Flexi Chassis an Appreciation

This section allows guests to comment or ask questions. Posts from guests require explicit approval (which generally takes a day or so), before they appear, so that we can prevent unwanted spam.
Terry Bendall
Posts: 1637
Joined: Sun Jul 27, 2008 7:46 am

Re: Flexi Chassis an Appreciation

Postby Terry Bendall » Sun Feb 19, 2017 9:14 am

Allan Goodwillie wrote:you did not want your locos coming across the extremes of track found in the test track.


This I think was one of the problems with that test track. We want to built track which is as flat and level as possible so to have a test track where bumps and twists are deliberately introduced is certainly disheartening to the beginner and in the end does not prove a lot except that it is possible to build models to cope with those extremes if that is what you want to do.

Allan Goodwillie wrote: whatever system we use to keep all the wheels on the road the important thing is that it works and that all comes down to how well you make it work and that is more to do with your construction skills rather than any particular system.


Very true. Discussions like this are important - very important for some, but in the end what we want are locos and stock which run well and stay on the track. How that is achieved doesn't really matter at all. :)

User avatar
Will L
Posts: 1656
Joined: Sun Jul 20, 2008 3:54 pm

Re: Flexi Chassis an Appreciation

Postby Will L » Sun Feb 19, 2017 1:58 pm

Proto87Stores wrote:
Will L wrote:
Alan Turner wrote:There is nothing magical about CSB. It is simply a simple way to tune each wheel spring (i.e. spring rate) to give the desired load distribution on each wheel/axle.

If you were able to manufacture miniature coil springs to your own design of spring rate you would achieve the same result as CSB.


Correct


But what about the effect of the partial equalization of using the stiffness of CSB wire running (continuous) through its support peg to add partial (possibly now only minimal?) equalization to the adjacent wheel?

That makes the two systems above different in wheel loading with displacement.


While what you say is true, the significance of the interaction between the spring segments is mostly felt when the chassis is being designed. This is why the placement of the fulcrum points tends not to be intuitive. But once a design is settled the basic spring rate experienced by each wheel is set by the design.

If you could substitute individual springs with the right spring rates, the fact that when the vehicle is in motion the CSBs spring rate will vary with slightly different characteristics than an individual spring, is not, I think, particularly significant.
That is because
1. they would start from the same value,
2. the changes are relatively small compared to the overall value and
3. they are transient, as the vehicle will seek to rebalance it self.

Proto87Stores

Re: Flexi Chassis an Appreciation

Postby Proto87Stores » Sun Feb 19, 2017 2:56 pm

Will L wrote:
Proto87Stores wrote:
But what about the effect of the partial equalization of using the stiffness of CSB wire running (continuous) through its support peg to add partial (possibly now only minimal?) equalization to the adjacent wheel?

That makes the two systems above different in wheel loading with displacement.


While what you say is true, the significance of the interaction between the spring segments is mostly felt when the chassis is being designed. This is why the placement of the fulcrum points tends not to be intuitive. But once a design is settled the basic spring rate experienced by each wheel is set by the design.

If you could substitute individual springs with the right spring rates, the fact that when the vehicle is in motion the CSBs spring rate will vary with slightly different characteristics than an individual spring, is not, I think, particularly significant.
That is because
1. they would start from the same value,
2. the changes are relatively small compared to the overall value and
3. they are transient, as the vehicle will seek to rebalance it self.


It's been well over a decade since Ted's original introduction of CSB's, but back then the "partial equalization effect" (but with no numbers supplied) was a big (YUGE 8-) ) selling point over individual plain beam springs. Are you saying now that the only value of the continuous wire aspect, is a perhaps slightly more simplified construction? That would make direct (and measured ) comparison with regular rigid beam equalization systems much easier.

And does the spread sheet program therefore not take any equalization effect into account?

Andy

User avatar
grovenor-2685
Posts: 3169
Joined: Sun Jun 29, 2008 8:02 pm

Re: Flexi Chassis an Appreciation

Postby grovenor-2685 » Sun Feb 19, 2017 4:54 pm

Perhaps the partial equalisation effect is not as 'huge' as might have been thought, but there is an effect so a CSB is not identical to a set of individual springs. The ease of adjusting the spring rates by changing the wires is a benefit.
The spreadsheel program does not do any dymamics, and it assumes that the vehicle is sitting on level track but it then calculates the individual axleloads and allows you to set them equal, or not as you prefer. Seeing as it is a sprung system only static equalisation can be done.
That would make direct (and measured ) comparison with regular rigid beam equalization systems much easier.

