Greenwich couplings her

[Terry Metcalfe]

Instead of using a magnet, I want to use an electromagnet.  Has anyone else done this?
Were there any problems or gotchas?  Which manufacturer should I use - the Gaugemaster one is more expensive than the Peco one - I can

[JulienW]

Whilst I haven't used Greenwich couplings with electromagnets I have used DG couplings with electromagnets and have had some guest stock with Greenwiches running on the layout, so I hope a few thoughts/observations may be useful to you.

First off my electromagnets came from Model Signal Engineering. Their PK/MAG costs

Edit: looks like the rest of that post got eaten in the data lost during one of the recent server transfers, so lets see what I remember...

So the Model Signal Engineering magnets I use now cost £8.10 from MSE, and I power them using a 15volt AC (1 amp) plug in transformer (surplus from a dead internet router)

[B.Meldon]

Rather than using electro magnets one other option would be retractable fixed magnets.

You will need to experiment with whatever electromagnets you want to use to make sure that they have a wide enough range for uncoupling the greenwich couplings, you may find that it is very dificult to position the vehicles in exactly the right location for uncoupling.
In general the rare earth (fixed) magnets have a wider opperating range than electromagnets so it is easier to position the vehicles when uncoupling.

I would also recomend you use a controller with a direction switch.
You can then set the speed to dead slow, use the switch to stop the vehicles in the correct position, then move the train back again using the switch so the couplings can release.
If you do this with a controller with out a direction switch you may find it far harder.

Again experimentation will be required.

As I mentioned above to uncouple the Greenwich couplings you need to push them together. The loop will not lift over the pin if the couplings are in tension.

Brian Meldon

[Terry Metcalfe]

I have  used Dapol Easyshunt couplings on my Bachmann Baldwin.   
I have also superglued the nem boxes supplied as spares by Dapol to the small logging wagons.  It needs a steady hand but otherwise no problem.   Having coupled up the Easyshunts i wonder why I faffed around with Greenwich types!

[Stefan Krebs]

'Retractable fixed magnet'   ??? ??? ???  :laugh: :laugh: :laugh:

What's the difference between a permanent magnet and a fixed magnet?   ;D

Anyway, you can switch off your de-coupler by using a switch on an electromagnet, or by moving a permanent magnet by mechanical means, e.g.  on a hinge.

To answer your questions:
1. Distance is VERY critical as the strength of the magnetic field diminishes by the power of 4 with distance; that's very rapid to the layman. More importantly, material in the gap between de-coupler and magnet pole can dissipate the field, i.e. weaken it further. Hence the suggestion made by Julien to mount the pole flush with the sleepers/ gravel is strongly recommendable!
2. Fortunately magnetic fields have the kind habit of sticking to magnetic materials rather than wandering off, so you can use a suitable piece of (ideally) iron (4 to 6mm diameter nail or rod) to cross your base material; no need to drill stepped holes etc.). Preferably you use something suitable to replace the core of your coil, rather than gluing it to the end; the joint produces some loss in strength. However, if you can't replace the core, just try, the loss is not big and might not be an issue. Bigger diameters may be shaped to a tip, which focuses the magnetic field. However, this has the effect that wagons need to be placed more accurately for decoupling. The other way round: the bigger diameter needs less precise shunting skills to work (provided the magnet is strong enough).
3. If you need cheap sources for solenoids (electromagnets) look for relays. They can be found for pence rather than pounds, and with the contact set removed you have your solenoid. Or you wind them yourself (see Internet for more info).
4. If you find the solenoid too weak you may try a capacitor discharge unit, it might do the trick.
5. The size of the magnetic material on the coupling is also critical to performance (no need to solder or wrap, just make the whole loop from piano wire, doubling the end where you want the magnet to pull)

Most importantly, as types of couplings and other factors influence performance, work out a set-up (brand of solenoid, mounting etc.) that works for you, and stick with it. What works for us does not necessarily work for you.

Good luck and happy experimenting!
Waldschrat

[Craig Deery-Taylor]

I've got my stock rigged with Greenwich couplings, a method I'm going to test uses a MERG EZ Points servo kit (although you can get a servo tester from Ebay which will work in the same way) and attach a magnet to the servo arm, that raises and lowers as needed. Then it's not a permanent magnetic field, which should allow for slow moving...without the dropper coming off the other wagon/loco.

[B.Meldon]

I've got my stock rigged with Greenwich couplings, a method I'm going to test uses a MERG EZ Points servo kit (although you can get a servo tester from Ebay which will work in the same way) and attach a magnet to the servo arm, that raises and lowers as needed. Then it's not a permanent magnetic field, which should allow for slow moving...without the dropper coming off the other wagon/loco.

This sounds like a great idea.
You will get all the range of the rare earth magnets without the unwanted uncoupling or attracting steel axles etc.
Do let us know how you get on.

Brian Meldon

[Stephen Rainsbury]

Rather than using electro magnets one other option would be retractable fixed magnets.

