New Magnets, New Possibilities

You can see from the opening picture above, the size range of rare earth magnets includes rings nearly impossible to manipulate. I enjoy exploring new components like these for their ultimate modeling possibilities. While working on a new project, I needed to try out a variety of different scenarios with mobile, electronic installations and I tired of building even the most simple power supplies for each installation. So I decided to build a “power car” carrying either a track derived power supply or some battery supply. The battery supply would be simpler. Being naturally lazy, “simpler” is a very good thing! Batteries and power supplies are relatively easy (See for example:  SMA17 – Cheap Flicker Free Car Lighting for DCC, DC, and AC – a New Kind of KAOS  https://forum.mrhmag.com/post/sma17-%E2%80%93-cheap-flicker-free-car-lighting-for-dcc-dc-and-ac-%E2%80%93-a-new-12200310  ) but I found the car to car connection I needed to be somewhat problematic. I wanted an easy connection that I could make without removing the cars from the rails. I consider the tender-locomotive decoder connectors commercially provided too cumbersome for my work.

I have been using magnets in modeling for many years, and stumbled across a new set of very small ring and tube magnets from SuperMagnetMan ( https://supermagnetman.com/collections/neo-rings ) and K&J Magnetics ( https://www.kjmagnetics.com/products.asp?cat=16 ). The small ring magnets were very significant because they enabled an easy wire attachment without soldering. My discovery of these also solved another issue I had understanding how magnetic brake line connections were made – more on this later.

I needed two separate electrical connections, carrying 5.0 or 3.3 Volts from car to car. My prototype power car was to be an old HO boxcar. Without revealing the intended application (still in-process and to be published later), my “target” connection car presented here is a four wheel bobber caboose. The connections are simplicity itself, diagrammed in Figure 1.

Figure 1.  Magnetic power connections – Glue ONLY to insulation after wire insertion

Bend the stripped wire back onto itself until it fills most of the width inside the magnet tube but does not extend beyond the length of the tube; insert up to the insulation and then glue in place from the back. I used gap filling super glue. Epoxy will work well too. Electrically conductive epoxy would be ideal but it is expensive for even small amounts. If you use a free flowing glue, like thin super glue, you run the risk of insulating the wire inside the ring magnet from completing the electrical connection. The magnets I used were from SuperMagnetMan.com part #R0500-50. They are 0.079" (2mm) OD x 0.039" (1mm) ID x 0.039" (1mm) thick N50 Neodymium rare earth magnets and are nickel plated. The electrical connections were made with 30 Gauge Silicone insulated wire (Amazon.com https://www.amazon.com/gp/product/B07THYFTJY ). After the backing glue dries, take the end of a toothpick or other sharp point and push the wire back into the open end of the magnet to insure a tight electrical connection. I then sealed the opening with a tiny drop of MG Chemicals 843WB Super Shield Water Based Silver Coated Copper Paint (Amazon.com https://www.amazon.com/gp/product/B071R4BGM6 ) to ensure a good connection. This sealing step may not be necessary, but I thought it was a good idea. Don’t use nickel paint or nickel print as it is magnetic, and will follow the stronger field present and make a small mess (ask me how I know).

    
Figure 2.  Power cables and magnet orientation for the MU connections --  open and connected

Check that the end of the magnet is flat to ensure a good tight magnetic and electrical coupling. I alternated the North/South poles on either side of the battery car and to make sure the electrical polarity would be correctly maintained. You could color the magnets or even the leads too. I used back wires for both connections to fake air hose connections. Obviously, there would nominally be only one air line, but electrical functionality was my goal. I was concerned about exposing the live battery connections to a possible short. The power car uses a 18650 Lion Battery. The built in DC-DC converter can put out 5 Volts at 3 Amps. You should easily be able to fit a 9 Volt battery or even three 1.5 Volt AAA batteries in a 40 foot boxcar. I created some MU sockets for the Magnet connections with .08 styrene tube that was glued to the floor of the car, with the “live end” placed far enough inside to house both magnetic ends simultaneously – easy, and it worked! I The wire connections were wound and tied off as a strain relief where they entered the car.

