Alex Jackson Dropper Location

GarethSmith
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Alex Jackson Dropper Location

Postby GarethSmith » Sat Apr 10, 2021 8:56 pm

Having put Alex Jackson couplings on a few vehicles and gained a little experience I am about to try it on a handful more. I note that the 'Alex Jackson The Man and the Coupling' book shows the droppers mounted just inbound of the axle. Indeed the dropper jig is designed to do just this. I also found some good guidance in Brian Self's useful article in Scalefour News 210 - his illustrations show droppers mounted just outbound of the axle.

This may be a pedantic matter - but does it matter? Is there now a convention? I can see that the 'outbound' location gives more leverage to the uncoupling magnet although the dropper is more likely to be visible. I have found the electromagnets have a narrow width of operation so standardization within one's own stock would be useful.

davebradwell
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Re: Alex Jackson Dropper Location

Postby davebradwell » Sat Apr 10, 2021 10:06 pm

Chris Pendlenton wrote about his own experiences with this coupling in MRJ in MRJ 223. It includes design of droppers and is about the only article to add anything new to the original material which just gets recycled. You'll find that most folk will confess, if pushed, that they don't actually use the uncoupling function and successful operation places certain conditions on the mounting. I'll confess that I was part of Chris's pre-Covid regular operating team on North Shields so can confirm the excellent reliability achieved with shunting taking place almost continuously all day.

In use, the train moves continuously over the magnet which is energised half a wagon length each side of the chosen uncoupling point so the narrow operating range is unimportant.

DaveB

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steamraiser
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Re: Alex Jackson Dropper Location

Postby steamraiser » Sun Apr 11, 2021 7:43 am

I place my droppers on the outboard side of the axle, with about a 1mm gap between the dropper and the axle. If you get the dropper too close to the axle it can impede the uncoupling operation.
This location hides the dropper behind the wheel and gives you a position to aim for when using electro magnets for un coupling.

Gordon A

bobwallison
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Re: Alex Jackson Dropper Location

Postby bobwallison » Sun Apr 11, 2021 8:05 am

Or you could try the Alex Jackson Dropper retailed by Lanarkshire Models & Supplies
http://www.lanarkshiremodels.com/lanark ... te_174.htm

The blurb says 10 hoops for 5 wagons but, of course, when real wagons were coupled up the hoops were only dangling at one end, not both. So for me, an etch of 10 hoops would do 10 wagons.

Haven't tried it myself (yet) but I can't imagine that Dave Franks would market a product that doesn't work.

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grovenor-2685
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Re: Alex Jackson Dropper Location

Postby grovenor-2685 » Sun Apr 11, 2021 12:19 pm

The important thing is to ensure that the magnet does not pull down the two couplings at the same time, uncoupling requires one to be pulled down while the other stays up.
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Keith
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bécasse
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Re: Alex Jackson Dropper Location

Postby bécasse » Sun Apr 11, 2021 1:21 pm

In the past I have had some success with U-shaped droppers made from paper-clips and suspended from, but not fixed to, the coupling wire either side of the axle (so that the axle passes through the middle of the U).

davebradwell
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Re: Alex Jackson Dropper Location

Postby davebradwell » Sun Apr 11, 2021 2:02 pm

This is the types that Chris recommends in his article - his have a clip which is much easier than either bending the top ends or the soldering operation used with original type droppers. They can swing, too, as the rigid type can be pulled to one side which can cause failure to uncouple. Basic material is iron binding wire from garden centres.

He uses a pulling post which avoids towing the wrong end of a vehicle and which we feel makes a significant difference with coaches.

DaveB

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CDGFife
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Re: Alex Jackson Dropper Location

Postby CDGFife » Sun Apr 11, 2021 2:50 pm

I also endorse looking for Chris P's article - much worthwhile and practical info in there. On Cadhay I use panel pins for droppers, with the head of the pin downwards and a groove sawn into the pin at the correct position for soldering to the coupling. Almost all Cadhay's stock has been converted to use pulling posts as per Chris' article. I put my droppers just outboard of the axle as Gordon describes. My own view is it matters not which variation of the ideas you go with so long as you are consistent and prepared to fettle to get consistency. Once you have that uncoupling will be reliable.

