# Wiring a Metal Track Without Lane Isolation



## Grandcheapskate (Jan 5, 2006)

I was reading the HO routing thread over at SCI when I came across a very interesting sub-topic. Someone routed their track out of metal and did not isolate each lane electrically from the next lane.

Of course each individual lane has the positive and negative isolated via the slot, but (for example) the positive of lane 1 shares the same "rail" as the negative of lane 2. This wiring requires the use of a seperate power source for each lane.

For those who are interested, you should check it out in the Routed Track subforum of HO. Start around post #284 (page 19). There is no need to recount everything here.

One of the questions I asked, just to get it clear in my mind, concerned the voltage difference between the innermost and outermost lane. Because of the way this track is wired, the voltage difference gets added each time you cross into the next lane. So for example, if the voltage for each lane was 20 volts, the voltage difference between the positive of lane 1 and the negative of lane 4 would be 80 volts.

I'd like to hear your thoughts on this method.

Thanks...Joe


----------



## Rolls (Jan 1, 2010)

If you're on the fence about reading more about this unusual metal track and it's wiring scheme, here's more info for you to decide with - a quick pic that highlights 3 out of 4 things the builder was able to achieve which I found interesting:

1. Extremely tight lane-lane spacing in corners

2. Metal surface rather than just rails minimizes or eliminates the abrupt fly-off mag cars do when when cornering forces coax them to stray from the rails.

3. He's able to run either HO or 1/32, and I imagine 1/43, too on the same track.

4. Self-marshaling capability. Many crashes that would be fly-offs or de-slots become spin-outs on this track. So to "marshal" a car, he flips polarity on the car's lane, hits the gas, then immediately flips the power back, which whips the car around 180, and he's racing again. The other lanes race on, unaffected by this, because each lane's voltage is relative to only it's closest lane's hot rail, instead of being relative to 0V or ground.

Hope it helps,

Rolls


----------



## NTxSlotCars (May 27, 2008)

Diagrams please. Is this AC voltage?


----------



## Rolls (Jan 1, 2010)

No, it's still DC. What's different is that the "-" surface of the inside lane also acts as the + rail of the next lane in. 

He uses the fact that the car and it's pickups care only about the difference in voltage between the pickups, so the car is just as happy with 0V on one rail and 18V on the other as it is with 80V on one and 98V on the other. It just sees the 18V difference and says giddy-up.


----------



## Rolls (Jan 1, 2010)

To Joe's original question, the big spread of DC voltage is a safety issue. 6 lanes at 18V adds up to over 100VDC, from power supplies that necessarily will supply deadly amperage to the careless or unlucky user. 

Of course, what goes to those "rails" is controller-fed voltage. So you get the sum of the voltages of all the controllers at a given moment. Worst case is only when all six controllers are "nailed" at the same time and then someone puts a wet hand on the innermost and outermost surfaces simultaneously. 

I don't think that situation will arise too often. Problem is, it seems to me the penalty is kind of severe if it does happen.

Lower lane voltages help. Fewer lanes help. A compromise, where the middle two lanes actually are isolated cuts the problem in half. I'm sure other less obvious approaches could be thought of to manage the risk, too.


----------



## Grandcheapskate (Jan 5, 2006)

I have a question for our electricity gurus. If the maximum voltage available at your home outlet is 120v, can you create more voltage than that across the surface of the metal? In other words, if you had eight lanes and each had a 20v power source, would you be creating a 160v difference across the entire track? I'm guessing the eight power packs combined could not draw more than a total of 120v at any one time, which I'm guessing could lead to power surges if someone deslots - much like what happens with underpowered wall warts? Or would the circuit breaker blow if all eight power packs wanted all 20v at the same time?

Also, to Rolls's point, could you wire in a fuse which would blow should someone contact across more than one lane?

And Rolls, good point about the controller. If there was only one person using the track, there would be no large difference between lanes 1 and 4 (let's assume a four lane track).

