Flexi Chassis an Appreciation

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grovenor-2685
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Re: Flexi Chassis an Appreciation

Postby grovenor-2685 » Thu Feb 16, 2017 4:14 pm

Somewhere among Bertiedog's postings in the RMweb archive there was a better description of the Varney system complete with an illustration from a Varney catalogue. If applied as intended it should not hold everything on the bottom bump stop, the adjustment allows the spring force to be set so it rides at the mid point like a CSB.
Regards

Julian Roberts
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Re: Flexi Chassis an Appreciation

Postby Julian Roberts » Thu Feb 16, 2017 4:51 pm

grovenor-2685 wrote:
The single leaf guitar springs and CSBs do a better job easier, the Brassmaster's coils also used by Comet are also simple if the spring rate is correct for the loco weight.
Regards


Maybe a slight deviation from the thread title but how do you calculate this? Exactoscale springs are sold in three strengths 30 40 & 50g. How strong are Brassmasters ones? Subjectively they feel quite strong. Is the idea of them to rest on the end stop like Gibson ones (but with more downward force perhaps) or to ride in midpoint like a CSB?

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Re: Flexi Chassis an Appreciation

Postby grovenor-2685 » Thu Feb 16, 2017 6:16 pm

My idea is that they should ride in the midpoint or thereabouts, but the two chassis with these in my to do box are some way from the top!
There are three possible adjustments:
1. The top of the hornblock slots can be filed to let the springs sit higher.
2. You can add/remove weight to the loco.
3. You can alter the spring, eg cut coils off and/or stretch it.
All rather more complex than just using a thinner or thicker wire with a CSB, and with a recent article on using a CSB with the brassmasters bearings that may be the best answer.
Regards

Proto87Stores

Re: Flexi Chassis an Appreciation

Postby Proto87Stores » Thu Feb 16, 2017 7:01 pm

billbedford wrote:It really doesn't matter how many people found the introduction of Flexichas an inspiration, the fact remains that the majority of people who build loco kits do not use the system. It is a commercial imperative any manufacturer of loco kits that they should be able to be built rigid using the traditional three rod method of squaring the frames, and all the evidence is that that is the method that the majority use.

While most people here would see this as as sadness, I believe that it really a failure to understand the difficulties that the majority of modellers have with systems based on Flexichas and similar systems. And it is that failure of understanding that underlies much of the animosity against finescale in general and P4 in particular. However understanding such failures should give an insight into how designs can be improved, at least in terms of easy of construction. In a recent post Tony Wright said something to the effect that he had put together a set of working pacific frames, from a kit, in an afternoon and doubted that he could have done the same if he was working in P4. And of course he is right. The way the kit market has developed has meant that newer kits have become more complicated and take longer to build, while there is still a healthy market for older kits which have the virtue of simplicity, if not accuracy.

The question is what is to be done. To my mind there is a need in the market for kits where the mechanics are very much simplified, not beginner's kits, but kits for people that would prefer to to spend more time on the aesthetics of the loco and less on just getting the bloody thing to work. Of course I have my own ideas about this, but I would be interested to know if others are thinking along the same lines.


Image :thumb

With at least some of the fundamentals defined, Lets talk about the real options. I went all the way back to the basic needs, rather than go only half-way and take some past decisions for granted.

billbedford wrote:
You have completely misunderstood the way springs work.


Er no. Not unless all the engineering mechanics, statics and dynamics textbooks are wrong. :o

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. If the spring become unloading in service there is something very wrong with the application that the springs are being put to. I would never expect to see a springs on a model loco either completely unloaded or rigid, after all we are modelling a railway, not all-terrain vehicles.



So why is the +/- 0.5mm in so much of the Society documentation and instructions? Perhaps back in the early days of Flexi-chas, the importance of understanding static deflection on curved grades for was taken into account? Even if it's missing from the later digest. The many larger coarser scale layouts face that issue am lot. For example, In the US, helixes abound.

Besides that, I differ in that I don't see the point in designing suspension that only works for those few people who really don't need it. But the beginners, the modellers with less patience and the "less than fine-scale" modellers don't always have "reasonably well laid track".

