7.25 inch gauge Milner Hunslet

[Roger]

Sept 26, 2021 20:57:50 GMT ejparrott said:

Sept 26, 2021 13:20:29 GMT Roger said:

If that were true, then all vehicles would have leaf springs. In fact they all have coil springs and dampers. Leaf springs are only better on a vehicle if there is no other form of damping. Locomotives are the only vehicles I can think of that don't have any additional damping. Presumably that's because the springing is very stiff and there's only a small amount of travel.
Friction is a poor damper compared to hydraulic forms, it adds stiction into the system which is undesirable. All modern rolling stock has springs and dampers.

We're not talking about vehicles, this is a mostly-railway forum.

True, but as I pointed out, all modern rolling stock including the diesels have coil springs and dampers. I don't doubt that leaf springs give some degree of damping on model locomotives and that probably helps a little. How much difference that makes is debatable without a controlled side by side comparison.

[suctionhose]

Sept 26, 2021 9:03:39 GMT terrier060 said:

Sorry Ross - see paragraph three at the beginning of the thread.  I have already tried that and it made things worse.

Apologies. I missed that sentence in a quick read of the long post. Can't understand how a less flexible spring can make matters worse but I'm not there to see it. Good luck with finding a solution. It's a lovely engine. There must be a simple explanation.

[terrier060]

Sept 26, 2021 10:14:47 GMT smallbrother said:

I was puzzling over this on a long dog walk just now and unless you increase the wheelbase I can't see how you improve stability.

Like Roger, I think the position of the springs won't affect it.

Perhaps some extra weight either fore/aft may balance things up better?

Pete.

Wonderful Pete what walking the dog can achieve.  You are probably right.  I had a chat with Roger on the phone and I still can't get my head around it.  It is rather like trying to understand infinity - to me at any rate!  I think if I can bite the bullet and remove the boiler, reverting to the Milner design is preferable.  This is not only much easier to adjust, and gives more room to experiment with longer springs, but it will also allow me to dampen the oscillations by the method shown in my last sketch.  By placing the springs in a tube with good fitting spring hangers and a piston at the bottom it will allow the air inside to dampen the motion, or add oil if air does not have enough resistance.

[terrier060]

I am really glad that this thread has stimulated so much interest, and it is fairly clear that it has made you all put your thinking caps on. My brother has just come up from Devon to stay and we were watching the F1 race. He is into formula one and he said that on an uneven track the engineers put on longer, softer springs with greater travel and vice versa on smooth tracks. Neil and his father also suggested softer springs giving greater travel. I may have gone the wrong way getting stronger springs with less travel.  The axleboxes have about 1/2 inch travel and the present very stiff springs (which are about twice as strong as the original ones), only give about 3/8 inch travel. The bouncing is definitely more violent. So maybe I should try longer, softer springs as advised.

The original springs were 1.25 inches free length with 8 coils giving about 3/8 inch travel and rated at about 220 lbs/in. The new springs are about 280lbs/in.  I could probably squeeze 1.75 inch free length springs in with 10 coils giving 0.6 inch travel rated at 240lbs/in. It may be worth a try before reverting to the Milner design and having to take half the loco to pieces.

This loco was meant to be a play thing while I was building the Terriers!! It has taken much longer than I expected to get it running properly!

And thank you Ross - yes it is a lovely engine and beautifully built by Royston, who spared no expense to use the best materials. It is just that finishing it off has proved rather more time consuming than I wished. And I really DO want to return to the Terriers, or they will never get finished.

[suctionhose]

I don't see much similarity between car suspension and a locomotive.

A track is basically a flat surface with minor twists in the horizontal plane eg entering super elevation (and other alignment anomallies) where you don't want a wheel to lift off the rail.

What would you want 3/8" travel for? I reckon 1/8" would be plenty. You're not trying to float along like a limousine, just absorb small shocks and keep 4 wheels touching the rails.

How far away from flat can a track be over the wheelbase of the engine?

I don't know if there are other alterations from the Milner design that could affect centre of gravity. Typically, copper boilers are much lighter than steel ones so, if anything, the C of G should be lower. Perhaps the lighter boiler has displaced the C of G away from centrally between the axles? Maybe the proportion of weight outside of the wheelbase is cause for a moment of inertia issue?

Suggest determining where the C of G is relative to the wheel base. If centred perhaps more mass is needed to cancel the lever effect of the cylinder weight?

I still think the springs should be MUCH heavier and travel limited to what is needed to negotiate track. I reckon 1/16 travel is enough for the driving axle and perhaps 1/8 to 3/16 for the leading axle. It should be really solid in my view.

[terrier060]

When I am down the track next I will have a look at the travel on Nick's Hunslet. From memory the axlebox travels the whole 1/2 inch and you can certainly see it moving quite a bit on the rougher parts of our track, but it does not seem to have the loose bouncing that mine has. In fact if memory recalls the springing seems as soft if not softer than mine. So maybe his does have some form of damping? I will have to investigate further. I did notice that his springs are encased in tubes, but I thought the bottom ends were open. I will take a closer look next time.