How about this. Would the track work if you are using only one lane and the all the other power packs are off?

I want a metal track!!!!

Joe


----------



## Rolls (Jan 1, 2010)

Joe, Great questions. 

On the 120VAC house voltage thing, it turns out it is in no way a limitation. You just want to have each lane powered by a supply with a "floating" output, in other words, isolated from ground. Many bench supplies are set up this way. In his (Charlie, I think?) track, he gave each lane its own transformer and bridge rectifier, which gives them floating outputs. A reasonable way to think of them is the lane power supplies become sort of like batteries. You can stack 20 9VDC batteries in series and and get 180VDC. Short answer - not a problem.

There are probably some simple or maybe clever ways to minimize the risk, but simply putting a fuse in isn't one of them. The fuse, by itself, has to let enough current flow to run the lane, which is already more than it would take to jolt us terribly badly if we have sweaty palms, one on the inner and the other on the outer, so the current uses our arms and chest as a circuit path. 

If there's only one person using the track, you're right - the voltage difference is just like our home track.

And you're right again - The track will work brilliantly for solo driving with all the supplies off except the one to power a single lane.


----------



## NTxSlotCars (May 27, 2008)

Couldn't you just have a powered controller then? positive rail / negative rail?


----------



## Rolls (Jan 1, 2010)

Here's something to consider...

You could do a metal track without the unique and possibly dangerous stacked power supply arrangement. Charlie's main driver was to bunch lanes up in the corners and get very realistic racing squeezes designed in. When you do that, you quickly hit the point where the rails are too close and your pickup can bridge to the next lane's rail and short. That's what got Charlie to come up with the scheme of stacked, floating lane power. If you're willing to forego such tight squeezes, you can isolate the lanes and use traditional lane powering.

You'd still get the huge benefit of uniform magnetic attraction for any slide angle. You'd also get the self-marshaling ability, too.

A midway compromise is to put an isolation cut in and stack only two or three lanes together. Still tight racing and more safety.

I want one, too!


----------



## Rolls (Jan 1, 2010)

Not following what you mean, Rich.

But that does remind me of another way to compromise... If you're willing deal with every other lane being wired "backwards," you get all the benefits and no increase in shock risk. Well almost none... If you drove only the + lanes and no cars in the - lanes, you could get double normal track voltage on a 4 lane and triple on a six lane. Not sure why you'd want to employ such an odd use case, but it's there.

Now you've pushed the compromise to having to prep your cars to to run either forwards or "backwards." Or be willing to swap magnets or crosswire pickups or some other manner of reversing the polarity of cars that run on the "negative" lanes.


----------



## Rolls (Jan 1, 2010)

OK, another thought on minimizing the voltage risk... The risk is greatest on the outermost and innermost areas, which are the biggest. Maybe just isolate the outer and inner areas from power, leaving only a small strip that's powered. 

Cuts down on the target area for a shock massively. Also really shrinks the area in contact with your sweaty palms, and that's a big deal, too, because your skin is a pretty good insulator. Shrinking the area of contact drops the current that gets through to shock you. 

You still get all the benefits of the metal outer sections in terms of smooth sliding from linear magnetic attraction - those big flat areas just aren't shock risks anymore.


----------



## NTxSlotCars (May 27, 2008)

Rolls said:


> Not following what you mean, Rich.


Okay, on a normal wired track, the controller is a resistor on either the positive or negative side of the circuit.

What I'm talking about is an 18v power supply in your controller.
one side of the controller is positive, the other side negative.
the resistor in you controller controls the voltage coming out of your controller to the rails
one rail is positive, one negative. SO all the car sees is the voltage from one rail to another.

you can stack them without consequence.


----------



## Grandcheapskate (Jan 5, 2006)

Rolls,
Clearly the safest thing to do is to isolate all the lanes. If you do, then you could use only one power source to power the entire track and the greatest shock you will receive would be the maximum voltage for any one lane.