And as an engineer myself, I can't possibly justify designing to "typical" conditions rather than"industry standard worst case". It's just asking for being plagued with difficult to discover and fix unreliability.

Then add the ideal situation that the same design will have a much larger market and the economy of scale if it is just as economical and desirable for the coarser scale modellers in 00, EM and by golly, even world-wide HO.

And the first components I found I didn't need at all, were those that require a great deal of expensive to manufacture accuracy and tedious assembly and installation, and that confound the pivot holes of coupling rods. Ie. Hornblocks

Andy

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Will L
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Re: Flexi Chassis an Appreciation

Postby Will L » Thu Feb 16, 2017 7:13 pm

Julian Roberts wrote:
grovenor-2685 wrote:
The single leaf guitar springs and CSBs do a better job easier, the Brassmaster's coils also used by Comet are also simple if the spring rate is correct for the loco weight.
Regards


Maybe a slight deviation from the thread title but how do you calculate this? Exactoscale springs are sold in three strengths 30 40 & 50g. How strong are Brassmasters ones? Subjectively they feel quite strong. Is the idea of them to rest on the end stop like Gibson ones (but with more downward force perhaps) or to ride in midpoint like a CSB?



Four post starting here back in my CSB archive covers this point and ways to use Brassmaster hornblocks with CSBs

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Re: Flexi Chassis an Appreciation

Postby billbedford » Thu Feb 16, 2017 11:48 pm

Proto87Stores wrote:So why is the +/- 0.5mm in so much of the Society documentation and instructions? Perhaps back in the early days of Flexi-chas, the importance of understanding static deflection on curved grades for was taken into account? Even if it's missing from the later digest. The many larger coarser scale layouts face that issue am lot. For example, In the US, helixes abound.


As Keith has pointed out the static deflection is alway positive. There is no ±. It is apples only to sprung systems, all unsprung system have no static deflect as the pivot points for the levers are fixed. As far I know the 0.5mm was a figure plucked out of the air by Chris Penlenton in his first article on springing in MRJ.
Bill Bedford
Mousa Models
http://www.mousa.biz

Proto87Stores

Re: Flexi Chassis an Appreciation

Postby Proto87Stores » Fri Feb 17, 2017 1:43 am

billbedford wrote:
Proto87Stores wrote:So why is the +/- 0.5mm in so much of the Society documentation and instructions? Perhaps back in the early days of Flexi-chas, the importance of understanding static deflection on curved grades for was taken into account? Even if it's missing from the later digest. The many larger coarser scale layouts face that issue am lot. For example, In the US, helixes abound.


As Keith has pointed out the static deflection is alway positive. There is no ±. It is apples only to sprung systems, all unsprung system have no static deflect as the pivot points for the levers are fixed. As far I know the 0.5mm was a figure plucked out of the air by Chris Penlenton in his first article on springing in MRJ.


Yes the static deflection on level flat track is (or should be) at the mid point. I think you'll find Keith was referring to measuring the 1mm from the lower stop or the unloaded fully horizontal wire of a CSB with the loco lifted off the track.

However, an example balanced symmetrical 4 sprung wheel vehicle chassis will have equal positive and negative deflections (and similarly different wheel weighting) across the diagonals on twisted track. Worse, it will also then likely rock.

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 . . . .

Andy

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Re: Flexi Chassis an Appreciation

Postby dal-t » Fri Feb 17, 2017 9:15 am

Proto87Stores wrote: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.


But surely that isn't equivalent to the CSB solution - that would be a single spring linking all four legs (or two linking each pair, if the stool happened to be sitting on rails as our vehicles do), wouldn't it?
David L-T

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Re: Flexi Chassis an Appreciation

Postby billbedford » Fri Feb 17, 2017 10:42 am

Proto87Stores wrote:Yes the static deflection on level flat track is (or should be) at the mid point. I think you'll find Keith was referring to measuring the 1mm from the lower stop or the unloaded fully horizontal wire of a CSB with the loco lifted off the track.


No he wasn't, he was talking about the deflection that is designed into the springs to accommodate the weight given the spring rate and the expected dynamic range of deflection. For locos the convention is to use a value of 0.5 mm, But other values would work equally well, indeed it is possible for different spring rates, and thus static deflections to be used on different axles.

