COG and suspension calculation 4-6-0

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jon price
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COG and suspension calculation 4-6-0

Postby jon price » Wed Apr 12, 2017 2:08 pm

This 4-6-0 could be built rigid, but I'd like it to have suspension. I'm fairly clear that the bogie can stay rigid (I could use the actual equalising beams, but I probably won't). My problem is how the COG will sit with the drivers. As far as I can gather from erudite discussion elsewhere If I use equalising beams and a fixed rear axle the COG would have to be just about on the first boiler band and so into the front of the firebox where the motor would logically sit. If I use CSB the COG would need to be just forward of the first boiler band. Either of these would significantly limit the overall weight I could add in. I know from Will's thread elsewhere there is also a danger of the front sitting too high and weighting to prevent that would move the COG further forward than would be efficient for the suspension. Any (useful) advice or ideas?
loco.jpg

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zebedeesknees
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Re: COG and suspension calculation 4-6-0

Postby zebedeesknees » Wed Apr 12, 2017 6:20 pm

One can receive from the CLAG website on the subject the impression that the positions of the fixed anchors and the center of mass, or gravity if you must, is of necessity of a precision that is in fact only desirable. A difference of a couple of mm in the placing of the inner anchors, or 10mm in the position of the CofM will make far less difference to the the ride and haulage than fitting equalising compensation.

For the bogie, have a look at http://www.clag.org.uk/class2p-bill.html

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Re: COG and suspension calculation 4-6-0

Postby Julian Roberts » Wed Apr 12, 2017 7:05 pm

Looks like its a tender engine. How about hooking that on resting the front on the loco back. EMGS coupling assembly allows tender to tilt relative to loco. Rear wheels of tender carry its rear weight. Then boiler towards front can be weighted too.

Just a quick thought... :?:

edit
obviously plenty of weight in the front of the tender and weight in boiler in front of motor etc. Each to balance the other.

On another edit I would be worried about all that front end swinging round a curve unless the bogie can provide guidance...which means springing it down...which means more weight in the boiler... :arrow: :?: :idea:
Last edited by Julian Roberts on Wed Apr 12, 2017 7:37 pm, edited 1 time in total.

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Jol Wilkinson
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Re: COG and suspension calculation 4-6-0

Postby Jol Wilkinson » Wed Apr 12, 2017 7:26 pm

Jon,

if that's the BIWO LNWR Bill Bailey kit, you could use the LRM sprung bogie I designed for the Jubilee. It should be possible to pre-load the bogie (adjustable with shims or a screw mounting) to carry some weight but leaving most on the coupled axles.

I don't know if the CLAG spreadsheet can provide a calculation for that approach.

Jol

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jon price
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Re: COG and suspension calculation 4-6-0

Postby jon price » Wed Apr 12, 2017 8:12 pm

Jol Wilkinson wrote:Jon,

if that's the BIWO LNWR Bill Bailey kit, you could use the LRM sprung bogie I designed for the Jubilee. It should be possible to pre-load the bogie (adjustable with shims or a screw mounting) to carry some weight but leaving most on the coupled axles.

I don't know if the CLAG spreadsheet can provide a calculation for that approach.

Jol

Jol,
It is Nick Easton's Bill Bailey, yes. i bought one of your bogies with the intention of putting it under a Brassmasters Precursor, but I might try it here and then get another for that. I'm not clear how using shims or a screw will keep the nose end at the right height though. Most of the CLAG examples appear to avoid the issue of bogies. Any 0-6-0 solution can't posibly be valid.

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Jol Wilkinson
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Re: COG and suspension calculation 4-6-0

Postby Jol Wilkinson » Wed Apr 12, 2017 9:12 pm

Jon,

the springing on the bogie will take some of the weight at the front of the loco. In the original design for the 4-4-0 Jubilee I had to assume that most OO and EM builders would go for rigid driving axles, so springing the bogie axles and mounting it with a bit of pre-load would keep it on the track while keeping most of the weight on the drivers. The Jubilee chassis also easily lends itself to compensation with a "fixed" rear axle and rocking front axle, while the bogie does its stuff as before.

