Crosland

But then there is vintage DCC in the shape of ZTC

And, indeed, well before ZTC.

Andrew

Someone somwhere should have prepared a detailed specification for the new 611 and its firmware. This is even more essential if the development work, including writing the new completely new firmware, is being done outside of the ZTC company itself. The programmer will work to the specification. If it's not in the spec then it won't happen, unless the programmer uses his initiative or experience, not always desirable as you can end up with the program doing something that you don't want. 

Exactly, hence my earlier comment "It wil have it's own completely unique set of new bugsfeatures :-)" which some people didn't seem to understand.

From my own dealings with the old ZTC, even they didn't understand all of their own products.

Andrew

If polarity switching is linked to the entry/exit point of your reversing loop you cant change that point - and hence the polarity of your switched section - until the tail of your train has cleared the point. Only a problem if running long trains through a short loop  and not a problem with solid state switching if point is controlled independently.

That's not realy an issue. The train has to be shorter than the reversing loop, otherwise it will collide with itself.

Andrew

 In my experience Perspex has excellent long term stability and does not degrade - as long as it's real Perspex and not a cheap substitute like the acrylic sheet sold for double glazing. Offcuts are often available from local plastics stockists and fabricators.

 

Alex.

Perspex is a trade name. I have always though it is acrylic. Anyone know for certain?

Andrew

Hi I've been on the Fencehouses site but I can't seem to find out how you order a kit

Anyone know

Regards. John

There is a price list with ordering details buried on the blog, but it is certainly not easy to find.

Andrew

The software is being completely re-written from scratch in a more modern programming language which will make it much easier to add new enhancements and maintain. So 511 software bugs wont move to the 611.    

BTDTGTTS.

It wil have it's own completely unique set of new bugsfeatures :-)

Andrew

And the control station decides which mode to use by querying whether the decoder supports direct bit mode, not by any action on the part of the user. This means that it is dependent on the decoder, not the control station.

 

Adrian

It depends how the command station implements direct bit mode. Digitrax decoders are (or at least used to be) particular about the exact sequence of operations (the spec allows for some variation) where other decoders are not.

Andrew

That is partly dependent on the decoder as well. My Lenz system reads values out of Digitrax decoders much faster than it does out of Lenz ones.

 

Adrian

That's more suggestive of different modes being used, e.g. it's using page mode for the Lenz and direct bit mode for the Digitrax.

Easy way to tell is if the time to read a CV varies with the value. Page mode tries up to 256 values until the decoder replies "correct". Direct mode can always do it in 8 or 16 operations.

Andrew

Thanks Andrew,

 

I'm sure he had something to do with ZTC in a previous incarnation though.

 

So ZTC was owned by someone.

Then Dave Nicholson who sold it to SBX, who then sold it Neil.

 

I thought I had read somewhere that Neil had been involved previously .

 

Cheers

 

Ian

Yes, I heard the same. There is some blurb on their homepage that states he was a sub-contractor to ZTC as well as a user.

Andrew

I thought Neil Kinison was the last owner who sold it to SBX?

Other way round.

Andrew

The day after the 2mm chassis workshop in Oxford. Ready to jump in at the deep end for my very first 2mm build:

It's not quite so tidy now!

Testing the chassis

Tender chassis

And body

Unfortunately progress has been stalled for quite a while. I hope to get going again over the Christmaas break.

Andrew

The problem is as I said, and it only applies to loads that are non reactive, Ohms law works with AC RMS values into a resistive load, but motors contain coils, (inductance), and plain Ohms law no longer works accurately.

Substitute the reactance for resistance and you are still using Ohm's law to all intents and purposes.

Even an RMS reading meter can only function correctly with resistive circuits, and do not work properly with non sine wave shapes, this is why an oscilloscope works better for waveform measurements.

A true RMS meter will work with any arbitrary waveform, that's what they are designed for.

It doesn't matter if the circuit is resistive or reactive, you are measuring the voltage at the terminals of the circuit, or the current flowing into it.

You may be getting confused with power measurement where you need to take the power factor into account for non-resistive loads.

Andrew Crosland

Well I hope electronic and electrical engineers do know that Ohm's law does not apply to AC! Even RMS calculations only approximate, and only work with Sine waves anyway.

I suggest you stop digging right there.

Pass an AC current through a resistor and Ohm's law applies just as it does anywhere else.

RMS calculations are accurate and work for any shape waveform and frequency.

Even measuring AC with a meter is fraught with problems,

Measuring AC with a cheap hobbyists multimeter is OK for 50 or 60Hz sinewaves, which these meters are designed for, i.e. signals derived from the household mains.