Since the axle does not need to be attached to the spring the position of the bottom stop is entirely arbitrary.

However, an example balanced symmetrical 4 sprung wheel vehicle chassis will have equal positive and negative deflections (and similarly different wheel weighting) across the diagonals on twisted track. Worse, it will also then likely rock.

A similar vehicle chassis that is "merely" fully equalized will be as firm and stable as on absolutely flat track.


For either those segments to be true, the height of the centre of gravity has to be taken in account. It is perfectly possible to build a full compensated model that will tip over at the slightest sign of can't.

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 . . . .



...yes but only if inappropriate spring rates are chosen. The are very many tables in the world supported on hard rubber springs that are usually judged to be stable enough to handle bowls of soup.
Bill Bedford
Mousa Models
http://www.mousa.biz

Julian Roberts
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Re: Flexi Chassis an Appreciation

Postby Julian Roberts » Fri Feb 17, 2017 12:08 pm

Thanks Will and Keith for your help on my question earlier.Is there a link to the article you mentioned Keith?

To change the subject slightly, Mike Sharman lays great stress on the axle being able to tilt,

due to the V groove


in the bearing (or bushes as he calls them) (Page 7 of his book)

However I have noticed that recent hornblock bearings I have bought from Comet, Brassmasters and Hi Level have not had the V groove apparent
in my earlier MJT and Gibson ones. The groove is straight sided; any tilt available is due to the metal on which it slides being narrower. Photos follow. I have used the Hi Level ones in the kit from the same firm I am making and the axles patently can
tilt to an extent, and the loco works fine on test tracks (of very limited length) as I showed earlier on this thread.

I am just putting this thought forward as a point of possible discussion and interest.... :?: If the bearings are no longer being made with a V groove, is that an improvement? - I venture to suggest it is not, but I may exaggerate in my mind the amount of tilt by and large needed.

20170217_075053-1.jpg
Hi Level

20170217_074504-2.jpg
Attachments
20170217_075937.jpg
20170217_080328-1.jpg
Gibson
20170217_090939.jpg
P8 Mike's book

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Re: Flexi Chassis an Appreciation

Postby Will L » Fri Feb 17, 2017 1:57 pm

Julian Roberts wrote:...Mike Sharman lays great stress on the axle being able to tilt,

due to the V groove


in the bearing (or bushes as he calls them) (Page 7 of his book)

However I have noticed that recent hornblock bearings I have bought from Comet, Brassmasters and Hi Level have not had the V groove apparent
in my earlier MJT and Gibson ones. The groove is straight sided; any tilt available is due to the metal on which it slides being narrower. Photos follow. I have used the Hi Level ones in the kit from the same firm I am making and the axles patently can
tilt to an extent, and the loco works fine on test tracks (of very limited length) as I showed earlier on this thread.

I am just putting this thought forward as a point of possible discussion and interest.... :?: If the bearings are no longer being made with a V groove, is that an improvement? - I venture to suggest it is not, but I may exaggerate in my mind the amount of tilt by and large needed.


The thought has crossed my mind also Julian, I have even been known to pass a triangular file down the groves just in case, but experience suggests, with the high level block at least, that there is sufficient difference between the grove in the axle block and the metal of the horn guide to provide enough movement. The amount of tilt required really is quite small. Another case of enough being enough and there being no advantage in exaggerating it.

One of the features of fexichasi was that unless you specifically avoided it, they tended to have impressively large amounts of relative movement, which serves no useful purpose on track (except the ability to surmount the occasional match stick which, apparently, some people leave lying about their layouts) and just make it harder to rerail them. CSBs are so much more controlled! The Sharman square hornblocks had quite deep groves, and obviously (?) the deeper the grove the more clearance is required. At a push doubtless somebody could prove all this mathematically but as I'm happy that the way I do it works, it wont be me.

Edited for spelling

Proto87Stores

Re: Flexi Chassis an Appreciation

Postby Proto87Stores » Fri Feb 17, 2017 3:17 pm

dal-t wrote:
Proto87Stores wrote: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.


But surely that isn't equivalent to the CSB solution - that would be a single spring linking all four legs (or two linking each pair, if the stool happened to be sitting on rails as our vehicles do), wouldn't it?


