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It's alive... on 2.4 GHz

Old 08-22-2007, 08:17 PM
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13BRV3
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Default It's alive... on 2.4 GHz

Greetings,

I've been following Mike's brushless conversion thread pretty closely, and that prompted me to do a little snooping with a scope. When Futaba came out with their 6 channel 2.4 GHz system, I bought two, and a few extra receivers, then promptly sold all my 72 MHz gear on Ebay. The only thing that remained on 72 MHz was the DF, and it really bugs me, though I realize this is largely a personal problem

A few days ago, I asked Mike Dammer if there were any plans to come out with a 2.4 GHz DF, and he said no, because it would interfere with the cameras. He's right about this, and I've had to get cameras on 900 MHz, and 1.2 GHz to avoid it with the fixed wing planes. Since I really want to use 2.4 GHz for the DF, I decided to see if I could make it work.

There are two main versions of DF boards, most have the built-in receiver, and the latest have a Berg receiver attached to the vertical board. I only have the old style to play with, but I have to believe the Berg style may be even easier to convert. On the old style, they receive the signal, but don't separate it out into individual channels like a normal R/C receiver does. Instead, they send the combined signal from the vertical board to the controller on the horz board, then let the controller do the separation in software.

I've never had a Berg board to play with, but they must either pick off the combined signal inside the receiver, or they have some hardware to recombine the channels so the controller will get what it's used to seeing. They might even reprogram the controller for the Berg. If they actually take the normal outputs, and recombine them in hardware, then it would seem like you could use any receiver in place of the Berg, as long as you get the signals in the right place.

Since I have the old board, I figured I either had to find the combined signal inside my Futaba receiver, or come up with hardware to recombine the outputs into a signal that would make the DF happy. I think the latter would be a better solution, since you could use any receiver without modification, but I'm pretty far out of the loop on current hardware design. I'm planning to try to figure out how to do this, but that solution will have to wait a while (hoping someone else will design the hardware).

I took my (employer's) trusty scope, and poked around until I found the combined signal in the Futaba receiver. It really wasn't that hard to do, since it's fairly obvious which chip does the decoding. The REALLY hard part is trying to solder a wire to that microscopic contact. The other problem is that the pulsed waveform is inverted from what the DF normally sees, but this is fairly easy to fix in hardware. Actually, it would be easier if Radio Shack still carried logic chips, but I guess they don't anymore. Did I mention I was pretty far out of the loop on hardware I needed an inverter, and don't have one, but fortunately I had a nand gate chip which will do in a pinch.

After inverting the signal from the bowels of the Futaba, I noticed that there were still some differences in the waveform, but it all seems to be in the 6th channel. For some reason, Futaba seems to have an extra delay before outputting the 6th channels, and the DF receiver doesn't. My hope was that the DF would handle the first 5 channels fine, and I wouldn't care if the 6th came through or not. Amazingly, and much to my surprise, that's exactly how it seems to work, though I'm suspicious that the 6th pulse is going to rear it's ugly head somewhere it's not supposed to be. Too soon to tell.

Well this is getting way too long now, so here's a link to my bench test video from this afternoon. It's about 35 MB, in windows media format, and no, I don't recall why I was so fascinated by the 5th channel switch

http://www.radrotary.com/2dot4GHzDFtest.wmv

This is very much a works in progress, so don't get too excited yet.

Cheers,
Rusty

Old 08-25-2007, 03:03 PM
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13BRV3
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Default RE: It's alive... on 2.4 GHz

I've had a chance to fly the DF with my 2.4 GHz mod, and it flies just like normal. I've flown a whole pack inside, as well as a few minutes outside with TI on. It will be interesting to see if there is any change in the power drop issues, since I was getting them on just about every pack that I flew outside. If the problem had anything to do with RF interference to the 72 MHz receiver, then there should be a change now. Note that I didn't say it would be "better"

I realized that the battery connector on the Futaba receiver doesn't have any electrical connection on the board, so I took the wire that I soldered inside the receiver, and ran it to this previously unused pin. Now I can just plug a normal 3 pin servo connection into the battery plug on the receiver to pick up the combined receive signal. Pretty tidy. The lump you see in the cable is a 7404 hex inverter chip, which I'm using to invert the combined receive signal to the polarity the DF expects to see.