The difficulty with CSBs is knowing how much load the bogie carries and how to allow for this in the calculations. The wires used for the bogie springs are easily replaced so different thicknesses can be tried. By increasing/decreasing the pre-load on the bogie - by slightly moving it up and down in relation to the main frames - the load carried by it can be changed. That's what I meant by adding/removing shims to increase/decrease the pre-load on the bogie. Alternatively a screw mounting which could be wound up/down would do the same thing.

Perhaps a way forward here might be to build the LRM sprung bogie, weight it until the springs are deflected a specific distance and subtract that weight from the overall loco weight and adjust the COG/COM accordingly. Then use the CLAG spreadsheet for a 0-6-0 to work out the CSB anchor locations. Assemble the model with the bogie "shimmed" to recreate the same spring deflection.

I have a Brassmaster 4-6-0 Experiment to build for which I have a set of AGW milled frames, which would lend themselves to a CSB set up, but so far it has remained firmly in the To Do collection until I can work out how to do it - or someone else works it out. All the examples on the excellent CLAG site, with the exception of a 2-8-0, appear to be of 0-6-0s so bogie locos are noticeable by their absence. Does that indicate that the application of CSBs to 4-4-0 and 4-6-0s has proved too daunting?



Jol

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Russ Elliott
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Re: COG and suspension calculation 4-6-0

Postby Russ Elliott » Wed Apr 12, 2017 11:06 pm

jon price wrote:Most of the CLAG examples appear to avoid the issue of bogies. Any 0-6-0 solution can't posibly be valid.

Yes, it can, Jon. Jol is correct. See http://www.clag.org.uk/beam-annex3.html ... components

Changing tack completely, and in response to your OP, it would be useful to know where the prototype's CofG is (from the axle weights and the wheelbase dimensions). If you are wedded to a fixed axle and twin beams for the other drivers, I think you might gain better weighting opportunities if the fixed axle was the front driver. (Much will depend of course on the real estate of the transmission.)
Last edited by Russ Elliott on Thu Apr 13, 2017 12:05 am, edited 1 time in total.

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Will L
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Re: COG and suspension calculation 4-6-0

Postby Will L » Wed Apr 12, 2017 11:54 pm

Jon

I can give you quite a detailed answer on this but I've been busy writing you a long answer on a different thread. I'll come back to it this tomorrow, hopefully, but it would be useful to know what sort or drive you have in mind, as the location of the motor will affect significantly how much weight you can get over the driving wheels. Did you see essdee's (Steve's Duckworth) tender dives at Scalefour north?

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Re: COG and suspension calculation 4-6-0

Postby dal-t » Thu Apr 13, 2017 7:35 am

Don't forget in your weight calculations to allow for replacing the undersized boiler with a piece of 20mm diameter tube, which could change the distribution significantly. I personally would not recommend the 'hung' tender approach - although I know others love it, years of building 'em that way in my EM days convinced me the main effect is to stop the loco ever moving realistically (but I like Will's idea of tender 'dives' - presumably that's what happens when they come unhitched?). :)
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Jol Wilkinson
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Re: COG and suspension calculation 4-6-0

Postby Jol Wilkinson » Thu Apr 13, 2017 8:02 am

David,

Is the supplied etched boiler under size? I haven't built a Bill Bailey but wasn't aware that there was an error.

The attached photo shows a BB constructed for John Redrup by Roger Stapleton, builder of the "LNWR Steam Shed 901" OO layout. I don't know too much about it, but expect it was build from the kit "as supplied" but with a fixed rear driven axle and single beam compensation on the front two. It has run satisfactorily on London Road at several exhibitions although hasn't been asked to haul much and I haven't noticed how well it "rides".

