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Electronic shutoff system

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1. How it works

The diagram below explains the process. The algorithm is quite simple. The transmitter is placed into the handle. For powering the transmitter we added a small lipo battery along with the button which is always pressed IN as long as the handle is in your hand. (*** another option is described below).
The transmitter generates frequency signals which includes the pilot's ID number. The Transmitter's output is connected to the lines. We tested different frequency ranges and found which range is best for passing a signal through the lines. A High Frequency signal can be transferred using just one wire.

So we have a signal which has encoded pilot's ID and this signal is going to plane through the lines. On the plane we have the receiver board which gets signal from the lines. The receiver can be connected directly to one of the lines inside wing, or via the bell crank's axis. Since two pilots can fly together at the same time (and lines tangle can happen) received signal may be mixed from 2 different signals, so the receiver has analyzer to detect its own pilot ID signal. Actually it will detect its own ID signal even in a mix of four different signals (I'm not sure if anybody really need it). Let's say analyzer didn't find his ID. Then it starts a timer and keeps trying to find the signal. If it fails during 300 milliseconds then it finally launch valve which brakes fuel flow. We took 300 miliseconds as initial value to avoid accidental stops. This needs to be tested and we are expecting that this time can be reduced.

2. Handle

We tried to make our solution as small as possible so everybody can embed it to existing handle. At the same we will offer new handles (different common types) with already included transmitters and replacable batteries for those who like ready-to-fly solutions.
So what is inside. Actually just 3 parts:

Transmitter board 0.7" x 0.7" ( 18x18mm ) and 0.11 " (3 mm) thickness

Replaceable 3V battery

Shutoff Button

The button is placed in a center of handle, so taking it you are automatically push the button to pressed state. This actually gives an interesting feature - if you press OUT the button during flying - it will shut off engine as well. This feature can be very useful everywhere, either in test flight so if you don't like how engine is working you can stop it immediately, or in a contests to stop engine right after combat time is finished.

*** Another option is to replace mechanical button with touch sensor. This is promising more convenient usage but it didn't fully tested yet.

3. Plane

For the plane there are also 3 parts (except wires):

Receiver board 1.07" x 0.9" ( 27x22mm )

Li-Po 3.6V battery

Shutoff Valve

Total weight with valve: 0.53 OZ (15 g)

The receiver system behaves as follows:
Once you connected the battery into receiver board it launches and stays in the listening state. During this state GREEN LED is blinking which indicates that system is ready and stays in a pre-flight state.
There is not ON/OFF button so you can not forget to turn it on. Once you start your engine GREEN LED will be ON continuously. The boarsd has a noise detector so once the noise becomes more than 60 db it turns the system ON.
A continuously green light is the indication that system is on and in a working state (this way a judges can get confirmation that the system is on and armed)
After you launched your engine it waits 5 seconds for pilot ID signal which should came from the lines. If pilot ID is not received during this time it stops the engine.
Current system now is not so good because sometimes there are situations when a pilot can not get his handle with in 5 seconds (Example: he is helping to untangle lines or other reasons) but for now this is what we have.
As a solution we suggest the button in the handle be pressed to the ON state even if it is not in the hand.
Another option which we are currently working on is having another touch sensor to detect that plane is currently taken by mechanic. Once we solve that problem we will introduce it separately.
If any problem is detected by the system such as is it detects that the battery does not have enough charge it will turn on a RED LED and this is a sign that shutoff can not be used.
Based on our latest tests full charged battery may work for one whole day**** without re-charging (using shutoff about 10 times).

****We are now in the process of testing another valve and plan to update this information soon.

4. What is inside transmitter

If you are not going to design your own electronic shutoff you may want to just skip the next 2 sections. The next sections are mostly for the people who want to understand the technology we used for designing our. We want to share our experience and we would be interested to get any information or feed back from others.

Below is our Transmitter diagram. It is actually very simple and uses standard RF ASK modulation. It has a High Frequency quartz stabilized generator, Low Frequency Pilot ID generator, and ASK modulator.
The pilot ID signal relies on a range from 200 Hz to 3 KHz with a step 100Hz so it gives (3000-200)/100 = 28 channels (could be increased). Actually even if the ID signals from 2 pilots will be the same it will still be working. The only issue could be that the pilot can’t stop the engine during a line tangled and it will only function if a line is broken. We are going to improve the ID algorithm in the future but for now it appears to be working good enough.

5. Receiver

The receiver is a bit more complicated. It has 5 different modules both analog and digital on the same board. The receiver has pre-amplifier which is amplifying both the signal and noise. Then signal is filtered from noise and goes to the amplifier module.
After amplifying it de-modulates it to remove the High Frequency part of the signal and leave only the pilot ID signal (or 2 pilot ID signals from both pilots if the lines are tangled). At that point the only task is to make sure that required ID signal is existing.
This task has been solved by using FFT detection algorithm (Fast Fourier Transformation). For that task we put microcontroller on a board (AVR ATMEGA88) which will perform FFT with a 25 KHz sample rate. The microcontroller is also used to detect noise level from a microphone which is embedded into the board.
The diagram bellow explains how all the modules work.
There are 2 options: (A) when only one pilot is flying and (B) when both pilots are flying as well as lines are tangled.