Cheers

CDG

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Re: Alex Jackson Dropper Location

Postby nigelcliffe » Sun Apr 11, 2021 3:30 pm

bécasse wrote:In the past I have had some success with U-shaped droppers made from paper-clips and suspended from, but not fixed to, the coupling wire either side of the axle (so that the axle passes through the middle of the U).


East Anglian experience of the looped-U approach suggests it works better with an iron wire which is somewhat fatter than a paperclip. Worked reliably on several layouts used by the group.

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Re: Alex Jackson Dropper Location

Postby davebradwell » Sun Apr 11, 2021 7:13 pm

I suppose one of the problems with all this is that there's no standard electromagnet to judge them by. Chris tests his couplings using weights so he has his own standard but the rest of us just have to find a coil that will do the job. Didn't Mr AJ himself specify a coil so I suppose he's covered but it's a pain having to wind your own coils - yes, it's not complicated but it's nice to be able to buy something. I believe MSE sell them but they draw an enormous current so certainly aren't the original type.

DaveB

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Re: Alex Jackson Dropper Location

Postby nigelcliffe » Sun Apr 11, 2021 7:26 pm

davebradwell wrote:I suppose one of the problems with all this is that there's no standard electromagnet to judge them by. Chris tests his couplings using weights so he has his own standard but the rest of us just have to find a coil that will do the job. Didn't Mr AJ himself specify a coil so I suppose he's covered but it's a pain having to wind your own coils - yes, it's not complicated but it's nice to be able to buy something. I believe MSE sell them but they draw an enormous current so certainly aren't the original type.


Of the commercially easily available coils, the SEEP branded ones are far better than others I've found. The SEEP's seem to draw about 0.5A on 12v DC, and that will reliably pull a coupling with a variety of droppers - the "washer" at the back of the SEEP has a role in shaping the magnetic field. The PK type which I think MSE supply just seem to waste electricity heating the room.

For switching magnets I now use cheap Mosfet switch circuits (about £2 on Ebay, Amazon, etc..) alongside the magnet, which mean the currents at the panel switch are tiny, so wires can be thin, switch contacts don't erode from the disconnect spark, etc..

- Nigel

GarethSmith
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Re: Alex Jackson Dropper Location

Postby GarethSmith » Sun Apr 11, 2021 8:56 pm

Thank you for all the useful comments. I haven't seen Chris Pendlenton's article in MRJ - but that issue (223) is still available and I've ordered one.

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Winander
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Re: Alex Jackson Dropper Location

Postby Winander » Sun Apr 11, 2021 9:42 pm

An alternative to using electromagnets I have seen suggested is to use neodynium magnets in a tube, raised and lowered by servos. Seems to me to be an altogether simpler solution. I imagine the price is comparable, but the overriding decider for me is the much reduced danger of burning the house down, and/or spinning the electrickery meter off the wall.
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Tony Wilkins
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Re: Alex Jackson Dropper Location

Postby Tony Wilkins » Sun Apr 11, 2021 9:51 pm

nigelcliffe wrote:
Of the commercially easily available coils, the SEEP branded ones are far better than others I've found. The SEEP's seem to draw about 0.5A on 12v DC, and that will reliably pull a coupling with a variety of droppers - the "washer" at the back of the SEEP has a role in shaping the magnetic field. The PK type which I think MSE supply just seem to waste electricity heating the room.

For switching magnets I now use cheap Mosfet switch circuits (about £2 on Ebay, Amazon, etc..) alongside the magnet, which mean the currents at the panel switch are tiny, so wires can be thin, switch contacts don't erode from the disconnect spark, etc..

- Nigel

On Green Street, I used a small relay mounted on the back of the SEEP magnet PCB for much the same reason.
Regards
Tony.
Inspiration from the past. Dreams for the future.

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Re: Alex Jackson Dropper Location

Postby nigelcliffe » Mon Apr 12, 2021 6:13 am

Winander wrote:An alternative to using electromagnets I have seen suggested is to use neodynium magnets in a tube, raised and lowered by servos. Seems to me to be an altogether simpler solution. I imagine the price is comparable, but the overriding decider for me is the much reduced danger of burning the house down, and/or spinning the electrickery meter off the wall.