LNWR 1400 Class Bill Bailey.jpg
BIWO CLass 1400


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Re: COG and suspension calculation 4-6-0

Postby Armchair Modeller » Thu Apr 13, 2017 9:04 am

As a complete novice in these things, my advice is hardly worthy of consideration.......

......however, glancing at the loco I wonder if you could treat the drivers as a kind of power bogie, just like a diesel. The chassis would then be a kind of Co-Bo, except that the front bogie is unpowered. I guess it would make the CSB calculation much easier, if nothing else.

I guess it would depend on how much space there is for the drivers to swing from side to side and how tight the curves are on the layout.

Probably a silly idea ;)

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jon price
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Re: COG and suspension calculation 4-6-0

Postby jon price » Thu Apr 13, 2017 9:33 am

I don't believe the boiler to be undersized, and in any case stuffing a sheet nickel silver boiler with lead is likely to be potentially heavier than just using a heavier guage tube isn't it? As far as motors and prototype are concerned, this is a four cylinder compound with both sets of pistons acting on the front axle, but without involving exotic extended drive trains the most likely way to motorise it is going to be a motor driving the rear axle. A tender-riser and underfloor cardan drive would be intriguing but I haven't embarked on any investigation of this method and I suspect it could be beyond my (meagre) design and construction ability. (The reason I'm looking at this is because another project has stalled pending working out how to construct a peculiar slidebar/crosshead assembly) This could be an interesting testbed if my purpose in life was to experiment with suspension systems rather than building model trains as essentially the same loco superstructure can be produced as a 4-6-0 ("Bill Bailey"), an 0-8-0 (B class) with a front overhang, or a 2-8-0 (E class). I do aspire to building them all at some stage, but whether this actually happens... I think I will follow Jol's suggestion about building the bogie first, or at least after the footplate as the reason I started with this loco is to see whether I could make the switcback footplate using the jig in the kit. With hindight perhaps I should have started with the B class which has the same footplate but is just an 0-8-0...

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Re: COG and suspension calculation 4-6-0

Postby Julian Roberts » Thu Apr 13, 2017 10:00 am

dal-t wrote:. I personally would not recommend the 'hung' tender approach - although I know others love it, years of building 'em that way in my EM days convinced me the main effect is to stop the loco ever moving realistically....


David I expect my contribution to this thread is fairly irrelevant, but as you mention the tender thing, I haven't noticed any unrealistic movement nor to my knowledge has anyone else on my two such set ups in regular operation. Given modifying the EMGS coupling assembly so that the coupling does not swing but only allow tilt between the two vehicles I can't see how loco movement can be affected...?

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Re: COG and suspension calculation 4-6-0

Postby dal-t » Thu Apr 13, 2017 2:48 pm

Jol Wilkinson wrote:David,

Is the supplied etched boiler under size? I haven't built a Bill Bailey but wasn't aware that there was an error.


Jol, you may remember that it was Roger who pointed out that the boiler comes out at 18.5mm rather than 20mm - unfortunately he only discovered after he had soldered it up, but warned others to beware of this 'undocumented feature'.

Julian Roberts wrote:Given modifying the EMGS coupling assembly so that the coupling does not swing but only allow tilt between the two vehicles I can't see how loco movement can be affected...?


Julian, you may well be right if using the EMGS coupling thingy - my builds probably pre-date that being available, because I don't remember it featuring in any sales sheets I saw, so they were all based on the peg in slot on bolster system. This certainly made my stud 'waddle' distinctively. although that may or may not have been prototypical in a couple of instances. My preference these days is very largely with tank locos for (very minor) branch line operation, so it's not an issue I've grappled with for a decade or two.
David L-T

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jon price
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Re: COG and suspension calculation 4-6-0