The charger/regulator/battery holder/3.3V and 5V DC-DC converters are all on the board. It charges via a standard 5V USB micro connector. I don’t particularly like this board and its arrangement. It has a pushbutton for on/off control (short push/long push). I used a tiny micro switch in parallel with the pushbutton, strategically placed inside a cracked open boxcar side door. It only requires the most gentle push to turn on. I can turn the power on and off, and attach the power couplings while the car is upright on the track. The battery works well for me because my intended application only uses about 60-90 ma and the 18650 is rated for 2.5 Amp-Hours at 3.6 Volts! That’s way more power than I need for a week! It works and does the job. These were purchased here:  https://www.amazon.com/gp/product/B07K7GZ2RK   I tried two other versions and still don’t recommend any of them. One, with a slide switch, did not function at all!  If you must try any of these be very careful not to insert the battery backwards, or to short the outputs (3.3 Volt or 5 Volt). There is so much power in these 18650 batteries that they will fry the circuitry instantaneously – no kidding! There is no short protection on the board. One version of this board kept the battery charge level LEDs on all the time (no way to turn off).

           
Figure 3.  Looking into the ends of the power cables and the power car insulating tubes for the MU cables

     
Figure 4.  Power car under floor power connections, -5 left [SOUTH] and +5 on the right [NORTH]

 
Figure 5.  Power car with battery board assembly mounted and wired, end power receptacles

 
Figure 6.  Power car with battery and secondary micro switch wired parallel to push button

 
Figure 7.  Power car with Lighted Caboose showing connections

 
Figure 7a.  Power car with Lighted Caboose showing connections

 
Figure 8. Power car and Caboose (Light off)

 
Figure 9. Power car and Caboose (Light on)

One should realize, however, that these were literally scale, working MU connections if applied to diesels or passenger cars. The 30 gauge silicone covered wire is very flexible and can only carry slightly over 0.8 Amps in this application, although I will likely use less than a tenth of that. Make sure you run the length of the wire connections so that there is enough flex to maintain the connections around your tightest curves.

The mystery of the air hoses

I had wondered how scale magnetic air hoses could be made to work for some time. Because of my investigation into the electrical connections described above, I found the answer. The R0500-50 magnets I used in the power car are axially magnetized. That is the north-south poles of the magnet are along the axis of the magnet tube. But I discovered that you could obtain part # R0500D-25 which is the same size and shape magnet but is diametrically magnetized (across its diameter), rather than axially magnetized. Big deal you say? Well… yes it is because it makes single line magnetic air hoses possible!

Figure 10.  Axial Magnetization                   Figure 11.  Diametric Magnetization

There is a slightly larger and longer magnet available from Supuermagnetman.com part # Tube 0115D that I used to convince myself of the viability of this solution. Let’s start by noting that the coupling for the connection in Figure 1 if applied to a single brake line would not work for both ends of a car. Regardless of the orientation of the brake line ends if a car were reversed in placed the polarity would not be correct in the general case. That is if you started with a train with a set of:  N=S   N=S   N=S   N=S   N=S  cars, reversing one car might yield:  N=S   N=S   S=N   N=S   N=S  and the brake lines would no longer attach. However, if the Diametric Magnets (DM’s) were set such that the poles were all set North-South and side to side, then reversing a car would make no difference:

Figure 12.   TOP view of rail cars and brake lines with DM magnets oriented correctly

The “trick” would be to get them all installed such that the DM magnet poles were all installed correctly side to side. How?  Easy – just randomly drop several into a plastic box or tray, and they will self align side to side, not end to end as in Figure 13. Next, take one off the end of the set without rotating it, and glue it into a holder (say a toothpick) such that all other air lines would be aligned to the one standard and mark the orientation.  If you align all installations on any car or loco to the “standard" orientation… you are done! You could “fix” your standard to track gauge and coupler height, for different scales. Regardless of the orientation of the car or loco on a track the air hoses will always be mounted correctly.

 
Figure 13.  Self aligned diametrically magnetized ring magnets

 
Figure 14.  Build the “standard” magnet orientation device (glued toothpick) top marked

 
Figure 15.  Note that if you turn the “standard” magnet around it will couple end to end with the other DM magnets

I do not have much interest in magnetically coupled brake lines, other than in solving how they worked.

