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Post by Roger on Sept 30, 2021 8:19:54 GMT
It seems to me that if it oscillates with both stiff and soft springs, then damping would be beneficial. It's not surprising really, when you consider how large the mass is and how small the base is it's supported on.
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Post by ettingtonliam on Sept 30, 2021 10:35:29 GMT
There is sense in that Roger. My VW Tiguan (coil sprung) started to bounce at the back end, but new shock absorbers cured it. When I had a 1960 Series 2 Landrover with leaf springs, the rear shock absorbers were missing completely when I got it, but even when I fitted some, I couldn't detect any difference in the handling. VW has coil springs with no inherent damping, Landrover had leaf springs which seemed to damp themsolves!
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Post by Deleted on Sept 30, 2021 11:34:08 GMT
Just to add to ettingtonliam's comment and my own thoughts on this, leaf springs have a built-in damper to them, they are also more suitable to heavy loads, spreading the load much more effectively and giving a lower deflection rate than a coil, hence why HGV's still have them. Leafs can withstand a more powerful shock than coil springs and thus again, more suitable for heavier loads. If all else fails I would agree with Ed and if possible, fit working leaf springs.
Pete
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Post by Roger on Sept 30, 2021 12:36:04 GMT
It's worth pointing out that leaf springs introduce friction, rather than rate variable damping. That's why those friction dampers you see on very old cars and motorbikes were quickly displaced by hydraulic types which don't introduce significant friction but genuine damping that increases with the velocity of displacement.
Full sized locomotives have very stiff springs and small displacements, just as lorries do. You'll find that lorries do have dampers, leaf springs don't give the required characteristics. Steam locomotives are the exception to the rule for the use of leaf springs and no damping. I suspect this is because the tracks are so smooth and the speeds are generally slow. I imagine it gets pretty scary at times without damping when running at speed.
Our situation is different because the tracks are much less even. Adding friction into a spring/mass system certainly makes it more stable, but the ideal is a perfect spring and a perfect damper without any frictions. That's what you'll find on all modern cars and rolling stock so that you get the best possible ride characteristics.
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Post by Deleted on Sept 30, 2021 12:56:14 GMT
Dampers are added for smoother riding...in the general scheme of things, leaf springs are better for this application. Coil spring/damper allow more fine tuning and smoother ride but are inferior for load and weight distribution. There are many advances in coil setups which can offset this but they cost, sometimes simpler is better.
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Post by Roger on Sept 30, 2021 15:15:38 GMT
Dampers are added for smoother riding...in the general scheme of things, leaf springs are better for this application. Coil spring/damper allow more fine tuning and smoother ride but are inferior for load and weight distribution. There are many advances in coil setups which can offset this but they cost, sometimes simpler is better. I have to respectfully disagree. Leaf springs add friction which only provides a linear force after the initial stiction is overcome. With leaf springs, you can pull them one way and they stick there, then you can push them the other and they will stick in the other side of the free position. This isn't a characteristic which is desirable. Look up any Mechanical Engineering source about spring/mass systems, and you won't find them extolling the virtue of friction or leaf springs. This is a topic we discussed at length on the Mechanical Engineering Degree. The other issue with leaf springs is that you get whatever you get in terms of the amount of friction, there's very little control over it. Hydraulic dampers have negligible friction, so the suspension doesn't 'stick' either side of a static balance point, it can return there with zero force. This is what you actually want. The more friction you have with leaf springs, the worse this effect is. You also want the damper to respond to the rate of displacement, so a really rough piece of track will result in a greater opposing load than a smaller one. This doesn't happen with leaf springs. I'm not suggesting that leaf springs are hopeless, or that they can't provide useful damping of unwanted oscillations. What I would suggest is that coil springs with dampers will outperform leaf springs, or leaf springs with dampers in every eventuality. How big the difference is will depend on the application. Clearly hundreds of Model Locomotives have used both arrangements, and all can be made reasonably satisfactory, at least enough to be usable. However, that doesn't mean we shouldn't aim to do things better where pure scale models are concerned. Obviously you wouldn't put them on your Flyin Scotsman, it's not in the spirit of what you're trying to achieve. However, for some of us it makes good sense to pursue the ideal solution from a performance point of view.
