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
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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
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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
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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
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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.

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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
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In this photo they are attracting each other.
IMG_1945.jpg
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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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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
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Rik
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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!

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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

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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
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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.
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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.

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Re: Magnetic couplings

Post by Trevor Thompson » Sat Dec 04, 2021 1:43 pm

I can report that I have a successful system for magnetically coupling my coaches with the chopper type couplings.

I have sent a heavy train up the line. The goods wagons are coupled with standard hooks, but they are hanging onto a locomotive and coaches fitted with magnetic couplings:
IMG_1981.jpg
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Note that the last 2 wagons are fairly heavy - they are full of real coal. The track is pretty rough at the moment with all the rubbish that the wind has thrown around and nothing uncoupled. So I think it works:
IMG_1982.jpg
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I am standardising on 6mm diameter and 3mm thick magnets in this type of coupling.

So next I will see if there is a way of replacing the hooks on goods wagons.

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Re: Magnetic couplings

Post by Trevor Thompson » Wed Dec 15, 2021 6:48 pm

The magnets with holes in them finally arrived from the other side of the world, but they didn't have holes in them. Ah well! So I worked out a way of fitting them into a holder to do the same job as those jewellery clasp magnets.

Of course I designed a holder with a hole in it to glue the magnet into, and a ring to add to the link of chain:
Screen Shot 2021-12-15 at 18.38.00.png
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That gives you the idea. I printed a dozen of them on the resin printer. Having washed and cleaned them up I have added them to the skip wagons:
IMG_2007.jpg
IMG_2007.jpg (1.61 MiB) Viewed 5441 times
They seem to hold the wagons together well enough to try them on the line. In the photo you can see how they attract and couple up of their own accord. It will be interesting to see if the rings are strong enough.

These are using magnets 3mm diameter and 3mm thick. So their attractive force is limited. Probably OK for a short rake of skip wagons but I think the coal wagons need something stronger. So I have modified the design to take magnets 6mm diameter and 3mm thick - which have proved satisfactory on the chopper couplings. I have made the rings thicker as well.

I will add a pair of these to the Wren and then try them outside with the rake of skip wagons.

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Re: Magnetic couplings

Post by GAP » Wed Dec 15, 2021 7:53 pm

Trevor Thompson wrote: Wed Dec 15, 2021 6:48 pm The magnets with holes in them finally arrived from the other side of the world, but they didn't have holes in them. Ah well! So I worked out a way of fitting them into a holder to do the same job as those jewellery clasp magnets.

Of course I designed a holder with a hole in it to glue the magnet into, and a ring to add to the link of chain:

Screen Shot 2021-12-15 at 18.38.00.png

That gives you the idea. I printed a dozen of them on the resin printer. Having washed and cleaned them up I have added them to the skip wagons:

IMG_2007.jpg

They seem to hold the wagons together well enough to try them on the line. In the photo you can see how they attract and couple up of their own accord. It will be interesting to see if the rings are strong enough.

These are using magnets 3mm diameter and 3mm thick. So their attractive force is limited. Probably OK for a short rake of skip wagons but I think the coal wagons need something stronger. So I have modified the design to take magnets 6mm diameter and 3mm thick - which have proved satisfactory on the chopper couplings. I have made the rings thicker as well.

I will add a pair of these to the Wren and then try them outside with the rake of skip wagons.

Trevor
Trevor just a thought about the polarity issue of magnets (N & S) perhaps putting two side by side with opposite polarity facing out would work.
The way to check polarity is trying to push them together if they repel the poles are alike.
To allow the couplings to rotate try using fishing swivels (small brass one are available) they will be strong enough for use.
This will make a stronger connection as there are 2 magnets power not 1.
Graeme
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Re: Magnetic couplings

Post by Trevor Thompson » Wed Dec 15, 2021 9:07 pm

GAP wrote: Wed Dec 15, 2021 7:53 pm
Trevor Thompson wrote: Wed Dec 15, 2021 6:48 pm The magnets with holes in them finally arrived from the other side of the world, but they didn't have holes in them. Ah well! So I worked out a way of fitting them into a holder to do the same job as those jewellery clasp magnets.

Of course I designed a holder with a hole in it to glue the magnet into, and a ring to add to the link of chain:

Screen Shot 2021-12-15 at 18.38.00.png

That gives you the idea. I printed a dozen of them on the resin printer. Having washed and cleaned them up I have added them to the skip wagons:

IMG_2007.jpg

They seem to hold the wagons together well enough to try them on the line. In the photo you can see how they attract and couple up of their own accord. It will be interesting to see if the rings are strong enough.

These are using magnets 3mm diameter and 3mm thick. So their attractive force is limited. Probably OK for a short rake of skip wagons but I think the coal wagons need something stronger. So I have modified the design to take magnets 6mm diameter and 3mm thick - which have proved satisfactory on the chopper couplings. I have made the rings thicker as well.