Magnetic Tie Down for Structures with Lighting Connections

I use magnets in modeling structures with two things in mind: holding pieces in place that need to be separated for maintenance or ongoing adjustment, and adding easy electrical connections for movable components. They are related. The electrical connections, as stated previously, need to be made mechanically rather than soldered to avoid demagnetizing the rare earth magnets due to exposure to high heat.

The example below shows how I attached the roof to this small house. Steel shim stick (0.005”) was glued flat to the roof. It could be painted over, but this is not seen in normal viewing, so I avoided the extra step. Note that the area covered by the steel is large compared to the size of the magnets used (5mm disks located inside the corners of the upper walls). This eliminated a precision match from magnet to steel and still allowed a tight fit. Another advantage was that the magnetic attraction was strong enough to allow irregular fitting, or minor gaps between the magnet and the shim stock.

 
Figure 16.  Roof with glued steel shim stock and magnets mounted in upper corners

       
Figure 17. Roof and magnets                                            Figure 18.  Steel pads for magnets

Power to Your Structures

You can easily use magnetic structure mounts for electrical connections (e.g. lighting and animations). The issue is usually how does one make the mechanical electrical connection without soldering? Remember heat damages the magnets. With low cost countersunk magnets and 2-56 screws and nuts the connection is easy.  You can try wedging the magnets and wire in place, allowing for direct contact for the electrical connection, or you can use a longer screw and grip a wire connection under the nut holding the assembly in place. Rare earth magnets are somewhat brittle, so don’t over tighten the screw-nut assembly or you will crack the magnet.

Figure 19.  Countersunk magnet orientation       Figure 20.  Screw and nut for electrical connection

Countersunk magnets built for various screw sizes are readily available from Supermagnetman.com ( https://www.kjmagnetics.com/products.asp?cat=15 ) built specifically for screw sizes 2-10, in pole pairs, separately, and in different magnetic strengths.  Be careful of the size, strength and number you use for attachment. You can easily build a mounting set that is far stronger than your wooden or plastic structure! Trying to remove overly powerful magnetic connections can damage a delicately built model.

Figure 21.  Mounting magnets for structure with electrical connection

It is also possible to use a single countersunk magnet and steel stock, making the electrical connection by soldering to a corner of the steel plate. You can also drill and tap the steel plate to accept a screw for wire attachment. Remember to select a variety of steel that is magnetic.

Magnetic Cargo for Your Model Railroad

The following application of magnets was first reported in an article in the January, 2016 issue of MRH  http://mrhpub.com/2016-01-jan/online/files/252.html . It demonstrates the use of different size magnets, all hidden in models, and also demonstrates an important fundamental principal: increasing the gap between magnets of a magnet and magnetic material weakens the magnetic field, and hence the strength of the grip of the magnet. Besides this last application you can read about the use of magnets in other animations,  here to guide a crane with magnetic sensors:

Model_Working_Cranes  http://mrhpub.com/2015-12-dec/port/files/216.html .

And Scale Model Animation 4 – Critter Guidance, Sensors, & Fun  https://forum.mrhmag.com/post/scale-model-animation-4-%E2%80%93-critter-guidance-sensors-fun-12193201 , and here to measure distance and speed:  SMA24 – Working Scale Dynamometer Car Recording: Drawbar Pull, Track Voltage, Speed, Distance, & More  https://forum.mrhmag.com/post/sma24-%E2%80%93-working-scale-dynamometer-car-recording-drawbar-pull-track-voltage-speed-distance-more-12203477

Let’s look at moving scale cargo, magnetically, using some animated cranes (of course). Realistic crates can be built with wood or plastic. A selection of crates can easily be had with crate set 8174 from Tichy Trains. Taking a lead from the old tinplate cranes, we can use magnetism to pick up a crate with a small piece of iron or steel embedded or attached. But prototype electromagnets didn’t usually lift many crates. However, one of the small rare earth magnets we considered with the Hall Effect sensors can do the job! These are available as small as 1x1x1 millimeter in size. By cutting out the bottom of the Athearn large hook (part #17017)pictured below, we can embed one of these small magnets in the bottom of the hook. An abrasive cutting disk in a Dremel moto-tool does the job well. See if you can pick out the magnet in the crane pictures – it’s barely visible. Epoxy or thick ACC glue will hold it in place. I completely covered the magnet with glue and then painted it after thoroughly drying.

