Slot Car Track Construction

Track building index

Magnetic Traction

There is increasing interest in building MDF/ timber tracks with magnet traction.

Magnet traction depends on a track built with something like iron that will be attracted to the magnet in the  car.  With a normal MDF/ timber track using copper tape or braid traction magnets don't work.  Of course the cars with traction magnets can still be driven on these tracks, but they have rather less grip than their makers intended.    If you want to build an MDF track for magnet traction cars read on.....If you are building a track for non magnet cars (such as cars built to BSCRA rules) you won't find this article relevant! 

Many home set / ready to run hard body cars have traction magnets.  These attract the cars towards the steel rails in plastic track and this increases the grip available from the tyres.    This article is about how to make a track that will attract magnets.

 I know some people have  strong feelings for or against magnet traction.  I am not going to get involved in that debate.  I'll try and give some help with one question:  

 If you want working magnet traction on a scratch built track how do you do it?

Firstly I should explain that I haven't built magnet traction tracks myself.  These pages are aimed at providing a practical guide to track building.  So a big thank you to everybody who has told me about their experiences building  magnet traction tracks.

The essential feature of a magnet traction track is that the magnet in the car is attracted towards it.  That means some  ferro magnetic material (usually iron/steel) has to be incorporated in or near the track surface.   Commercial plastic track usually has plated steel pick up rails, which are flush with the surface - or in some makes protrude a fraction of a millimeter above the surface.  When scratch building a track you can choose to replicate this, or spread the magnetic material more widely.  

Normally  magnet traction tracks are built with magnetic material all the way round the lap, but there may be advantages in just having magnet traction in corners (See below). 

Magnetic Braid

This is by far the most widely used way of scratch building a track with magnet traction.   Magnetic braid looks pretty much the same as copper braid, and everything I've said above about building a track with copper braid applies equally well to magnetic braid (for more see the main track building pages ).  All braid is woven from strands of metal wire. In normal track braid the strands are tin coated copper. Magnetic braid has the strands made of steel, plated with another metal such as nickel, copper or tin. The widely used Magnatech braid has steel wire with a thick layer of copper and an outer layer of tin.  Traction magnets are attracted to the wire and the coatings stop corrosion. The magnetic braid I've handled feels a bit stiffer than copper braid (hardly surprising given the relative stiffness of copper and steel), but can be laid in exactly the same way.  

I would recommend that the surface of the braid is laid slightly below the track surface.  Some makes of commercial plastic track have the pick up rails slightly above the track surface.  Solid steel rails are plenty robust enough to withstand cars running over the exposed edge.  Braid is much more prone to damage, so mounting it slightly below flush gives the edge some protection.   People with experience of magnetic braided track tell me frayed strands of braid can occur (as indeed they can with non-magnetic braid).   The  frayed strands of magnetic braid get attracted to the magnets, so stick up. I’m told this can be repaired by cutting off the loose strands with scissors then sticking down the loose end with super-glue. Obviously it's it's a good idea not to spread the super glue over any more of the contact surface than necessary (glue doesn't conduct electricity!) 

I don't know of any tracks using magnetic braid in corners and copper braid on the straights, but it could be tried.

Solid Metal under the Tapes

The only example I know of was built by Gary, although I have seen discussions on the subject from other people.   Gary's track uses tin plate underneath the copper tape to provide magnetic traction in corners.    It used an large tin can flattened out and cut to fit the shape of the tape in the corner. have a look at Gary's web site for more detail.   Thanks to Gary for answering a few questions.

This is certainly a low cost option - recycling tinplate is free!  However, there is quite  a lot of work in producing and fitting the tinplate bits. Gary said it took him about 3 weeks at 2 or 3 hours a night  His 2 lane layout is rather smaller than a club track.  Obviously for a track with bigger corners or more lanes you can multiply that time up in proportion.   That seems to confirm that it takes longer to build than magnetic braid.  Personally I'd suggest that makes the tinplate method too time consuming  for anything bigger than a 2 lane home track. As well as the extra straight line speed, only using tin plate on the corners has the very significant advantage that  the total quantity of tinplate to be cut is not too daunting. 

 It looks to me that there could be challenges in aligning the tinplate bits accurately.  Gary's track uses tinplate strips no longer than 2-3 car lengths which minimizes alignment problems, but does make for quite a few joints. The tinplate was stuck down with Evo Stick, the sections were butt jointed, the gaps filled  and sanded down smooth.  (There is copper tape over the top provides continuity, so electrical connections to the tinplate is not an issue.)  

