edited by Philip Hall on Fri Dec 08, 2017 11:17 pm, edited 1 time in total.

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Re: Flexi Chassis an Appreciation

Postby grovenor-2685 » Fri Dec 08, 2017 11:05 pm

Almost at the buffer beams will give good clearance for the transmission, but outwards will magnify any fore/aft tipping caused by the track. Inwards will of course reduce the tipping effect of the track, but give you much less room for the motor, etc.

I don't understand this bit, if the transverse beams have centre pivots that they are always in contact with, then any tipping from track irregularities has to be identical no matter whether the transverse beams are located inboard or outboard of the axles. I can see the simplicity of this approach for an 0-4-0.
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Re: Flexi Chassis an Appreciation

Postby billbedford » Sat Dec 09, 2017 11:22 am

proto87stores wrote:Will,

Before we get into possible misunderstanding by comparing apples and oranges, I need to let you know my estimated finished weighting for the Airfix model wagon is 160-190 gm, modeled as loaded. Not the 50 gm you mention as being the typical design weight of Bill's chassis. I.e., I am talking about a near 4:1 ratio difference.


So you are advocating that people build 'one way railways'? since it's impossible to get 160 gms in a empty open wagon returning coal trains could not be modelled.

I still think that 50gm is too heavy for a wagon, especially if modelling late 19th century prototypes. Here the advantage of using spring wires is that the wires, and hence the spring rates can be chosen to match the weight of the wagon.
Bill Bedford
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Re: Flexi Chassis an Appreciation

Postby Le Corbusier » Sat Dec 09, 2017 11:38 am

billbedford wrote:
proto87stores wrote:Will,

Before we get into possible misunderstanding by comparing apples and oranges, I need to let you know my estimated finished weighting for the Airfix model wagon is 160-190 gm, modeled as loaded. Not the 50 gm you mention as being the typical design weight of Bill's chassis. I.e., I am talking about a near 4:1 ratio difference.


So you are advocating that people build 'one way railways'? since it's impossible to get 160 gms in a empty open wagon returning coal trains could not be modelled.

I still think that 50gm is too heavy for a wagon, especially if modelling late 19th century prototypes. Here the advantage of using spring wires is that the wires, and hence the spring rates can be chosen to match the weight of the wagon.

I would be interested in your preferred weight Bill and why? Would white metal kits pose a problem to this?
Tim Lee

proto87stores

Re: Flexi Chassis an Appreciation

Postby proto87stores » Sat Dec 09, 2017 3:11 pm

grovenor-2685 wrote:
Almost at the buffer beams will give good clearance for the transmission, but outwards will magnify any fore/aft tipping caused by the track. Inwards will of course reduce the tipping effect of the track, but give you much less room for the motor, etc.

I don't understand this bit, if the transverse beams have centre pivots that they are always in contact with, then any tipping from track irregularities has to be identical no matter whether the transverse beams are located inboard or outboard of the axles. I can see the simplicity of this approach for an 0-4-0.
Regards


Ooops, Yes Keith, I misstated the pivot position effect, because I was mistakenly thinking of the absolute height of the pivots, not the tipping angle they caused to the body.

My apologies. You are correct.

Andy

proto87stores

Re: Flexi Chassis an Appreciation

Postby proto87stores » Sat Dec 09, 2017 3:30 pm

billbedford wrote:
proto87stores wrote:Will,

Before we get into possible misunderstanding by comparing apples and oranges, I need to let you know my estimated finished weighting for the Airfix model wagon is 160-190 gm, modeled as loaded. Not the 50 gm you mention as being the typical design weight of Bill's chassis. I.e., I am talking about a near 4:1 ratio difference.


So you are advocating that people build 'one way railways'? since it's impossible to get 160 gms in a empty open wagon returning coal trains could not be modelled.

I still think that 50gm is too heavy for a wagon, especially if modelling late 19th century prototypes. Here the advantage of using spring wires is that the wires, and hence the spring rates can be chosen to match the weight of the wagon.


No, I'm saying that people like me who favour "operating" (running and shunting) with more realistically heavy vehicles are free to do so, without having to assemble each with different wire spring diameters for each different weight vehicle, in order to keep the track holding good enough. In the 4 point Flexichas case, the track holding of all the vehicles is always optimal, (not merely good enough) for their respective weights, no matter what weight that is.

In fact, if you want to modernize the empty in, loaded out example, you can actually use the same wagons, and move a "merely resting" steel based "load" from a full to an empty wagon, using a simple hidden electro-magnetic lift. And of course vice versa. But the track holding of the wagon in both before and after situation will still be optimized.

And BTW, you just halved the number of wagons needed for such a simulation.