 
Figure 22.  Magnet Equipped Hooks

For the first attempt at modifying crates for pick up, I used 0.001inch steel shim stock, glued to the top of the crate. The modified hook easily lifted the crate – success! When glued to the underside of the top of the crate, the gap weakened the grip enough that the crate sometimes fell. A 0.005 inch piece of styrene substituted for the crate top narrowed the gap to allow the steel shim to be placed inside the crate. A tiny sliver of steel was also cut and attached to chains mounted across the top of the crate. This also worked well for pick up.

But how do we drop the crate, once the crane has transported it? Magnetism was the obvious answer again. An electromagnet was placed under a model loading dock, and a larger piece of steel was placed on the inside bottom of the crate. Once the crane lowered the crate onto the dock, the electromagnet would grab the crate with a force greater than the small magnet in the hook. The crane could then simply pull the hook away, and continue on its way. This worked – in part. When the crane pulled up and away, the tension applied made the boom act like a trebuchet and rocked the entire crane in an exaggerated manner – again not a realistic effect! The answer came after quite a few engineering trials, resulting in a relatively simple solution. The key was to use the “problem” described above to advantage. By increasing the gap between the hook magnet and the crate steel insert, we are able to disconnect the hook. We could open the hook gap simultaneously with grabbing the bottom of the crate. The electromagnet used was more powerful than the hook magnet by far, so it easily pulled the crate away from the hook. We also help the electromagnet by making the steel at the bottom of the crate larger than the metal at the crate top.

Quite a few attempted mechanisms are poor or intermittent performers. The best solution is a spring-loaded column with a small steel target on the top of a brass tube, attached to a larger steel “plate” on the bottom. The spring raises the column and the top metal pin to the underside of the top of the crate. This allows the hook magnet to grab it at will. But if the crate is placed on top of a working electromagnet, the magnet grabs the bottom plate and pulls the column down, developing a gap at the top, and dramatically weakening the pull from the hook magnet. This effectively disconnects the hook. After the crane lifts the hook or boom up, the electromagnet can be turned off. Thus, the crate stays in place on the loading dock with no trebuchet effect. The top metal pin is made from a #14 nail/brad. Shortened Kadee #861 G-Scale Centering Springs support the column. The top and bottom steel pieces are cut from steel key stock obtained from the local Ace Hardware Store.  The top and bottom panels of the Tichy box were replaced with black 0.010 sheet styrene.

      
Figure 23. Box and Parts                                             Figure 24.  Putting the Box Together

     
Figure 25.  Ready for Insertion                                Figure26.  Mechanism Inside

     
Figure 27. Box Ready for Transport                                Figure 28. Lifting the Crate

The last problem dealt with the use of the electromagnet. This solution did work, but the crate needed to be placed on the electromagnet with too much precision.  This was a bit too limiting and would not permit dropping multiple crates on the same platform without providing an array of electromagnets.

 
Figure 29.  Loading Dock and Crates

Again the solution was to forcibly increase the gap mechanically, with a servo motor-driven platform covered with thin rare earth magnets (1.5x10 mm). You can see the solution in the figures below. The “hinges” are made from stiff 0.025 inch wire (brass, phosphor bronze, or steel) formed into a rectangle and inserted top and bottom  into 1/16 brass tubes glued in place.  The servo arm is attached to the underside of the platform and is controlled by an Arduino Pro Mini. You can even use the multifunction Arduino decoder described here: https://forum.mrhmag.com/post/sma15-new-dual-acessorymultifunctionl-17-channel-configurable-dcc-decoders-for-about-5-with-configurable-servo-12198949 ). Now instead of turning an electromagnet on and off, you simply raise or lower the magnet platform under your loading dock for effect.

     
Figure 30.  Magnet Platform Lowered                                    Figure31.   Magnet Platform Raised

     
Figure 32.  Dock-Platform Lowered                                        Figure 33.  Dock-Platform Raised

As things would happen there was one last problem to solve. When the first magnet platform was built it worked very poorly! It made absolutely no sense, until I happened to drop a crate on the edge of the platform and it grabbed the crate like glue. Moving the crate to the obvious middle of the platform had little effect. What was going on? The first platform had an even array of magnets placed so that all were mounted with the same polarization – all with the same pole up.