	1. How it works The diagram below explains the process. The algorithm is quite simple. The transmitter is placed into the handle. For powering the transmitter we added a small lipo battery along with the button which is always pressed IN as long as the handle is in your hand. (*** another option is described below). The transmitter generates frequency signals which includes the pilot's ID number. The Transmitter's output is connected to the lines. We tested different frequency ranges and found which range is best for passing a signal through the lines. A High Frequency signal can be transferred using just one wire. So we have a signal which has encoded pilot's ID and this signal is going to plane through the lines. On the plane we have the receiver board which gets signal from the lines. The receiver can be connected directly to one of the lines inside wing, or via the bell crank's axis. Since two pilots can fly together at the same time (and lines tangle can happen) received signal may be mixed from 2 different signals, so the receiver has analyzer to detect its own pilot ID signal. Actually it will detect its own ID signal even in a mix of four different signals (I'm not sure if anybody really need it). Let's say analyzer didn't find his ID. Then it starts a timer and keeps trying to find the signal. If it fails during 300 milliseconds then it finally launch valve which brakes fuel flow. We took 300 miliseconds as initial value to avoid accidental stops. This needs to be tested and we are expecting that this time can be reduced.
	2. Handle We tried to make our solution as small as possible so everybody can embed it to existing handle. At the same we will offer new handles (different common types) with already included transmitters and replacable batteries for those who like ready-to-fly solutions. So what is inside. Actually just 3 parts: Transmitter board 0.7" x 0.7" ( 18x18mm ) and 0.11 " (3 mm) thickness Replaceable 3V battery Shutoff Button The button is placed in a center of handle, so taking it you are automatically push the button to pressed state. This actually gives an interesting feature - if you press OUT the button during flying - it will shut off engine as well. This feature can be very useful everywhere, either in test flight so if you don't like how engine is working you can stop it immediately, or in a contests to stop engine right after combat time is finished. *** Another option is to replace mechanical button with touch sensor. This is promising more convenient usage but it didn't fully tested yet.
	3. Plane For the plane there are also 3 parts (except wires): Receiver board 1.07" x 0.9" ( 27x22mm ) Li-Po 3.6V battery Shutoff Valve Total weight with valve: 0.53 OZ (15 g) The receiver system behaves as follows: Once you connected the battery into receiver board it launches and stays in the listening state. During this state GREEN LED is blinking which indicates that system is ready and stays in a pre-flight state. There is not ON/OFF button so you can not forget to turn it on. Once you start your engine GREEN LED will be ON continuously. The boarsd has a noise detector so once the noise becomes more than 60 db it turns the system ON. A continuously green light is the indication that system is on and in a working state (this way a judges can get confirmation that the system is on and armed) After you launched your engine it waits 5 seconds for pilot ID signal which should came from the lines. If pilot ID is not received during this time it stops the engine. Current system now is not so good because sometimes there are situations when a pilot can not get his handle with in 5 seconds (Example: he is helping to untangle lines or other reasons) but for now this is what we have. As a solution we suggest the button in the handle be pressed to the ON state even if it is not in the hand. Another option which we are currently working on is having another touch sensor to detect that plane is currently taken by mechanic. Once we solve that problem we will introduce it separately. If any problem is detected by the system such as is it detects that the battery does not have enough charge it will turn on a RED LED and this is a sign that shutoff can not be used. Based on our latest tests full charged battery may work for one whole day** without re-charging (using shutoff about 10 times). **We are now in the process of testing another valve and plan to update this information soon.
	4. What is inside transmitter If you are not going to design your own electronic shutoff you may want to just skip the next 2 sections. The next sections are mostly for the people who want to understand the technology we used for designing our. We want to share our experience and we would be interested to get any information or feed back from others. Below is our Transmitter diagram. It is actually very simple and uses standard RF ASK modulation. It has a High Frequency quartz stabilized generator, Low Frequency Pilot ID generator, and ASK modulator. The pilot ID signal relies on a range from 200 Hz to 3 KHz with a step 100Hz so it gives (3000-200)/100 = 28 channels (could be increased). Actually even if the ID signals from 2 pilots will be the same it will still be working. The only issue could be that the pilot can’t stop the engine during a line tangled and it will only function if a line is broken. We are going to improve the ID algorithm in the future but for now it appears to be working good enough.
	5. Receiver The receiver is a bit more complicated. It has 5 different modules both analog and digital on the same board. The receiver has pre-amplifier which is amplifying both the signal and noise. Then signal is filtered from noise and goes to the amplifier module. After amplifying it de-modulates it to remove the High Frequency part of the signal and leave only the pilot ID signal (or 2 pilot ID signals from both pilots if the lines are tangled). At that point the only task is to make sure that required ID signal is existing. This task has been solved by using FFT detection algorithm (Fast Fourier Transformation). For that task we put microcontroller on a board (AVR ATMEGA88) which will perform FFT with a 25 KHz sample rate. The microcontroller is also used to detect noise level from a microphone which is embedded into the board. The diagram bellow explains how all the modules work. There are 2 options: (A) when only one pilot is flying and (B) when both pilots are flying as well as lines are tangled.