Flexi Chassis an Appreciation

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proto87stores

Re: Flexi Chassis an Appreciation

Postby proto87stores » Tue May 02, 2017 8:41 pm

Horsetan wrote:
proto87stores wrote:.....Given the large number of P4 Steam Loco Builders in the Society, did anyone build a steam loco chassis with single independent sliding wire springs per wheel and do a running comparison with a similar model with the then new CSB's? ....


Well, there are Dave Bradwell chassis kits which are designed with this principle in mind, and he derived his design ideas from Chris Pendlenton, who has built a fair few of his own....

I have tried individual leaf springs on chassis for a "Duchess" and LWB Black 5, and the idea certainly has something going for it. My problem was that the springs had a irritating tendency to drop out of the (Exactoscale) grub screw adjusters at one end.

I thought that if I drilled a small hole in the top of the otherwise hollow grub screw, just big enough for the end of the spring to feed through and be retained by it, this would at least keep the spring in place when the chassis was "unloaded". That went well :-|


I assumed that any such chassis would have (per each wheel bearing) 2 bent out mounting brackets with holes supporting the sliding wire at each end, with little right angle bends on the ends of the wire to stop it going all the way through the mountings.

Mounting holes and wire as per the CSB spreadsheet, for that particular loco.

Andy

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Re: Flexi Chassis an Appreciation

Postby Horsetan » Wed May 03, 2017 6:48 pm

proto87stores wrote:...I assumed that any such chassis would have (per each wheel bearing) 2 bent out mounting brackets with holes supporting the sliding wire at each end, with little right angle bends on the ends of the wire to stop it going all the way through the mountings.

Mounting holes and wire as per the CSB spreadsheet, for that particular loco.


Not if the spring and axlebox height are designed to be adjustable, hence the grubscrew at one end.
That would be an ecumenical matter.

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Re: Flexi Chassis an Appreciation

Postby grovenor-2685 » Wed May 03, 2017 7:30 pm

Mounting holes and wire as per the CSB spreadsheet, for that particular loco.

The spreadsheet is irrelevant for individual springs.
The Dave Bradwell design mentioned uses a standard span with one end of the spring adjustable by grubscrew.
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proto87stores

Re: Flexi Chassis an Appreciation

Postby proto87stores » Thu May 04, 2017 4:01 am

I don't think we are talking about the same construction.

If you can spreadsheet the wire dia and spring length for a CSB, no height adjustment needed, then why can't you use that info for a set of no-height adjustment needed, separate per wheel sliding wires. ???

Static physics is almost the same, except perhaps requiring a slightly thicker wire to restore the same static equilibrium height value to compensate for the lack of the Pre-bent "equalization" with adjacent wheels.

Andy

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Re: Flexi Chassis an Appreciation

Postby Will L » Thu May 04, 2017 9:43 pm

proto87stores wrote:However, I have a related question. Given the large number of P4 Steam Loco Builders in the Society, did anyone build a steam loco chassis with single independent sliding wire springs per wheel and do a running comparison with a similar model with the then new CSB's? Obviously the prototype does it that way, but I don't seem to see that subject, or a comparison, coming up here or elsewhere. And presumably Bill chose not to make his 4 wheel wagon wire continuous for more than just convenience reasons.

As Keith has pointed out, the nearest equivalent thing is the Dave Bradwell product, available from the Society stores, as well as in his kits. Like any individual sprung system, the real issue is knowing how closely the spring rate available meets the weight bearing requirements of your loco. Unlike other individual sprung systems (Brass masters, Alan Gibson etc.) the Bradwell units are adjustable, but that just begs the question of how you know what you should adjust them to?

The single individual spring system are allways, unless your are lucky, going on or near one end stop or the other. The springs in the brassmaster variant are said to be rated so as to suit the likely loco weight, but does anybody know what weight that is? All I know is that we don't all model locos of the same size.

We have spoken before of the difficulty of measuring the weight being carried by any one individual axle so any adjustable system is inevitably going to depend more on guesstimates and the niceity of the builders judgment.

A non adjustable two fulcrums and a wire system might prove simpler, as we can work out what weight each wire will carry, so working out what size wires we need to suit a given loco weight should be practable, but that will work out siginifanctly more complex than an equivalent CSB with more fulcrum point and even more wires to fit, so I see no advatages. Also, fitting a spring wire through 3 or more fulcrum points automatically straightens out any natural curvature in the wire, while just 2 fulcrum points won't, which may prove significant under an asymmetrical multi wheel chassis.

So I think CSB works out to be both simpler to set up and more closely adjusted to the locos actual weight than any other springing system.