What is it you want to measure? And why?
Regards

User avatar
Will L
Posts: 1656
Joined: Sun Jul 20, 2008 3:54 pm

Re: Flexi Chassis an Appreciation

Postby Will L » Sun Feb 19, 2017 5:47 pm

Proto87Stores wrote:It's been well over a decade since Ted's original introduction of CSB's, but back then the "partial equalization effect" (but with no numbers supplied) was a big (YUGE 8-) ) selling point over individual plain beam springs. Are you saying now that the only value of the continuous wire aspect, is a perhaps slightly more simplified construction? That would make direct (and measured ) comparison with regular rigid beam equalization systems much easier.

And does the spread sheet program therefore not take any equalization effect into account?


Oh the equalisation effect is important, and yes the Rodger Wyatt spread sheet, and my extension of it take it fully into account, going round four iterations before the impact becomes to small to be worth taking any further. And the impact, as I said, is on the placement of the fulcrums so that, taking the interaction into account, we have the right spring rate needed to get the right spring depression on each wheel. This is all to do with what happens when the vehicle is static. Nothing we have allows us to do analysis on the dynamic situation.

Characterising this all as just a slight simplification is to have missed the "If" in Alan's original post
Alan Turner wrote:If you were able to manufacture miniature coil springs to your own design of spring rate you would achieve the same result as CSB.

User avatar
Will L
Posts: 1656
Joined: Sun Jul 20, 2008 3:54 pm

Re: Flexi Chassis an Appreciation

Postby Will L » Sun Feb 19, 2017 6:55 pm

Allan Goodwillie wrote:...Will's thread is very good...
Thank you Allan
... but ... none of the starters were wanting to start with the system - all the calculations being a bit off putting, when they could get a loco working fairly quickly just following the system required for the kit. A couple of the LIvingston Starters group have taken on springy beams for their first attempt at a loco.

So I hope you will forgive me for taking exception to the
all the calculations
remark.

Just for the record, the user need not do any calculations.

The spreadsheet does all that, at its simplest all you have to do is feed in the wheel base and read out the answers. I will except that my spread sheet can look a bit complicated. I like it like that because I can see what it is doing and if needed you can read off all the dimensions required to set out a chassis for your self from scratch. But, for the new user, Alan's alternative has what you might call a graphical user interface, which looks much easier to use. Taken together with an etched chassis kit and the CSB Jig sold by Highlevel, setting out the fulcrum points is a strait forward process.

After that building the chassis is very little different from and no more difficult than, building a compensated one.

allanferguson
Posts: 354
Joined: Sun Jul 20, 2008 6:27 pm

Re: Flexi Chassis an Appreciation

Postby allanferguson » Sun Feb 19, 2017 8:41 pm

Recently I dug out of one of my boxes the Scalefour Society Locomotive Springing Unit, a set of etchings together with a couple of pages of instructions. I never used it, because I didn't understand it, and because I was at the time firmly wedded to compensation, which I did understand. This was, I think, well before springy beams crossed our horizon.
What I'm wondering is, has anyone used this suspension system; indeed has anyone else ever heard of it?

Allan F

Crepello
Posts: 95
Joined: Thu Jan 31, 2013 11:32 am

Re: Flexi Chassis an Appreciation

Postby Crepello » Sun Feb 19, 2017 9:13 pm

allanferguson wrote:Recently I dug out of one of my boxes the Scalefour Society Locomotive Springing Unit, a set of etchings together with a couple of pages of instructions. I never used it, because I didn't understand it, and because I was at the time firmly wedded to compensation, which I did understand. This was, I think, well before springy beams crossed our horizon.
What I'm wondering is, has anyone used this suspension system; indeed has anyone else ever heard of it?

Allan F

If it's what I think it is, then anyone who's built a Dave Bradwell chassis kit has indeed used this system; it is in effect a set of standalone per-axlebox units for use with other manufacturers', or home-cut components.

allanferguson
Posts: 354
Joined: Sun Jul 20, 2008 6:27 pm

Re: Flexi Chassis an Appreciation

Postby allanferguson » Mon Feb 20, 2017 12:02 am

You're right of course..... If I'd read the thing more carefully I'd have seen Dave Bradwell's name on it.

