Bill Bedford W Irons

[JimG]

I'm used to a recommended axle weight of 25g/axle; 50g/wagon in S4 and wondered if there is an equivalent in S7 for sprung wagons. I've come across 1g/mm; 125g minimum. For a typical wagon of 15'6" over the headstocks that would work out at 110g, so the 125g would apply. Any thoughts?

If you can dig back in the S7 newsletters into the 1990s, a member did research into wagon suspension. I do remember he had a test track of a crossover on a slight incline and he would let wagons roll through the crossover to test how well they ran. He tested fixed bearings, compensated and sprung and the sprung won out on his tests. I can't remember the weight he recommended for a sprung wagon at this remove, but I do remember that it was quite heavy and I remember sticking strips of lead in a Slater's wagon underframe to get to his recommendations.

Jim.

 

[Peter]

If you can dig back in the S7 newsletters into the 1990s, a member did research into wagon suspension. I do remember he had a test track of a crossover on a slight incline and he would let wagons roll through the crossover to test how well they ran. He tested fixed bearings, compensated and sprung and the sprung won out on his tests. I can't remember the weight he recommended for a sprung wagon at this remove, but I do remember that it was quite heavy and I remember sticking strips of lead in a Slater's wagon underframe to get to his recommendations.

Jim.

Hi Jim,

I cannot help with S7 publications. Peter Kirmond had two articles in Model Railway Journal in 1998. They were issues 101 and 104 covering S7 standards and 7mm Finescale standards respectively. In each test, the wagons weighed 150 to 200 grams.

Peter

 

[Ian@StEnochs]

When I ran Auchlin on the exhibition circuit I had a variety of scratch built and kit wagons. Most were sprung but a few had only 3 point compensation. I didn’t add weight to any and even the Plastikard pig iron wagons, with Slaters sprung w-irons and their S7 wheels, which are quite light, performed faultlessly. We never had a problem even though there were quite wide differences in weight between cast metal and plastic wagons.

I am a believer in NOT adding weight to anything unless it is required for operating reasons. Making stock heavier than required wears out locos quicker and makes transporting them a bit more of a burden.

Ian.

 

[PaxtonP4]

The weight of the wagon should be sufficient to compress the spring fully. That will then ensure that the wagon is riding at the correct height.

Alan

 

[Ian@StEnochs]

The weight of the wagon should be sufficient to compress the spring fully. That will then ensure that the wagon is riding at the correct height.

Alan

Alan,

No, the ride height should be set when the spring is compressed to about its midpoint. When a bump is encountered the spring absorbs the shock and the wheel lifts but the body, due to inertia, will hardly move, in the vertical direction. When a dip appears the wheel is pressed into it and equally the body remains static.

You can still get better running with the springs fully compressed and wagons effectively running on the stops, the wheel will get pushed into hollows but at humps the body has to lift. I used that system in my early P4 days on locos, compensation on rolling stock, but when I changed to S7 full live springing on all stock is possible.

It is fascinating to watch a train negotiate some less than level track with the wheels following the humps and hollows while the vehicles appear to glide along. You can see the same effect in full size from a moving train when approaching a terminal with a train running on a parallel track, just watch the bogies!

Ian.

 

[Steph Dale]

...the ride height should be set when the spring is compressed to about its midpoint. When a bump is encountered the spring absorbs the shock and the wheel lifts but the body, due to inertia, will hardly move, in the vertical direction. When a dip appears the wheel is pressed into it and equally the body remains static.

Kinda - it's more due to the unloading of the spring causing it to extend.

You can still get better running with the springs fully compressed and wagons effectively running on the stops, the wheel will get pushed into hollows but at humps the body has to lift.

Kinda - actually on vehicles with bearings outside the wheels the axle dynamics are a little more complex. If you think of it as a lever, under dynamic conditions the fixed fulcrum is outside the wheel, so the effect would be to lift the unloaded wheel - not drop it. Under slow running conditions there's probably little in it, but there will be a speed at which the vehicle will gain a short, low, declining earth orbit without any obvious reason why...

