Magnetic couplings

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Trevor Thompson
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Magnetic couplings

Post by Trevor Thompson » Tue Nov 23, 2021 4:51 pm

I am experimenting with making magnetic couplings.

Firstly the background.

I have been making my own couplings for a while. Firstly 3 D printed hooks for slate wagons, and secondly an interpretation of the early "Norwegian type" couplings used on the Ffestiniog railway, again 3 D printed:
IMG_1959.jpg
The hook has a square cross section which I found easier to hold with tweezers when attaching it to another wagon. They work fine - but it is a fiddle coupling them up.
IMG_1950.jpg
The early couplings on coach 15 and 16 had only one hook, and had a tendency to uncouple - so I used a hook on each coupling. Initially I made these from brass, soldering the arm to a body made on a milling machine. The hooks were filed up out of brass sheet. Time consuming to make but they worked. Latterly I have been 3 D printing them, with different versions for locomotives and coaches. To enable wagons to connect to these couplings I have added a brass wire loop under the coupling - which is visible in the photo. It is tucked up under the coupling and can be pushed down if needed.

The couplings work fine and the plastic hooks on the coaches are well able to take the normal strains of being hauled along the track. However if a locomotive (accidentally) bangs into them at speed it tends too break the hook. So I wonder if magnets might be worth investigating?

Trevor

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Re: Magnetic couplings

Post by Trevor Thompson » Tue Nov 23, 2021 5:28 pm

I have bought magnets to add to the couplings. Firstly 6mm diameter magnets 1mm thick, and 3 mm diameter ones 3mm long with a hole in them. The first are for the Norwegian couplings and the second type for wagon couplings.

So firstly my experiments with the coach couplings.

I have modified the cad files for the coupling to make a 6mm diameter recess in the front face of the coupling, printed them, and bonded a magnet into that recess:
IMG_1960.jpg
I have added these new couplings to the Kerr Stewart diesel loco 4415, 2 coaches and the carriage wagon, and tried them on the line outside:
IMG_1955.jpg
The train successfully ran all the way to the end of the line, and back. However it did uncouple a couple of times at the top end after the viaduct when it hit the recently ballasted section leading to and into Dduallt and the passing loop. This was caused by ballast sticking to the inside of the rails - and it is surprising that nothing actually derailed here. So that shows I need to clean up the track, and that the magnets are not really strong enough.

Back in the workshop I have added another magnet between the couplings and found that it is much more difficult to pull them apart now. So the trick will be to work out the right strength of magnet. I think my next step will be to add 2 1mm thick magnets to each coupling.

Trevor

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Re: Magnetic couplings

Post by Trevor Thompson » Tue Nov 23, 2021 5:34 pm

There is an interesting side issue when using magnets as couplings in this way. Magnets are directional - one way around they attract and the other way around they repel:
IMG_1944.jpg
In this photo they are attracting each other.
IMG_1945.jpg
and in this one repelling.

So stock can only face one way round on the railway - not an issue on an end to end line but it could be if locomotives can end up facing the other way around. Perhaps more importantly the couplings need to be made in pairs. If a magnet is put in the wrong way around, then you have a coach where both ends will couple to one end of the loco, and neither end will couple to the other end of the loco.

As an aside the coupling on K1 is a model of the original from New Zealand and has a hole in it for a bar to act as a coupling in the centre of the buffers. It just happens to be 6mm diameter so the magnet just slotted in. I have yet to see if that will work.

Trevor

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ge_rik
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Re: Magnetic couplings

Post by ge_rik » Tue Nov 23, 2021 6:12 pm

Looks interesting. I've seen these necklace clasps being used for couplings - mounted on the ends of chains to help overcome problems with undulations in the track

https://www.ebay.co.uk/itm/333852882778
s-l1600.jpg
Rik
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Trevor Thompson
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Re: Magnetic couplings

Post by Trevor Thompson » Tue Nov 23, 2021 8:10 pm

ge_rik wrote:
Tue Nov 23, 2021 6:12 pm
Looks interesting. I've seen these necklace clasps being used for couplings - mounted on the ends of chains to help overcome problems with undulations in the track

https://www.ebay.co.uk/itm/333852882778

s-l1600.jpg

Rik
Yes I had come across this - which is what set me off on this tangent. These are 10mm diameter which seems a bit big - and intrusive. I await some smaller ones with a hole in them, and I will try to make something like what you have identified from them. If they don't work then something slightly bigger until they do work!

Trevor

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Re: Magnetic couplings

Post by ge_rik » Wed Nov 24, 2021 8:27 am

These are 5mm but not sure how they attach. I wonder if the barrel and magnets are hollow??

https://www.ebay.co.uk/itm/170825553391

Rik
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Trevor Thompson
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Re: Magnetic couplings

Post by Trevor Thompson » Thu Nov 25, 2021 9:23 am

ge_rik wrote:
Wed Nov 24, 2021 8:27 am
These are 5mm but not sure how they attach. I wonder if the barrel and magnets are hollow??

https://www.ebay.co.uk/itm/170825553391

Rik
Interesting - they are cheap enough!

Trevor

PS I have added stl files for the printed couplings I have used up to now into the files section. The non magnetic ones that is.

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Re: Magnetic couplings

Post by ge_rik » Thu Nov 25, 2021 9:56 am

Trevor Thompson wrote:
Thu Nov 25, 2021 9:23 am

PS I have added stl files for the printed couplings I have used up to now into the files section. The non magnetic ones that is.
That's really helpful. I'd probably have been sorely tempted had I not just finished installing my own hook and loop style couplings on all my stock.

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Re: Magnetic couplings

Post by gilfachphil » Thu Nov 25, 2021 4:18 pm

Have a look at First4magnets.com, specifically jewellery clasp ones. I have used them as magnetic couplings on some O gauge stock. They are drilled through and can be attached with things like suitable bolts or split pins.

Phil

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Re: Magnetic couplings

Post by gregh » Thu Nov 25, 2021 9:40 pm

Long ago I experimented with mag couplings. To overcome the problem of only being able to couple one way, I tried using 2 magnets at each end of the wagon. As I normally use hook and chain, I epoxied the 2 magnets to some chain like this...
DSCN3307.JPG
Note that the red one is the N pole and the other is the S pole
The 'hope' was that the ones on each end of wagons to be coupled, would always align themselves N-S, so I would have automatically coupling..
My initial attempt used my normal jewellery chain which is magnetic! and the magnets wrapped them selves around the chain very nicely. So I had to make some chain from copper wire.
The idea wasn't perfect! They didn't always couple up face-to-face but side to side. And Uncoupling was almost impossible.
So they went into the scrap box.
Greg from downunder.
The Sandstone & Termite's website: http://www.members.optusnet.com.au/satr/satr.htm

Trevor Thompson
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Re: Magnetic couplings

Post by Trevor Thompson » Fri Nov 26, 2021 5:15 pm

I think I have the chopper type couplings working. I am currently fitting the stronger magnets to the coaches with the intention of creating a longer train for a better test.

Whether I can get the wagon type to work is something I won't be able to explore until some 3mm diameter and 3mm long disk magnets with holes in them arrive. They will take a while to arrive because the only place I could find such a small size (with a hole through it) was from that place on the other side of the world via the well known auction site.

More feedback as the experiments take place.

Trevor

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