That's a very fair question. But I'm trying not to get to CSB's until I've tried to make all the physics of using single springs per wheel agreeable to the interested folk.

CSB's have multiple qualities that have/cause interaction between multiple wheels, with a little, but variable, bit of equalization thrown in. So they are more complex to analyze than just a spring per wheel. But they do depend on also having hornblocks to keep the wheel movement vertical. So they aren't an inexpensive or novice solution.

In the case of the restaurant table, you'd be stringing a single wire through four firm pegs sticking up out of the floor, with loose holes fixed in a square about 6 inches off the floor. Then turning the table 45 degrees and placing the bottom of each (shortened by 6 ") leg in the middle of each section of wire between its two pegs.

Do you immediately think of that as an obvious, simplest, practical and stable solution for a table on an uneven floor?

Andy

Proto87Stores

Re: Flexi Chassis an Appreciation

Postby Proto87Stores » Fri Feb 17, 2017 5:19 pm

billbedford wrote:
Proto87Stores wrote:Yes the static deflection on level flat track is (or should be) at the mid point. I think you'll find Keith was referring to measuring the 1mm from the lower stop or the unloaded fully horizontal wire of a CSB with the loco lifted off the track.


No he wasn't, he was talking about the deflection that is designed into the springs to accommodate the weight given the spring rate and the expected dynamic range of deflection. For locos the convention is to use a value of 0.5 mm, But other values would work equally well, indeed it is possible for different spring rates, and thus static deflections to be used on different axles.
{1}
Since the axle does not need to be attached to the spring the position of the bottom stop is entirely arbitrary.

However, an example balanced symmetrical 4 sprung wheel vehicle chassis will have equal positive and negative deflections (and similarly different wheel weighting) across the diagonals on twisted track. Worse, it will also then likely rock.

A similar vehicle chassis that is "merely" fully equalized will be as firm and stable as on absolutely flat track.

{2}
For either those segments to be true, the height of the centre of gravity has to be taken in account. It is perfectly possible to build a full compensated model that will tip over at the slightest sign of can't.

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 . . . .



...yes but only if inappropriate spring rates are chosen. The are very many tables in the world supported on hard rubber springs that are usually judged to be stable enough to handle bowls of soup.

{3}

I didn't want to get general agreement by having to explain lots of individual non-relevant examples, but I think it may be necessary to answer these in order to move forward.

RE {1}. Where you place the datum point does not affect the maths of relative movement.
RE {2}. Track Cant is a leaning to one side. Track Twist is having different cants at different points along the track. My statement was about twist and symmetrical twist (no net cant) for that particular circumstance to be most obvious to everyone else.

You certainly could build a diabolical chassis that has it c of g on the edge of cant stability, so that it would tip over on the slightest cant. (see digest). The only problem with that as an example is that if that same chassis was sprung instead, it would tip over earlier, and be completely tipping unstable even on flat track.

RE {3}. If you can find small block of "hard rubber" that will be stiff to hold the weight steady, yet flex enough to take up 0" - 1/2" of leg movement on a typical uneven restaurant floor, you'll make your fortune. And Physics history. The practical rubber leg bases of today are mounted on screw threads as well, to adjust the effective static leg length instead of springing.. That wouldn't be much help on a model.

Andy

Proto87Stores

Re: Flexi Chassis an Appreciation

Postby Proto87Stores » Fri Feb 17, 2017 5:54 pm

Will L wrote:
Julian Roberts wrote:...Mike Sharman lays great stress on the axle being able to tilt,

due to the V groove


in the bearing (or bushes as he calls them) (Page 7 of his book)

However I have noticed that recent hornblock bearings I have bought from Comet, Brassmasters and Hi Level have not had the V groove apparent
in my earlier MJT and Gibson ones. The groove is straight sided; any tilt available is due to the metal on which it slides being narrower. Photos follow. I have used the Hi Level ones in the kit from the same firm I am making and the axles patently can
tilt to an extent, and the loco works fine on test tracks (of very limited length) as I showed earlier on this thread.

I am just putting this thought forward as a point of possible discussion and interest.... :?: If the bearings are no longer being made with a V groove, is that an improvement? - I venture to suggest it is not, but I may exaggerate in my mind the amount of tilt by and large needed.


