CSB questions.

[johnarcher]

A good many years ago I did some P4 stuff, and at least got some simple things working reasonably. Looking now at doing some more (though I may yet go for EM, just thinking of age and how much time I have to come) one new factor seems to be the advent of the CSB.

I quite like the idea, I always found beam flexichas a bit floppy, especially if, say, test running in the air. However looking at some of the CLAG stuff (including spreadsheets - not an area I am familiar with, but preferable to the maths that seem necessary otherwise) I am a bit puzzled.

It always seemed natural to me to build the chassis first, get it working, and then the body, giving the chance to adjust clearances etc while building. However it now seems necessary to have the body basically completed, even ballasted, as one needs to know weight and centre of gravity in order to set something so basic to the chassis construction as fulcrum positions?

Or have I grabbed the wrong end of this strange modern stick?

[Nimbus]

3 hours ago, johnarcher said:

Or have I grabbed the wrong end of this strange modern stick?

 

Slightly. To get an optimum traction and track-holding balance you start by considering the relative axle loads. Driving axles for instance provide best traction when equally loaded. The axle loads and their spacings mathematically determine where the centre of gravity will need to be in the completed loco. This may influence the driveline layout in order to provide the optimum placing of voids in which to locate ballast to achieve the desired centre of gravity. In a parallel analytical thread, the axle loads and their spacings, via the spreadsheet, determines where the spring anchors need to be. 

 

The technique has been around long enough now for various rules of thumb to have emerged regarding relationships between driving and carrying wheel axle loads, acceptable tweaks to anchor locations, wire diameters etc.

 

The Nim.

[davknigh]

John,

 

You might want to pose your question in the Guest Book thread on the Scalefour website https://www.scalefour.org/forum/ 

There are a number of members who post regularly who may be able to help plus you can also search the site for ideas.

 

HTH

 

David

[Miss Prism]

10 hours ago, johnarcher said:

However it now seems necessary to have the body basically completed, even ballasted, as one needs to know weight and centre of gravity

 

I feel that is a slightly misleading picture. It is true one has to be mindful, during construction, about where the eventual CofG will need to be, or at least close to, if reasonable balance is to be achieved. In perspective, CofG error would in many cases need to be large to make a discernible difference to intended axle loadings. The CSB diameter can be changed to cope with different overall weights, but again, a particular design diameter will be reasonably tolerant of overall weight variation without discernible difference to axle deflections.

 

[johnarcher]

Thanks for all replies, Miss P I am encouraged that there is some tolerance for variation in these parameters, I suppose it might get me close enough to with the etches, motor, gearbox and a likely amount of lead even unassembled.

I will also look at the S4 Soc. thread, maybe post this same query there.

 

Thanks again.

[Miss Prism]

4 hours ago, johnarcher said:

I will also look at the S4 Soc. thread, maybe post this same query there.

 

Threads. Will LItchfield has done a useful starting point in his 'CSB source book'.

 

[garethashenden]

I tend to stick the whole kit on a scale and then round up. It seems to work so far.  

[drduncan]

Which kits are you referring to? A BG 1076 per chance? 

[garethashenden]

5 minutes ago, drduncan said:

Which kits are you referring to? A BG 1076 per chance? 

Me? Every CSB locomotive I’ve built. Your Buffalo is compensated because I didn’t have space for something, I don’t remember what at the moment. 

[drduncan]

2 hours ago, garethashenden said:

Me? Every CSB locomotive I’ve built. Your Buffalo is compensated because I didn’t have space for something, I don’t remember what at the moment. 

No space!  It’s Broad Gauge.  The gap between the frames  is almost as big as if it was a SG 7mm loco!!!!!!! 

D

[Tigermoth]

On ‎31‎/‎07‎/‎2019 at 09:10, Miss Prism said:

 

I feel that is a slightly misleading picture. It is true one has to be mindful, during construction, about where the eventual CofG will need to be, or at least close to, if reasonable balance is to be achieved. In perspective, CofG error would in many cases need to be large to make a discernible difference to intended axle loadings. The CSB diameter can be changed to cope with different overall weights, but again, a particular design diameter will be reasonably tolerant of overall weight variation without discernible difference to axle deflections.

 

 

For a CSB locomotive balance is important at least in reducing dipping and pitching at the ends of the chassis, i would avoid using CSB on a 0-4-0 for that very reason and go for compensation instead.

Edited August 1, 2020 by Tigermoth