[smallbrother]

I visited the Bridgend track some years ago and thought it was very good regarding smooth riding. Has something gone wrong meantime?

Pete.

[nonort]

Just to put a real spanner in the works does the bouncing stop if you run with the drain cocks open. Just a thought that you may be experiencing over compression in the cylinder particularly at short cut offs. Try with the cocks open at long cut offs and short, it has also happened on my engine that it seems to pick up a harmonic from the axle pump at certain track speeds. The pump harmonic seems to happen more when running light. I also drive an old car with leaf springs on all wheels, the manual says not to lubricate the leaves the car has no dampers whatsoever and it has always driven perfectly with no bounce.

[chris vine]

The problem with stiff springs is that they may not follow the track well enough to avoid derailments.

The trouble is not as a wheel is forced upwards, but if there is a dip in one rail. With a stiff spring, the downward force becomes much less as the wheel travels downwards, to the point that it may not be pressed down onto the track at all. Then it will lift off and there is a risk of a derailment.

with much softer/lower rate springs, the force changes much less with movement/deflection. Now, as the wheel moves up and down, the force will change less. In other words, if there is a dip in the rail under one wheel, it will still be pressed firmly downwards to keep it in touch with the rail.

If you extend this to the extreme and don't fit springs at all - IE a very stiff spring as it is only the chassis which can flex - then the vehicle will come off the track the moment there is a dip in a rail which is deeper than the flange.

Hope this helps
Chris.

[suctionhose]

Hi Chris,
I agree with what you say. However, there's a difference between 4 wheels and 6 or 8. I found with my 2-8-0, softer springs gave best adhesion. As built, it was a bit firm, but I really wanted to use those particular springs, until one day I got upset with it slipping on big a load and took it home in disgust. Changed the springs that night and went back next day and set a new load record on the hill... What a difference!

My 0-6-2 has firm coils on the four corners and softer rate springs on the centre axle. The idea is to provide support like 4 legs of a table and let the middle axle rise and fall with the humps and hollows. this works very well except for some rocking under heavy pulling which will always occur with coil springs. This is an engine that I changed the steel boiler to copper after 20 years and needed to add 30kgs ballast to compensate the weight loss.

For an 0-4-0, CofG should be central about the wheel base and it should sit on four points if the track is flat. where the track has a hole or a twist the engine will find 4 points again with quite small movement of one axlebox or the diagonal two. Something has to be firm to provide the basic stability. It can't just float along like a hovercraft. Of course the whole superstructure tilts with the track but that's inherent with 0-4-0's. Quite a different proposition to wanting the leading axle of a 4-6-0 to drop into a hole while the bogie is lifting the front up.

I'm just wondering whether Ed's problem is magnified by poor weight distribution or something we are assuming is right when it's not.

[NickM]

Evening Ed and others.
Just to clarify, I am the owner of the 'other' Hunslet. Our engines are very similar other than the springing arrangement. Mine is cabless, Ed's has a cab but mine has much deeper buffer beams so I would guess they weigh within a few kilos of each other. Both have John Ellis copper boilers. Distribution of weight might have an effect; the extra weight of the upper cab is behind the wheels on Ed's whereas my extra weight is front and back in the buffer beams so potentially more balanced. Mine is currently much softer sprung than Ed's, and softer than Ed's was when he was on the original softer springs. So far mine has never derailed, at Bridgend or anywhere else. Just to confirm for Pete who has driven there, the track is still in excellent condition. We have a few other 0-4-0 locos that do not derail. I wonder if maybe the stiffer springs being of heavier gauge wire are becoming coil bound?
Just to confuse the issue, our club petrol hydraulic 0-4-0 locos have no springs as such at all, just rubber blocks and they never derail!

[chris vine]

Hi again,

I certainly agree with Roger that where the springs are mounted will make no difference to anything - if the combined spring rate is the same.

Ross, I am sure you are correct about softer springs. It is true of cars that softer springs tend to give better road holding, as long as you can control the vehicle body from swaying about too much. Colin Chapman realised this years ago and his cars had much softer springs than was usual at the time. Again, it is to do with the force on the track being more constant if the spring rate is low.

One thing to try is to have more solid springs at one end, and softer ones at the other. This will tend to stop if from rolling too much, as one end will be fairly stiff, while the other end can follow the track if there is any unevenness. If it nods too much, some more experimenting will be called for!!

The Americans always tried to make the suspension on their locomotives work like a tripod. So that one end was very stiff from side to side, while the rest of of the wheel base was flexible from side to side by using compensating bars. (I think from side to side.) In the early days, I think their track was quite rough.

Chris.