Bill's wagon spring system can't use a single spring per side as the wheels are too far apart, but weight distribution on a 4 wheel chassis is less complex, and any subtle bowing of the wire will only has a marginal effect on final buffer heights.

billbedford

Re: Flexi Chassis an Appreciation

Postby billbedford » Fri May 05, 2017 7:26 am

Will L wrote:Bill's wagon spring system can't use a single spring per side as the wheels are too far apart, but weight distribution on a 4 wheel chassis is less complex, and any subtle bowing of the wire will only has a marginal effect on final buffer heights.


That is not the case. The wagon springing system could use a single wire each side, but there would have to be three anchor points instead of four. The bogie kits have single wires and three anchors, but for the wagon I decided that separate wires in each axle would give a more universal and simpler system that was and more easily understood by people unused to springing.

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Re: Flexi Chassis an Appreciation

Postby Russ Elliott » Fri May 05, 2017 4:02 pm

Bill's sprung wagon units are discrete for the good pragmatic reasons (IMO) that they would need extra brass real estate if they were not discrete, they can accommodate different wheelbases, and a central fulcrum would get in the way of plastic kit brake mouldings. Seems eminently sensible to me.

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Re: Flexi Chassis an Appreciation

Postby Russ Elliott » Fri May 05, 2017 4:17 pm

proto87stores wrote:I assumed that any such chassis would have (per each wheel bearing) 2 bent out mounting brackets with holes supporting the sliding wire at each end, with little right angle bends on the ends of the wire to stop it going all the way through the mountings.

Making little right angle bends on both ends of the wire is very difficult to do without distorting the straightness of the wire, and makes the spring non-removable.

proto87stores

Re: Flexi Chassis an Appreciation

Postby proto87stores » Tue May 09, 2017 2:46 am

The first attempt at producing P4 compatible Airfix mineral wagons using just modern Flexichas ideas have been sent off for etching. I hope to have results back here in the USA within about 30 days. Note these are only intended as Full Flexichas functionality evaluation units, not for absolute cosmetic perfection. If successful, more visually accurate parts can be the goal of improved versions.

Provided there are no serious goofs, I should be able to produce a few unpainted wagons to play with a few days after their arrival. And then hopefully some testing and videos. Also the same parts should be capable of being used to create freestanding basic chassis for other forms of 9ft wheelbase wagons. I can easily make copies available for any interested other modellers to experiment with.

My goals are for non-derailing, weight independent, free rolling wagons with high inertia and low friction, for realistic movement when running, bumping, coupling and shunting. Ultimately, even being capable of fly shunting as well

Andy

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Re: Flexi Chassis an Appreciation

Postby Will L » Wed May 10, 2017 12:54 pm

proto87stores wrote:The first attempt at producing P4 compatible Airfix mineral wagons using just modern Flexichas ideas have been sent off for etching. I hope to have results back here in the USA within about 30 days. Note these are only intended as Full Flexichas functionality evaluation units, not for absolute cosmetic perfection. If successful, more visually accurate parts can be the goal of improved versions.

Provided there are no serious goofs, I should be able to produce a few unpainted wagons to play with a few days after their arrival. And then hopefully some testing and videos. Also the same parts should be capable of being used to create freestanding basic chassis for other forms of 9ft wheelbase wagons. I can easily make copies available for any interested other modellers to experiment with.

My goals are for non-derailing, weight independent, free rolling wagons with high inertia and low friction, for realistic movement when running, bumping, coupling and shunting. Ultimately, even being capable of fly shunting as well

Andy


I await your results with real interest.

Will

proto87stores

Re: Whoops - small maths error

Postby proto87stores » Tue May 16, 2017 11:33 pm

Will L Apr 27, 2017, 5:33pm wrote:
I think Russ explained what's going on better than I can, and the picture above shows you that this isn't a theoretical thing. CSB work so isn't it a bit pointless to go on thinking of good reasons why they might not?

There is a practical issue with only designing a CSB model to have a much smaller up/down movement than +/- 0.5 mm.


No problem using the spread sheets to design CSB with less than 0.5mm static deflection, if that's what turns you on. You only need to be able to set the fulcrum points out reasonably accurately (to the nearest 0.5mm) and fit the right size wire. I agree that wouldn't work if you went as low as .1mm which. as you point out, is as near as dammit rigid anyway. However what I was pointing out was, not that the deflection was limited to a small value, but that with the full normal 0.5mm static deflection, the actual range the suspension normally works over is no more than 0.15 either side of the static deflection point, or 0.25 if you must indulge in party trick size track faults. You'll only ever get the full 0.5 if you can persuade the loco to balance on all the wheels on one side, stunt driver style.