Old CD-ROM Drives often had a 5V servo in them for lifting the heads. Fujitsu ones had a 2mm travel, but could easily drive a lever mechanism to get more travel. I have used loads in the past typically with a 100ohm resistor in series to stop them getting fried.

[Stefan Krebs]

Dear Stephen,

Wouldn't that be a bit of an overkill? :laugh:

If I use electrickery to move a permanent magnet mechanically out of the way, why not use that same electrickery to just energise an electric magnet??? :laugh:

I use those very permanent magnets from DVD and CD drives as they are small, powerful and cheap (I have a steady supply of knackered CD-drives at no cost), and I use cheap and cheerful GEM and Ratio levers to move them, which puts the cost per uncoupler in the region of £2. But I have better use for those servo motors from thee CD-drives.  :laugh:

While I would use electromagnets if mechanical wasn't an option, so far the need hasn't arisen; I have 2 lying around, which came as bycatch with some stuff I fished from the bay of 2nd hand...  ;)

Just my thoughts
Waldschrat

[Graeme Dunbar]

One advantage of using a retractable permanent magnet is available field strength. Potentially also cost.

I have just one commercial electromagnetic uncoupler and it comes with warnings only to energise it briefly when needed as it gets hot running at the current needed to generate sufficient field. It was also quite expensive. Moving a permanent magnet with manual rod or lever is less expensive and no harm other than perhaps unwanted uncoupling is likely to occur.

I have a friend who uses cheap RC servos to move the magnets.

However one advantage of using an electromagnetic uncoupler is that they are often designed to use the same 16 Vac supply as point actuators, which is fine if you have a 16 Vac auxiliary supply on your controller. Also using ac to energise the magnet means any ferrous metal in the vicinity will not become magnetised. If dc or permanent magnets are used any pole pieces or iron on the coupler that is attracted should be soft iron and not mild steel.

On the other hand if, say, one was keen on electronics and Arduino microontrollers, and one was being used on the layout then a servo driver comes "free".

What works out as the best option depends very much on circumstances.

[Stefan Krebs]

Dear GreameD,

One man's disadvantage is another man's advantage:
While your statement is technically correct, it is sort of only half the story.

Those electromagnets, like any coil have a certain voltage at which they can remain energised permanently. If the manual tells you that they can't be left on at 16V than that certain voltage is lower. All capacitor-discharge units make use of that fact as they produce 24V or 30V to slam the point motor (which essentially comprises 2 decoupler magnet coils), i.e. overcome any stickiness; even though the point motors are designed for 12V or 16V only.
That neat trick can be applied to electromagnetic uncouplers, i.e. power them through a capacitor-discharge unit, and you don't need that high an operating voltage.
Once you've attracted the armature of the coupling, much less voltage is required to hold the coupling open. Unfortunately, the naughty manufacturers don't tell us the maximum permanent voltage that can be applied, i.e. you have to find out by trial and error (burnt-out decoupler). On the other hand, it's easy enough to find out what voltage you need: connect to an AC train controller, e.g. Maerklin, and reduce the voltage until the coupling closes. To work reliably you want to use 1 or 2 more volts. If you dare, you can attach a thermometer to the coil (in a sheet of cloth for thermal insulation) and check how hot it gets. If it doesn't exceed 40 degree Celcius it won't burn out, at 50 it'll most likely be alright too, but I wouldn't push it. So, if the temperature exceeds 50 degree Celsius, I would abandon the trial.

Where the powerful permanent magnet can 'grab' the steel axle of a little truck causing it to derail, an electromagnet with a capacitor discharge unit may just be that bit weaker to avoid such problems.  ;)

And yes, you can 'push' the peak voltage of the discharge unit to 50V, which should place you in the same league as the strongest permanent magnets.  :laugh:

A word of caution:
I haven't come that far yet with my permanent magnets, but there are tales if couplings becoming magnetised by DC-operated electromagnetic uncouplers. I can't confirm that yet (noting that the decouplers don't work on DC proper)

Food for thought
Waldschrat

[B.Meldon]

Perhaps we should wait and see what Craig Deery-Taylor comes up with before bashing the idea.
It sounds good to me, so lets wait and see how he gets on with it.

I use Egger/bemo type couplings with ramps.
However I have opperated several layouts with fixed rare earth magnets and others with electro magnets, both had problems.
I have also used a layout that had retractable rare earth type magnets, these were manualy opperated and that worked very well indeed.

Brian Meldon

[Stephen Rainsbury]

Wouldn't that be a bit of an overkill? :laugh:

If I use electrickery to move a permanent magnet mechanically out of the way, why not use that same electrickery to just energise an electric magnet??? :laugh:

Much lower current, and they are designed to stay activated for ages so shouldn't overheat :-)  I THINK that you can drive them directly from a arduino pin, but I have never tried it personally.
Stephen

[Dave Cooper]

Interesting discussion topic but what, pray, is the significance of "her" in the topic title ?

I refer to mine as "it" (or, "them") but, am not averse to the odd female here and there....!
Regards,
Dave

[Graeme Dunbar]

Spelt Chequer glitch? - "Greenwich couplings help"??  :)