Allan F

User avatar
Allan Goodwillie
Posts: 766
Joined: Sun Jul 20, 2008 7:00 pm

Re: Flexi Chassis an Appreciation

Postby Allan Goodwillie » Mon Feb 20, 2017 1:21 pm

Hi Will, :D

the comment about the sheet of calculations was not me complaining, on the contrary it has excellent uses, my comment was more to do with the initial response of the beginners when seeing all the figures. The two who are using springy beams for the first time are doing it because the kits come with springy beams and they had already bought the kits some time ago. Both had failed to start them considering the kits perhaps to be beyond their ability as starters, however, they are both progressing with the kits and I am hoping they may manage to get them complete and running soon.

Since you already had a good stream going on using springy beams I have suggested looking at it. I did not cover springy beams in my West Scotland "Build a loco" thread as none of the first group were wanting to do an engine using them - again it all came down to what everyone had at hand and what they wanted to learn about building chassis for themselves. Most of what I am putting up on the forum is basically teaching material for our group courses as those taking part can go over what has been covered when they go home and work on their models - they can also ask questions and put up photographs for me to get back and suggest what might be needed next.

What has been good is the fact that there have been so many experienced members like yourself adding useful information and ideas of you own in a positive way. :thumb

The fact that the various threads have had such a huge number of hits shows that they are being well used outside our two groups, which has made it all even more worthwhile. It is lovely that people that you do not know come up to you at exhibitions and haul locos out of pockets and tell you this is because of your thread. I am sure you must have had similar. :)

Although there is much very good information on track making available from a number of sources I still intend to cover what we are doing as a group in much the same way. :)

User avatar
Will L
Posts: 1656
Joined: Sun Jul 20, 2008 3:54 pm

Re: Flexi Chassis an Appreciation

Postby Will L » Mon Feb 20, 2017 1:53 pm

Hi Andy, like the pictures...

Proto87Stores wrote:
Image

BTW here is one prototypical mass (whole industry?) application of using equalization and not using horn blocks.

Image

And its proto-scale, RTR, manufactured and inexpensive model equivalent.


..but I'm beginning to wonder if some of the differences being aired here aren't as much "cultural" as anything else. When you think of a 4 wheel truck the images that come to your mind are as above. When I think 4 wheel truck I get something more like Image (My apologies to Gareth Thomas for having pirated this picture off his Not so Edwardian wagons thread.)

If I wanted a wagon with bogies like yours I would fit them like a shot, however appropriate wagons in 1930's eastern England were thin on the ground, as a solution to the traditional UK 4 wheel wagon I'm not clear they have much to say. I will steer clear of coach bogies for now.

In terms of solutions to the UK 4 wheel wagon problem, this is something that the P4 community has had some practice at, given that orthodoxy suggests some form of suspension is de rigueur (but let us not have that discussion right now). The compensated method of choice (one fixed and one rocking axle) works well enough to have made P4 practical, but experience over time has shown its limitations. Having one pivot point in the centre at one end, particularly on cast white metal vans that have a high Centre of Gravity, has an unfortunate effect on their stability. Most particularly when being pushed. (More cultural differences, the buffering forces involved with UK pattern buffers again is not a normal part of the American railroad modelling experience and I'm not sure you have too many cast white metal van kits either). While it is just possible this incipient instability could lead to such a wagon toppling over on a track with a lot of cant, more commonly it is experienced by a wagon derailing while being pushed round a corner because it has lifted a wheel.

The development of spring systems which provide exactly the "spring at each corner" that has concerned you, has proved to be significant not only in terms of producing a wagon that rides better, but also because it doesn't suffer its compensated brethren's bad habits. Not to mention leaving the wagon nut free to complete the under frame detail uncomplicated by the presence of rocking W irons. Cue another picture pirated from Gareth.Image

So why don't such wagons full fill your table with springy legs prophecy?
Proto87Stores wrote:.. A similar vehicle chassis that is "merely" fully equalized will be as firm and stable as on absolutely flat track.

To visualize this better, consider the classic four legged table in the restaurant with the uneven floor. Instead of stabilizing it with a wedge or an equalized pair of legs, the waiter puts springs on all four legs. And then you order a brim full bowl of soup and a plate of peas . . . .