Again this is where leaving the fixed beam designs behind creates new added complications. None of the above is any concern for a properly equalized flexi-chas. It's just a case of build it, and it will run perfectly on completion.


Thing is all these "additional complications" are not things that trouble us in practice, if they exist at all. When I built the O4, all I did was apply the method to define the fulcrum points, build a mechanically simple chassis to the tolerances I was used to, and bingo it worked like a charm.


There seems to be some serious difficulty (impossibility without significant chassis modification?) in establishing the correct ride height for the 4F mentioned on a different current thread, due apparently to an unexpected final loco weight that a CSB design is not sufficiently adaptable to allow for? That does rather support my point that CSB's are not as complication free as desired

Andy
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Re: Flexi Chassis an Appreciation

Postby dal-t » Wed May 17, 2017 7:38 am

Err, I thought it had been made clear that the 4F chassis giving ride height problems isn't a CSB design - or am I missing something (again)?
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Re: Flexi Chassis an Appreciation

Postby Knuckles » Wed May 17, 2017 9:11 am

Will L wrote:
proto87stores wrote:However, I have a related question. Given the large number of P4 Steam Loco Builders in the Society, did anyone build a steam loco chassis with single independent sliding wire springs per wheel and do a running comparison with a similar model with the then new CSB's? Obviously the prototype does it that way, but I don't seem to see that subject, or a comparison, coming up here or elsewhere. And presumably Bill chose not to make his 4 wheel wagon wire continuous for more than just convenience reasons.


A non adjustable two fulcrums and a wire system might prove simpler, as we can work out what weight each wire will carry, so working out what size wires we need to suit a given loco weight should be practable, but that will work out siginifanctly more complex than an equivalent CSB with more fulcrum point and even more wires to fit, so I see no advatages. Also, fitting a spring wire through 3 or more fulcrum points automatically straightens out any natural curvature in the wire, while just 2 fulcrum points won't, which may prove significant under an asymmetrical multi wheel chassis.

So I think CSB works out to be both simpler to set up and more closely adjusted to the locos actual weight ...




Something that has always bothered me about giving a CSB a shot is working out the weight prior to entering the values into the spread sheet (or working it out on paper...no chance for me). How are we supposed to know what weight the model sill be once completed and lead stuffed before setting everything up for CSB?

I may be missing something obvious here but other than estimating or throwing the whole kit, some solder and a guessed amount of lead on a scale beforehand I'm at a loss here.

:-/
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Re: Flexi Chassis an Appreciation

Postby Alan Turner » Wed May 17, 2017 9:33 am

Knuckles wrote:
Will L wrote:
A non adjustable two fulcrums and a wire system might prove simpler, as we can work out what weight each wire will carry, so working out what size wires we need to suit a given loco weight should be practable, but that will work out siginifanctly more complex than an equivalent CSB with more fulcrum point and even more wires to fit, so I see no advatages. Also, fitting a spring wire through 3 or more fulcrum points automatically straightens out any natural curvature in the wire, while just 2 fulcrum points won't, which may prove significant under an asymmetrical multi wheel chassis.

So I think CSB works out to be both simpler to set up and more closely adjusted to the locos actual weight ...




Something that has always bothered me about giving a CSB a shot is working out the weight prior to entering the values into the spread sheet (or working it out on paper...no chance for me). How are we supposed to know what weight the model sill be once completed and lead stuffed before setting everything up for CSB?

I may be missing something obvious here but other than estimating or throwing the whole kit, some solder and a guessed amount of lead on a scale beforehand I'm at a loss here.

:-/


You should be able to have a good guess to start with.

If it turns out lighter or heavier then simply adjust the spring wire diameter. The spread sheet does it all for you. What you need to ensure is that the DISTRIBUTION of the weight stays as originally assumed, i.e. the CoG.

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Re: Flexi Chassis an Appreciation

Postby Russ Elliott » Wed May 17, 2017 11:09 am

Knuckles wrote:I may be missing something obvious here but other than estimating or throwing the whole kit, some solder and a guessed amount of lead on a scale beforehand I'm at a loss here.

That will probably take you less time than it did to post your message.

Armchair Modeller

Re: Flexi Chassis an Appreciation

Postby Armchair Modeller » Wed May 17, 2017 11:38 am

I took the view that the world will not come to an end just because I dare to try a CSB chassis. I started with a Mousa chassis, so the thinking was already done for me - apart from maybe needing to swap the spring wires for thinner or thicker ones. That worked fine. Even better, the world really did not come to an end.