[terrier060]

Well gentlemen - we have those suggesting stronger springs and those softer. I have tried stronger and it has exacerbated the problem, so for the sake of £40 I will buy some longer softer springs and try that. I think there is a lot of sense in what Nick has said. His springing certainly seems to be softer and yet the loco is quite stable on our track. Mine responds to every irregularity on the track, but as Nick says there have not been many derailments, though there have been some. It could be that his springs in tubes are acting as shock absorbers. We will have to have a closer look next time we are at the track together.

There are some stock springs at Lee springs which are 1.75 inches long with 10 coils and will give over full travel on the axleboxes. This would compare better with Nick's loco which I am pretty sure has full travel in the horns.

I will keep you all posted - it will certainly be better than taking the loco to pieces to revert to the original design!

[suctionhose]

I worked for a manufacturer for a time and whenever there were problems - which was everyday - his only interest was how many ideas you'd tried.

Discussions are helpful up to a point but success comes from changing something and seeing what happens.

Too much talking these days. Not enough action. Looking forward to the results of softer springs!

[terrier060]

Sept 28, 2021 0:19:57 GMT suctionhose said:

I worked for a manufacturer for a time and whenever there were problems - which was everyday - his only interest was how many ideas you'd tried.

Discussions are helpful up to a point but success comes from changing something and seeing what happens.

Too much talking these days. Not enough action. Looking forward to the results of softer springs!

  Here, here - I quite agree!  Try something out and see what happens.  The result will be unique to each loco or whatever.  I am lucky to have a fine Hunslet in the club to compare mine to!  That helps a lot because it eliminates a lot of variables.

[ejparrott]

Have you weighed the axles?

[Roger]

Sept 28, 2021 0:19:57 GMT suctionhose said:

I worked for a manufacturer for a time and whenever there were problems - which was everyday - his only interest was how many ideas you'd tried.

Discussions are helpful up to a point but success comes from changing something and seeing what happens.

Too much talking these days. Not enough action. Looking forward to the results of softer springs!

Although this seems illogical, the bottom line is that sometimes you can't just think your way out of a problem. Even if trying certain things seem pointless and unlikely to have any effect, you have to shake the tree to see if something falls out. If you're out of ideas, you have to change something.

[suctionhose]

Sept 28, 2021 22:22:11 GMT Roger said:

Sept 28, 2021 0:19:57 GMT suctionhose said:

I worked for a manufacturer for a time and whenever there were problems - which was everyday - his only interest was how many ideas you'd tried.

Discussions are helpful up to a point but success comes from changing something and seeing what happens.

Too much talking these days. Not enough action. Looking forward to the results of softer springs!

Although this seems illogical, the bottom line is that sometimes you can't just think your way out of a problem. Even if trying certain things seem pointless and unlikely to have any effect, you have to shake the tree to see if something falls out. If you're out of ideas, you have to change something.

I think it reinforces "it's what you do that counts, not what you talk about". Countless times, we eventually find a way forward through a process of elimination. My Dad and I worked through many hard ones together fixing cars, plumbing, appliances, steamers; buying a new one = giving up! Sometimes we'd sit in the shed staring at the floor until one of us came up with something. No idea was too ridiculous. Blue Sky thinking they call it now. It was fantastic training to 'think outside the box'.

I do feel these days people have become conditioned to "answers at a single click" when, in reality, most products that make it to market have endured many set backs and revamps. Listen to James Dyson's story.

[terrier060]

I have a confession to make, in that the new springs I tried were only fitted to the rear axle. So yesterday I fitted the front ones as well. It was a much more difficult job, as access is limited and the method of adjustment near impossible on the completed engine without removing a lot of parts.

The result was definitely a stiffer loco, but when the loco did bounce it was more violent and on our down gradient it got into a fore aft oscillation when coasting and I had to drive at a very slow walking pace. This is OK when I am the only one on the track but I means that I could not run carrying passengers and help on open days. The one day the loco has run carrying passengers was fun, though quite an intense 5 hours. It ran well and there was hardly any ash in the smokebox at the end of the run, and no clinker.

The cab is very heavy and unlike Nick's engine a lot of that weight is in the roof and high up. If the softer springs do not work I will try removing the cab and see if that has an effect.

So my last option is to try softer springs and if that fails think up ways of damping the motion. I don't think though that this can be done without removing the boiler, and making a lot of alterations to the chassis. Sadly I did not build this engine, so unlike the Terriers I have no idea of the easiest way of getting it apart. I would like to remove the smokebox with the boiler and leave as much of the smokebox pipework in place and undisturbed as possible. It is also the dirtiest part of the engine with a sooty-oily mixture over everything. Anyone managed to get a smokebox clean before working on it?

[terrier060]

The spring rates for those interested were stock springs from Lee Springs - Hefty die springs.
LHL 625C 02
OD 0.6
ID 0.344
Free length 1.25
Rate 470lbs/in
Solid height 0.87
Wire diam 0.118
Material Music wire
Load at solid height 178.6lbs/in
Active coils 5.3
Total coils 7.3
Travel 0.39