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Q1 0-6-0 Compensation questions


97xx
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Am rebuilding a rather tatty Keyser's Q1, and decided to go for a SEF etched chassis plus a High Level gearbox to take a Mashima.

 

Fancying a bit of a challenge, I then decided to I'd like to compensate it. Having never done this before. I have gone for High Level CSB and hornblocks.

 

I have three questions:

 

1. Should I 'fix' the rear axle, make it the driven one, and then compensate the front two only? Much as I'd like to boast a fully compensated chassis, a contributory factor is that the chassis has firebox etches soldered to its inner faces - all of which makes fitting a CSB spring wire very tight/awkward/impossible between those and a gearbox)

2. To ensure that any compensation 'works', I assume that the coupling rod holes need to be oversize to allow for the effective extension in the wheelbase as the axles slide vertically in the hornblocks? 

3. I need the loco to negotiate 2' radius curves. The frame width will be around 12.2mm. The rear axle (whether fixed or not) will have be shimmed to have minimal sideplay as it's driven. I'd appreciate views on allowable/permissible/necessary sideplay on the 1st and 2nd axle?

 

If it has any influence, it would seem that the weight distribution will be pretty equal across the axles.

 

Thanks!

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If you’re going for CSBs, spring all three. You’ll loose the smoothness of operation if the rear is fixed. I would aim to have the motor completely above the frames, so go with one of the higher gearboxes. That should reduce the clearance problems in the firebox. 
The crank pins only need a tiny bit of clearance. If they need to move more than say 0.5mm you’re better off fixing your track problems. A super sloppy chassis won’t run well. 
Shim the rear axle for no side play, the front for a bit, and no shims on the middle. 

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Hi,

Although you don't specify it would appear that you are modelling in OO.  Have you ever compensated or sprung a loco before?  If this is your first then I would recommend you go for a simpler solution for your first attempt.  I would hate that you try something to complicated and fail as a result never to try compensation again.  It is very rewarding to build a compensated chassis that runs smoothly.  

 

I would suggest that compensation in OO can be more challenging than in EM or S4  because of the amount you are trying to fit around the geared axle.  Going for a fixed rear axle and either springing or simple compensation of the front two axles will be far simpler and will leave you with more meaty rear axle bearings that you might not appreciate now but will in the long term. 

 

My early attempts at compensation used a single fixed beam between the front axles.  The next development for me was to replace the single beam with two phosphor bronze sprung beams in line with the horn blocks just inside the frames but still pivoted on the same beam axle as a single compensation beam would have been. 

 

Because I now model in EM and there is more space to play with I next moved to full compensation with twin beams between the rear (driven) and middle axles  and a short fixed beam above the front axle to allow the front wheels to rock.  And finally I have started using CSB's but have used the Scalefour Society's spreadsheet to determine the offset of the CSB supports to ensure that the loco sits level.

 

I think if I was still modelling in OO I would stick with my phosphor bronze sprung beams.

 

As to your Q1:

 

You don't need to increase the size of your crank pin holes!

 

Sideplay: 

I have done some quick calculations in CAD.  If the front and rear axles have no sideplay then for a 15ft wheelbase (I'm having to guess the wheelbase of the Q1 because I couldn't find any details on-line) then for a 24ins radius the centre axle needs .74 mm sideplay in each direction.  If the rear axle remains fixed and both the front and middle axles move equally then the sideplay required on each axle is more like 0.5mm in each direction. 

 

Hope this helps you to decide how to proceed.  

 

Regards,

Frank

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For an 0-6-0 really only the centre axle needs sideplay.  The front axle needs to control the front end so needs just a running clearance, same for the rear axle.

 

I would fix the rear axle and compensate the front two on a central beam.  Compensation is not really required for OO but can improve current pick-up assuming you are picking up on all 6 wheels.

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Your first option is well worth doing, even though it isn't full compensation. You do need to articulate the rods though - if they are in two layers just cut them in two so that they overlap on the middle crankpin. One middle crankpin hole on the outside layer, the other one on the inside layer. You only need sideplay on the middle axle. Compensating beams just inside the frames at each side work far better than central ones - and you don't need much movement either, 0.5mm up and down is sufficient.

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Good input, thank you.

 

Yes, 00, sorry - quite important...