I still think the best overall solution will be to come up with some bit of hardware to take the separate RX channels from any receiver, and convert them to the combined signal that the DF wants to see. Since my current solution works fine for my needs, I'm less motivated than I could be to try this

Cheers,
Rusty
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Old 08-25-2007, 10:00 PM
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Old Man Mike
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Default RE: It's alive... on 2.4 GHz

Rusty,

Congrats on an excellent detective job. Your discovery explains something that I had wondered about for sometime: how did Dammer get the five/six channels from a berg receiver that has just 4 channel outputs. The answer is now clear. Individual channels are not used by the DF controller. The microcontroller uses the demodulated signal before channel extraction. The modification on the Berg receiver card that made it unique to DF is simply the same thing that you did on the Futaba receiver. That allowed all the advantages of the RX DSP processing without having to pay for the more expensive 7 channel receiver. Clever.

I see no reason to combine the signals. Your approach should work fine. You can also use the individual throttle output channel from the Futaba receiver for the brushless motor conversion. Good work.

Mike
Old 08-26-2007, 10:55 AM
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Default RE: It's alive... on 2.4 GHz

Thanks Mike. I'm still fairly amazed that it was this easy to make it work. I just flew a whole pack in the back yard, and it's the first time in weeks that I didn't get a power loss. It's way too early to get excited about that, but reducing, or getting rid of that problem would be icing on the cake. Getting rid of those arcing and sparking brushed motors is more likely to be the real fix, and yes, I will be using the channel 3 signal for your brushless mod

The only reason I think it would be better to combine the individual channel outputs from the receiver is that it would provide a solution anyone could use, with any receiver. On the other hand, maybe no one else cares, so problem solved

As for the Berg setup, I'd be REALLY interested in knowing more about how they have the receiver hooked up. In pics, I can see that the normal output pins seem to be soldered to the vertical board, and the antenna wire goes to the vertical board as well. Are there any other wires from the receiver? If they brought out the unmodulated receive signal, where is it? Did they use one of the pins that had been for an individual channel (not ch3 of course)? I imagine they could have soldered the pins to the vertical board as a mechanical attachment, and maybe there isn't any electrical connection to most of them. I'm sure they bring in 5V and gnd though. Inquiring minds...

Cheers,
Rusty
Old 08-30-2007, 04:04 PM
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Default RE: It's alive... on 2.4 GHz


ORIGINAL: 13BRV3


As for the Berg setup, I'd be REALLY interested in knowing more about how they have the receiver hooked up. In pics, I can see that the normal output pins seem to be soldered to the vertical board, and the antenna wire goes to the vertical board as well. Are there any other wires from the receiver? If they brought out the unmodulated receive signal, where is it? Did they use one of the pins that had been for an individual channel (not ch3 of course)? I imagine they could have soldered the pins to the vertical board as a mechanical attachment, and maybe there isn't any electrical connection to most of them. I'm sure they bring in 5V and gnd though. Inquiring minds...

Cheers,
Rusty

Rusty,

I'll be purchasing the DF VTi (with the newer Berg board) this week and I'm VERY interested in converting over to 2.4Ghz. I current have a Spektrum DX7 transmitter and AR7000receiver...I would love to try this mod once the DF is in my possession...any tips would be much appreciated.

Thanks
Old 08-30-2007, 04:38 PM
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Default RE: It's alive... on 2.4 GHz


ORIGINAL: MORENOENNYC

Rusty,
I'll be purchasing the DF VTi (with the newer Berg board) this week and I'm VERY interested in converting over to 2.4Ghz. I current have a Spektrum DX7 transmitter and AR7000receiver...I would love to try this mod once the DF is in my possession...any tips would be much appreciated.

Thanks
At this point, I'm not sure how much help I can offer. If you've suffered through the previous posts, you know that I've never had a Berg board to play with, and so far, Mike has not taken the hint to provide me with any details The most current guess is that they're taking a combined receive signal from inside the Berg receiver, and feeding it down to the controller.

If that's true, then the next problem is finding that signal inside your receiver. I can tell you where it is inside a Futaba 6ch 2.4GHz receiver, but have no idea about the AR7000 receiver. Even if you find it, soldering the wire is almost microsurgery, with significant risk to your receiver.

I still have some hope of making a hardware conversion that would take the normal outputs of any receiver, then combining them to feed back to the DF. Unless something like this can be done, 2.4 GHz won't be a very realistic mod for most people. Unfortunately, I don't imagine doing this for a couple months, if I get around to it at all.