The simple answer is that their springs are sufficiently damped by the way the axle bearing carriers rub against the fixed W irons, and the net result is a significant improvement on compensation. I'm not saying that it isn't possible to design a sprung suspension that does full fill your worst fears, when I was playing with wagon springing some years ago I managed just that, but the now accepted design does not. The same "sufficiently damped" by fiction on the bearing blocks argument applies to CSB sprung locos too, which equally do not display any tenancy to isolate on their springs.

And yes I know Compensation and Equalisation are not the same thing. There are several Coach Bogie designs about in the UK with fixed axle bearings in sides that move relative to one another which will be much closer to your truck design. I think the jury is out on whether there are significantly better or worse or different from than the fully sprung variety, or if the orthodoxy really does apply a fully rigid bogie doesn't do just as well.

Proto87Stores

Re: Flexi Chassis an Appreciation

Postby Proto87Stores » Mon Feb 20, 2017 7:14 pm

Will L wrote:Hi Andy, like the pictures...

..but I'm beginning to wonder if some of the differences being aired here aren't as much "cultural" as anything else. When you think of a 4 wheel truck the images that come to your mind are as above. When I think 4 wheel truck I get something more like Image (My apologies to Gareth Thomas for having pirated this picture off his Not so Edwardian wagons thread.)

If I wanted a wagon with bogies like yours I would fit them like a shot, however appropriate wagons in 1930's eastern England were thin on the ground, as a solution to the traditional UK 4 wheel wagon I'm not clear they have much to say. I will steer clear of coach bogies for now.

In terms of solutions to the UK 4 wheel wagon problem, this is something that the P4 community has had some practice at, given that orthodoxy suggests some form of suspension is de rigueur (but let us not have that discussion right now). The compensated method of choice (one fixed and one rocking axle) works well enough to have made P4 practical, but experience over time has shown its limitations. Having one pivot point in the centre at one end, particularly on cast white metal vans that have a high Centre of Gravity, has an unfortunate effect on their stability. Most particularly when being pushed. (More cultural differences, the buffering forces involved with UK pattern buffers again is not a normal part of the American railroad modelling experience and I'm not sure you have too many cast white metal van kits either). While it is just possible this incipient instability could lead to such a wagon toppling over on a track with a lot of cant, more commonly it is experienced by a wagon derailing while being pushed round a corner because it has lifted a wheel.

The development of spring systems which provide exactly the "spring at each corner" that has concerned you, has proved to be significant not only in terms of producing a wagon that rides better, but also because it doesn't suffer its compensated brethren's bad habits. Not to mention leaving the wagon nut free to complete the under frame detail uncomplicated by the presence of rocking W irons. Cue another picture pirated from Gareth.Image

So why don't such wagons full fill your table with springy legs prophecy?
Proto87Stores wrote:.. A similar vehicle chassis that is "merely" fully equalized will be as firm and stable as on absolutely flat track.

To visualize this better, consider the classic four legged table in the restaurant with the uneven floor. Instead of stabilizing it with a wedge or an equalized pair of legs, the waiter puts springs on all four legs. And then you order a brim full bowl of soup and a plate of peas . . . .


The simple answer is that their springs are sufficiently damped by the way the axle bearing carriers rub against the fixed W irons, and the net result is a significant improvement on compensation. I'm not saying that it isn't possible to design a sprung suspension that does full fill your worst fears, when I was playing with wagon springing some years ago I managed just that, but the now accepted design does not. The same "sufficiently damped" by fiction on the bearing blocks argument applies to CSB sprung locos too, which equally do not display any tenancy to isolate on their springs.

And yes I know Compensation and Equalisation are not the same thing. There are several Coach Bogie designs about in the UK with fixed axle bearings in sides that move relative to one another which will be much closer to your truck design. I think the jury is out on whether there are significantly better or worse or different from than the fully sprung variety, or if the orthodoxy really does apply a fully rigid bogie doesn't do just as well.


Thanks,

I agree there are major cultural differences in UK vs. US RR infrastructure. Historical overly rapid laying and poor maintenance of huge distances of mostly used for freight track is one of our inherited problems. So the ubiquitous simplified, bogie wagon, with wide range equalization was a natural solution. The extra cost of smoothing springing was typically only added for passenger carrying vehicles, which is why the trucks on cabooses have non-linear leaf springs rather than linear coil springs, on their bolsters. But even then, the equalized side frames were retained for better track holding on the bumpier track.