The thought has crossed my mind also Julian, I have even been known to pass a triangular file down the groves just in case, but experience suggests, with the high level block at least, that there is sufficient difference between the grove in the axle block and the metal of the horn guide to provide enough movement. The amount of tilt required really is quite small. Another case of enough being enough and there being no advantage in exaggerating it.

One of the features of fexichasi was that unless you specifically avoided it, they tended to have impressively large amounts of relative movement, which serves no useful purpose on track (except the ability to surmount the occasional match stick which, apparently, some people leave lying about their layouts) and just make it harder to rerail them. CSBs are so much more controlled! The Sharman square hornblocks had quite deep groves, and obviously (?) the deeper the grove the more clearance is required. At a push doubtless somebody could prove all this mathematically but as I'm happy that the way I do it works, it wont be me.

Edited for spelling


I agree that the ability of the axles to (freely) tilt is critical. You wouldn't have suspension otherwise.

I would quibble with the idea that amount of tilt required is quite (very?) small ( do you have numbers?) for the general, less skilled at track laying, population. Again it depends on track flatness and AFAIK, there has never been a specification of worst track flatness (yet) in any small scale model railway "standard".

CSB's are controlled by having a relatively short throw suspension overall. You'd achieve the same control by putting short throw stops on equalized movement, with no ill effect other than the lesser ability to only handle the same size bumps as CSB's.

Andy

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Re: Flexi Chassis an Appreciation

Postby grovenor-2685 » Fri Feb 17, 2017 7:33 pm

Julian Roberts wrote:Thanks Will and Keith for your help on my question earlier.Is there a link to the article you mentioned Keith?

Here you go, http://www.rmweb.co.uk/community/index.php?/topic/29013-sprung-chassis-principles-and-easy-applicaton/#entry306663
Regards

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Re: Flexi Chassis an Appreciation

Postby Will L » Sat Feb 18, 2017 12:43 am

Proto87Stores wrote:CSB's have multiple qualities that have/cause interaction between multiple wheels, with a little, but variable, bit of equalization thrown in. So they are more complex to analyze than just a spring per wheel. But they do depend on also having hornblocks to keep the wheel movement vertical. So they aren't an inexpensive or novice solution.

Nice to see you agreeing with Bill, and I well see why both of you are keen to appeal to all levels of modelling ability, but remember where you are. To achieve reliable running not just in terms of sayimg on but also electrical continuity, many experienced modellers in P4, EM and 00 find suspension systems desirable, and since the advent of Fexichassis and functional hornblocks, eminently doable. Their relevance to the novice is not really the point.

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Re: Flexi Chassis an Appreciation

Postby Julian Roberts » Sat Feb 18, 2017 8:45 am

Keith thanks but your link took me to the Varney system, I was wondering if you could give me a link from your mention here:
grovenor-2685 wrote:All rather more complex than just using a thinner or thicker wire with a CSB, and with a recent article on using a CSB with the brassmasters bearings that may be the best answer.
Regards


But maybe you are talking about what Will has written and given me the link to...?

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Re: Flexi Chassis an Appreciation

Postby Julian Roberts » Sat Feb 18, 2017 9:09 am

Will L wrote:
The Sharman square hornblocks had quite deep grooves, and obviously (?) the deeper the groove the more clearance is required. At a push doubtless somebody could prove all this mathematically but as I'm happy that the way I do it works, it wont be me.

Edited for spelling


Will I assume you mean here that a deeper groove will increase the up and down travel thus requiring even more clearance. I agree in that at the topmost position things are going to be clouted that wouldn't normally - e.g. steps fouling crankpins, or clearance at the end of slide bars for the connecting rod at its maximum up or down wheel crank position. I just assume that in normal running if I have done it as per the information (e.g. crank throw), drawing, and kit as best as I can, in normal running these things won't happen, borne out by experience so far.

However in general we may occasionally have moments of unrealistic amount of suspension movement being required particularly at baseboard joins, but I agree that the full travel of the bearings is more than necessary.

