Model Railway Electronic Inertia

[ljcox]

HV will break down an oxide film but you scheme does not apply high voltage to the film which occurs between the track and the train. Yes it does. The voltage on the track stays essentially constant whether the oxide film opens that connection or not.

If the contact between the track & the wheels goes open, the diode turns off and the voltage rises to the point where the insulating film breaks down.

 

[ljcox]

Higher voltages would create more sparks, which would deteriorate the rails and wheels quicker. The current would be limited to a low value.

Online Sketch: Untitled Sketch by Anonymous Author Your drawing does not make sense. The motor should be across the tracks & the H bridge should control the direction.

First, rectification, then an inductor to prevent huge sparks when the wheel reconnects to the track after breaking, then big capacitor.

Then you need to control the motor's direction, this can be done with an integrated 4-mosfet H-bridge. Not represented is a sensing circuit which uses the last seen voltage on the rails to choose the motor direction.

A H bridge makes it more complicated, but I don't see any reason why the idea cannot be made to work with a H bridge.
I don't understand your point about the "sensing circuit".

 

[Mr RB]

Part of the problem may be track switching junctions that have gaps.

I like the idea of some big electro caps, you can get very small 2200uF 16v ones commonly used now on PC motherboards. If you connect them series inverted they will work as non-polarised caps with no diodes needed (but you need 2 for each cap).

Still it would be pretty easy to fit 8 or 10 of those small electros in a train engine. I'd put the caps across the motor, then connect to the track through a resistor of about 4.7 ohms. That should reduce sparking and give a soft "inertia" start too.

 

[MikeMl]

...I'd put the caps across the motor, then connect to the track through a resistor of about 4.7 ohms. ...

I tried that, and it works when the train is running fast, but doesn't help much when running the train slow. The reason is that the energy in the capacitor(s) is proportional to V², so at low voltages there is not enough energy to cause the loco to coast across the dead spot, and it just stalls. Pumping the storage capacitor to say 12V, when the track voltage is only 2V, and then using an SMPS to keep the loco motor at 2V while traversing the dead spot works well...

 

[MikeMl]

duplicate duplicate duplicate duplicate

 

[crutschow]

If the contact between the track & the wheels goes open, the diode turns off and the voltage rises to the point where the insulating film breaks down.

You are right. I wasn't thinking clearly.

 

[dkvfx]

Wow.... some real grey matter exercises going on here. Me personally am getting lost, but it seems to me there is a solution out there. But what is it.
I'm afraid that if its up to me I would need a component wiring diagram down to resistor values. I'm not that clever.
If someone can find a solution to this, it would be a potential money maker.
All i ask is for the solution for free.
If there is one.
Theres got to be, electronics can solve almost anything

 

[ljcox]

Part of the problem may be track switching junctions that have gaps.

I'm puzzled by this comment.

I know very little about model trains, but I would have thought that contact with the rails is through more than one pair of wheels.

If this is true, then why do small gaps in the tracks matter?

 

[dkvfx]

Hi Len.

You'd be surprised just how often lack of electrical supply occurs. Just riding slowly over points can cause a loco to stall because of the tiny dead spots. Really experienced modellers can get this down to a minimum, but the problem can still be there.

The only thing you can do is give the loco a bit of a push.

It can happen any where along the track. Just for a moment nag you get a less than smooth motion.

An electronicic inertia would solve this beautifully

 

[ljcox]

G'day dkvfx,
You did not answer my question.

I asked if "contact with the rails is through more than one pair of wheels"

Also, I think my suggestion of applying a high voltage will solve the problem.

Many years ago, I worked on the design of electromechanical systems.

Switch & relay contacts that carried small signals needed "contact wetting".

This was a 50 Volt DC voltage connected via a resistor to limit the current.

It broke down any contact resistance due to oxidisation of the metal.

So I don't see why it won't work for Model Trains.

 

[Mr RB]

MikeMl-

I tried that, and it works when the train is running fast, but doesn't help much when running the train slow. The reason is that the energy in the capacitor(s) is proportional to V², so at low voltages there is not enough energy to cause the loco to coast across the dead spot, and it just stalls. Pumping the storage capacitor to say 12V, when the track voltage is only 2V, and then using an SMPS to keep the loco motor at 2V while traversing the dead spot works well...

