converting syma s107 to radio control

I'm working on converting a syma s107 to radio control. These are great little helicopters for under $30 except they use IR, and it can be choppy. (this is the helicopter for reference)

I have an ASK/OOK transmitter/receiver (**broken link removed**), it's small enough that it doesn't encumber the heli too much.

My progress so far is this:
+Located control signal output of the chip on the controller
+Realized that the signal needed to be inverted, and implemented a simple NOT gate

Current hurdle:
since the receiver needs 5V and the heli is 3.7V it still can't work without external power. With 5V applied the radio control works, but adding another battery would add too much weight.

Does anyone know if they make a small transmitter/receiver set that can work on less than 3.7V, or have a recommendation for a circuit that can boost 3.7V (which in operation may be only 3.2) up to atleast 5V in a small and simple enough package to fit in the helicopter? I have some MC3406 chips on hand, I don't know if they would work in this case.

I have an E-flite Blade mSR micro helicopter. It has a normal single main rotor with swash-plate and a small rear rotor. It has a gyroscope on its receiver/servos circuit board. It operates from a 3.7V lithium rechargeable battery and at 2.4GHz so its antenna is only about 1.25 inches long.

Newer E-Flite Blade micro helicopters can fly upside down.

That is a pretty nice one, when I think about what you could get just 10 years ago for 3 times that much money the difference is crazy.

I think I almost have my conversion working, this heli only cost $22, and it flys great except when communication breaks off. I had it to the point where the radio was controlling it but it needed an outside 5V source. Then I hooked up the power wrong and burn out my receiver. No big deal, it cost about $5. I'd still like to complete this little project. For now I'm just going to try to build a little voltage booster and hope the Vripple doesn't interfere with the radio. I've never built a voltage booster before either so it would be a good skill for me to add.

Another reason I'm doing this is that I teach intro to mechatronics. We can spend about $50 a student on an electronics project for them, and usually it's nothing that cool, maybe a burglar alarm kit. The class already involves using an IR camera and IR LEDs for position tracking, and computer interfacing with an arduino, both use processing language and could be easily integrated together. Imagine instead of a lame kit if I figure out a way to take a $5 radio transmitter, a $22 helicopter, and convert it into a radio controlled drone using IR position tracking and the arduino to control the radio. Right now this is impossible due to IR cross talk, also the heli tends to go out of range and fall too often. Even before I get it simple enough for them to each build one, I could make a drone to let them practice with. I think the project could eventually be made simple enough, they would get the heli, cut off the IR receiver, wire up the not gate involving two resistors and a transistor and connect the 3 wires of the RX module. Then they would connect the 3 wires of the TX module to their controller, cut the LED off the helicopter and wire in the two tracking IR LEDs, and then use the existing arduino and processing code for the camera to track and control the drone. I could have the code already done for them to make it more accessible.

Castle Creations sells a Berg receiver that is rated to 3V ($35):

**broken link removed**

I have used Berg's. They are decent. You might also try:

https://www.hobbyking.com/hobbyking/store/__116__190__Tx_Rx_Systems_Parts-All_Receivers.html

Unfortunately, HobbyKing doesn't list specifications right up front. All of the ones I checked were 4.8V, but since HK sells copies of almost everything, there might be a low voltage receiver lurking there somewhere.

John

That is a pretty interesting thing. I could see it being useful in a micro RC. I was meaning ASK or OOK transmitter/receivers. These RCs already do the encoding, I just need to transmit the pulse. I just found this one that specifically claims low power 2.4-5v operation (**broken link removed**). So I'm going to give it a try. I know that they can work, hopefully this will get the device working.

I have tried that receiver with Holtek encoders for other control purposes, it might work. What frequency do you want to use?

Syma and others make a slew of 27 MHz units. Here are some examples:

**broken link removed**

Unfortunately, the brief description doesn't give voltage, but I suspect there is a good chance they are operated off a single LiPo cell or similar.

I just searched on "micro RC 27 MHz." Even Target has some. Ten years ago or so, I ripped a 27 MHz receiver out of an RC blimp that was OOK and built a twin-engine micro scale airplane for it. It was essentially a glider that was steered by differential operation of each motor. Very difficult to fly in any sort of breeze. It was low voltage too.

John

I do have some broken micro rc cars in my parts bin. They only had a 1.5 volt battery to begin with so that's probably what the little receiver runs on. The only problem is that I'd have to figure out where to tap into the transmitter. If I can find the diagram for whatever chip they use I can simply locate it by the output pin. I have ordered some of these low power TX/RX sets because for the class I would still need a way of doing this in bulk.

Here are some more details of the model. It was described in the March, 1997 issue of Model Aviation, which is published by the AMA. My how time flies. That was 15 years ago. The model is still in my model hangar.