In short - on outside-bearing wheelsets it is preferable to aim for a settling point somewhere around the mid-point of spring compression.

Steph

 

[Ian@StEnochs]

Kinda - it's more due to the unloading of the spring causing it to extend.


Kinda - actually on vehicles with bearings outside the wheels the axle dynamics are a little more complex. If you think of it as a lever, under dynamic conditions the fixed fulcrum is outside the wheel, so the effect would be to lift the unloaded wheel - not drop it. Under slow running conditions there's probably little in it, but there will be a speed at which the vehicle will gain a short, low, declining earth orbit without any obvious reason why...

In short - on outside-bearing wheelsets it is preferable to aim for a settling point somewhere around the mid-point of spring compression.

Steph

Steph,

I think you are kinda agreeing with me!

Ian.

 

[SimonT]

axle dynamics are a little more complex

And then there is your secondary precession to consider as the speed increases

 

[NewportRod]

Now I think you're all trying to scare me off! Thanks to all for your replies.

Peter Kirmond’s trials described in S7 NL26 (1996) and MRJ 101 are useful and support the use of springs (pushing at an open door in my case), but didn’t address (nor intended to) the question of finding an optimal weight. BTW the 1g/mm guideline came from the G0G manual

So my current plan is to aim at something like 150g, with springs somewhere near the middle of their travel. This should allow me to add a bit more weight and/or change the spring diameter should I not be satisfied with the running qualities.

Rod

 

[Steph Dale]

BTW the 1g/mm guideline came from the G0G manual

Aah, right. Neither betwixt or between then. My guess is that this came from the NMRA standards; for 0-gauge they recommend it 4oz/vehicle + 1oz/inch; the 1g/mm is a close approximation to 1oz/inch. Bearing in mind that it's focused on 4-axle, rigid, coarse-scale (3-rail), those rates are almost certainly too high for 2-rail, compensated, 4-wheel vehicles: it's worth bearing in mind that the Guild's D4.2.3 doesn't state what wheel/rail standards are in force. A battle I unfortunately lost a few years ago...

Steph
Once Guild Technical Chairman

 

[NewportRod]

the Guild's D4.2.3 doesn't state what wheel/rail standards are in force.

Nor does it say if the recommendation applies to rigid, sprung or compensated stock (or all three), which would have been useful info.

 

[Lancastrian]

I don't know if this is of any use if attempting to replicate prototype weights:



Ian

 

[JimG]

I've just been doing a bit of investigation using Russ Elliot's formula for a simple spring wire setup. In the smaller scales like 4mm and S, the major consideration for the weight of the vehicle is what can be achieved with the smallest diameter of spring wire which can be obtained, and that is usually the steel 0.008" (0.2mm) guitar string. In S scale with a distance of 16mm between the spring pivot points, a deflection of 1mm (+/- 0.5mm) can be achieved with a weight of 20gms per axlebox or 40gms per axle. The required weight increases if the distance between pivots has to be reduced due to constraints in the underframe. But if you use the same diameter of spring wire in a 7mm scale model with, say, 24mm between spring pivots, then the weight required to give 2mm deflection (+/- 1mm) drops to 12gms or 24gms per axle. So it could be quite possible to have a wagon in 7mm scale with an all up weight of about 50gms on 0.008" springs which should work well.

I can't remember all Peter Kirmond's arguments for the weights in the 150 - 200 gms range. If I remember correctly, in addition to the wagons negotiating a crossover on his test track, there was also an intentional very bad rail joint as well and I wonder if the heavier weights were a requirement to provide some inertia to stop bouncing.

Jim.

 

[GWR Jim]

Is there a happy outcome to the use of Mr Bedford W Irons? I do hope so as I purchased 3 sets at Telford over the weekend.

Thanks, James