I also concur that Bill's 4 corner springing is helpfully symmetrical on the typical UK 4 wheel wagon and therefore a far better model solution than the rocking W iron and three point suspension of the past. May I presume the most used end result is just 4 separate springs and not just two side CSBs in that case?

As we progress, you'll find I'm actually very happy with having a body symmetrically connected to its chassis with 4 springs. My "what's the best of breed?" concerns are mostly with multi-axle locomotives and bogie coaches having the primary suspension as individual, per wheel springing, when equalization gives better track holding and less complicated, easier and hence less expensive construction. Having the body then separately sprung on the unsprung equalized chassis should give the best of both worlds. whether the track is smooth or bumpy, at any speed, and at any vehicle weight.

Clearly the already simple structure of the UK 16 ton Mineral wagon is not going to be much of a difference in cost, even if full equalization was used instead of 4 wheel springing. It's the usual steam locos, and especially ones that are more than 6-coupled, that would be affected most in terms of ease of construction and cost (or far more available as RTR plug in chassis units/kits).

My own efforts will be initially directed at my nostalgic LNER N7 0-6-2T's. But I if live long enough, I would hope to have some P87 SP 4-8-8-2's rolling realistically heavily around 100% derailment free.

Andy

billbedford
Posts: 682
Joined: Tue Oct 02, 2012 2:40 pm

Re: Flexi Chassis an Appreciation

Postby billbedford » Tue Feb 21, 2017 9:33 am

Proto87Stores wrote:As we progress, you'll find I'm actually very happy with having a body symmetrically connected to its chassis with 4 springs. My "what's the best of breed?" concerns are mostly with multi-axle locomotives and bogie coaches having the primary suspension as individual, per wheel springing, when equalization gives better track holding and less complicated, easier and hence less expensive construction. Having the body then separately sprung on the unsprung equalized chassis should give the best of both worlds. whether the track is smooth or bumpy, at any speed, and at any vehicle weight.


You really ought to define what you mean by 'better' here.

FYI while the wagon kits have four individual springs, the etched bogie centres have a single spring wire each side.
Bill Bedford
Mousa Models
http://www.mousa.biz

Proto87Stores

Re: Flexi Chassis an Appreciation

Postby Proto87Stores » Tue Feb 21, 2017 4:54 pm

billbedford wrote:
Proto87Stores wrote:As we progress, you'll find I'm actually very happy with having a body symmetrically connected to its chassis with 4 springs. My "what's the best of breed?" concerns are mostly with multi-axle locomotives and bogie coaches having the primary suspension as individual, per wheel springing, when equalization gives better track holding and less complicated, easier and hence less expensive construction. Having the body then separately sprung on the unsprung equalized chassis should give the best of both worlds. whether the track is smooth or bumpy, at any speed, and at any vehicle weight.


You really ought to define what you mean by 'better' here.

FYI while the wagon kits have four individual springs, the etched bogie centres have a single spring wire each side.


billbedford wrote:After 15 or 20 years of explaining to you why springing is superior to 'equalisation' you still don't get the point, and I suspect that most people that have tried to help you have just given up.


Perhaps I should ask for a substance based definition from you first? ;)

But we have established that equalization keeps the weight per wheel the same while going over those small (or even large) perturbations in track flatness, as well as being unaffected by track twist.

In the sprung wheel dynamic case, a short distance impulse (track bump) will compress a per wheel spring , and under Hooke's law, pass an increased upward force directly to that supporting part of the rigid chassis above it.

In the equalized wheels dynamic case, the same impulse will lift one wheel the same amount, but the connection to the rigid chassis will only be lifted by that amount divided by the ratio of the beams and fulcrums between the wheel and the rigid chassis support point.

If you want a more obvious example of that fact that direct wheel springing is worse at track holding than more equally weighted wheel following, then test drive a sports car. The harder the suspension, the better the handling.

If you then spring the body from the chassis, you have maximized the track holding of the chassis, then smoothed considerably reduced impulses applied to the body with just the minimum amount (4 probably ) of springing devices.

Andy

billbedford
Posts: 682
Joined: Tue Oct 02, 2012 2:40 pm

Re: Flexi Chassis an Appreciation

Postby billbedford » Tue Feb 21, 2017 7:47 pm

Proto87Stores wrote:If you want a more obvious example of that fact that direct wheel springing is worse at track holding than more equally weighted wheel following, then test drive a sports car. The harder the suspension, the better the handling.


