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Train Magic

1724 Views 16 Replies 5 Participants Last post by  Graham Plowman
Has anybody got information about Danish company having invented a system by which a computer knows the exact position of locos. It is called Rail Magic .
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I suppose the first question is: how does this magnetic implementation comply with radio/interference legislation ?
That's the easy bit - it complies. They are scattering small permanent magnets around a layout. There is no legislation covering that, so its fine. No different to using fixed magnets for uncouplers.

Their loco-mounted detector appears to have a three-axis magnetic sensor in it (not dissimilar to the compass sensor in phones), which can measure the field created by the magnets (which is over the field for the layout room from other magnetic sources, plus the earth's magnetic field).
They then compute something from that field (possibly strength, orientation in three axis) and transmit it back to the base unit over the rails. The base unit knows the magnetic-field reports from each loco for each cluster of magnets, so knows position as a cluster of magnets are passed by a particular loco.
I think its then using back-EMF pulse counting from thereafter to compute position of loco between clusters of magnets (so can't work with a Dyna-drive loco which has a free-wheeling clutch, but there are not many of those around).

The rest, I agree, is unlikely to fly as currently presented.
The booster issue is not the product-killer (though its serious), its the detector piggy-back installation. That makes it impractical for most owners (those who regard plug-in decoders as their technical limit). The maker proposes to build a new DCC decoder, but I can't see how they'll replicate the sound options on ESU and Zimo decoders, so that's a "no sounds" option (or "generic chuffs and grunts"), and another large category of users no longer interested.

- Nigel
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Thanks for the clarification Nigel.

I guess it remains to be seen how accurate the magnetic proximity detection is and then the subsequent application of BEMF measurement to control motors and the actual positioning of a loco. Given that every motor is different, I would imagine that there must be some sort of tuning and synchronisation process.

Something that isn't clear to me: does this system use Railcom to send the positional information back to the logic box or does the logic box detect 'disturbances in the force' from the magnets ?

Personally, I think more effort should be put on resolving the network stack issues of DCC in order to significantly improve its longevity. It only needs a new feature to come along and everyone is up for hardware changes again, like they were for RailCom. A proper network stack would negate that necessity and facilitate numerous enhancements.
First para - don't know how they do it, but assume they are "tuning" things against every loco. Given they measure a loco during a calibration process, assigning a value to BEMF-pulses:distance ratio for each loco would be relatively simple, and thus distance travelled per-loco can be known. (Not fundamentally any different to the speed calibration used in Traincontroller and iTrain, so those software packages can calculate distance travelled beyond spot-detectors).

Second para - no idea what method they're using for back-communication. Something RailCom-ish would seem logical. (If I found a bit of information on which systems did and didn't work reliably with their setup it would give clues about whether its RailCom. ).
There's no way (with the physics I understand) they will be able to detect magnetic issues at the main control box; the magnet detection is only in the device in the loco, which then sends some data back to the main control box about the magnetic field the loco is passing through.
Logically, one would only need a handful (possibly as few as 3 or 4) magnetic field orientations to cover an entire layout because the track (including all turnout positions, which have to be known to their system) also comes into consideration. A loco can only move on the track. From field shape detected as "B", the track will allow the loco to go either forwards to "C" or backwards to "A". Similarly at "C", the loco can go to either "D" or "B", so I could re-use the same magnetic shape as "A" at "D". If I knew the orientation of the loco on the track (probably do from the detected field shape), then the question as to whether the next field from "B" is "A" or "C" is already known; going forwards it must be "C", the only question is when will I get to "C".

I agree with your sentiments over a proper upgrade to a bidirectional stack architecture for "DCC-version-2" or whatever it is to be called. But see no large moves in that direction.

- Nigel
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This is what they say in their setup document -

"This system will use the address 8191 for special operations and this address must therefore not be used by any locomotive."
Thanks, but doesn't tell us anything about how the return data gets from the on-train magnetic sensor to the central control unit. Just that their system "reserves" address 8191, but that's a decoder address, for information going from centre out to decoders (not the other way).
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