I am going to stick to Flexichas until or unless I buy a kit where CSBs are the default suspension. My Barclay is the first one without a fixed driven axle and preliminary running shows it to be a step change smoother over pointwork. But I quite see that CSB is or can be a step further in quality.

Bill and Andy's discussion left me (unlike Jeeves having an average hat size) behind long ago. But I think one thing Bill said was that with Flexichas' fixed axle it couldn't be defined how much weight was carried by each axle. Your drawing on a concurrent thread, with Keith's NB alteration to the fulcrum points, showed a Flexichassis with exactly equal axle loading given a central CofG, as you said there.

viewtopic.php?f=19&t=5293

JP.jpg
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Alan Turner
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Re: Flexi Chassis an Appreciation

Postby Alan Turner » Sat Feb 18, 2017 10:53 am

Julian Roberts wrote:
Will L wrote:
Bill and Andy's discussion left me (unlike Jeeves having an average hat size) behind long ago. But I think one thing Bill said was that with Flexichas' fixed axle it couldn't be defined how much weight was carried by each axle. Your drawing on a concurrent thread, with Keith's NB alteration to the fulcrum points, showed a Flexichassis with exactly equal axle loading given a central CofG, as you said there.

viewtopic.php?f=19&t=5293

JP.jpg


That diagram would not result in equal axle loading. The centre axle would carry half the load and the outer axles a quarter of the load.

You have to have the pivots at 1/3 positions, as Keith has said, for equal axle loads.

Turning to the four legged table. Putting springs under each leg may eliminate the rocking but it will not result in the table being horizontal. That will depend on the load distribution on top of the table and the unevenness of the floor beneath.

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.

regards

Alan

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Re: Flexi Chassis an Appreciation

Postby grovenor-2685 » Sat Feb 18, 2017 11:04 am

But maybe you are talking about what Will has written and given me the link to...?

Sorry Julian, you are right, Will gave you the link for that one, it was just on my mind that the Varney article mentioned earlier was not so clear.
Regards

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Re: Flexi Chassis an Appreciation

Postby Will L » Sat Feb 18, 2017 11:34 am

Julian Roberts wrote:
Will L wrote:
The Sharman square hornblocks had quite deep grooves, and obviously (?) the deeper the groove the more clearance is required. At a push doubtless somebody could prove all this mathematically but as I'm happy that the way I do it works, it wont be me.


Will I assume you mean here that a deeper groove will increase the up and down travel thus requiring even more clearance.


Actually no, it is purely that the deeper the grove the greater its potential to restrict the amount of tilt available. The grove on the Highlevel hornblock are significantly shallower than that in the Sharman original.

...Bill and Andy's discussion left me (unlike Jeeves having an average hat size) behind long ago. But I think one thing Bill said was that with Flexichas' fixed axle it couldn't be defined how much weight was carried by each axle.


Afraid you read Bill wrong, as it is always possible to work out the weigh carried on each wheel of a compensated chassis by back of the fag packet principle of moments type calculations, given that you know where the CofG is. This is not true for a sprung chassis, hence the fancy spreadsheets

And Alan is correct about the weight distribution on that chassis (assuming the CofG is Central)

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Re: Flexi Chassis an Appreciation

Postby Will L » Sat Feb 18, 2017 11:38 am

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

Proto87Stores

Re: Flexi Chassis an Appreciation

Postby Proto87Stores » Sat Feb 18, 2017 3:16 pm

Will L wrote:
Proto87Stores wrote:CSB's have multiple qualities that have/cause interaction between multiple wheels, with a little, but variable, bit of equalization thrown in. So they are more complex to analyze than just a spring per wheel. But they do depend on also having hornblocks to keep the wheel movement vertical. So they aren't an inexpensive or novice solution.

Nice to see you agreeing with Bill, and I well see why both of you are keen to appeal to all levels of modelling ability, but remember where you are. To achieve reliable running not just in terms of sayimg on but also electrical continuity, many experienced modellers in P4, EM and 00 find suspension systems desirable, and since the advent of Fexichassis and functional hornblocks, eminently doable. Their relevance to the novice is not really the point.