Andy

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Re: Flexi Chassis an Appreciation

Postby billbedford » Sun Dec 10, 2017 10:20 am

Le Corbusier wrote:I would be interested in your preferred weight Bill and why? Would white metal kits pose a problem to this?


I don't have a preferred weight per se, but tend to think in terms of a ratio of 4 grams per prototype ton. The tare of a wooden wagon was in the 5-7 ton range giving a model weight of 20 - 30 grams empty. Frankly with the resin wagons, it is impossible to make them much heavier than this using hidden lead. Of course there would another 30-50 grams for the load, but apart from mineral wagons it would have been relatively uncommon for a wagon to be loaded to it's weight capacity.
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Re: Flexi Chassis an Appreciation

Postby Le Corbusier » Sun Dec 10, 2017 11:21 am

billbedford wrote:
Le Corbusier wrote:I would be interested in your preferred weight Bill and why? Would white metal kits pose a problem to this?


I don't have a preferred weight per se, but tend to think in terms of a ratio of 4 grams per prototype ton. The tare of a wooden wagon was in the 5-7 ton range giving a model weight of 20 - 30 grams empty. Frankly with the resin wagons, it is impossible to make them much heavier than this using hidden lead. Of course there would another 30-50 grams for the load, but apart from mineral wagons it would have been relatively uncommon for a wagon to be loaded to it's weight capacity.


Thanks. Bill - Appreciated.

Do you think there has to be a uniformity as far as weights are concerned for operational reasons ... your post suggests you vary them, or do you settle on the nearest average and apply through out within a typical goods train for example?

Edit ...Following which question I will apologise and let this thread get back on to topic :?
Last edited by Le Corbusier on Sun Dec 10, 2017 3:38 pm, edited 1 time in total.
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proto87stores

Re: Flexi Chassis an Appreciation

Postby proto87stores » Sun Dec 10, 2017 2:39 pm

billbedford wrote:
Le Corbusier wrote:I would be interested in your preferred weight Bill and why? Would white metal kits pose a problem to this?


I don't have a preferred weight per se, but tend to think in terms of a ratio of 4 grams per prototype ton. The tare of a wooden wagon was in the 5-7 ton range giving a model weight of 20 - 30 grams empty. Frankly with the resin wagons, it is impossible to make them much heavier than this using hidden lead. Of course there would another 30-50 grams for the load, but apart from mineral wagons it would have been relatively uncommon for a wagon to be loaded to it's weight capacity.


Image

Yes, if weight scaled, so many more realistic running situations could be modelled.

Andy

Proto87stores

Re: Flexi Chassis an Appreciation

Postby Proto87stores » Tue Dec 12, 2017 3:00 pm

I'm not sure upon reflection, if the previous "flying train" picture properly illustrated that prototype weight does not scale down to a model vehicle in any meaningful way. I.e. There is no useful or logical power/weight/time relationship between the real thing and its model for moving vehicles.

Any train set locomotive will typically pull along a long rake of wagons or coaches from rest to 80 mph in a second or so. But if faced with a 3% grade and the same train, will often stall or preferably spin its wheels. OTOH, a prototype locomotive might take many minutes to accelerate a 12 coach passenger train on the level to 80 mph, but it will also be able to haul it up a 1.5'% grade at a still reasonable speed.

So the weight of a model vehicle is best determined by its convenience, reliability and intended use in its model setting. And there is a definite opposite need between the weight of the puller and the weight of the pulled.

There has been plenty of advice published from various individuals and institutions based on their own model experiences and ideas. Certainly, my un-traditional, much heavier per model vehicle weight, will cause other issues if I plan to have them hauled up model 3% grades with traditionally designed and constructed locomotives. But I'm not treating that as my particular priority.

Scale speed shunting of wagons is best done on the level in both real and model situations, with zero expectation of derailments. And making that and other movements a far more realistic model exercise, is my goal.

Andy

proto87stores

Re: Flexi Chassis an Appreciation

Postby proto87stores » Wed Dec 13, 2017 2:40 pm

Errr, that should be "shunting", not "hunting", of wagons. :(

I'm happy for that typo to be edited by the moderator instead of posting this.

Andy
Last edited by John McAleely on Wed Dec 13, 2017 2:51 pm, edited 1 time in total.
Reason: Thanks - it was easy to do both!

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Re: Flexi Chassis an Appreciation

Postby Tony Wilkins » Wed Dec 13, 2017 10:31 pm

Hi Andy.
Since the mass relates to the volume and is the cube root of the prototype, whilst friction relates to area, which is the square root, there is never going to be a universal solution that suits everyone’s model situation. So we individually have to find the most appropriate solution for ourselves. Yes, there are guidelines to follow, but these should only be used as a starting point. I have tried to use down grades to replicate free rolling stock, but the results can be inconsistent even with selected rolling stock and strict quality control, i.e. weeding out the wagons that don't meet the required criteria. What works at home also doesn't necessarily work quite so well at exhibition either, in a different environment.
You have the advantage of more generous volumes with American rolling stock for weight compared to our British short wheelbase wagons. I am trying to do the above with 16ton mineral wagons that have just been emptied by a working wagon tippler. Anybody got any depleted uranium to spare?