For now, I'd suggest flying it just like it comes from DFI until you get the learning curve behind you. If there's any damage in the mean time, the stock board can be repaired for a reasonable flat fee from Spectrolutions, so there's not so much to risk. If the board is modified, I don't know if they'll offer the same repair service it if it's damaged.

Sorry there isn't better news, but at least there's some hope.

Rusty
Old 09-02-2007, 09:58 PM
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Default RE: It's alive... on 2.4 GHz

How will RC devices not be affected by other 2.4 GHz devices like WiFi routers and many other numerous wireless consumers devices?
Old 09-02-2007, 10:17 PM
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Default RE: It's alive... on 2.4 GHz


ORIGINAL: Sky High

How will RC devices not be affected by other 2.4 GHz devices like WiFi routers and many other numerous wireless consumers devices?
It's magic

Seriously, the FCC assigns frequency ranges to keep devices from interfering with each other. "2.4 GHz" can mean 2.400 GHz or 2.499, which has a lot of range. If you're having trouble sleeping, this sort of info is probably public record, but I assume the FCC has assigned narrow bands to certain types of devices, and they don't overlap.

That being said, the 2.4 GHz video does get messed up by the Futaba radio, though the Futaba doesn't seem to hurt the video transmitter. I've run the Futaba in my office, where the 2.4 GHz router lives, and it doesn't seem to cause any problems with either device. FWIW, I have 900 MHz and 1.2 GHz video cameras.

Rusty
Old 09-21-2007, 07:55 PM
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Default RE: It's alive... on 2.4 GHz

Will someone please make an attempt to do 13BRV3 2.4 ghz mod on the newer DF Berg board...pleease, pretty please
Old 09-21-2007, 09:14 PM
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13BRV3
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Default RE: It's alive... on 2.4 GHz


ORIGINAL: MORENOENNYC

Will someone please make an attempt to do 13BRV3 2.4 ghz mod on the newer DF Berg board...pleease, pretty please
With the standard disclaimer "I haven't actually seen a Berg board", I would be willing to bet a good chunk of money that the mod I made will work just the same with the Berg version of the board.

Can you post some closeup pics of the receiver area of the Berg board? I'd like to see the back side of the board as well. Particularly, I'm looking for how many wires go from the Berg to the DF board.

Cheers,
Rusty
Old 09-22-2007, 09:29 AM
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Default RE: It's alive... on 2.4 GHz

Hey 13BRV3, don't bash me for my response but I have not yet purchased the DF...I'm actually selling my T-Rex 600 w/AP2000i Stabilization system today so that I can UPGRADE, yes upgrade to the draganflyer for Aerial photog. I've been a quite observer of you and Old Man Mike's brushless/super sized DF conversion board and once I receive and master the flight of the DF I will, well hopefully do the 2.4 ghz mon...I currently have the DX7 and AR7000 TX/RX. I'm one who likes to plan far ahead and...believe it or not I have already purchased half of the brushless mod parts. But if I had to choose between the brushless mod and 2.4 mod, It would unquestionably be the 2.4 ghz.

Could someone please post close up pics of the Berg board for 13BRV3???
Old 09-22-2007, 10:05 AM
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Default RE: It's alive... on 2.4 GHz


ORIGINAL: MORENOENNYC

I currently have the DX7 and AR7000 TX/RX. I'm one who likes to plan far ahead and...believe it or not I have already purchased half of the brushless mod parts. But if I had to choose between the brushless mod and 2.4 mod, It would unquestionably be the 2.4 ghz.
Nothing wrong with planning ahead [8D]

The biggest challenge will be the AR7000 receiver. Unless you can find some documentation of where the PPM signal is located, it will take an oscilloscope, and some time to find it. There's even a possibility that it can't be made to work. The Berg signal is a perfect match for the DF board, but the Futaba ends up being inverted, so you have to invert it for use with the DF. The AR7000 is a big unknown to me.

BTW, your plan of learning to fly it stock first is a good one.