 Also I wonder how easy it it to get the tin plate to stay flat enough and to stay glued down adequately.  On Gary's track the tinplate is not recessed into the track surface except at the ends where the MDF is cut to give a slight ramp rather than a sudden bump where the copper tape joins the tinplate surface. Gary tells me he wasn't sure if this would work before he built it, but in fact this works fine for homeset type cars.  (People used to higher performance non-magnet cars may be a bit surprised by that - I guess it's "horses for courses".)   It turns out that  Gary's pick up rails protrude by just under 0.4mm above the track surface which is typical of some makes of plastic track.   This still leaves the question of how well the exposed edge of the copper tape will stand up. Gary's track was built about a month before this was written, so we don't yet know if there will be any concerns about maintenance. 

 If anybody has tried this then please let me know - I'm sure the readers of this page would be interested in any practical tips. 

Magnetic Paint

An alternative is painting the track with magnetic material and using normal copper tape or braid. I've not tried this myself, but there is an interesting example on  the Slot Forum International posting from Nils explaining more about how he painted his track with magnetic material (you'll need to scroll down to the 7th posting on page 2.)   Nils mentions one US supplier of ready mixed magnetic paint, put magnetic paint in a search engine and you find  several others both UK and US based. This paint can be quite expensive,  Nils mentions you can make  your own using an oil-based primer mixed with a powdered iron which works well.  Nils used about 1½ gallons (7 litres) of paint for his 65 ft (19.8 meter) 3 lane track. He used three light coats of magnetic paint with a smooth foam roller, covered by a light top-coat of ordinary water-based interior paint. Obviously this can be multiplied in proportion to the number of lanes and lap length.
On Nils track this provides a noticeable magnetic traction effect.  As there is less magnetic material in the track surface, the  magnetic attraction is  less than magnetic braid or plastic track. After 2 years use Nils track was still working fine.  
A builder could choose to use magnetic paint in and near corners and ordinary paints on the straights. Given the price of magnetic paint, this will  make a healthy cost saving. 
Magnetic paint has been tried on a scratch built track for digital lane changing system, and there is a difficlty - see Slot Forum International posting from "Gundam2000".  The problem occured when the tapes were laid direct on top of the magnetic paint because the paint is slightly conductive casing a problem  with high frequency signals used with digital systems .  This is not a problem with normal slot cars, the current passing through the magnetic paint is too small to make any difference.  A simple solution is to put a layer of ordinary paint between the tape and the magnetic paint.
The laws of physics make it  obvious that the amount of grip will depend on the amount of iron in the track surface.   So the amount of iron powder mixed with the paint and the thickness of paint / number of coats is important.   If anybody else has tried this then please let me know - I'm sure the readers of this page would be interested in any practical tips.

Magnetic Rails and car handling

The  effect of magnetic braid and solid metal under the tapes on car handling is very similar to running on plastic track.  Cars with central traction magnets  have to be driven so they slide very little; once they start to slide much the magnet no longer over the magnetic rail in the track so they loose grip and break away very suddenly.   Drivers who are used to this characteristic on plastic track will feel at home on magnetic braided tracks.

Magnetic paint is different, the whole track width is painted, so magnetic grip is available even with the tail well out of line with the slot.  Therefore the sudden break away of magnetic braid/ plastic track doesn't occur.  Nils confirms that this allows  the magnet cars slide progressively near the limits of adhesion in very much the same way as a non-magnet car that's handling well.

Do you need magnetic traction all the way round?

Several people have pointed out that grip is really important in corners, but isn't critical in a straight line (unless the cars are so powerful that wheelspin is a problem).    Magnet traction certainly provides extra grip, it also provides extra friction which reduces maximum speed on the straight.  This leads to the idea that magnet traction is only really needed in corners, and not on straights.  Obviously with commercial plastic track you've got steel rails on straights as well as the corners.  With scratch built tracks it is possible to choose where you put the magnetic material.  There are reasons why magnetic material might need to be extended a little before and after each corner.  On entry to a corner the guide starts going round the bend while the traction magnet is still on the straight, so in theory it might be good to have the magnetic material extending about a cars length down the previous straight to stop cars twitching too far sideways at the corner entry. After the exit to a corner cars with insufficient grip do wag their tails as you accelerate out of a corner, so in theory it might be good to have the magnetic material extending a short distance down the following straight rather than substantially reduce the grip at the corner exit. There are some illustrations of how long non-magnet cars take to straighten up after a corner here.  How long do magnet traction cars take to straighten up?   I'd be very interested to hear from anybody who has tried it.

Chris Frost

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Painting and Laying the Braid / Tape

Page updated June 2012