Now I am trying a couple of cheap chassis that require me to do all the thinking for myself - using a CSB spreadsheet and the High Level CSB jig. Even if I am not successful, the cost will be minimal, so not worth a lot of worrying about whether I ought to give it a go - or question whether it really will work.

As I see it, compensated chassis sound simpler and more predictable, but once you get over 2 axles they quickly become very complicated. Ensuring adequate weight on all wheels becomes more and more difficult - as could stability. I think both compensated and CSB chassis have their place. It is not the black and white issue that some people have portrayed on here - not by a long way.

I can see how CSBs can make some of the more complicated chassis much easier to build. On very small 4-wheeled shunters compensation has its benefits though - particularly as it can be difficult to get an even weight distribution. Also, fully sprung chassis where both axles need to be driven direct from the motor (no coupling rods) may require a more complicated transmission with floating gearboxes. I don't like the idea of one fixed axle and the other with a pivot in the centre though. Having one side of the chassis fixed and the other pivoting seems far more stable to me.

Lets not get ideological. Whatever seems most suitable for the task in hand!

billbedford

Re: Flexi Chassis an Appreciation

Postby billbedford » Wed May 17, 2017 11:56 am

Knuckles wrote:Something that has always bothered me about giving a CSB a shot is working out the weight prior to entering the values into the spread sheet (or working it out on paper...no chance for me). How are we supposed to know what weight the model sill be once completed and lead stuffed before setting everything up for CSB?

I may be missing something obvious here but other than estimating or throwing the whole kit, some solder and a guessed amount of lead on a scale beforehand I'm at a loss here.


Perhaps by weighing other locos in your collection and getting a feel for the work they can do.

billbedford

Re: Flexi Chassis an Appreciation

Postby billbedford » Wed May 17, 2017 12:00 pm

Knuckles wrote:Something that has always bothered me about giving a CSB a shot is working out the weight prior to entering the values into the spread sheet (or working it out on paper...no chance for me). How are we supposed to know what weight the model sill be once completed and lead stuffed before setting everything up for CSB?

I may be missing something obvious here but other than estimating or throwing the whole kit, some solder and a guessed amount of lead on a scale beforehand I'm at a loss here.


Find the drawbar pull of the biggest train you are likely to run.

The drawbar/adhesive weight efficiency of a CSB loco is around 20%

Therefore you should be aiming for an adhesive weight of around 5 time the maximum likely drawbar pull.

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Re: Flexi Chassis an Appreciation

Postby Will L » Wed May 17, 2017 2:51 pm

Alan Turner wrote:
Knuckles wrote:
I may be missing something obvious here but other than estimating or throwing the whole kit, some solder and a guessed amount of lead on a scale beforehand I'm at a loss here.

:-/


You should be able to have a good guess to start with.

If it turns out lighter or heavier then simply adjust the spring wire diameter. The spread sheet does it all for you. What you need to ensure is that the DISTRIBUTION of the weight stays as originally assumed, i.e. the CoG.


Sorry Knuckles but you are indeed missing something. You don't need to guess or estimate. The loco can be what ever weight it turns out to be, you just have to weight it so, as Alan says, the CofG is in the right place. When you've finished, then you weigh it, feed the real weight back into the spreadsheet to work out what size wires you need. Simpl.....

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Re: Flexi Chassis an Appreciation

Postby Will L » Wed May 17, 2017 3:01 pm

dal-t wrote:Err, I thought it had been made clear that the 4F chassis giving ride height problems isn't a CSB design - or am I missing something (again)?


No that is correct the 4F is definitely not a pucker CSB, as It has a pair of fulcrum points per wheel, but with a single spring wire through all the ones on one side, rather than individual springs per wheel, as discussed above somewhere. A system which might work if the fulcrum points were in the right place, but it appears they aren'the, and we are unsure of the effect of using a single continuous spring in these circumstances.

proto87stores

Re: Flexi Chassis an Appreciation

Postby proto87stores » Wed May 17, 2017 4:09 pm

Will L wrote:
Alan Turner wrote:
Knuckles wrote:
I may be missing something obvious here but other than estimating or throwing the whole kit, some solder and a guessed amount of lead on a scale beforehand I'm at a loss here.

:-/


You should be able to have a good guess to start with.

If it turns out lighter or heavier then simply adjust the spring wire diameter. The spread sheet does it all for you. What you need to ensure is that the DISTRIBUTION of the weight stays as originally assumed, i.e. the CoG.


