Greenwich magnets

[Stephen Rainsbury]

Could somebody tell me what diameter the standard Greenwich coupling magnets are please?
Thanks

[Robin Webster]

Hi Stephen, what i received in my Greenwich package was rectangle magnets 7mm x 5mm.
Hope this helps.

[cp.409067]

*

All those I have ever had supplied are 6mm diam x 3mm thickness.

CP

[Hobby]

6mm diameter according to this description.

https://www.narrowplanet.co.uk/products/mag1

[Stephen Rainsbury]

Thanks, I tend to buy mine from Dundas, and didn't think to check other shops.

Mine are only 5mm but I have been experimenting with putting strips of steel can over the sleepers to increase the area of effect. It works better with some models, but not at all with others.
I plan to investigate the delayed action modification that I have seen mentioned before going much further, but I need to remember where I saw it  ???

[Graeme Dunbar]

Regarding using irons with magnets, I've done something similar for another application entirely (a Lego robot competition!)

It is a matter of thinking about the magnetic circuit and the coupling dropper will tend to want to move from where the magnetic field lines are less concentrated to where they are greater.  Rather than a piece of iron on one of the poles, having two small magnets with a pole piece between them may be better:

        dropper
             |
NS----------------NS
magnet:iron:magnet

In that way it may be possible to get away with fairly low overall magnetic flux (small magnets) but have a high flux density where it is needed.


(It shares some similarities with the design of electric guitar pickups.)

[cp.409067]

.....
I plan to investigate the delayed action modification that I have seen mentioned before going much further, but I need to remember where I saw it  ???

*

This can be very simple achieved assuming the layout is devoid of return loops or turntables.

On one end of the loco or item of rolling stock fit the standard Greenwich coupling - complete with the loop and soft iron wire on the tail.

On the other end omit the loop, but add a non-moving pin. This simply requires a small hole in the buffer beam (headstock) and the pin glued into it either horizontally or perhaps at a slight inclined angle above the coupling. One might use a Peco (thin) track pin with the head cut off. The protruding end of the pin should very slightly oversail the upturned thumb of the coupling so that the gap between the two is just enough for the opposing loop to enter - for the loop to hook over the thumb.

In operation it is as follows.

[1]  The train is stopped with the relevant item of rolling stock adjacent to the magnet.

[2]  The loop lifts to the underside of the pin.

[3]  The train is very slightly pulled back so that the loop now flips higher than the pin.

[4]  The uncoupled vehicle can be left where it is.

[5]  Or (with the loop going onto the top of the pin) pushed to somewhere else.

I take no credit for the the idea of using a fixed pin in this way. I understand the originator to be Paul Windle.

I have used Greenwich couplings thus on all three of my "O9" layouts extensively under exhibition conditions.



CP

[Graeme Dunbar]

Would the inverse be equivalent?

I.e. have loops and hooks on both ends of rolling stock and have no loops on the loco (both ends), but have delayed action pins instead? A number of locos come without loops in any case.

[cp.409067]

Would the inverse be equivalent?

I.e. have loops and hooks on both ends of rolling stock and have no loops on the loco (both ends), but have delayed action pins instead? A number of locos come without loops in any case.

That would work for fixed rakes of (say) carriages where the loco coupled to one end or the other.

However, for a goods train to and from which wagons might be added or removed, or indeed a brake van moved from one end to the other, it would not.


CP

[Stephen Rainsbury]

This can be very simple achieved assuming the layout is devoid of return loops or turntables.

On one end of the loco or item of rolling stock fit the standard Greenwich coupling - complete with the loop and soft iron wire on the tail.

That make sense thanks, I will give that a go.

I only planned to have loops on one end of most stock anyway, partially because I am tight but several people have said that you get more reliable uncoupling that way.