The transmitter is described as a "1-Chip Transmitter." It uses the Samsung KA2312 chip with a 27 MHz, 3rd overtone crystal. The receiver uses the Samsung KA 2311 chip. The spec sheet shows the receiver rated at 3.0 to 6.0 volts.

You might want to check into you parts bin. Some of the cars may use the same old chips.

The TX was 9V. Pin 1 (left channel) was brought high; right channel used pins 3 and 4 and was brought low. Power was pin 9, ground was 5, crystal was 6 and 7, and output was too smudged (pin 8???) to read.

John

Do you have pictures and or any further info on how you are doing the conversion for the SYMA S107? We are building these things in a tent in the desert (mostly out of boredom) something with a longer range would be a lot more fun.

Sure nitrousscout, the circuit is as simple as can be:

**broken link removed**

**broken link removed**

To the right there is an example of how I laid it out. So far this is my best working version. Note that other models of RX may not work, this one is rated for as low as 2.5V, the syma is 3.7V and many similar transmitters are 5v.

To tap into the control signal for the TX (my photo of the open handset came out blurry) but if you are holding the PCB with the back facing you and the IR LEDS at the top, the chip that outputs the signal should be on the lower left, its a 14 pin DIP and I think the only one on the board, the pin at the bottom left side of that (closest to the corner of the board) is the one you need. Wire from that pin to DATA on your TX, then just pull the power from the battery lines. For the antenna a 17.2cm wire is specified.

For future improvements, I'm experimenting with using a RX with an inverted output but the pulse frequency capability of the one I got seems too low, it goes rythmically in and out of control at about 1 Hz, as in, if you hold the throttle on the helicopter runs on for about 3/4 a second then stops for about 1/4 second over and over, but the speed while it's on responds. Also, I've tried putting the NOT gate at the TX end, but it didn't work, perhaps the amplification is necessary.

On an amusing side note, I posted about this on an RC forum, and a guy there insists, saying he will eat crow and his hat if he's wrong, that this is not possible and I'm a liar. He gave several explanations as to why and even wrote some formulas. To my surprise even after I posted a video where I showed the heli up close, then covered the IR emitter and flew the helicopter, he said I was lying and it can't be done. Just funny how some people can be so sure of themselves when they haven't even tried something. Video is here if anyone's curious. I wouldn't have responded to him, but he started out like he was curious how it worked, if he had let on that he was just a cynical doof right off I would have ignored him.

Thanks for the update.

I'm with you and can't see any reason your approach won't work. I don't even need to see the video. Besides, videos can be faked too easily. How do we know the real controlling pilot is not off screen -- like hiding behind your bar?

Those helicopters are great fun indoors on a snowy day. Mine wore out fairly quickly from stripped/worn gears. I have several of the IR "radios" and batteries just sitting around waiting for another project. As far as I am concerned, it is about the most fun you can have for <$20 today.

John

Hey thank you for posting all of that, for viewing. I cannot speak for your project but I have seen a engineer where I am located do something like this with a different IR heli. Unfortunately he left and we never learned how he did it. I ordered that part today so hopefully in a month when I get the part I will post some pics to back up your statement.

Hey John, do you have any pics of the actual board after you installed the new transmitter. I am have a bit of an issue viewing your drawing. (not that it is bad)

Thanks

nitrousscout said:

Hey John, do you have any pics of the actual board after you installed the new transmitter. I am have a bit of an issue viewing your drawing. (not that it is bad)

Thanks

Click to expand...

I think you may mean Paul (aka Triode).

John

Do you have a pic of how you wired the remote? Thanks.

Paul,
Can you take a look at the attached pictures and tell me if I wired something wrong?


View attachment 63498

View attachment 63499

Sorry it took a while, I just turned in my thesis today. I've been busy. If you have the same transmitter as me you might be tapping in to the wrong pin. The signal pin on mine was the one farthest from the rectangular notch where the IR LEDs attach, and nearest the corner of the board. If you look closely, even on your picture, you can see that the trace from that pin goes to a surface mount transistor which is traced to the LEDs.

It also looks like you have a diode on your data out line rather than a resistor. Other than that the connections could be right, I don't know what kind of transistor you've used, so I can't tell if you are using the correct pins.

Here are the steps I used to assemble the receiver and inverter in a neat and compact way:

View attachment 63526
Break apart pins with diagonal cutters and desolder them

View attachment 63527
Attach the components to the transistor

View attachment 63528
Insulate the middle lead

View attachment 63529
Wrap it in electrical tape, place it against the board and cut the leads to length, then solder into place

Paul,
Thanks for putting up the pics, once I scrounge the right parts I will let you guys know how it came out. Thanks a ton!