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Jun 25, 2009, 08:27 AM
Thermal Wrangler
DrFragnasty's Avatar

automatic F3B trigger system

Automated F3B turn signal system

With all the high-tech companies involved with modern RC why is it nobody has developed a reliable F3B pylon trigger system?

Imagine having base A & B automatically triggered without the need for people sited at either pylon? Safer, fairer and it liberates at least 2 to 10 people from the arduous task in the hot sun.

Surely a gps system exists that can do this?

Propellor heads, your time starts now...

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Jun 26, 2009, 06:21 PM
working to the closest cm
jirvin_4505's Avatar
Hi Chris
There has been some similar discussion in the High Performance forum. Without any successful conclusions. Seams GPS won't hold lock in High G turns.

cheers Jeff
Jun 27, 2009, 03:30 AM
Thermal Wrangler
DrFragnasty's Avatar
Thanks for the link Jeff.

I've passed my question onto a US manufacturer and they're looking into it.

I would dearly love to see a system developed. I have fond memories of doing base-b at Albury Nats 2006 for 3hrs in 40C 100% humidity ;0)

Jun 27, 2009, 07:53 AM
smokin electrons...
skyzking's Avatar
Hi Chris, i put some thought into it a while back as i asked a similar question here as well a while ago.

As well as flying rc i also do full scale flying. You may be aware of a navigation aid called an NDB (non-directional beacon). Its basically a miniature station which transmits a discrete signal on a designated frequency (usually AM bandwith i think). There are receivers inside the aircraft called an ADF which pick up the signal and point to the station. You can also tell when you are above or abeam the transmitting station as the ADF needle will change direction.

We can reverse this system and put the transmitter in the plane and the receiver on the ground so when the plane goes past the pylons the receiver can trigger the beep. The transmitter inside the plane will be small and light weight.

The free flight people use a similar transmitter for their tracking devices. Maybe something like this can be thought out for F3B...

Hope it helps...
Jun 27, 2009, 09:54 PM
Thermal Wrangler
DrFragnasty's Avatar


Interesting Abdullah,

Something like NDB (Wikipedia ) might be the way to go.

Ideally it needs to track up to 10 gliders for a distance task.

And not interfere with full-size air traffic.

Might need 2 RXs; one on base A, one on the base A line some distance away to provide the coord data for calculating distance from the base A line.

The glider houses the TX which also has an altimeter to provide the value to calculate distance:

distance from base A line = root[ distance to glider ^2 - altitude^2]

The key is to have the altitude data in the equation.

Which equation? Dunno. I'll have to track down a mathematician

Jun 28, 2009, 11:31 AM
Registered User
timmig's Avatar
Seems we could use the real race car transponders---but you have to find a way to boost the reciever signal for 3D space!! Cars just have to drive over or under it---plane pilots are not accurate enough at this time to make the existing system feasable.
Jun 28, 2009, 09:16 PM
Tragic case
davidleitch's Avatar
I'b buy at least one such system if it was less than $1000 or maybe even more and reliable. I have to practice F5B on my own and therefore miss out on proper competition timing practice. There must be a few of us in the same "boat".
Jun 29, 2009, 02:18 AM
Registered User
The motor racing here in Australia use some kind of bar code system where a little black box in the car registers 100's of a second when they pass special recording markers on the track.
The person to talk to Chris is Craig Wilson at Natsoft in Launceston, he is the supply and timer for Australia motor racing on the timer system.
But we need a system that will cover 180 degree at base A and B and span to the moon.

Jun 29, 2009, 03:39 AM
Registered User
The car racers are using the AMB timing system, do a search for AMB or Serpent RC car, this system is a very successful in rc car as well as real car racing application. Internet has their stories. Yes, it cannot work for 3D application, though.
Jun 29, 2009, 06:32 AM
I do this for fun!
Hi guys,

I'm an old Electronic Warfare and sensor operator. The problem here is accuracy and reliability vs cost. Jeff is right, GPS has reception issues, also its accuracy is nowhere near good enough for signalling the crossing of a base line.

You have to remember that no-one has come up with a sensor that is anywhere near as good as the Mark 1 Mod 0 human eyeball. So what happens is the designers of sensor systems have to spend lots of money overcoming the shortcomings of the sensors themselves, if reliable, repeatable results are needed.

Can you imagine how impressed everyone would be, if at the end of a distance flight one of the 4 planes did not register a Base B turn? Either the competitor gets shafted and loses the comp, or the entire group have to be re-flown. So whatever technology solution gets put in place has to be accurate and reliable enough to basically never make an error, and that's a very costly thing to ask for.

Having said all that, if I was going to design a system I would use 2 scanning lasers on the ground, 1 at Base B and 1 about 50m away, both inline with each other and the vertical plane the planes must cross. So both lasers scan a beam very rapidly back and forth vertically across the sky and this beam defines the end of course. There would be 2 laser stations to overcome one plane being shielded from the laser by a closer plane.