Ahh, good point! Well then from a "perfect solution" perspective, what about a small battery (9v rechargable?) in the train, and a circuit that monitors the incoming track voltage into a cap, then uses that cap to control the voltage from the battery to the motor?

In that way the motor will always run from the battery and the size of the control cap will give the inertial start/stop feature. Obviously small breaks in the track will be immaterial.

Then the battery could be charged with a little boost regulator IC so the battery is kept topped up from practically any track voltage.

It's now got a little beyond the "add some caps" simplicity but it is still quite do-able and work work really well.

 

[4pyros]

This is all useless unless you can still stop and start the train normally. How would you hook up cars?

 

[dkvfx]

G'day dkvfx,
You did not answer my question.

I asked if "contact with the rails is through more than one pair of wheels"

Also, I think my suggestion of applying a high voltage will solve the problem.

Many years ago, I worked on the design of electromechanical systems.

Switch & relay contacts that carried small signals needed "contact wetting".

This was a 50 Volt DC voltage connected via a resistor to limit the current.

It broke down any contact resistance due to oxidisation of the metal.

So I don't see why it won't work for Model Trains.

Sorry Len for not answering your question.

Yes, usually the contact with the rails is done by as many wheels as possible. My superb Flying Scotsman has 3 pairs of wheels on the main loco.

If one of the wheels hits a dead spot, there will be a momentary lapse in power.
It also has a delicate coupling to the tender with tiny slip contacts to those wheels aswell. I had a fiddle with those today to improve contact. And the running is better. But still as the wheels pass over dead spots, there is a drop in power.

I attached a 12v bulb to the track the loco is running on. As the dead spot problems hit and there is a loss in power, the bulb will also dim momentarily. In my simple head, it shouldn't because the supply is constant.
Could this be some back EMF thing going on? Don't confuse my use of fancy ideas with knowledge.

Dunc

 

[4pyros]

Sounds like your loco is shorting out the track supply. Are the dead spots on switchs?

 

[dkvfx]

Sounds like your loco is shorting out the track supply. Are the dead spots on switchs?

Switches or points are always the problem area as the wheel pick-ups are are searching for the juice. If it is a short, whats the best way of finding out? If the loco has in-built inertia, it could travel over this.

 

[dkvfx]

I tried that, and it works when the train is running fast, but doesn't help much when running the train slow. The reason is that the energy in the capacitor(s) is proportional to V², so at low voltages there is not enough energy to cause the loco to coast across the dead spot, and it just stalls. Pumping the storage capacitor to say 12V, when the track voltage is only 2V, and then using an SMPS to keep the loco motor at 2V while traversing the dead spot works well...

Sounds like you've spent a lot of time trying to solve this.
If the loco is traveling fast, it has its own physical inertia. Its definitely the slower speeds that cause the problem. I like the idea of just giving a 2v oomph. thats clever.

BTW what does "duplicate duplicate duplicate duplicate" mean?

Dunc

 

[4pyros]

If you have three sets of wheels going over frogs one could short to the branch while one of the others is still on the main line. Put a 12 volt bulb in series with one leg of track power. If it gos out when the loco hits the dead spot then the train is losing power, if it gets brighter than the train is shorting out the supply. If the train is shorting out the tracks than built in inertia is just a band aid. Andy

 

[4pyros]

BTW what does "duplicate duplicate duplicate duplicate" mean?

He posted the same thing twice.

 

[dkvfx]

If you have three sets of wheels going over frogs one could short to the branch while one of the others is still on the main line. Put a 12 volt bulb in series with one leg of track power. If it gos out when the loco hits the dead spot then the train is losing power, if it gets brighter than the train is shorting out the supply. If the train is shorting out the tracks than built in inertia is just a band aid. Andy

Absolutely its a band-aid! I wont deny it.

You'd have to explain to an idiot how I put a bulb in series, as for my puny mind the whole thing works in a parallel world. Any chance of a quick sketch what you mean then we can find out what the band-aid is trying to achieve.

Dunc

 

[Mr RB]

4pyros-

This is all useless unless you can still stop and start the train normally. How would you hook up cars?

What's the problem? You just drive it back and forth as usual. Obviously you compensate a little for the added "inertia" just like a real train, by using less speed and allowing a small distance for it to slow down.