I am interested to know what is in the timing transponders (for remote controlled cars or karts) and how they actually work. There are relatively few manufacturers and the prices are rather high!

The basic idea is that you have a loop of coax in the ground with a resistor half-way (more info halfway down here). Even this loop of coax costs an extortionate amount from the suppliers

So I was wondering how the magnetic inductance works to send a digital ID. I am interested in building something for less than the few hundred $ the transponders sell for. I know that DIY timing can be done with IR or other methods but want to know if building some sort of transponder system is possible first.

 

I'm not sure what that coax thing is for but it kinda sounds like some kind of duplexer. You know so that the transmit and receive signals are offset just enough that they don't interfere with each other.....Just a guess.

 

They are RFID devices.

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Well from reading the link you supplied this is not a trivial system. The 'loop' is just a passive pick-up, like an antenna. The real complexity is in the decoder as each car's transponder has to transmit on a separate frequency unique from every other car in the race. That means the decoder is possibly a multi-channel receiver that can process all channels at the same time and then send the processed timing information digitally to a computer for display and storage purposes. While I'm sure one could design and built such a system, it does require a lot the effort and would not be a simple or low cost project.

I'm curious if the device in each car is really a 'transponder'? A true transponder doesn't transmit a signal unless it is first sent an interrogation signal. If that is the case then the so called decoder has even a more complex function of continuously sending unique interrogation signals for each car's transducer and waiting for a possible response before interrogating the next possible transducer. The method would not require that each transducer work on a seperate frequency but rather respond on the same frequency but only after receiving a proper signal.

So the link it short on details and I can't really tell if it's an independent multi-frequency system or a polled transducer type system. Either way there is probably a reason these systems cost what they do

Again this is not a simple project nor a simple application. If every car was physically limited to stay in a fixed lane then some optical sensing would be possible and the whole project would be quite simpler in design. But that would limit tracks to straight run drag race types as fixed circular tracks would not have equal lengths for each racer.

PS: I don't think a simple RFID type device would work because of the high possiblity of detection collisions as many cars may be triggered at the same time if reaching the loop at the same time.

Lefty

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See this link.
http://en.wikipedia.org/wiki/Transponder_timing

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They don't all transmit on a different frequency, the AMB (most popular manufacturer) use the same frequency but transmit a unique identifier. The decoder unit recognises this.

And I know for sure that the AMB devices are magnetic inductance, rather than RF. Perhaps they are still 'RFID', but not in the same way as what people now consider 'RFID' (e.g. door swipe) and therefore not what appears on Google!

I don't think the box is a duplexer, from reading online it can contain a resistor but basically just combines the two ends of the loop into the single coax which goes back to the decoder.

For my use, I can guarantee only one car across the line at once (at a narrow part of the track). The reason I'm not sure 'normal' RFID would work is because of the possible speeds, even 10mph across the loop might mean it isn't detected? 1/100th of a second resolution would be nice, but not essential.

 

So, any ideas how these work quickly enough to time something travelling at e.g. 10mph (obviously the professional ones manage much faster speeds).

Are there any active RFID solutions that would work? Or is it possible to build something similar to the timing transponders that mostly work on magnetic inductance (which I still don't fully understand!).

If not, I guess I'll be looking at IR solutions

 

Yeah there's stuff out there. It's been around a long time. Well, the technology. Your right they use a certain bandwidth of frequency than use ID codes. It's a TDMA (Time Division Multiple Access) system. As more cars go on the system undoubtedly it will require more bandwidth. Pretty soon we will all look like micro-waved chickens...lol. Oh, and then they will want more power for the upper end models. Never fails. That's the reason we all have small dish antennas for satellite TV today. They used to transmit about 15 watts from the satellite because we understand anything more could be dangerous to our health. So they upped it to I think 200 watts. Thus a smaller dish is needed to pick the signal up.

Though I have dabbled in a little VHF/UHF design, nothing higher. I still like my HF. And I a licensed ham. So, word to the gov't....

Keepa you hands off!

 

You're talking utter rubbish again - the power was restricted simply due to power restraints on the satellites. Increasing the power requires a larger heavier satellite, bigger solar panels, and larger heavier batteries.

Power levels on earth are miniscule by the time it's travelled 20,000 odd miles

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Combine that with all the rest of the rf pollution out there.

I never speak rubbish. I just pay attention to what's going on by not watching TV (propaganda tool).

 

Well I have to admit the rest of your post confuses me completely

But as far as I understand, the AMB system works by each active transponder sending an ID with a random time between (to remove collisions if more than one crosses the line).

What I don't understand is how they use inductance to send an ID. Perhaps some form of RFID would work, but I don't know enough about it. So are there any RF or similar devices that can:

1) Detect quickly enough for a vehicle travelling between 10-20mph
2) Be reliable to detect with some accuracy

 

I can assure you, systems like the AMB use RFID technology. I know this because I use to be a member of an RC club. We purchased a system from AMB and were told by the reps that it used RFID for the transponders, and it worked well above 10mph. I raced a Ofna Buggy, see pic

Attached Images

ofnaPD.jpg (178.7 KB, 6 views)

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Heh excellent! Well I guess my desires & requirements are as follows:

1) something that will be used for 1 week a year, hence the desire for a cheap solution
2) differentiation between 6 fixed karts (or 32 changing drivers for bonus points)
3) no need for multiple detections at once, the track narrows to 1 kart at places that could be used for the loop
4) detection between 10-20mph

Could anything be built with RFID for significantly cheaper than the cost of AMB kit, which would hardly be used for most of the year!

 

Funny, much of what you post is rubbish from your wild imagination (like this one).

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For just one week a year, anything fancy hardly seems worth it. Prior to the AMB system, our RC club used vid cams to determine winner.

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