I see two advantages in Charlie's method. One is that there are less slots to cut. Now you only have to cut out the slot (plus potentially an extra slot outside the innermost and outmost lanes). And two, the "rail" section can be wider than in a normal setup (since lanes 1 and 2 can share a rail), or you can bunch the lanes together because you are combining two rails into one (again, because rails are shared).

Or wire every other lane "backwards".

If you are going to do a metal track, the key question would be what metal to use to get you the level of downforce you want, yet make sure it won't rust. I imagine you want as thin a metal as practical. Then it would be a matter of finding out how much someone would charge to cut the slots. If there is not a great difference in price to cut the extra slots for lane isolation, that sounds like the safest route. If however you want the ability to really sqeeze the lanes, then you accept the shock risk and share the rails. I don't think cutting the metal with our home routers is an option for most of us.

I still think you can use a soft material directly under the track (like a hard foam board) as long as it is supported by something more stable underneath. Do you think it matters what material is under the metal as it perstains to slot and or guide pin wear?

And, I wonder if you can play electric football on a metal track???

Joe


----------



## Rolls (Jan 1, 2010)

Joe - Yes, I definitely see that routing fewer slots is a huge benefit, though I didn't mention it. And I like that it's the rail slots, arguably the harder slots to route, that you get to skip. Huge. 

While a simple fuse approach won't do it for lane protection, there might be some clever circuitry that could be designed that could sense something unique about a person shorting the max voltage difference, but I haven't thought of anything so far.

I do think there's lots of unexplored opportunity in choosing the metal. Charlie states that he just got the thinnest sheet metal readily available. I'd guess there's lots of metal choices and with some research and willingness to go beyond home improvement store offerings you could probably optimize for ease of routing and magnetic characteristics. 

I'd be concerned with too soft a material, like foam, for bonding the metal to. I think the sheet metal's sharp, small edge would act to much like a cutting blade on the guidepin, if you don't have channel walls that are willing to do their part in sharing the load on the guide pin. Charlie's experience with the router bits always wearing at the metal contact point reinforces that in my mind.

Second, I think the role that the board (or whatever acts as the substrate for the metal) plays in keeping the slot separation stable is pretty significant. Same for providing stiffness to the sheet metal in general, too. Sheet metal is very flexy, bendy and wobbly by itself.

There'd have to be a pretty compelling reason to stray from a known good track material, imho. And I'm a big styrofoam user, too.

Last, there's definitely a good joke to be made somehow with electric football and Aurora Vibrators, but I just can't put it together this morning.


----------



## Rolls (Jan 1, 2010)

Between Charlie's metal track concept and DSlot's poured form track ideas, I'm really thinking that however you do it, the key to a breakthrough track lies in *separating* the function of providing magnetic downforce from the function of getting juice to the car. They were just lumped together out of tradition and happenstance in the first place. 

Separating them allows you to optimize both independently. Then, if there are any happy coincidences to exploit after the fact to simplify manufacturing or whatever, that's great. But who ever would've picked out skinny rails under the car as a way to provide downforce to enhance racing characteristics of our cars, if those rails weren't there already??? It's an absurd way to do it. Maybe the worst way you could think of to provide magnetic downforce. Optimized for abrupt fly offs and prevention of realistic slide characteristics.

OTOH, rails have some inherent goodness when it comes to getting the juice to the car. So does Charlie's way, actually, where he solders a mini-inverse-rail of wire to his pickups. But here again, the magnetic function and the electric are jammed together, resulting in arguably too much mag attraction and too much area to be shocked from.

My mind wanders towards a sheet of metal routed slot like Charlie's for magnetics, with a wire bead or an actual Tomy-type rail laid on top and welded in place for electric duties. Then a thin sheet of plastic covering the mag surface, but letting the rails protrude. You could even pour plastic sort of like DSlot's thread or spray it or brush it on like Bill Hall does with goop. End goal is optimized magnetic characteristics for realistic racing through the turns, smooth, continuous electric rails, and safety. You can control mag force by choice of material and by how deep the material is set in the plastic.