But such suspensions don't always keep all four wheels on the road:

Image
Bill Bedford
Mousa Models
http://www.mousa.biz

Julian Roberts
Posts: 765
Joined: Sat Jan 09, 2010 11:33 pm

Re: Flexi Chassis an Appreciation

Postby Julian Roberts » Tue Feb 21, 2017 8:19 pm

I also concur that Bill's 4 corner springing is helpfully symmetrical on the typical UK 4 wheel wagon and therefore a far better model solution than the rocking W iron and three point suspension of the past.

(Proto 87)

I wonder whether there is a simple but effective way of making one wheelset of a wagon sprung while keeping the other rigid? As an easy alternative to compensating one axle? Downward thrust must be adequate - around a quarter of the vehicle weight on each wheel I would imagine
Last edited by Julian Roberts on Tue Feb 21, 2017 9:19 pm, edited 2 times in total.

User avatar
Will L
Posts: 1656
Joined: Sun Jul 20, 2008 3:54 pm

Re: Flexi Chassis an Appreciation

Postby Will L » Tue Feb 21, 2017 9:03 pm

I feel an "are but" coming on

Proto87Stores wrote:But we have established that equalization keeps the weight per wheel the same while going over those small (or even large) perturbations in track flatness, as well as being unaffected by track twist.

While that may be true with a stationary wagon, I'm not so sure when the vehicle is in motion. As a wheel lift must accelerate the weight of the body upwards and by newtons third law.... So I'm not so sure that, once in motion, this distinction between sprung and equalised suspension is anything like so clear cut.

In the sprung wheel dynamic case, a short distance impulse (track bump) will compress a per wheel spring , and under Hooke's law, pass an increased upward force directly to that supporting part of the rigid chassis above it.

In the equalized wheels dynamic case, the same impulse will lift one wheel the same amount, but the connection to the rigid chassis will only be lifted by that amount divided by the ratio of the beams and fulcrums between the wheel and the rigid chassis support point.

But then that the amount by which chassis will be lifted in the sprung example will also be less than the amount the wheel lifts. When static, analysis on a 4 wheeled vehicle suggests 50% less. Could your equalisation improve on that? On individual wheels possibly but not on average over whole vehicle .

Then when you consider the dynamic case with vehicle in motion, with equalisation, the vehicle body must lift by the full amount required instantly, where as in the case of the sprung suspension, the lift to the body will occur relatively slowly (because the weight of the wheel is small compared to the weight of the body and the body's inertia will predominate), and, unless the wheel remains raised over a relatively long period, will the never achieve the full amount of lift to be expected in the static circumstances.

If you want a more obvious example of that fact that direct wheel springing is worse at track holding than more equally weighted wheel following, then test drive a sports car. The harder the suspension, the better the handling.

billbedford wrote:But such suspensions don't always keep all four wheels on the road:

In case nobodies noticed high performance cars have sprung suspension, even in a FI car where its is mostly in the walls of the tyres. The difference in handling Andy describes is primarily the difference between short travel firm springing as against long travel soft springs.

Proto87Stores

Re: Flexi Chassis an Appreciation

Postby Proto87Stores » Tue Feb 21, 2017 11:21 pm

billbedford wrote:
Proto87Stores wrote:If you want a more obvious example of that fact that direct wheel springing is worse at track holding than more equally weighted wheel following, then test drive a sports car. The harder the suspension, the better the handling.


But such suspensions don't always keep all four wheels on the road:

Image


Nor does Amtrak when cornering too fast either unfortunately. Railway curves have speed limits and the centrifugal force toppling effect has little to do with suspension in that case. Unless it's way too soft and the c of g moves more easily sideways relative to the wheels. ( Where's a banana-skin emoji when you need one :D )

Similarly the harder suspension in the race car scenario is prevent either front or back wheels sliding sideways (break away) on a curve before toppling starts. It's the same familiar physics that you use to maximize model loco tractive effort (pull). The wheels with the least weight on them will slip first, causing the whole locomotive to go into wheelslip earlier than necessary. So you want all four wheels to stay grounded as much as possible. Front engine with front wheel drive cars oversteer and front engine with rear wheel drive cars understeer. But Porsche favours mid engine cars.