Simpler ? No, its got more electronics (servo control board), bits have to be joined and mounted. Its noisier, "bzzzz" as the servo swings into position and away again. And its often slower to respond as have to wait for servo to move.
Price is about the same, depending where parts are sourced will swing it one way or the other.
Power consumption being intermittent and running at a low voltage is like the electromagnet: both are almost unmeasurably small for mains consumption and the servo consumes broadly the same amount as the Seep unit.

Having tried the approach, yes it works, and I'll use electromagnets instead. Neodyniums on sticks/strings are fine for totally manual operation.


- Nigel

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Re: Alex Jackson Dropper Location

Postby shipbadger » Mon Apr 12, 2021 8:27 am

I've mentioned this before but as the topic of electromagnets has come up again it may be worthwhile repeating it. Many years ago I wound quite a few coils using AJs original specification. When I connected 12v to them they had a miserable amount of pull. Eventually I remembered that back in the days when AJ was writing he and his colleagues were using 24v for their layouts. I have the legacy of this as I still have a 24v feed for the uncouplers to this day. You have been warned.

Tony Comber

ralphrobertson
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Re: Alex Jackson Dropper Location

Postby ralphrobertson » Mon Apr 12, 2021 8:49 am

On our Slattocks Junction layout and on my own layout servos and a magnet are being used instead of electromagnets. They allow you to adjust the power of the pull simply by changing the height of the magnet to the dropper and it works very effectively. You can see more about it on my Gt Jackson St thread here https://www.scalefour.org/forum/viewtopic.php?f=9&t=5499&start=25#p55420.

Much safer than electromagnets in my opinion. One evening at the club I turned the power to the layout on and a few minutes later saw smoke coming from under the layout. I couldn't see anything wrong at all so switched off and on again looking under the layout. The coils were smoking and it then became apparent someone had left a ring binder on top of all the push button switches so they were all energised. That is when the moving magnet was invented!

Ralph

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Re: Alex Jackson Dropper Location

Postby davebradwell » Mon Apr 12, 2021 9:19 am

Some catching up to do. I was always amazed at the servo system with it's brackets, links, guides and all when it was first published - the solenoid must be simpler and no moving parts. There is also a danger that with powerful magnets it's creating a super system incompatible with Mr AJ's originals that the rest of us use. The delay finally sinks it for me as you have to be pretty snappy catching the right coupling on a moving train. Retired railwaymen complain if we shunt too slowly. If dropper is too far from axle and rigidly mounted, coupler can dig into the ballast and cause a mighty pile-up.

I found some solenoids on ebay which draw around 0.5A at 12v so perhaps we've established an unofficial, if rather loose, spec. MIne have the bits to complete the magnetic circuit too as they were sold as solenoids to which I fitted a lengthened core. They can be operated continuously so no fire hazard, although I suspect the glue holding them to the layout would melt.

Nigel, do your MOSFETS still require a spike catching diode or is this inherent in the device itself? I should know but never actually got round to using a FET and my device knowledge is well out of date. Diode essential with a switch, of course.

DaveB

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Re: Alex Jackson Dropper Location

Postby nigelcliffe » Mon Apr 12, 2021 9:52 am

davebradwell wrote:Nigel, do your MOSFETS still require a spike catching diode or is this inherent in the device itself? I should know but never actually got round to using a FET and my device knowledge is well out of date. Diode essential with a switch, of course.


I've never thought about it: I put a diode over the coil as matter of course when the coil is used on DC. I have hundreds of diodes in my "might be handy" components drawer.

We put a lot of Mosfet circuits on Burntisland-1883 in 2019, as part of a layout-wide electrical robustness programme. The layout had two shows after those changes, when those parts were totally reliable, since then its been in store with no work done on it.

Example pre-made circuit, similar to the ones we've used. Screw terminals for the high-current stuff, plug pins for the low current control switch.
https://www.ebay.co.uk/itm/IRF520-MOSFE ... 4183523893


- Nigel

davebradwell
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Re: Alex Jackson Dropper Location

Postby davebradwell » Mon Apr 12, 2021 10:32 am

A handy little thing, indeed. I should have just assumed the diode would be needed - laws of physics and all that - so thanks for confirming. Like you I have a stock of project leftovers to raid for such things.