 

I've gone for a high motor mount and reduction box - yes keeps it well clear of the frame gubbins, gets the motor back over the centre wheels (weight and CofG wise) and the boxy Q1 lends itself to that nicely.

 

I will indeed be articulating the rods - should have said that - and the double etches lend themselves to that.

 

Interesting on sideplay, my calcs initially came up with a larger requirement, but then I realised that there is a fair bit of flange to rail clearance given the 00 B2B dimensions.

 

I've designed the CSB pivot dimensions/spacing using the S4 calculators, and currently have it with ca. 0.4mm 'set' on each axle using 00 handrail wire. 

 

Ideally, I would do 3-axle, but I'd rather go front and middle which work as opposed to spoiling my first attempt trying to shoe-horn it all in past the back axle/box etc.

 

If I go for a 2-axle CSB, how do I run the calculations? Immediately, I'd assume use 2-axle calculator, with two-thirds of the loco mass (as it was almost equally spread) applied 50% to each of the 2 axles?  However, with a fixed rear, that doesn't smell quite right surely as the middle axle moment will now be 'derated' by the distance from the fixed rear?

 

Sorry if this is a silly Q, but perhaps it demonstrates that this is my first go.

 

Finally, I would concur that this probably isn't necessary fr a simple 0-6-0 in 00 but the large natural weight of a white metal body and the fact I HAVE to rebuild it all simply presented an opportunity to challenge myself. See this thread for another unexpected 'challenge'... 

 

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The 2' radius curves would worry me, whilst not desirable flangeless center drivers may be a last resort for good running on those curves

 

One 00 gauge chassis I inherited had initially a twin beam suspension, this was later altered to fixed axles at both ends and the center wheels sprung. Resulting in excellent running qualities

 

What I would do first, is to concentrate on getting the chassis running well round those sharp curves before fitting brake gear etc or doing too much with the body

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3 hours ago, 97xx said:

If I go for a 2-axle CSB, how do I run the calculations? Immediately, I'd assume use 2-axle calculator, with two-thirds of the loco mass (as it was almost equally spread) applied 50% to each of the 2 axles?  However, with a fixed rear, that doesn't smell quite right surely as the middle axle moment will now be 'derated' by the distance from the fixed rear?

 

You have two options for the two sprung axles: this or this.

 

Regarding c of g placement:

6-coupled-one-fixed-axle.gif.a561f1882ea3e72158d601ad8f3f5078.gif

 

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Good, thanks that's helpful. Needless to say the single pivot design is appealing as I may be tight on front frame overhang to locate the front of a 3-pivot far enough out.

 

I've also plenty of spring wire to choose from if I need to tweak the compliance/set.

 

Will read up more on clag - seems there is a mass of interesting guidance there.

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24 minutes ago, 97xx said:

Good, thanks that's helpful. Needless to say the single pivot design is appealing as I may be tight on front frame overhang to locate the front of a 3-pivot far enough out.

 

I've also plenty of spring wire to choose from if I need to tweak the compliance/set.

 

Will read up more on clag - seems there is a mass of interesting guidance there.

What is clag?

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Sorry if I'm being dense, but I can't actually find any calculations or worked examples for on 0-6-0 with one driven fixed axle.

 

Unless, as I hinted, you treat it as an 0-4-0 with 2/3 the total unsprung weight split equally (or in whatever proportion you believe it is) on the two sprung axles?

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Yes I understand that - which leads to my assertion that it's basically half of 2/3 unsprung loco weight on each sprung axle (let's assume it's equally balanced and equally spaced for simplicity).

 

However, with a fixed axle there is no deflection, and it's this that is troubling me.

 

So if I apply what I've just said to a 4-coupled sprung pair of axles with a rigid rear, the loco will attain a slightly nose down stance if the wheel centres are in line when unweighted.

 

Intuitively I'd say that I need to actually drop the front and centre axle centres versus the rear by the amount of compression I calculate I will get, so that they sit level when all three axles are on the track.

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25 minutes ago, 97xx said:

Yes I understand that - which leads to my assertion that it's basically half of 2/3 unsprung loco weight on each sprung axle (let's assume it's equally balanced and equally spaced for simplicity).

 

Correct.