I suggest you read http://cp.literature.agilent.com/litweb/pdf/5988-6916EN.pdf and then explain where you think the approximation comes into an RMS calculation, and why it only works for sine waves. It's simply a series of mathematical operations and the accuracy is limited only by the precision of your calculator.

Buy a "true RMS" meter and you can measure any waveform and frequency with an accuracy subject to the limitations of that particular meter.

Andrew Crosland

Ohms law does not work with Ac

Try telling that to any electronics engineer!

None of the above applies to DCC, the output can be adjusted in the chip code, or special chips used for coreless motors.

Virtually any chip worth buying can be used for coreless motors these days. All it needs is a high frequency PWM, usually 15KHz or more.

Andrew Crosland

 

 

This means they run on far lower applied voltages, and if loaded, even on DC, can overheat.

This is a significant issue. In simple terms, the lack of an iron core means the heat in the armature windings has nowhere to go.

Andrew Crosland

2) PWM? that's pulse wave modulation? isn't that meant to be a good thing for motor contol?

It can be, depends on the details of the controller

I've got Machimas, chucky Tri-ang Hornby X04 open frame types, and the modern cheap small open frame motors in the latest Hornby.

No core-less types.

I'd give it a try in that case.

Andrew Crosland

For those of us who are not very good at soldering electronics and getting the circuit to work here is a cheap solution from the gadget shop chain Maplin.

 

I think it's order number RN41U “Panel Mounted Speed Regulator Moduleâ€, all it needs is a change over switch and we're in action.

Be aware that this has a PWM output. It may not suit all motors and I wouldn't use it with a coreless motor without knowing the frequency.

Andrew Crosland

Therefore, the 'Short-circuit' or maximum current which can be SUSTAINED WITHOUT TRIPPING is likely to be much higher: 2.5A,3A,5A, or 10A etc

The "maximum current which can be SUSTAINED WITHOUT TRIPPING" is just the normal operating limit of the booster.

A "short circuit" is a fault and should *always* cause the booster or controller to trip.

Andrew Crosland

I have a Prodigy Advance 2 and I run sound locos. What worries me is when a loco runs into an incorrectly set point and shorts. Rather than completely shutting down, the advance keeps applying bursts of power and you get that high pitched buzzing from the decoder. Surely this can't be good? I usually shut the unit off but it means i can't leave the room or stray too far from the controller.

That's fine. The system is reapplying power but then shutting down again because the short is still present. If the short is cleared then the system will come back up normally. Otherwise every momentary short would result in a complete shutdown requireing the power to be re-applied manually.

Andrew Crosland

Unfortunately as far as increasing the frequency of the PWM type, you can't do much, as above the lower frequencies of about 100 hz it becomes very audible, and would then need to jump to 20 khz to work without the sound generated.

 

PWM would work at 20khz, but only to adjust the range of speed around a value, control from zero to max impossible because of hysteresis in the magnetic field in the motor. It works with specialist coreless motors quite well for laboratory uses etc, and control equipment, but not models.

 

Stephen.

DCC decoders use PWM drive. Almost all modern ones use a high (inaudible) frequency and it works fine with ordinary motors. It is *required* for coreless motors which can very easily be damaged by low frequenct PWM.

Andrew Crosland

Are you sure?

Yes:-)

Why does applying a high-frequency clean the track? The only reason I could think of is that a varying current would create a varying magnetic field which scrambles some of the dirt. It shouldn't actually even have to be AC, although that would be better because it reverses the field.

A relco gives out a high frequency, high voltage limited to a very low current when the normal DC is interrupted by dirt. The idea is that the high voltage breaks down the dirt, or ionises the air, or something like that, and allows the DC to flow again.

Andrew Crosland

Good reason for that:

 

HF cleaners use a high-frequency signal to keep the track clean.

DCC systems use a high-frequency signal to talk to decoders.

 

Anyone see a similarity here?

No, they are very different in all respects (voltage, current, frequency). The fact that DCC is AC has nothing to do with track cleanliness (or not).

DCC also uses full voltage all of the time, so the age old DC problem of trying to make a small voltage push current across a poor connection (rail to wheel) is eliminated completely since this is always max voltage.

That's far more relevant.

Decoder features can also help. Zimo decoders, with the capacitor backup supply, can be set to only stop on a section of track where there is good reception. A slow moving DC loco can stop on dirty track and then cannot be started without the hand of god.

Andrew Crosland

If they are what I think they are then start at this page http://www.rapidonline.com/Cables-Connectors/Connectors-Terminal-Blocks and look at the pluggable types.

You need to know whether you want metric (e.g. 5mm) or imperial equivalent (e.g 5.08mm) pitch.

Andrew Crosland