Postby jon price » Thu Apr 13, 2017 4:28 pm

OK it appears I need a 20mm boiler. But to get back to the suspension: I'm still no wiser as to how I calculate the CSB. Do I
a) calculate as though it was an 0-6-0, with the COG above the central axle, then just move the COG slightly forward to move some weight onto the bogie whilst sticking my tongue out of the corner of my mouth
b) treat the bogie attachment point as an axle, calculate as if it were an 0-8-0 with 25% on each axle, but end the beam at the fulcrum between the driven wheels and the bogie (remembering the bogie is idependently sprung) as though it was an 0-6-0, leaving the COG centered on the whole nominal wheelbase,
c) carry out choice b,with the COG central to the nominal four axles, but in the spreadsheet skew it so the weight is only evenly distributed across the driving wheels, with the bogie "axle" taking less than its fair 25% (maybe 10%, 30% 30% 30%)

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Russ Elliott
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Re: COG and suspension calculation 4-6-0

Postby Russ Elliott » Thu Apr 13, 2017 6:11 pm

It's (a), Jon.

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Will L
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Re: COG and suspension calculation 4-6-0

Postby Will L » Thu Apr 13, 2017 9:27 pm

Strangely enough, our old mate Armchair, as Knuckles likes to call Richard, comes closest to what I think is the easiest way of doing what is required when he said

...however, glancing at the loco I wonder if you could treat the drivers as a kind of power bogie, just like a diesel. The chassis would then be a kind of Co-Bo, except that the front bogie is unpowered. I guess it would make the CSB calculation much easier, if nothing else.
... Probably a silly idea ;)


Not so silly.

Assuming you do want some loco weight on the bogie, and with this prototype I really think you will, there are two theoretical solutions.

One is to treat the bogie pivot point as another axle and set it up as a 4 axle CSB. This would put 25% of the loco weight on the bogie. The CofG is located as normal. However you then have to find a way of attaching the bogie and its pivot point to the two CSB wires so the bogie stays in the right place for and aft, and then, arrange that the hight from wheel rims to the fulcrum under the wire for the bogie is the same as for all the other wheels. Not easy with a rigid bogie and distinctly tricky with a sprung one. I'm sure this must be possible but I have yet to see a working example.

The second way is pretty much as Richard suggests and corresponds, as Russ Says, to your option a. But we should be able to avoid the sticky out tongue bit.

The process is as follows if you want to dictate how much weight falls on the bogie

  1. Design the CSB over the 6 driving wheels as if it was an ordinary 0-6-0. You will need to take note where the loco CofG for a 0-6-0 would be. To try and avoid confusion (some hope) I will call this the Centre of Load (CofL) for the CSB chassis.
  2. The bogie, which can be sprung, rigid or compensated, it matters not, will take its load at its pivot point which is it's CofL. There needs to be the space for a washer or two between the bogie and the bogie pivot point.
  3. You then work out (measure) the distance between the two CofL points.
  4. You decide what percentage of the loco's body weight you want to carry on the bogie. (15% to 20% on the bogie is normal I think, but I wouldn't be pedantic about that).
  5. The loco's real CofG must lie that percentage of the way from the Chassis CofL to the Bogie CofL. (Say you wanted 20% of the loco weight on the bogie (i.e.1/5), and the two CofL are 50 mm apart, then Loco CofG must be 10mm forward of the chassis CofL (1/5 of 50)
  6. Ballast the loco body so the CofG is in the required place, weigh it and work out the CSB chassis share of the weight.
  7. Substitute the weight to be carried on the CSB back into the spreadsheet and use that to work out the right size of wire. Fit that size wires to the CSB
  8. Pack up the bogies pivot so the loco sits level as can be (put a 300mm rule on the footplate and measure the height to the rail head at both ends)
And that's the job done. You will be one of the few people about who aren't just guessing how much weight is on the bogie. I was a bit surprised when I first realised that the suspension, or lack of it, fitted to the bogie has no influence on the weight it will carry, or the eventual ride hight of the loco, so the choice of bogie suspension is purely personal preference.