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Post by Deleted on Sept 30, 2021 15:27:36 GMT
We think that my problem is having the springs directly over the axleboxes, basically on the wheel centres. This is fine on an 0-6-0 or locos with more driving axles as they are more inherently stable. The Milner design has the springs on the ends of the spring hangers which in effect gives nearly six inches extra outside the axle centres and therefore must help with stability. You can see this in the pictures below. Hi Ed forgive me but I should have answered your question directly, I have already laid out details as to why Leaf springs are better for this application and would agree with your statement above. Looking at your pictures is a good way of seeing what's wrong. Ok so both are using Helicoil springs, yours with the spring directly over the axlebox and the other with two springs, one on either side with a dummy leaf spring in between. There is a difference here and it's one of the good points about leaf spring setups compared to coil, yes I know that the leaf here is a dummy but the two springs on either side of it are giving you in part the larger load bearing area of a leaf if not the benefit of dampening from the leaf itself. You say the two locos have similar weight although personally I don't see this as a weight issue other than the more weight put on a coil the worse the effect than on a leaf, I don't see that as the problem here, the weights are too close. Of the options you give, I would go with proper working leaf springs if possible, if not, then the two spring setup to balance the spring load and rebound would be the next option, an option which you already know works. If you went for working springs you could use the dummy as a guide for dimensions and in some respects deflection too if you take the curve of the dummy into account. You'd need to experiment in spring thickness and whether to make them from spring steel, bronze, or a mixture with Tufnol. If you make the spring hangers adjustable as they should be then you have room for adjustment. These are my views, others may differ but this is what my head says is the answer, hope they help rather than hamper. Pete
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Post by ejparrott on Sept 30, 2021 19:30:31 GMT
You'll be much better off fitting proper leaf springs than pissing about with dampers. Have you weighed the axles yet?
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jma1009
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Post by jma1009 on Sept 30, 2021 21:44:48 GMT
I've been mulling over this and I totally agree with Ed P and Pete.
I would also add, Ed C that you ought to consider the connection with the 'tender' that you sit on and the drawbar connection between the loco and the tender. And you also ought to consider the balancing of the wheels on the loco - do they have balance weights and if so in the correct position? Those outside cranks are quite big, and inclined cylinders etc.
I would also like to suggest a certain risk assessment sort of stuff. You have no fall plate between loco and tender, and the position of your granddaughter in a pic of your other thread alarms me somewhat if there were to be a derailment or some sudden stop for whatever reason, or that she should extend her legs/feet between loco and tender.
I've been present and witnessed 2 locos on a raised track bounce off. IMLEC at Bristol, and the late John Edwards' Collett Goods at Highfield Road Cardiff. Not pleasant. If you have a 'bouncy' loco on the track I would suggest it involves rather more than a discussion of springing; instead whether the loco is fit to run and the risks involved.
Faffing about with different springs in a compromised arrangement that you already know doesn't work is really not the right approach. Ed Parrot ought to know, and I added something a few pages ago on page 1. Ed P has full size experience of working on the footplate of TR locos as does Malcolm on short and long wheel base locos of narrow gauge type 0-4-0s.
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Post by terrier060 on Sept 30, 2021 22:47:49 GMT
You'll be much better off fitting proper leaf springs than pissing about with dampers. Have you weighed the axles yet? I do not think there is any need for bad language here, in what has turned out to be a very interesting discussion. No I have not weighed the axles as I do not have the equipment to do so, unless you have a clever method you have used?
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Post by Deleted on Sept 30, 2021 23:01:48 GMT
Hi Ed
Regarding weighing axles, I did a writeup on how I made mine using a cheap set of digital bathroom scales which you might find useful. It's deliberately a simple design which works well, is very accurate and can be made by anyone quickly. When I get time and my club has built its new steaming bay, I'll make another set designed to fit the rails in the bay. You'll find the article on my blog, it will also be published in ME in due course but at this time I don't know when. The design is very quick to build if you already have a stand, just a few hours.