The problem with having too short throw a suspension is that on roads rather than smooth race tracks, you can quite often hit bumps that are higher than the short throw of the suspension. It's painful, potentially damaging and occasionally very scary. Hence longer throw suspension on family cars and the "hump back bridge" road sign.

This is probably the right time to point out that an P4 loco trundling happily back and forth on a shunting plank at 20 mph is probably going to be very happy with short throw suspension

billbedford wrote: The static deflection for a model loco is given as ± 0.5mm, but the dynamic deflection is much smaller than this, probably in the range of less than ± 0.1 mm for reasonably well laid track.----- after all we are modelling a railway, not all-terrain vehicles.


However, the recent P4 modeller, working on his APT-E, would hit the same minor track bumps six times faster = HARDER. Which makes the likely dynamic spring deflection around six times greater. If you only design dynamic suspension for the typical Scaleforum exhibit pre-war GWR terminus case, you won't have a viable solution for more modern finescale, nor for the average open the box enthusiast.

Andy

User avatar
Horsetan
Posts: 940
Joined: Tue Jul 29, 2008 9:24 am

Re: Flexi Chassis an Appreciation

Postby Horsetan » Fri Feb 24, 2017 11:40 pm

A pity we can't have oleopneumatic suspension for models, then :mrgreen:
That would be an ecumenical matter.

User avatar
James Wells
Posts: 121
Joined: Sun Oct 24, 2010 4:03 pm

Re: Flexi Chassis an Appreciation

Postby James Wells » Mon Feb 27, 2017 9:56 pm

Proto87Stores wrote:If you want a more obvious example of that fact that direct wheel springing is worse at track holding than more equally weighted wheel following, then test drive a sports car. The harder the suspension, the better the handling.


That doesn't actually bear out - really hard suspension isn't always good for handling. I've driven modified cars with incredibly stiff suspension and this can adversely after the handling. All the elements need to work together, springs, shocks, geometry, steering, wheels and tyres. A car which corners flat gives the driver confidence but it can be a false sense of confidence in some cases. However the 'feel' of a car can be just as important as the actual ability of a vehicle.

You can also confuse handling and body role by assuming hard suspension is automatically better - a car can have body role due to suspension being slightly softer than other cars. My Alfa has softer suspension than the other cars I've owned and it handles beautifully.

Proto87Stores wrote:Front engine with front wheel drive cars oversteer and front engine with rear wheel drive cars understeer.


Other way round! Hence why drift cars are rear wheel drive!

I really don't think we can directly compare sports car suspension with railway suspension.

User avatar
Allan Goodwillie
Posts: 766
Joined: Sun Jul 20, 2008 7:00 pm

Re: Flexi Chassis an Appreciation

Postby Allan Goodwillie » Tue Feb 28, 2017 7:18 pm

Julian there are some alternatives we could have a look at -

I wonder whether there is a simple but effective way of making one wheelset of a wagon sprung while keeping the other rigid? As an easy alternative to compensating one axle? Downward thrust must be adequate - around a quarter of the vehicle weight on each wheel I would imagine -Julian Roberts


There is a form of equalization which Mike Gilgannon used Julian, which used the torsion bar system at each end of the wagon, I will bring one along to our next meeting to let you see. I remember others rubbishing Mike's approach telling him that it would not work, but his stock behaved beautifully and he continued to use the system until he died. Remember, however, he spent a lot of effort getting his track right and there were no cambers although there were gradients on his original main line system. I intend using Mike's wagon on Grayrigg (for testing only) when I get the garage back in use later this year. Being a low flat wagon it will be interesting to try it in various positions within trainloads to see how the system copes with cambers and gradients and long mainline trains.

We are straying a bit from the point here with this so we can have a look at it when we get a chance to discuss such things together, rather than take the discussion away from dealing with engines. Hope you don't mind. :)

Proto87Stores

Re: Flexi Chassis an Appreciation

Postby Proto87Stores » Wed Mar 01, 2017 6:41 pm

James Wells wrote:
Proto87Stores wrote:If you want a more obvious example of that fact that direct wheel springing is worse at track holding than more equally weighted wheel following, then test drive a sports car. The harder the suspension, the better the handling.


That doesn't actually bear out - really hard suspension isn't always good for handling. I've driven modified cars with incredibly stiff suspension and this can adversely after the handling. All the elements need to work together, springs, shocks, geometry, steering, wheels and tyres. A car which corners flat gives the driver confidence but it can be a false sense of confidence in some cases. However the 'feel' of a car can be just as important as the actual ability of a vehicle.