This all works because of the fact that a simple CSB chassis is designed to have the loco CofG at a specific place and the chassis will only sit level if the CofG is in the right place. More importantly from the point of view of fitting a load bearing bogie, the converse is also true. That is if the chassis is sitting level then the weight it is carrying is being distributed as the CSB calculation intended. If you would like to understand how and why this works you should read this thread CSBs a question of Gravity which contains this summary diagram which some may find self explanatory
Image

Or you can just take my word for it.

I asked the question about where the drive will be, and suggested you think about tender drives because I suspect there may be difficulties in getting enough weight at the back end of the loco to counter balance that long front overhang, when most of the boiler space over the driving wheels is full of motor. Alternatively you can weight the loco as best you can, work out where the real CofG comes between the two CofL and just accept that that percentage of the weight will be carried by the bogie.

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jon price
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Re: COG and suspension calculation 4-6-0

Postby jon price » Thu Apr 13, 2017 9:55 pm

thanks Will
This makes a lot of sense. You are right that there isn't much space for motor, gearbox AND weight given the placement of axles. I know Chris at High Level has made a tender drive unit which makes running the drive shaft low under the floor straightforward because I remember seeing something about it on his stand at Scalefour North, but I can't find any information on his site or by web searches. Anyone got a link to info before I send Chris a begging email?

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Russ Elliott
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Re: COG and suspension calculation 4-6-0

Postby Russ Elliott » Thu Apr 13, 2017 10:41 pm

Jon, the HL TendeRiser etch is shown on the High Level site. Here's an extract from the drawing I did of Steve Duckworth's drive, as featured in a recent Snooze:

tenderiser-part.png

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Will L
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Re: COG and suspension calculation 4-6-0

Postby Will L » Thu Apr 13, 2017 10:44 pm

jon price wrote:thanks Will
This makes a lot of sense. You are right that there isn't much space for motor, gearbox AND weight given the placement of axles. I know Chris at High Level has made a tender drive unit which makes running the drive shaft low under the floor straightforward because I remember seeing something about it on his stand at Scalefour North, but I can't find any information on his site or by web searches. Anyone got a link to info before I send Chris a begging email?


You can't link into the Highlevl website, its the way they wrote it. But if you click on Grearboxes and Planning the TendeRiser is the bottum one in the right hand collum. Click on that.

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Jol Wilkinson
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Re: COG and suspension calculation 4-6-0

Postby Jol Wilkinson » Fri Apr 14, 2017 8:14 am

The Mashima 1424 Russ illustrates is no longer available from most suppliers. The 1426 or 1428 are still available but will probably start to get scarce soon.

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jon price
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Re: COG and suspension calculation 4-6-0

Postby jon price » Fri Apr 14, 2017 9:34 am

I have a Mashima 1424, so if I go down the rear axle route I'm OK. I'll face the problem again with the small boiler eight coupled locos, but Mr Gibbons assures me that he will be able to source Cannon replacements when Mashima dries up.

Regarding a motor in the tender I found the info on the TendeRiser, including the new planning sheet (which of course I had ignored as I have the old one!). This still leaves the shafting and axle gearbox to sort out. By sort out of course I probably mean ask someone with more knowledge or experience. I can't find a lot out there though 2mm people appear to use the system with a springy wire shaft which is less obtrusive, and doesn't need flexible joints. though I'm not sure about torque reaction and tender axle suspension. After a bit more searching and pondering I may start a new thread.

Anyway thanks to everyone who inputted to this question.

Lindsay G
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Re: COG and suspension calculation 4-6-0

Postby Lindsay G » Fri Apr 14, 2017 9:37 am

Mashima motors are getting scarce around the UK at present. However, I've just received 2 1424's (yes I'm also planning to emulate Steve D's examples!) and a few 10 series motors from Branchlines. They had most motors in stock but are keeping some such as the 1420's back for supply with their kits.

That should see Brian Osborne's phone ringing non stop and his inbox full!

Lindsay


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