I actually more than agree with Bill and Ted (Zee's Knees) on two issues. The second inspired me greatly and I'd like to credit them for it. 8-)

But I can't yet get past Bill's strewing of alt-banana skins on the pavement ;) re understanding wheel movement physics yet. So there's no point in going that far as in my case the value of the second advance depends on it.

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.

If you want to see them run, then visit
http://www.proto87.com/Proto87_track_holding_demo.html

Andy

Proto87Stores

Re: Flexi Chassis an Appreciation

Postby Proto87Stores » Sat Feb 18, 2017 3:24 pm

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.

Andy

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Allan Goodwillie
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Re: Flexi Chassis an Appreciation

Postby Allan Goodwillie » Sat Feb 18, 2017 10:01 pm

I am enjoying this discussion and all the theoretical information. It reminds me of a memorable evening sitting alongside Derek Genzel one Scalefour Society dinner long, long ago and Derek having all the figures in his head which was impressive and all the conversation being one way, which was less so, however interesting just the same.

A few years later and as a member of the East of Scotland 4mm Group I found myself for several years at Scalefourum on the Scalefour Society test rig. Derek had quite a bit to do with the construction of the rig and the test track. Since it was up in Scotland in between times it did allow those who wanted, to test their own locos if they wished and one or two of us did during that time.

My goodness what an eye opener it turned out to be in so many ways and in particular the weighting on individual axles - one of the gauges allowed a reading of each axle in turn. Freedom of the bearings being crucial. It was also possible to give some read out of tractive effort. The test track had worst case scenarios built in and a fair bit of effort had been put in to its construction.

There was a competition each year, I think to encourage individuals to take part. It could be very disheartening for some, I remember that one year we had one individual who did not have a layout at home turn up with a range of several large locomotives (about 9 or 10 if I remember correctly) None passed the test track, but we were able to tell him just where the problems lay and he went off seemingly content. I would be very interested to know if he was able to correct all the faults as his engines would have formed a very impressive stud of locomotives.(Mainly Pacifics) Others would go off a bit crest fallen as their favourite engine failed to come up trumps - some locos looked wonderful, but ran poorly, but visa versa was also true.

I remember being very disappointed :cry: with a new locomotive which I had just finished, a J37 which trundled about OK, but when it came to weight distribution seemed to have virtually none on the centre pair of drivers! (It was sprung as most of my locos had been since I started way back in the early 70's.)

Most of the bigger engines came to grief on the test track with bogies and pony trucks and trailing wheels giving most trouble. :shock: A consequence of all this was that a simple 0-6-0T seemed to win the trophy each year, perhaps not too surprising.

I think we should consider the beginner reading a thread like this as at the beginning they simply want a locomotive which will will stay on the track and pull a reasonable length of train and hopefully run slowly as well as at speed with equal ease. Our Livingston Starters Group started with a run by of engines. Each engine had to run very slowly and also at speed and they had to guess just what suspension system had been used. The results were interesting as they all found it very difficult to tell. An experienced eye could probably tell, but they all would have been very happy to have any of the locos running past in terms of behaviour. ;)

In the West Scotland 4mm Group's "Build a loco" thread you will notice that I did not run a thread on using springy beams. Will's thread is very good and I had no wish to double up on it, but equally 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.

It is possible to have too perfect a glide, a Y9 without a distinctive waddle is not correct in my book, a K3 at speed without its rear end giving the crew "laldy" seems equally wrong. The real locomotive was a dynamic thing in terms of weight distribution as water in boiler and tanks varied as well as coal carried in the fire box and ash building up in the smoke box, but even empty they had mass which would keep them on track, so 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. Me, I've built locos using all the systems, but have not developed a preference for any single system, rather choosing the system according to the locomotive to be built. :)

The test rig and track have now been discredited by some - was this a consequence of the results with certain engines I wonder? Derek is no longer with us, but I am sure that he would have had a strong opinion as to suspension/compensation, etc. :)

It struck me that the track is an even more crucial part of the system than I had fully realised as you did not want your locos coming across the extremes of track found in the test track. I am covering track making on the Livingston starters thread soon. Our teach in for the West Group has paid dividends as all the members have had a go at making points and laying track over the last year and are turning into competent builders in this area, so the same course will be covered with the Starters group over the next few months. I am not suggesting we go on to discussing track at this point by the way.


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