I will add a pair of these to the Wren and then try them outside with the rake of skip wagons.

Trevor
Trevor just a thought about the polarity issue of magnets (N & S) perhaps putting two side by side with opposite polarity facing out would work.
The way to check polarity is trying to push them together if they repel the poles are alike.
To allow the couplings to rotate try using fishing swivels (small brass one are available) they will be strong enough for use.
This will make a stronger connection as there are 2 magnets power not 1.
I am not worried about the polarity issue - I have an end to end line so everything will always be the same way around. I like the simplicity of there only being one magnet - and as small as can be made to work reliably. What I have on these skips is not obtrusive as well as seeming to be strong enough for this application. The printed components are stronger than they look by the way particularly when they are properly cured.

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Re: Magnetic couplings

Post by Old Man Aaron » Thu Dec 16, 2021 8:24 am

Tidy as, and easy to use. Impressive work as always, Trevor. :salute:
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Re: Magnetic couplings

Post by Trevor Thompson » Fri Dec 17, 2021 1:13 pm

More experiments and some unexpected results!

The initial couplings with 3mm diameter magnets disconnected at the slightest irregularity - so they are not powerful enough even for the skip wagons. So the same thing but using 6mm diameter magnets 3mm thick.

They are more obtrusive, of course being a light colour does not help, but they are stronger. It's an experiment and a final coupling would be black. So a long train with two types of magnetic couplings. This is climbing 1 in 60 and on a bend of course:
IMG_2013.jpg
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The couplings worked fine nothing uncoupled. So the coaches and the carriage truck were coupled using the chopper type magnetic couplings I had already tested, and the goods wagons and skips using the 6mm magnets hanging on chain links. To couple the chopper couplings to the wagon couplings I had added hanging magnets to some of the chopper couplings. Sort of emulating the wire loop I have always fitted to chopper couplings so that hook coupled wagons can hang on the end of a chopper coupled train. This is where the stray fields from magnets upset the calculations. With this type of magnet even the stray fields around their edges are strong. I knew that having different polarity at one end would be a problem, but I should have realised that even using the same polarity facing outwards would do the unexpected:
IMG_2021.jpg
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You can see how that hanging magnet is trying to attach itself to the back of the magnet in the chopper coupling. It isn't actually a problem in that if a goods wagon with a hanging magnet approaches it sometimes flips over and sometimes needs a helping push to get it to turn around and couple to the magnet on the other wagon. On the other hand the hanging magnet tucked up under the chopper coupling is out of the way of other magnetic influences - some of which will be apparent in the next post!

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Re: Magnetic couplings

Post by Andrew » Fri Dec 17, 2021 1:42 pm

That's very impressive! Could work well on a long rake of slate wagons...

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Re: Magnetic couplings

Post by Trevor Thompson » Sat Dec 18, 2021 9:31 am

So to the unexpected.

On the bottom half of the line everything worked out OK. But on the top half above the red bridge things happened - and I noticed what was happening as the back of the train crossed the first point:
IMG_2020.jpg
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You can see how the rear hanging magnet has attached itself to the rail - and that caused the couplings further up the train to part - you can see the locomotive and first carriage going gayly on their way.

Just a few inches further on it happened again. So that hanging magnet hasn't just uncoupled the train it has also derailed the last wagon:
IMG_2019.jpg
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Having sorted out the immediate issue of crossing the point ( diamond crossing actually) and setting the train off again I could see how that magnet was being drawn to the right hand rail - and was putting a twisting force on the last wagon which could easily derail it - before it is derailed by the next point.

So there is an issue with these tipper wagons and this particular version of the coupling.

So far I have only tried pulling a train. What about pushing as in shunting?

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Re: Magnetic couplings

Post by Trevor Thompson » Tue Dec 21, 2021 2:49 pm

Shunting, or at least pushing the wagons.

My initial tests in the workshop on my test track using the Wren and the tipper trucks led to the locomotive derailing as well as some of the trucks near the locomotive. The issue was partly lack of weight in the printed locomotive, and partly the couplings preventing the trucks touching each other when being pushed. Because the couplings were taking the pushing strain they were pushing the coupling pivots sideways, making the wheels try to climb the rails - hence the derailing.

So I printed magnet holders to specifically take the 6mm diameter and 1mm deep magnets. These are much more successful with these light wagons:
IMG_2022.jpg
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Here is the Wren pushing 6 tippers and two large bogie vehicles around a double curve. Nothing derailed. Here is the same train going the other way (the bogie vehicles were not attached), and everything worked fine. The couplings are 4mm shorter and that allows them to fold under the wagons when being pushed so that the drawbars touch as per the real thing.

Now I need to establish that these thin magnets are strong enough to keep these wagons together:
IMG_2023.jpg
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I also checked that the magnets don't attach themselves to stainless rail held in the middle of the track. They work in the workshop but the final test will be on the line this afternoon.

Trevor

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