Sorry Knuckles but you are indeed missing something. You don't need to guess or estimate. The loco can be what ever weight it turns out to be, you just have to weight it so, as Alan says, the CofG is in the right place. When you've finished, then you weigh it, feed the real weight back into the spreadsheet to work out what size wires you need. Simpl.....


And if the C of G turns out to be somewhat off the right place, Hookes Law will give you a (CSB) un-correctable static front-back tilt of some small amount.

Whereas, in the same situation, a purely equalized chassis will stay exactly level, but will have a similarly small different weight distribution on the wheels.

Andy

proto87stores

Re: Flexi Chassis an Appreciation

Postby proto87stores » Wed May 17, 2017 5:22 pm

Armchair Modeller Wed May 17, 2017 11:38 am wrote:I took the view that the world will not come to an end just because I dare to try a CSB chassis. I started with a Mousa chassis, so the thinking was already done for me - apart from maybe needing to swap the spring wires for thinner or thicker ones. That worked fine. Even better, the world really did not come to an end.

Now I am trying a couple of cheap chassis that require me to do all the thinking for myself - using a CSB spreadsheet and the High Level CSB jig. Even if I am not successful, the cost will be minimal, so not worth a lot of worrying about whether I ought to give it a go - or question whether it really will work.


I'm not sure what the minimal cost of an extra jig is, for a new P4 member starting out with one locomotive

As I see it, compensated chassis sound simpler and more predictable, but once you get over 2 axles they quickly become very complicated.


An equalized chassis is EXACTLY predictable - A a well-designed etched equalized chassis can easily be less complicated, even at the largest USA wheel arrangements - e.g. 4-8-8-2 and the less common UK ones - e.g. 2-2-2 and 0-4-4

Ensuring adequate weight on all wheels becomes more and more difficult - as could stability.


Absolutely not. That's fundamentally the basic problem of sprung chassis. And more wheels usually means more stability

I think both compensated and CSB chassis have their place. It is not the black and white issue that some people have portrayed on here - not by a long way.


Compensation has no limits of construction method. Equalization is closer to the black and white alternative for springing. And, where it makes practical sense, I'm proposing a mixture that has equalized chassis and sprung body

I can see how CSBs can make some of the more complicated chassis much easier to build. On very small 4-wheeled shunters compensation has its benefits though - particularly as it can be difficult to get an even weight distribution. Also, fully sprung chassis where both axles need to be driven direct from the motor (no coupling rods) may require a more complicated transmission with floating gearboxes. I don't like the idea of one fixed axle and the other with a pivot in the centre though. Having one side of the chassis fixed and the other pivoting seems far more stable to me.

Lets not get ideological. Whatever seems most suitable for the task in hand!


I agree with the last sentiment. It's the factors underlying the choice of "most suitable" that concerns me.

Andy
Last edited by grovenor-2685 on Wed May 17, 2017 9:13 pm, edited 1 time in total.

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Re: Flexi Chassis an Appreciation

Postby Knuckles » Wed May 17, 2017 8:07 pm

Ok, many thanks to you all for your input.

So what I'm gathering is the main thing really is to just establish the fulcrum points, build it and then simply try out different wire/spring thickness until the desirable spring rate is achieved. If so then great, problem solved.

This helps a lot, thanks.
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Re: Flexi Chassis an Appreciation

Postby Armchair Modeller » Wed May 17, 2017 9:13 pm

Knuckles wrote:Ok, many thanks to you all for your input.

So what I'm gathering is the main thing really is to just establish the fulcrum points, build it and then simply try out different wire/spring thickness until the desirable spring rate is achieved. If so then great, problem solved.

This helps a lot, thanks.


That's certainly how I understand it, as another novice.

Out of curiosity, I just wonder how the experts test their chassis? Do they wait until the body is finished and run the whole lot as one, or have they worked out a way of testing the chassis alone? Thinner CSB springs, for example, to compensate for the lack of body weight, or do they weight the chassis temporarily to simulate a body on top?

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Re: Flexi Chassis an Appreciation

Postby grovenor-2685 » Wed May 17, 2017 9:22 pm

A a well-designed etched equalized chassis can easily be less complicated, even at the largest USA wheel arrangements - e.g. 4-8-8-2 and the less common UK ones - e.g. 2-2-2 and 0-4-4

Andy, you do keep making this sort of remark, but don't present any evidence for us to compare with the complexity of Mike Sharman's flexichas book or the S4 digest. Don't bother with the 0-4-4 or 2-2-2 as they are simple cases, the complexity comes with the big ones.
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