Syma Forum

When i tryed my board rated at 3v the signal would drop out when i tried to run the motors at full throttle.

The only way that I could run it properly was with a second battery to power it.

When the circuit is working correctly, the LED on both the transmitter, and the one you connected to your receiver should look the same. (i.e. half brightness)

P.s. Are your antennas tuned to the correct frequency? (they should be 32mm/16mm long for your transmitter/reciever)

After looking over the details that you have linked, it seems that your receiver needs 5V to function correctly.

However the helicopter can only supply 3~4.2V which is below the spec of your receiver.

I have also had this problem when trying to source the boards for this mod, even with boards rated as low 3v i have still had difficulties with the motors drawing too much current and making the receiver drop out.

The only board that i have successfully got this mod working with (without using a second battery) is the RXA33 by onshine as  it can run on any voltage between 2.4-5V

iowahc Said

should the signal out of the receiver always provide power, or should it be equal to ground?

the signal directly on the receiver board should be off, when there is no signal,

however transistor inverts the signal to the helicopter, to mimic the Ir receivers signal (Hi=0, Low=1),

so yes the signal should be high under normal conditions.

- Ben

Hi iowahc, welcome to the forum

I believe that the motor wiring should be similar the image below, for most clones.

The simplest way to test the circuit, is by connecting a LED to the helicopters receiver board. 

It should give a constant glow. 

If it doesn't light up, or starts flashing, then it implies that you have a problem.

The alternative method would be to use a Oscilloscope (or make a sound card oscilloscope, i will give some details if you are interested) 

Here are the completed circuits, tested and fully working.

The Optional part, is recommended as it allows for basic diagnostics, without the need of a oscilloscope or multimeter.

Parts required:

433MHz Transmitter / Receiver Pair (2.4v)

1x PNP Transistor

1x NPN Transistor

1x Small sheet of Veroboard/ Perfboard/ Stripboard.

1x IR receiver (can be taken from helicopter)

3x 1K resistors

3x 10k resistors

1x 2.2k resistor

1x 3mm red LED (optional)

1x 100ohm resistor (optional)

1x 174mm piece of coax for transmitters antenna

And about a meter of telephone/network/data cable to connect it all together.

Here is a potentially removable version, that I will be working on.

It would require the direct battery connection mod to power it. But should be fully removable when it isn't needed.

As suggested, here is a video of the helicopter in flight.

Why is it's so hard to control it properly with only one hand 😛

the range issue seems to be fixed, i'm not sure what the maximum range is yet, as its too windy outside 🙁

I have tried the above circuit, unfortunately it doesn't work, the 38Khz carrier signal is too fast for the transmitter, the receiver only picks up static. 

Therefore it seems that I will have to go back to the previous circuit connected directly to the helicopters PCB.

One good side to this is that I've found and ordered some ultra low voltage receivers that may be able to run directly off the on-board battery. >Here<

I have to wait for a couple of weeks for them to arrive in the post, when they do I will let you know if this mod is truly viable.

Edit: Please Delete the duplicate posts above. Not sure if this is because of post lag, or my incompetence :P.

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Thanks , If this mod works, it should be compatible with almost all RC Copters, and could potentially allow 4x S107's to be used at a time.

I managed to fix the extreamly short range issue, it seems I pulled transmitters antenna off

Now that's fixed, I'm getting over 2 meters range. (still needs improvement to get the potential >100m )

The circuit has problems running of the copters main battery, as it seems the the motors, when running at anything less than full create too much interference / drop the batteries voltage below the critical 3v/5mA needed by the receiver. So far the fix seems to be using a 70mAh from an old 2ch helicopter.

I'm also looking into further reducing the component count.

Without further adieu, here are some images of the Alpha WIP

The RF pair that I used in this mod (found on ebay) (they were cheap, claimed to have good range, and the lightweight receiver runs on 3v)

The IR receiver and signal inverter circuit can be seen in the left of the transmitter.

And finally here is the helicopter, its a bit of a mess as its had some of my other new mods tested on it (mainly to do with the gyro turning speed)

But as you can see there is a second Li-Po suspended below the nose, the RF receiver is connected to the helicopter by 2 wires (blue/ground and Green/signal) into the port where the IR sensor used to be.

Thanks , I hope this mod goes successfully. (and if should also work on other copters)

It is really in its infant stages, but I've managed to fix the range issues, it seems that I pulled off the transmitters aerial Now its fixed I'm getting over 2 meters.

The next problem I've had is the power source, I cant run it off the main copters battery because the main motors seem to drop the battery below the 3v/5mA the receiver needs to run. Other than a second small (~70mah) li-po, has anyone got any suggestions?