 

Quote

However, with a fixed axle there is no deflection, and it's this that is troubling me. So if I apply what I've just said to a 4-coupled sprung pair of axles with a rigid rear, the loco will attain a slightly nose down stance if the wheel centres are in line when unweighted.

 

It will be slightly nose up when unweighted.

 

Quote

Intuitively I'd say that I need to actually drop the front and centre axle centres versus the rear by the amount of compression I calculate I will get, so that they sit level when all three axles are on the track.

 

Try reading this and subsequent posts.

 

 

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Good evening 97xx. I have attached 3 pictures showing my method of triple beam compensation which is self leveling and ensures an even distribution of weight to either 3 or 4 axle vehicles particularly in 18.2 and 18.83 gauges but I have managed to fit a HL gearbox between the double beams in an 'OO' chassis successfully. The pictures I have attached show the arrangement under a scratchbuilt LNE G/S 3500 HF tender once towed by 61701 and latterly by a J39. (64971 I believe)  All 3 beams are independant and are used with HL 2mm. hornblocks. The beams, with rounded contact surfaces, bear down onto the top surface of the axle bearings in the hornblocks. The single axle cross beam, also bearing down on the axle bearings either front or rear, has vertical adjustment for fine tuning enabling a perfectly level vehicle. This same system works perfectly well on six and eight coupled locomotives. Incidentally, axle sleeves are missing on the Exactoscale tender wheels. I could find them! When these vehicles are run along a length of rail with indents in the railhead a very reassuring series of  even 'clicks' give an indication of the even distribution of the weight. Cheers. HL 

IMG_1666 (2018_10_24 10_38_18 UTC).JPG

IMG_1675 (2018_10_24 10_38_18 UTC).JPG

IMG_1669 (2018_10_24 10_38_18 UTC).JPG

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On 27/10/2020 at 19:26, 97xx said:

1. Should I 'fix' the rear axle, make it the driven one, and then compensate the front two only? Much as I'd like to boast a fully compensated chassis, a contributory factor is that the chassis has firebox etches soldered to its inner faces - all of which makes fitting a CSB spring wire very tight/awkward/impossible between those and a gearbox)

There's no need for the firebox etches to run the full depth of the frames; if you attach them only to the lower edge of the frames that should allow you to plot a line for the CSB wire which avoids them, eliminating one problem. As for the other obstruction - the gearbox - you don't say which model you are using; are you aware of the "slimline" gearboxes from High Level? They were designed for 3mm chassis and should give you room for compensation beams, springy or otherwise. If I recall they are 9mm wide - someone may be able to confirm. 

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14 hours ago, 97xx said:

Sorry if I'm being dense, but I can't actually find any calculations or worked examples for on 0-6-0 with one driven fixed axle.

 

Unless, as I hinted, you treat it as an 0-4-0 with 2/3 the total unsprung weight split equally (or in whatever proportion you believe it is) on the two sprung axles?

Hi 97xx - I think the issue you have here is that CSB is designed to NOT have a fixed axle. There are some very enthusiastic CSB fans on the Scalefour Society forum, and one of their biggest stated advantages is that the whole loco floats along, there is no fixed axle to lurch around etc. I don't therefore think you will find anything on the CLAG site that exactly fits your requirements. My advice would be to either fully embrace CSB in a fully floaty kind of way or, if you like the idea of a fixed axle, ditch the CSBs and have a simple compensation beam between the other 2 axles. This is very easy to produce and absolutely works, though the CSB types will say it is not as sophisticated in terms of ride quality. I'm sure they are right though I've not tried it myself.

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Thanks all. 
 

I can appreciate I’m at risk of a Frankenchassis here so will reconsider my approach.
 

As an aside the problem with the firebox etches is that there are holes in the frames through which the firebox is visible, right in line with CSB wire.

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8 minutes ago, 97xx said:

As an aside the problem with the firebox etches is that there are holes in the frames through which the firebox is visible, right in line with CSB wire.

I see. But that shouldn't space the wire off the inner faces of the chassis any more than the CSB support pillars themselves, surely? 

 

Do you have a slimline gearbox? 

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3 hours ago, 97xx said:

Quick update - went for fixed rear axle and compensated front and middle.

 

First time I have ever attempted such a thing and am delighted. A super smooth runner and faultless pickup.

No turning back now then.  Welcome to the dark side.

Congratulations on a successful outcome.

Frank

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