Bogie Positioning

[DafyddElvy]

If I was to design and build a bogie coach from scratch I would position the bogies such that the end and centre through were not far off equal but with a bias to the ends.

In garden scale modelling I am assuming that this philosophy isn't always followed because sharp curves and large end throws of vehicles don't support the use of some couplings, especially any that don't use simple slack 3 link chains.

So, my question is, if converting 2 x 4 wheel coaches to a single bogie coach, how far from the end of the vehicle would the builder normally plan to position the bogie pivot?

 

[Paul M]

A lot depends on whether the couplings are body or bogie mounted

 

[JimmyB]

A lot depends on whether the couplings are body or bogie mounted

If the coupling is bogie mounted, then I think the positioning is so the frame of the bogie is in line with the chassis, however if the coupling is chassis mounted, then as and where you feel it looks best - Rule 8

 

[DafyddElvy]

The couplings are body mounted link and pin type.

 

[PhilP]

The couplings are body mounted link and pin type.

Then you may need to move the pivot-points from the centre of the bogie, towards the end of the vehicle.
You may also need to use a longer link than you would really like, as our radius curves are very tight. - Though tramways are probably much tighter than standard railways, anyway.

I think you will have to experiment, and compromise?

PhilP

 

[DafyddElvy]

Then you may need to move the pivot-points from the centre of the bogie, towards the end of the vehicle.
You may also need to use a longer link than you would really like, as our radius curves are very tight. - Though tramways are probably much tighter than standard railways, anyway.

I think you will have to experiment, and compromise?

PhilP

I suspected experimenting would be the case, my minimum radius is 750mm which I think equates to your r2, the mainline ruling radius will be about 1.2m.

 

[dunnyrail]

If I was to design and build a bogie coach from scratch I would position the bogies such that the end and centre through were not far off equal but with a bias to the ends.

In garden scale modelling I am assuming that this philosophy isn't always followed because sharp curves and large end throws of vehicles don't support the use of some couplings, especially any that don't use simple slack 3 link chains.

So, my question is, if converting 2 x 4 wheel coaches to a single bogie coach, how far from the end of the vehicle would the builder normally plan to position the bogie pivot?

I believe the norm on the real thing is to have the gap from end of bogie to end of vehicle to be 2x that difference between the end of each bogie in the middle. But not sure tyat this will always work and never checked it out, however I would think about couplings, take into account the buffers and mount bogies as appropriate.

 

[tac foley]

If I was to design and build a bogie coach from scratch I would position the bogies such that the end and centre through were not far off equal but with a bias to the ends.

In garden scale modelling I am assuming that this philosophy isn't always followed because sharp curves and large end throws of vehicles don't support the use of some couplings, especially any that don't use simple slack 3 link chains.

So, my question is, if converting 2 x 4 wheel coaches to a single bogie coach, how far from the end of the vehicle would the builder normally plan to position the bogie pivot?

According to Martin Crapper of the 16mm Association -

Martin Crapper
You can calculate the end throw, E = (L^2 - A^2) /8R where L is the coach length, A is the bogie centre to centre measurement and R is the curve radius, if that helps.

 

[Rhinochugger]

The couplings are body mounted link and pin type.

With body mounted couplings, the issue is that you need to position the bogies such that the body doesn't have too much overhang in the bends. There's no exact science, but it's a matter of trial and error.

When I scratchbuilt a bogie coach, I moved the bogies in towards the centre a little bit, to prevent too much overhang on 8ft curves.

 

[PhilP]

With body mounted couplings, the issue is that you need to position the bogies such that the body doesn't have too much overhang in the bends. There's no exact science, but it's a matter of trial and error.

When I scratchbuilt a bogie coach, I moved the bogies in towards the centre a little bit, to prevent too much overhang on 8ft curves.

Errrr...?

IN, to reduce overhang on curves? - That doesn't sound right..

PhilP

 

[Greg Elmassian]

Yep, backwards...

So, there is no "free lunch"... trucks closest to the ends, less overhang BUT cuts a "chord" across the inside of the curve...

For a single track, if you have plenty of clearance on the INSIDE of the curve, then put the trucks at the ends of the cars and you have the least overhang, and least issues with body mounted couplers.

BUT

Now you have this clearance issue on the INSIDE of the curve, so parallel tracks will be an issue. Also, now that the cars are mostly no longer over the rails on a curve, "stringlining" happens more easily.

There is no free lunch.

 

[dunnyrail]

Indeed there is end overhang and centre overhang to consider.

 

[Greg Elmassian]

Yes, I have seen people move the trucks to the ends of cars and then the first time that car encounters another car on the 2nd track in the curve, it collides. To a certain point, it is robbing Peter to pay Paul.

Greg

 

[Rhinochugger]

Errrr...?

IN, to reduce overhang on curves? - That doesn't sound right..

PhilP

Sorry, I was talking about the underhand as it were - inside of the curve.

That's the balancing act - making an assessment of the coach end overhang and the centre body underhang.

It's worth fiddling with the chassis, and testing various bogies positions.

Now the memory is working better, the other issue is the amount of bogie swing, and whether it will foul the end steps (if there are any). Moving the bogies inwards reduces the bogie swing.

We're not talking large amounts, but everything counts

 

[Greg Elmassian]

For passenger cars in the US, trying to get prototype "closeness" between cars looks great but puts further restrictions on coupler shank length, and truck placement. The diaphragms are also a challenge, if they touch normally they cause problems.

A balancing act to be sure.

Greg

 

[DafyddElvy]

Thanks for all the replies folks, I am just waiting on the bogies being delivered, I suspect for my purposes I might need to make a coupling with lateral movement which wouldn't be un-prototypical for a tramway cum light railway.