 
Figure 34.  Weak Field Magnet Grouping

 
Figure 35.  Strong Field Magnet Grouping

The resultant magnetic field in the middle of the array had only a weak interaction with the steel in the crate. The solution was to alternate the magnets’ orientation in the array – north/south – across the platform. This worked very well. It also enables you to build as large a platform and “landing area” for your crates as you would like, allowing multiple crates to be placed and removed from your loading dock.

The sequence of events would typically be: 1. Have your crane pick up and carry a crate to the loading dock, 2. Lower the crate onto the dock above the lowered magnet platform, 3. Raise the magnet platform under the loading dock, 4. Lift the hook away from the crate, 5. Lower the magnet platform leaving the crate in place. The crate is ready to be picked up and moved somewhere else as well. Now you really can realistically move cargo on your layout!

I think this barely scratches the surface of all the applications for magnets in modeling. My very first use of magnets was to simply hold down loads on flatcars. There are undoubtedly way more uses that I have never even considered. I hope this stimulates modelers to discover even more . Michael T, a friend and fellow modeler, aptly stated:  ”Creativity is Magnetic!”

As always, appropriate comments and suggestions are always welcome.

Have fun! 
Best regards,
Geoff Bunza

Wow

Just a myriad of wonderful ideas here Geoff. I have solved my issues with the barge with a hybrid combo of magnets and steel screws used as adjustable contacts. I found out the hard way about the CA becoming an electrical insulator. I saw a You Tube video where a guy had actually soldered to the edge of one of the small neodymium disc magnets. I tried it as an experiment and it's possible to do it without destroying the magnet but you really have to be quick about it. The slightest bit too long and the magnet is worthless. In the end I decided that it wasn't worth the risk.

@Michael

Hi Michael,

'Glad to hear you are successful with your barge. I look forward to enjoying your progress.

Have fun! 
Best regards,
Geoff

Different modelling with magnets - bicycles anyone??

Hi Dr Geoff, Michael, all, 

Operating bicycles with magnets?? Has already been mentioned, see  https://forum.mrhmag.com/post/working-scale-bicycles-wow-12215978

soldering

Hi Geoff,

Friend of mine use magnetic couplers for long time. He have solved soldering and mounting problems (before 3D printing) Unfortunatelyfor you he use Czech language. http://www.honzikovyvlacky.cz/2015/03/15/magneticka-spojka/

It is good to spend some time with translator, the article describe some troubles and some theory that is good to know, before you will start. 

Google Translate

Dear MRHers,

For those wanting a direct link for the above Czech article
https://translate.google.com/translate?hl=&sl=cs&tl=en&u=http%3A%2F%2Fwww.honzikovyvlacky.cz%2F2015%2F03%2F15%2Fmagneticka-spojka%2F

Interesting takeaways:
- Use of pin headers similar to those used for Arduino projects, drilled-out to accept magnets,
thus forming nice tidy "multi-pole magnetic couplings"

- Use of Low-Temp (Lead-Bismuth) Solder-paste to apply just-enough at just the right place,
thus reducing the dwell-time of the soldering iron and the heat-applied,
and (presumably) thus reducing any heat-induced magnetic-flux reduction...

There is also some comments that refer to "pogo pins", these are the kind of electrical spring-loaded pins which are combined with magnets to form the power-connections for "break-away" changing cables for mobile phones, and things like recent MAC Laptops...

(the big silver bit around the outside are the magnets,
the gold pins on the cable are the spring-loaded "pogo pins",
and the gold dots on the laptop edge are the contacts)

Happy Modelling,
Aim to Improve,
Prof Klyzlr

Loads, crates, and pickup/put-down

Dear Dr Geoff,

Astounding work as always, and it's great to get to see the innards of the "pick'em up and put'em down" crates...

...now, to adapt the technique to a "crate" which is actually a hollow (plastic, looking like wood) tube,
with no defined/consistent/reliable "UP" part of the cylindrical surface...

Happy Modelling,
Aiming to be just like Dr Geoff when I grow up,
Engineering Student Shaymax Feisler
(Prof Klyzlr's younger protegè )

Following

Following

Instead of trying to solder to a magnet…

…why not solder to a piece of tin, then let the magnet adhere to it?
K&S still sells tin in sheets. 