You could also do this in one process, I think, if you choose the right sheet material for magnetics and electricity, route the slots and then machine away all but the rail contact area to a small depth, just enough for a layer or film of plastic or other track surface material, optimized to tires and insulating electrically for safety. Just a shallow recess machined everywhere but the rails. They could be narrow like Tomy or wider like Charlie's. (There are some significant advantages of Charlie's soldered wire on the pickup method - shoes last forever and dust and dirt become a non-issue electrically, at least. Plus you can get 3 scales running on the same track.)

Of course there are challenges in cost and building techniques, but this is the direction for "new" track that's been on my mind for a little while now.


----------



## Grandcheapskate (Jan 5, 2006)

Rolls,
I think you could achieve the seperation of rail and magnetic surface fairly easily.

You could rout a track out of a thin metal (with the appropriate sub-board). Then use copper tape on top of the metal for your "rails". The underside of copper tape does not conduct electricity so (in theory) the current running through the copper tape will not bleed through to the metal.

Or, how about routing the track in metal and then painting the surface? This should reduce (somewhat) the magnetic attraction. A thick paint might put a decent enough coat on the metal to make enough of a difference in the magnetic field. You could even paint only the areas outside the "rails", leaving those areas exposed. Or use copper tape again.

Just two simple ways I can think of achieving your objective.

Joe


----------



## Rolls (Jan 1, 2010)

Hmmm... Paint instead of plastic. Much simpler. I like it. I was thinking the metal "floor" performing the magnetic part of the work would be recessed deeper to have less attraction. Maybe thinner, less magnetic metal could allow the floor to be up on the surface, and painted. Hmmm... more to think about.


----------



## Grandcheapskate (Jan 5, 2006)

Rolls,
Here's another thought. Use magnetic paint on an MDF surface. In theory, this would allow your board to be magnetic but not carry electricity; well, almost none. Because magnetic paint contains iron power, there is a small current which could pass through the paint, although a coating of regular paint on the surface would isolate the magnetic paint from surface mounted rails (like tape). Any kind of recessed rail would cut through the paint and should (for the most part) isolate the lane.

I posted a thread on here some time ago on this topic with a link to other posts. I experimented with putting iron powder in regular paint but the paint left a very rough surface and I didn't really feel any magnetic attraction - but that could be due to not enough iron in the mix.

Premixed magnetic paint is expensive but may be worth the expense if it really worked. All the magnetic benefits of a metal track while still being able to rout it yourself. Plus it would let you use the less expensive non-magnetic braid.

Joe


----------



## chopchange (Oct 25, 2010)

Cool concept, and food for thought as we have been thinking about out-of-the-box solutions to retardation of de-slotted cars.

What is the fascination with squeeze tracks though, I just do not get that.


----------



## slotcarman12078 (Oct 3, 2008)

The squeeze adds a bit of excitement to the race by keeping the curve passing in check. It also adds a bit of realistic flavor to the mix. Watch a real race, and pay attention to the curves (not talking about circle tracks here, though it occurs there too; with short tracks especially). There is usually only one sweet spot where the maximum speed can be maintained through the turn. Outside wall to inside wall (or chicanes) to outside. Maximum arc, minimum slowdown. With the example shown, I think it's a little of both.

The whole +/- with the - being the + for the next lane thing puzzles me. The tiny bit of electrical know how I have has always used the flowing water analogy to make it understandable. In this case, the water is flowing in both directions in the conduit at the same time. :freak: I don't get it!! I guess I could look at the schematics and try to comprehend the concept...