You can also confuse handling and body role by assuming hard suspension is automatically better - a car can have body role due to suspension being slightly softer than other cars. My Alfa has softer suspension than the other cars I've owned and it handles beautifully.

Proto87Stores wrote:Front engine with front wheel drive cars oversteer and front engine with rear wheel drive cars understeer.


Other way round! Hence why drift cars are rear wheel drive!


Image

Not in my experience. I'm talking about powered vs. coasting cornering. The RWD Vette needs some throttle, or the steering tends to want to center. The FWD Legend (Honda) basically effortlessly goes where you point it.

James Wells wrote:I really don't think we can directly compare sports car suspension with railway suspension.


Image

Only if you don't try :P

Sorry for replying out of sequence. I'll answer Will shortly.

Andy

Julian Roberts
Posts: 765
Joined: Sat Jan 09, 2010 11:33 pm

Re: Flexi Chassis an Appreciation

Postby Julian Roberts » Thu Mar 02, 2017 12:17 am

Thanks Allan. I wondered if anyone had seen my post. I rather think the whole discussion (as immediately above) has moved a long way from appreciating the elegant simplicity of Mike's concept, and shows good reason for his frequently expressed scepticism for the opinions of "experts".

What I am interested in though is something really easy to P4-ize a RTR wagon - and only one axle needs any work. I think the rigid 4 wheel wagon is just not good enough on P4 layouts running-wise, but my quest is to make it easy, VERY easy, to give it fool-proof-ly successful suspension - even easier than the MJT compensation, and possibly even more reliable in that the weight would not teeter around in the middle but bear down directly above the wheels in question if it was basically a pair of springs acting on the 2 wheels.

The issue in P4, it seems to me, is making trains that actually stay on the track and that can accommodate reasonable track faults given realistic speed control. Not pages of incomprehensible debate about indiscernibly minute differences of ride quality.

Philip Hall
Posts: 1289
Joined: Mon Aug 10, 2009 7:49 pm

Re: Flexi Chassis an Appreciation

Postby Philip Hall » Thu Mar 02, 2017 12:53 am

I must say that I differ here, in that I think that a rigid wagon is good enough in P4, subject to certain qualifications. Provided the wheels are perfectly round and true, a short wheelbase 4 wheel wagon with a bit of weight in it, about 50 grams, will quite happily stay on decent track. It won't wobble as the wheels are round, and a little bit of play in the bearings will take care of most irregularities. I can't speak for monster length trains (although I guess there are those on here who can) but a lot of folk have had no trouble. I see no reason to complicate matters with suspension unless you really want to. However, I usually don't build them this way, only if it's a RTR job. They can get them square much more easily than I can.

It is undoubtedly true that a sprung wagon moves differently, and very nicely, but as far as simply moving smoothly along and not falling off is concerned, there is no need to complicate. I have a lot of compensated wagons which behave well, but a lot of rigid ones as well, and since I started being a lot fussier about the wheels in them I am quite satisfied. Where I do use compensation it's usually the inside bearing MJT etch.

I think this really is the quickest way. But I am keen to try sprung suspension, in spite of all I have said. It's just than in building stock for a fairly large layout, there have got to be some serious, albeit effective, short cuts!

Philip

Julian Roberts
Posts: 765
Joined: Sat Jan 09, 2010 11:33 pm

Re: Flexi Chassis an Appreciation

Postby Julian Roberts » Thu Mar 02, 2017 7:20 am

Philip Hall wrote:and a little bit of play in the bearings will take care of most irregularities.

Philip


Philip I hope you will forgive me if I say that this is the issue IMHO. That play in the bearings yes it will give a kind of suspension, but it is a sloppy floppy kind and at any time doesn' t give any downward force on one of the four wheels. And as I said in my first Snooze article, quoting from an accident report into a derailment on the real railway, if the sideways forces on the flange are stronger than the downward ones the flange will climb up and eventually over the rail.

Of course I agree absolutely about 50g weight. Compensated stock where the weight is in the load derails too without that load.

On a large layout there are bound to be small track issues that may come and go with heat and humidity. A robust suspension system on every vehicle that really works as intended seems to me the sine qua non of realistic operating.


Return to “Guest Book”

Who is online

Users browsing this forum: No registered users and 1 guest