Mechanical connection

I wasn't advocating soldering to magnets, I just tried it as an experiment, I managed to do it one try out of two and the time it worked, I still might have reduced the power of the magnet, no way to know. The other try, the magnet was destroyed.

Regardless of whether you solder to tin or something else, you still have to have a good mechanical connection so the magnetic contacts separate from each other rather than from your leads. One my barge project, I fanned out the strands of good copper wire and trapped them between two magnets and then used a tiny bit of CA to bond them together. Worked wonderfully well on the layout end of things but not so well on the barge itself. I suspect it was some bad quality junk box wire I used on the barge end and maybe too much CA but I had an intermittent connection issue and ended up with my hybrid solution.

Low-Temp (Lead-Bismuth) Solder-paste

Hi fulda, Prof K, et al,

The lowest melting temp I could find for Low-Temp (Lead-Bismuth) Solder-paste is in the 138-140 Celsius range ( https://www.surfacemountprocess.com/low-temperature-lead-free-solder-paste.html ). The max working temperature of most all the rare earth magnets I work with is 80 Celsius. The failure mode of exposure to excessive heat is loss of magnetization.These little magnets do not have much to loose!

So, no, I do not recommend soldering by any means to these tiny magnets.

Simple magnetic contact alone, via a soldered connection to a magnetic covering material will definitely work, if there is no pulling force exerted on the junction during normal operation. The structure magnetic electrical connection is such an example. The power car electrical connection is not an appropriate example.

Your mileage may vary... of course! 

Have fun! 
Best regards,
Geoff Bunza

@Engineering Student Shaymax Feisler re:Making a tube a crate

Hi Shaymax,

...now, to adapt the technique to a "crate" which is actually a hollow (plastic, looking like wood) tube,
with no defined/consistent/reliable "UP" part of the cylindrical surface...

I think this is do-able. There is no reason why the inner spring mechanism could not be dimensionally modified to fit in the "log/cylinder." You would need to make sure that the top and bottom of the piston has enough metal for the magnet to grab to raise the log and lower the piston, with enough travel to weaken the associated magnetic bond. To align the log (stop it from rolling) you could add a branch or two, or bevel one side to force a particular orientation.

As a protegè of Prof Klyzlr you have a great person from which to learn! 

Have fun! 
Best regards,
Geoff Bunza

Low Temp solders

Dear Dr Geoff,

I do know that Carrs (UK) has 70-degree solder, albeit not in paste form

https://www.hamodels.net/carrs-c1001-70-c-solder.html

The label on the solder used by the Czech modeller would seem to suggest it's 140-160deg C solder,
maybe he just happened to find that it "works" with his soldering iron set to a lower 80-degree temp?

Happy Modelling,
Aim to Improve,
Prof Klyzlr

@Prof K re:Soldering Temp and Magnets

Hi Prof K,

There are many different kinds of materials that are used to make rare earth magnets. Some are quite exotic like samarium. The composition of the magnet will change its strength and ability to withstand higher temperatures, including soldering. So it may be that the Czech modeler used different magnets as well. Also the thermal mass of the magnet (bigger, more mass = more robust) could affect its ability to withstand heat. 2 mm ring magnets are pretty small and the warnings about heat exposure (not just from soldering) are pretty explicit. The N40 and N52 material used in the magnets I specified are on the low cost end of the spectrum (by design) so I am sure one could find other, more costly, more robust substitutes if necessary. You likely already realize I try to find cheap and relatively easy modeling solutions.

Have fun! 
Best regards,
Geoff

PS. I hear you have a new protegè !

Geoff

Geoff,

Thanks for posting the tutorial!  Just what I needed to point me in the right direction to use magnets for structure mounting and electrical connections.

Just one (more) question:  Where do you buy the .0005" steel shim stock?  I found large quantities of it (rolls), but I only need just a small amount - a few strips.

Thanks,

Al Carter, Mount Vernon, WA

@Al re:Steel shim stock

Hi Al,

Believe it or not, I purchased my roll of steel shim stock at my local Ace Hardware store about 15 years ago! (unfortunately now closed). you can also get a variety of thicknesses from zorro.com like: (  https://www.zoro.com/precision-brand-shim-stock-roll-cold-low-steel-00030-in-16245/i/G1788367/?recommended=true ). I have even contacted the manufacturer (Precision Brand  https://precisionbrand.com/)  to buy rolls of brass shim stock, which are very hard to find for low cost. I have never seen a (small one time) modelers amount packaged and sold. I have sometimes "built-up" the thickness of the steel material I need for better attraction by cutting a strip and then folding it over again and again -- that works!