DaveB

Steve Carter
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Re: Alex Jackson Dropper Location

Postby Steve Carter » Mon Apr 12, 2021 4:56 pm

Has anyone used Dingham electromagnets for AJ couplings please?

Written on the Dingham website-

"The DC resistance Dingham electromagnets is approximately 8.5 Ohms, which is substantially higher than the 3.7 - 3.8 Ohms of alternative products. This means that Dingham electromagnets take a current of less than 1.5 Amps on 12 Volts DC. They are therefore much less likely to burn out if misused and are also less likely to cause switches to burn out. 

Important note
The Dingham electromagnets are intended only for operation of automatic couplers in which the moving parts are hinged. These include Dingham, DG, B&B, Sprat & Winkle. They are not powerful enough to operate 7mm Alex Jackson couplings which require them to bend a spring steel wire."

Are they powerful enough for 4mm AJ's without the need to have the top of the pole piece level with the top of the sleepers?
Thanks
Steve Carter

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Winander
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Re: Alex Jackson Dropper Location

Postby Winander » Mon Apr 12, 2021 5:27 pm

The length of the AJ coupling from its fixing point to the dropper is the measure of how hard it is to pull down, so I don't know how Dinghams can make that blanket assertion. The mass and material of the dropper will affect it also.

Chris Pendleton's article in MRJ 223 is extremely good and is very thorough.
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jasp
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Re: Alex Jackson Dropper Location

Postby jasp » Mon Apr 12, 2021 7:35 pm

Dave (Bradwell)
are you able to provide a link to the solenoids you got on ebay?
Thanks
Jim P

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Re: Alex Jackson Dropper Location

Postby davebradwell » Mon Apr 12, 2021 7:52 pm

The only way to tell if the magnet is safe is to connect power and leave it for an hour. We had a whole dept at work dealing with this sort of thing and dreaming up fault conditions to try - it's worth keeping this philosophy in mind. In fact I'm surprised layouts at exhibitions aren't subject to more scrutiny. 1.5A still seems a fair current so I suspect it'll get pretty hot if the switch welds shut.

Isn't putting the pole piece level with the top of the sleeper part of the A/J spec? I suppose you might drop it down 10 thou' and stick a piece of paper and ballast over the top but the force drops off rapidly with distance. It's important to consider what's happening to the magnetism coming out of the bottom of the pole as mentioned in the first reply. You get far more pull if some steel brings this up the side of the coil to the top as with a proper solenoid or relay - I can't tell from the Dingham drg.

Sorry the solenoids were just a batch and they've disappeared. The coil is 40mm long and about 20mm diameter, armature 8mm dia into which I drill and push in a piece of 6" nail after cutting off the forked end. I take off the front plate so it doesn't provide a short path for the magnetic field. They allegedly have a built-in diode but they're all dud so probably the reason for disposal.

DaveB

dmsmith
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Re: Alex Jackson Dropper Location

Postby dmsmith » Wed Apr 14, 2021 7:29 am

I have been experimenting with Dingham magnets (http://www.dingham.co.uk/electromagnet.htm), with a 12 V DC power supply and diodes. I did think about winding my own, but wanted something reproducible that I could use as a standard. I was also attracted to this design because the pole is simply an M5 bolt that can be made to cut a thread through the baseboard, and so allows easy adjustment of height.

I’ve tried using unhinged AJs with a panel-pin dropper mounted just behind the axle and the head of the bolt level with the top of the sleepers, as directed in the instructions. There was certainly plenty of pull, and if anything the issue was the head of the dropper digging in to the ballast if shunting too slowly. I’ve also tried some of the Lanarkshire droppers (http://www.lanarkshiremodels.com/lanark ... te_019.htm). These work well too and look good, especially where a missing three-link or instantly coupling would be obvious. Once again, the bottom link touches the ballast if shunting slowly.

I’m still experimenting, but my next job is to lower the poles below the heads of the sleepers.

Best wishes
David


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