----------



## ggnagy (Aug 16, 2010)

Here's a crazy idea. How about a pcb, with one side copper and the other side steel. (or a multi-layer with steel in the middle layers. Only need to cut out the slots and then photo-etch the copper power strips. The depth of the fiberglass substrate would effect the magnetic attraction, but you can get some pretty thin boards.


----------



## Rolls (Jan 1, 2010)

PCB is a great idea. I think the board material (FR4?) would be strong for a guidepin and easy to route and the layers could work out great - very clever idea. Great thinking, ggnagY!


----------



## slotcarman12078 (Oct 3, 2008)

Circuit board material is an interesting thought, but the copper layer is very thin, and on the soft side. It wouldn't take too long to wear through it. I guess it would all depend on what was done to the pick up shoes. Adding braid would help, since copper tape is used on some routed layouts. The method of adding soldered wire to the pick up shoes would chew through tape or the circuit board copper cladding in no time. Not trying to be negative, just realistic.


----------



## Grandcheapskate (Jan 5, 2006)

slotcarman12078 said:


> The whole +/- with the - being the + for the next lane thing puzzles me. The tiny bit of electrical know how I have has always used the flowing water analogy to make it understandable. In this case, the water is flowing in both directions in the conduit at the same time. :freak: I don't get it!! I guess I could look at the schematics and try to comprehend the concept...


 I am sure I'm stepping way over my knowledge limit here, but...

Assume four lanes, each with a 12v supply.

Using the water analogy, I do not believe the water is flowing in two directions. The water flows only in one direction - from positive to negative. So when a lane shares a negative and a positive, the negative side can only dump out the amount of "water" supplied by "it's own" positive side (12v). So each negative dumps out 12v while each positive adds another 12v. So in essence you've got the potential for 24 volts at each lane, but since the negative will only allow 12v to flow, the net result is 12v across each lane.

A water pipe can flow only as much water as the pipe size and outlet end allows to pass no matter how much water is available. 

However, since each lane is adding 12v, the resulting voltage potential across the four lanes is 4x12v or 48 volts if a sufficient negative is available.

And, I have no idea what I just said.

Joe


----------



## AfxToo (Aug 29, 2003)

Water and electricity do not mix well. You can only take the analogies so far before they no longer make sense. Which direction current flows is a 150 year old academic argument.

I have not seen the detailed schematics for this setup but I assume that the secret to obtaining the shared conductor for adjacent lanes is due to the fact that the power is really being supplied by what is effectively one ganged multi-tap transformer power supply. The individual step down transformers are wired so they act like one large multi-tap transformer with each transformer tap pair feeding a full wave bridge rectifier for a lane. 

The only thing that matters is the voltage *difference* between adjacent rails. The full power supply voltage supplied across each rail pair is a function of the step down transformer that is wired to the rail pair. This voltage is rectified to turn AC into DC and supplied to the slot car controller. The controller in turn determines how much of that fully rectified voltage is made available to the pickup shoes of the car in that lane. Ultimately the voltage difference at the shoes is solely a factor of the lane controller but the transformer/rectifier determines how much voltage is available to the controller. 

The secret here is that the absolute voltage applied to the rails does not really matter, only the voltage difference matters. Instead of having a single power supply where the reference voltage on one rail is fixed at ground, or zero volts, and the other rail is at a difference from ground, say +18 volts, you have a set of floating reference voltages at each transformer tap. The reference voltages can move in either direction, but it still comes down to the delta between adjacent rails being all that matters, whether the reference tap is fixed or floating. 

Note that you would not be able to replicate this shared rail setup with multiple independent power supplies because each power supply has a fixed reference set to ground. It's essential that the reference voltages be tied together and floating.


----------



## NTxSlotCars (May 27, 2008)

Too,
Could you not then just have powered controllers to create the same effect?
Controllers independent from each other could then be connected to shared rails,
and create that 18v difference we are looking for. Unless, hooking them up in series
makes some sort of unknown outcome. 

Would that be crossing the streams?


----------