Make sure you get "cold" steel and not stainless, which may not be magnetic.

Have fun! 
Best regards,
Geoff Bunza

My local source of magnets

Harbor Freight. For those in the US, if you just want something to experiment with, you can get these at a local HF store.

https://www.harborfreight.com/10-piece-rare-earth-magnets-67488.html

@Michael re:Harbor Freight Magnets

Hi Michael,

Are those magnets so strong that it is difficult to disengage your barge? That is, does the model flex to the point where you have any concerns about breakage? This has become one of my worries for structures.

Have fun! 
Best regards,
Geoff

Magnet force

Geoff,

I didn't notice any real issues, I think mainly because the barge is easy to grab and give a pull and the foam and wood construction is light but pretty structurally substantial. It might have been an issue with the intermittent connection issues I encountered since the wire was trapped between two magnets for contact and then there was a little CA added to hold them. That was a stress point when the contacts were separated but the layout side magnet contacts were done the same way and so far have exhibited no continuity issues.

At any rate my change to the steel screws for the contacts on the barge reduced the amount of force needed to separate the barge but not by a lot and all seems to be working well now.

Re tin

I think this is a great idea.  Solder wire to tin and let the tin make the connection to the magnet. I would think that so long as a magnet is well glued in place There should be no issues with pulling on the magnet.

I do also like the idea though of soldering a wire to a brass “just the right size” countersunk screw and “threading” it into the ring magnets. Maybe a bit of glue at the back end to “help out”.
 

I’ve never tried to tap a ring magnet … so many projects.

Re: using tin as the contact…

I was trying to come up with a way to reduce the magnetic power of rare earth magnets so that they didn’t pull off the piece of tin. Obviously, you can’t use plastic or some other insulating material to do this… But I think you could use an appropriate thickness of brass. That would still conduct electricity, but give you the spacing you need to reduce the attraction between the magnets a little bit. Anyone else have any thoughts? I am thinking this would be particularly handy for buildings or lighting on buildings.

Don”t glue it of course..cut it oversized and bend it over the magnet.

reduce the magnetic power of rare earth magnets

 For things like buildings why not just eliminate the magnet and use some kind of pin plug?  For car to car or engine connections or other things that move one can use a sliding wire in a hole and let it conduct as a wheel wiper does, I used to MU O scale engines that way......DaveB

soldering

Greetings All

instead of soldering, why not glue with conductive glue. Jaycar in New Zealand list part number NM2831 they call Wire Glue. Have not tried it.

https://www.jaycar.co.nz/wire-glue-9ml/p/NM2831

How well it would stick to the magnet I don't know.

Michael

Inserts, Pin Plugs, and Conductive Glue

Hi All,

If you have of prefer low cost, larger magnets, you can easily reduce their effective strength by inserting a non-magnetic layer between attracting magnets or between a magnet and magnetic material (iron, magnetic steel, nickel, and cobalt). The thicker the insert (larger the gap) the weaker the attraction. Separation is the key and it can even be made with an air gap. If you are trying to effect an electrical connection as well, obviously the insert needs to be electrically conductive, like brass, aluminum, stainless non magnetic steel, etc. Attaching the insert in place is another issue, but the insert can be larger than the magnet and the outer perimeter of a larger insert (or corners) can be attached over the face of the magnet. Using most glues might insulate the connection.

Pin plugs can be also be used, as suggested, but requires more precise alignment, and in my case, using tiny pins allows my big fingers to shear the pins off at will !

@Michael, I have not had good luck with similar conductive glues to Jaycar's, both due to poor holds and poor conductivity. I cannot attest that it is exactly the same material, although the cost was similar. The best conductive glue is silver laden electrically conductive epoxy -- but only the one that cures at room temperature. There exists an electrically conductive epoxy that is higher-heat cured. However, his will likely damage the small magnets, as I explained in the article. Both glues are expensive.

'Glad to see this is of interest to modelers. Have fun! 
Best regards,
Geoff Bunza