In each plane would be a laser detector with filters so only the right frequency of laser is 'seen' by the detector. When the laser is detected a transponder in the plane sends a signal which is detected at Base A and sounds the appropriate buzzer for that plane.

Problems to be overcome with this system:

1. cost and legality of lasers with enough power and focus to give sufficient range.

2. design of a laser detector/transmitter sensor which is small enough, light enough, with low power consumption and yet sensitive enough with good enough optics that it detects the laser signal with 99.9% repeatability regardless of aircraft aspect to the laser beam. Detection, signalling, reception and buzzer sounding must happen within 0.1 sec of the plane crossing the base line, and whatever lag there is, it must not vary from one lap to the next, or one plane to the next. All this at low enough cost for hobby use.

3. design of an interface to the scoring system so that planes can be listed, organised and 'recognised' by the system when it's their turn to fly.

4. the whole system to be portable, robust and weatherproof.

If you had to pay a technology firm with the relevant expertise to develop such a system I doubt you would see change from $250,000 for the first system, and it could well be more than double that amount.

All of which makes me sad because I am very keen to get into F3B and without a system like this it is very difficult to practice. Sigh...

Jun 29, 2009, 06:57 AM
F3B and F3K
RetoF3X's Avatar

In plane position sensing via signal correlation

I am watching this discussion with great interest.

I have an idea that relies on a geometrical construction. Place two opposing detectors on a line normal to the turning plane (base A or B) at equal distances "L". The two detectors record the same signal (in terms of phase or time lag) only when the emitter is somewhere on the turning plane. It can be positioned at any point on the turning plane, still the two detectors record the signal with the same phase.
What you have to compute is the auto-correlation of the two signals, when this function reaches its maximum, the emitter has to be somewhere in the plane ( provided the two detectors have a synchronous read out). You don't have to compute that by yourself. There are circuits around that can perform the task with MHz bandwidth (you can actually just mix the analog signals of the detectors).
The signal from the plane must be varying in time in order to make that scheme work (like in the case of GPS). It could be also a low coherence source that only "interferes" when it is in phase.

Last edited by RetoF3X; Jun 29, 2009 at 07:17 AM.
Jun 29, 2009, 07:51 AM
Thermal Wrangler
DrFragnasty's Avatar


Thanks for the contact Mick, ditto the AMB transponder info Polar Bear...worth a look even if the system is optimised for ground level activity.

Ken has lots of valid points; expecially the reliability issue in a competition in all-weather. The laser option is interesting since the latency for the optics is negligible.

The laser detection would need reflectors on the aircraft so that an unrestriced view for all angles would be presented; top/ bottom/ both sides; maybe reflective tape on nose/ boom/ tips but then how would the reflected laser hit a ground-based receiver when it could just be reflected into space?

My gut feeling still goes with radio freqs/ 2 to 4 GgHz microwaves since it's omni-directional and assuming it's mounted on the glider it presents a signal almost regardless of atitude.

Reto...I'm still studying your idea...where is the glider in your diagram? ;0)

Last edited by DrFragnasty; Jun 29, 2009 at 07:55 AM. Reason: animal logic tidy-up
Jun 29, 2009, 07:59 AM
F3B and F3K
RetoF3X's Avatar
Hi Chris

No glider in the drawing yet. The emitter or the source of the signal originates from the glider. The black dots just illustrate the position of an emitter and that is what we want to localise.
Maybe I was too mathematical. Just place a source wherever you want in that plane. The two detectors will detect the same signal with the same time lag just by geometrical reasons (you can draw it in 2D and connect some points to understand it).

The rest is just the math and some signal processing to evaluate if the signals are "in-phase" or not. My suggestion reduces the general 3D localisation problem to a 1D problem (which is the case here, we just need one coordinate, say the x-axis to be localised. The height z and the lateral position y is not relevant. We just need to know if the plane is on the turning plane or not).

You could use microwaves for the source, the signal just has to be varying in time, as mentioned.

Last edited by RetoF3X; Jun 29, 2009 at 08:06 AM.
Jun 29, 2009, 08:17 AM
Thermal Wrangler
DrFragnasty's Avatar
Like this?
Jun 29, 2009, 09:00 AM
F3B and F3K
RetoF3X's Avatar
Hi Chris

Yes this is more or less what I am suggesting. For clarity (to avoid confusion, the signal is emitted from the F3B-plane), one could also draw a glider in the plane of Base A and B. From your drawing it should be obvious now that if a signal is emitted from the current position of the schematic glider, it will result in different time lags/phase of the signal arriving at the different detectors.

For the guys working in optics this is quite a familiar problem, in some research they are mixing the signals from two detectors that measure the same photon source. Thereby they can calculate the correlation function. That framework should also apply for our localisation problem.

Last edited by RetoF3X; Jun 29, 2009 at 09:18 AM.

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