A Question of Balance

[mike morley]

So where should a loco's centre of gravity be?

 

Having built mostly 0-6-0's and 0-4-0's I had, without really thinking about it, come to assume that the balance point should be roughly at the mid-point of the driven wheelbase.

 

Now I've built a 2-4-0T with a considerable overhang at the front end that has made me realise my assumption does not always apply.  I've crammed lead into every available nook and cranny aft of the leading drivers (It's even got a lead-lined cab roof) but the balance-point is still some way forward of where my old assumption says it should be.  Yet, despite that, I'm finding there is so little weight at the front end of the loco the compensation won't work properly and the leading pony wheels keep derailing.

 

So where should the balance-point be?

I'm looking for guidelines here, rather than rules, and quite definitely not equations (The maths involved has made me give up all hope of ever building a CSB chassis)

[Nearholmer]

This is very similar to the 0-4-4 tank engine problem.

 

I think you want the greatest proportion of mass on the drivers, so centre of mass between the driven axles, and a small proportion, probably regulated through a soft spring, onto the pony axle.

 

In short, my feeling is that your initial assumption was correct.

 

Have you tried taking the pony off, then setting the loco up so that it rides level and neat while it is an 0-4-0, then adding back the pony, with said light spring?

 

And, you're sure that the pony isn't fouling/snagging on something?

 

Kevin

[mike morley]

And, you're sure that the pony isn't fouling/snagging on something?

 

 

 

Not so much fouling or snagging, more a case of being new and still quite stiff.

[Will L]

Need more info really, like how you compensated it.  Is the leading axle really a pony truck or is it just mounted in the main frames, like most 2-4-0. 

 

If the leading axle is just mounted in the chassis frames you build it like a standard compensated 6 wheel chassis and like any 6 wheel chassis the weight needs to be near the middle of the overall wheelbases.   A real GER E4 actually carried more weight on the leading axle than either of the driving wheels.

 

If you want to be clever about it and not put so much weight on the leading axle...  I can tell you how to do it, but you'll need to turn off the prohibition on numbers.

 

But nothing will work well if the font axle isn't free moving.

 

Wil

 

P.S. Don't know why people believe that to build a CSB you need to solve any equations, you just enter the wheel base into what there days we would call a computer app (otherwise known as a spread sheet), ask a friend, or see if somebodies done it  before and recoded the answer on the CLAG web site http://www.clag.org.uk/beam-annex3.html, you don't have to  read all the tecnical stuff if you don't want to.