Kind regards
Pete
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jma1009
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Post by jma1009 on Sept 30, 2021 23:04:23 GMT
To Ed C re Ed P; Ed P is a highly respected member on here. His "p---ing about" isn't that far removed from my "faffing about". Semantics of use of language in a forum? I saw nothing inherently wrong in what Ed P posted, and totally agree with the points he has made, and those of Pete S-H.
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Post by suctionhose on Oct 1, 2021 0:11:21 GMT
No I have not weighed the axles as I do not have the equipment to do so, unless you have a clever method you have used? You can use bathroom scales, a hydraulic jack and length of timber vee'd to fit the axle. With the loco on your workshop stand / trolley, just take the weight - wheels just clear of the rail and read the dial.
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Post by terrier060 on Oct 1, 2021 8:11:42 GMT
Thanks Pete and Ross. I will have a look at your thread Pete and could you do a quick sketch Ross.
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mbrown
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Post by mbrown on Oct 1, 2021 9:20:29 GMT
You'll be much better off fitting proper leaf springs than pissing about with dampers. Have you weighed the axles yet? I do not think there is any need for bad language here, in what has turned out to be a very interesting discussion. No I have not weighed the axles as I do not have the equipment to do so, unless you have a clever method you have used? LBSC used to call it "Railroad Esperanto"! Malcolm
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Post by ettingtonliam on Oct 1, 2021 11:18:03 GMT
After a lifetime in the heavy construction industry, 'p---ing about' is pretty mild. Lets not get diverted from the main topic.
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Post by chris vine on Oct 1, 2021 11:18:27 GMT
Just to reiterate, as there seems to be some confusion: If the action of the spring is vertically onto the axle box, then it doesn't make any difference where the spring(s) is/are connected to the chassis.
For the riding of the engine, it is only the spring rate, as seen by the axle boxes, and damping which will make a difference.
Yes, leaf springs do have damping because of friction, but this gives a rougher action than a spring and a viscous damper. That is why modern cars and rolling stock all use these. I suspect that coil springs are much cheaper to make than leaf springs too!
The Great Western Railway had some locomotives with coil springs (some of which were actually inside the cab). They didn't have as much damping as leaf springs and the enginemen reputedly got sore knees from the bouncing. They called this coil-spring knees.
All best Chris.
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Post by Deleted on Oct 1, 2021 12:06:30 GMT
Just to reiterate, as there seems to be some confusion: If the action of the spring is vertically onto the axle box, then it doesn't make any difference where the spring(s) is/are connected to the chassis. For the riding of the engine, it is only the spring rate, as seen by the axle boxes, and damping which will make a difference. Yes, leaf springs do have damping because of friction, but this gives a rougher action than a spring and a viscous damper. That is why modern cars and rolling stock all use these. I suspect that coil springs are much cheaper to make than leaf springs too! The Great Western Railway had some locomotives with coil springs (some of which were actually inside the cab). They didn't have as much damping as leaf springs and the enginemen reputedly got sore knees from the bouncing. They called this coil-spring knees. All best Chris. Hi Chris Other railways also used coil springs, GNR's first A1 pacific 1470 Great Northern when launched had coil springs on the crank axle, these proved unsatisfactory and were soon dropped and all following A1/A3's, A4's P1's P2's W1.. etc, etc (i think you get my point) used leaf springs only for the main drivers, the front bogies were the only wheels to have coil springs throughout their career. Perhaps coil was seen as a better option here for its longer/quicker drop when a wheel drops in a dip and thus better odds against derailment? I agree in part with your comment on spring position but where I disagree is it's a different situation when one spring becomes two and spaced further apart, a spring directly above the axle box is a worst-case scenario, space them apart and you spread the load and I guess in some respect soften the ride as in part they are acting against each other. Modern coil spring setups are much different, they have a whole host of extras to take away the negative action of a coil in its rebound, too soft they can't support the weight even when unloaded, too strong, and an empty train bounces along the track. Today we have various air cushions or multiple springs, or even diagonal setups. Multiple springs can be in two stages. softer springs for an unloaded