Regards
Tony.
Like the picture by the way, but I would not like to have been the one taking the picture!

proto87stores

Re: Flexi Chassis an Appreciation

Postby proto87stores » Thu Dec 14, 2017 4:08 pm

I don't feel qualified to make any estimates about comparisons between prototype and scaled down model friction. I think that there are too many external complicating issues to offer a simple algorithm. I instead have opted for using modern miniature ball bearings that have very low stiction and running friction resistance at a manageable cost, without having to worry about and factor in what the model weight is.

Further, miniature ball bearings often have other modelling advantages in that they can double as dependable free moving suspension and axle pivots that do not stiffen up under load, and do not require precision mountings and assembly techniques that would otherwise affect plain and pin point bearing running qualities.

Andy

Proto87Stores

Re: Flexi Chassis an Appreciation

Postby Proto87Stores » Sun Dec 17, 2017 10:07 pm

While the subject of vehicle weight is currently being discussed, I would like to try and re-stress the importance of understanding the effect of spring rate in relations to vehicle weight.

So to recap the basics:

In order to safely ride over even small bumps and twists in track, each wheel must be able to independently and freely move up and down relative to the chassis/body of the vehicle.

This movement can be achieved by a) equalization/flexichas moving beam/levers, as already well covered, or by b) relatively free springing.

However, what doesn't seem to be mentioned much on the forum is that merely fitting springs to wheel bearings does not itself provide a springing motion unless the spring rate is low compared to the weight of the vehicle supported by that wheel.. For those using horizontal wires, what seems to be the only consideration, even for CSB's, is balancing the wire thickness to achieve the required 50% static displacement position. But the thickness of the wire and its length between fixed supports affects its spring rate. You can therefore accidentally, or deliberately end up with different spring rates while still achieving the 50% balance position.

For an analogy, consider two balloons hanging down on strings. One filled with air and one filled with water. Think of them as light and heavy vehicle bodies respectively, and their rubber surfaces as partial springs. And their hanging straight down is the same as their being at their static balance position

If you horizontally poke the air balloon with your finger (like using a hard spring), the (light weight) air balloon surface will barely depress before the balloon shoots immediately away from the touch. Poke the (heavy weight) water balloon similarly and the water balloon surface will depress and the balloon will move much more slowly and probably stop still staying close to your finger. I.e. for the water balloon you have created a useful springing system, because the force to depress the same springy skin is much less than the force needed to move the balloon. I.e. you have soft springs on a heavy body.

However, if you now instead poke the light air balloon with a soft feather instead of your hard finger, the feather will bend and the light balloon barely move, much like the heavy balloon poked with a hard (strong spring) finger. I.e to achieve the same degree of springing with a light body, you need much softer springs.

But in 4mm scale practice, unfortunately, like feathers, very soft springs are difficult to statically balance and also make to consistent spring rates. In the case of a softer straight wire, you may find that the wire needs to be much longer than will fit in the body. Which is why coil springs can often be more convenient. Because the much longer wire length is contained in the compact spiral shape.

From the above, it is easy to see that regardless of the static balance setting being correct, the spring rate still drastically affects whether the vehicle actually has useful springing or not. And in practice, if you do have a sprung interface to the body, it's much easier to construct suitable springing if the body is heavy rather than light.

And of course if the springing is 4 point between the body and the chassis, rather than between the various (many) wheels and the chassis, you typically have much more flexibility in using different spring sizes/types and do not have to worry about achieving a 50% static balance in so many places, or even at all.

Andy

Alan Turner
Posts: 503
Joined: Sun Jul 20, 2008 4:24 pm

Re: Flexi Chassis an Appreciation

Postby Alan Turner » Mon Dec 18, 2017 3:14 pm

Tony Wilkins wrote: Anybody got any depleted uranium to spare?



Tungsten is denser than Uranium - and easier to get hold of as well.

regards

Alan

billbedford
Posts: 605
Joined: Tue Oct 02, 2012 2:40 pm

Re: Flexi Chassis an Appreciation

Postby billbedford » Mon Dec 18, 2017 5:21 pm

Will L wrote:3. The CSB spread sheets came about because of the need to work out where the fixed fulcrum points must go.


We need a spreadsheet because the deflections on a beam with more that two supports is mathematically indeterminate. ie there aren't enough equations to be able to solve the problem.
Bill Bedford
Mousa Models
http://www.mousa.biz


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