Rusty

Old 09-22-2007, 11:12 PM
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Default RE: It's alive... on 2.4 GHz

Thanks Rusty, I'm actually thinking about purchasing the Pro version...a bit expensive but the size and the fact that the crew over at DF confirmed that they would be able to build one using my existing 2.4GHz TX/RX...all I would have to do is send it to them. 700 bucks would be subtracted from the cost if i use my own TX/RX. Still a bit expensive but it is a beaut of a machine. [link=http://www.rctoys.com/videos/draganfly-innovations/video.php?sku=DF-XPRO&url=DF-XPRO_4.mov&type=mov&title=none&tn=none&mode=video]Pro Version[/link] Look at the size of that thing! But seriously, I've read over and over that the V version is pretty durable in crashes, I can only image how durable the pro version is...look at the thinkness of the CF arms. My only concern is replacement blades and cost.
Old 09-23-2007, 12:11 AM
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Default RE: It's alive... on 2.4 GHz


ORIGINAL: MORENOENNYC

Thanks Rusty, I'm actually thinking about purchasing the Pro version...a bit expensive but the size and the fact that the crew over at DF confirmed that they would be able to build one using my existing 2.4GHz TX/RX...all I would have to do is send it to them. 700 bucks would be subtracted from the cost if i use my own TX/RX. Still a bit expensive but it is a beaut of a machine. [link=http://www.rctoys.com/videos/draganfly-innovations/video.php?sku=DF-XPRO&url=DF-XPRO_4.mov&type=mov&title=none&tn=none&mode=video]Pro Version[/link] Look at the size of that thing! But seriously, I've read over and over that the V version is pretty durable in crashes, I can only image how durable the pro version is...look at the thinkness of the CF arms. My only concern is replacement blades and cost.
That is the Xpro and you will want to hold off buying it until Dammar releases the next version any time now. It has been upgraded to a brushless design which should be quite an improvement over the current version.

Mike
Old 09-23-2007, 12:26 AM
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Default RE: It's alive... on 2.4 GHz

CRAP....Thanks for that Mike! Wow that's great news. I wondered why they didn't go with brushless from the start.
Old 11-09-2007, 05:18 PM
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Default RE: It's alive... on 2.4 GHz

I-ve poked around the AR7000 quite a bit. No PPM signal to be found. Instead you can get at the two receiver signals as normal serial digital bits. Eventually that may be the most elegant solution.

For now, with the help of RC-CAM man, I-ve come up with a simple circuit which can be used to combine the 7 PWM outputs on the servo output pins back into a reasonable PPM signal. See http://www.rc-cam.com/forum/index.php?showtopic=2064. On the ground my mikrokopter flight controler accepts that signal OK. But haven't reached flight test status with it yet. On problem is that you can reprogram the AR7000 to output the pulses on the output pins in a different sequence, e.g. to have two aerolon servos operate very close together in time. That would cause havoc in an MK with my circuit as suddenly the channel numbers would be shifted.

Probably a cleaner way to do the same would be to use an ATMega8 to track each PWM pulse and make sure the channel sequence is maintained. And the best way would be to feed the two RX signal to that ATMega and output a clean PWM signal. For info on the digital signal see this thread: http://www.rcgroups.com/forums/showthread.php?t=714299
Old 11-10-2007, 01:17 PM
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Default RE: It's alive... on 2.4 GHz

This is a follow-up to answer some questions about how the Futaba FASST conversion was done with the R606FS receiver.

From what I've read, the R606FS is the same as the upcoming R607FS, except that they left off one resistor that would connect the 7th channel to the signal pin location on the battery plug. Since I'm using that pin to output the PPM signal, the R606FS version works great.

The PPM signal in either of these receivers is only 5 channels, with the 6th and 7th channels being sent directly from the processor to the output. I'm guessing they're sending the 6th and 7th channels simultaneously on a second stream, but that's only a guess. What this means is that the DF will only see 5 channels with this method, though the 6th and later 7th channels will be available on the receiver outputs if you want to use them for servos or some other function. The only reason that's a problem is if you have one of the latest boards that allows the 6th channel to adjust the Ti sensitivity.

The PPM output is inverted from what DF wants to see, so you have to invert it to make it work. In the pics, I've use a 74OL6001 opto-isolator inverter, and as you can see, I've just connected the power and ground from input to output, so there's no isolation for the power. This just makes a nice tidy package when heat shrinked. I've also used a common 7404 hex inverter, which works fine as well. Simply use one of the 6 inverters on the chip, put the PPM from the receiver into the input, and take the output to the DF. Both chips can use the same power that the receiver does.

Any questions, let me know.

Cheers,
Rusty

PS- Good to see Arthur P here[8D]



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