train and another set are usually set inboard which are much stiffer and only come into play when the train is loaded and thus sitting on the shorter stiffer springs as well as the outer softer springs. A bit Heath Robinson IMHO when compared to other methods but clearly work. I can't speak for other railways as I've never studied them but for LNER they don't just use leaf springs, each spring also has shock absorbers on either side, in fact so do the bogie coils which also have shock absorbers. These used to have two shock absorbers per spring hanger (four per wheel, 8 per axle) these were later changed to only two shock absorbers per wheel, four per axle, at least in as far as I have found on the pacifics. I do believe that Ed's issue is the springs sitting directly over the axle box, if bouncing they are clearly too stiff in their present setup, I take on board what others have said that this isn't such an issue when more wheels are concerned, this brings us back to spreading the load. The main point here is that we already have the proof, two locos near-identical, one with 8 springs and one with 4, the practical test has already been done. If it was my loco I would fit working leaf springs, they are far superior for this application, I don't know if this loco design ever had dampers (shock Absorbers), if it did I'd add those too. If sticking to the current design I'd try modifying the single spring to become two, one inside the other, one softer and longer for the first rate of spring 9softer than the current springs) and another shorter and stiffer to catch the hard drops. High-performance car valve springs have the same setup but for different reasons. I am fully aware of Roger's argument for coil springs, after all, I have a very good setup on my car which benefits the car greatly but not for our application, IMHO leafs are the way to go. regards Pete
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Post by Roger on Oct 1, 2021 12:47:11 GMT
Just to clarify one point that Chris correctly makes and that's about the way the force is applied to the axlebox. It doesn't matter how many springs you have, or how far apart they are it makes absolutely no difference. That's because the point load on the axlebox is all the axlebox sees. So you can have one spring in the middle, or 10 springs at 1/10th of the rating spaced either side at any distance you like and it's exactly the same. Even if you put different spring ratings at different distances, the axlebox will see whatever point load that works out to be.
Whatever happens, you can't improve the stability of the system by changing the arrangement of the springs, provided that the same point load ends up on the axlebox. The axlebox is unaware of whatever is going on above it.
Sharing the load between springs is merely a way to make a practical arrangement that you can physically fit to the locomotive, nothing else.
Personally I'd model the existing spring arrangement to see if there's room for a damper inside the coil springs, along the lines of those used on the rear suspension of motorbikes. Dampers are really simple to design and make, and they are readily adjusted simply by drilling larger holes in the pistons or using a different grade of Silicone Oil. There may not be room, but if there is, the whole arrangement could be put inside a tube so it's not even visible.
Let's not kid ourselves that it's dead easy to design a set of leaf springs, there's going to be a lot of experimentation needed to find the right combination by trial and error.
Let's not also assume that the better of the two locomotives has the ideal solution either. If not jumping the track is the only criteria, then it's clearly better. However, it's almost certainly rocking and rolling more than it would with damping.
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Post by Deleted on Oct 1, 2021 13:12:04 GMT
I disagree with your view Roger...it's not about how many springs you have. It is about contact point and it is about with two springs spread apart they can be softer and in some respect will can be acting against each other further softhenibg the rebound. Both springs don't always work in unison, we are not talking about a static situation where yes you are correct, we are talking about a moving object on an undulating surface. The difference may be small but a difference none the less. The two springs spread the load just as a leaf spring does and why they are used on HGV's to carry heavier loads. Modern railway stock with coil springs use rows of mutiple springs, this not only spreads the load but also means the springs can be softer and thus not bounce along the track leading to derailment as Ed is experiencing with his model.
Edit: I fogot to include that a single coil spring does one thing, it supports the load above it. It has no bearing on braking, accelerating which leaf springs do, two coil springs on the fore/aft axis also have some affect here, not the same as they have no dampening but in my mind it does make a difference.
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