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Apr 25, 2012, 02:38 PM
Registered User
Hi OlliW,
I can't wait to try my heli with your gyro software. But I have a little problem. The gyro starts up well and I'm also able to configure it. But when it's in the "blue-blinkink" fase of its start-up, then it emmits some sort of signal on the servo signal wire (it looks like a few UART bytes on oscilloscope) that makes my digi servo going all the way in one direction.
If i try analog servo it only makes some noise, but doesn't move.
I'm afraid of it may can be harmfull for the servo, or can bend something in my tail control.
I use the V0.15 firmware. (I couldn't get the 0.16 yet)
Do you have any solutions to this?
Thanks in advance!
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Apr 25, 2012, 03:51 PM
Thread OP
Hey Itiricz,
what you describe is the intended way of operation. During the blue-blinkblink, which takes about 1 second, the gyro tries to detect a programming box at the servo port, for which it emits the signals you detected. None of my servos had any problems with it. And its kind of strange that a servo attempts to digest these signals. Anyhow, sad to hear that your particular servo causes problems (maybe you might tell which one it is?). Since this issue never occured so far (I don't have it and no one else reported it yet), there is no solution I can suggest. Sorry for that,
Apr 25, 2012, 11:08 PM
Registered User
I thougt as much. I just don't understand why can't the gyro start sending its data after it detected some communication from the PC software. That also sends something very rapidly when it tries to connect. My servo is an E-sy ek2-0508. But as I mentioned my analog servo also digests this signal although it dosen't move.
Anyway I pick up my heli and give it a fly before work even if I have to by a new servo aterwards.
Apr 26, 2012, 12:57 AM
Thread OP
I just don't understand why can't the gyro start sending its data after it detected some communication from the PC software. That also sends something very rapidly when it tries to connect.
the connection with the PC software works via the bootloader, i.e., a connection is posible ONLY while the main firmware is NOT running! Its possible (and I initially did that) to program the Robbe Box such as to allow to do that (though it needs a slight hardware modification), however that's not what I wanted to have. If you want to allow for some programming during firmware operation, i.e., after the gyro had been switched on and the firmware started running, the action has to be initiated by the gyro for synchronisation reasons. Ideally a further port is available, but that would require more solder work on the GA250.
Apr 26, 2012, 05:51 AM
Registered User
i OlliW,

I have tested the gyro on my TRex 450, and it works very well (at least to my quite limited experience of flying ).

To make the adjustment easier, I put together a program box with parts I had in my bin.
It also worked very well - thanks for your schematic and firmware.
It took some time for me to find out that a long press on "+" gave the "save EEPROM" function .

One question of minor importance: Is the Buzzer implemented? - I get no sound from it - what kind of buzzer should it bee (active or passive) ?

Apr 26, 2012, 06:42 AM
Registered User

I'm glad your program box works well. I've also tried to build one, but I am not able to flash it with the firmware. AVRootloader would not connect no matter what I try.
AVRdude has loaded and verified the bootloader - all was OK.
I am a bit confused with 1wire communication, especially 0ohm resistor between Tx and Rx. Is this right, or did you modify the schematics in any way?

Apr 26, 2012, 07:03 AM
Thread OP

my usual question(s):
- may I list you as a user on my webpage?
- what transmitter/reciever system are you using?

As regards the buzzer, no, it's not currently supported. I always planned to do so but always something else was more important. . (in a previous version of a prog box I had this implemented, so I would have the code snippets already ready, but as I said... there is always something else which I find more pressing LOL). As regards the type of buzzer it would have then to be a passive one.

It took some time for me to find out that a long press on "+" gave the "save EEPROM" function
yes, LOL, one of the typical questions...

If you build your own programming box, you may just ignore the resistors R8 and R24, i.e., just shortcut the Rx and Tx pins and wire them to your USB adapter. These two resistors in the RobbeBox are the source of a lot of the issues with the USB adapter. Without them everything works much better.

In order to activate the bootloader you have to keep the LEFT button pressed during power on!

Don't power the prog box through the USB adapter.


BTW: I "developed" also a version of the programming box which uses and Arduino board and the Arduino keypad shield, as well as a simple DIY version for less than $10... I only didn't find the time yet to post this stuff
Apr 26, 2012, 10:26 AM
Registered User

Yes, you can add me to the list of users.

I use a Graupner MC22 35 MHz Tx with a Jeti 7 channel Rx for my TRex (Yes, I have some 2.4 GHz systems also ).
I have ordered another GA250 gyro for my second TRex


I made no modifications on my Progbox regarding input resistors.
But, I did not use any bootloader.
I programmed the file ("Robbe_ProgBox_v014b_m88") directly to the Mega88 with an AVRISP programmer using ISP.

Apr 26, 2012, 10:31 AM
Registered User

Note, that if you use a Mega88 in DIL package, you have to watch the pin layout which differs fram the SMD package (but that you probably already knew...)

Apr 26, 2012, 04:31 PM
Registered User
Hello, firstly I must thank OlliW for all the interest and hard work put into this project, and for HolgiB’ Idiots Guide without which I could not have taken part.

I have these modified gyros on my 450 Heli’s HK450V1 HK 450V2 Hk450MT
I build cheap, nothing expensive on these machines and if parts do not fit so good I generally make them fit, all part of the challenge.

I must add that I do not fly hard 3D.

I have 5 of these gyro’s which I purchased throughout last year as Assan supposedly made improvements, always liked them but was never able to get rid of the stop bounce, and eventually changed them for the Leaders Hobby GY520 nice stops but hold not so good.

Very pleased with these Gyro’s now and need to look no further, that is until fly barless kits are available at similar costs.

Feel free to add me to your users list.

Tail servos are Henge MD922
Spektrum RX
Spektrum DX6i
No silly head speeds 2200 to 2500 on flat throttle curves.

Tonight I fitted one to my HK500CMT which has Align DS520 Servo and this is going to be good.
Unfortunately had to abandon the job for now as I hit the boot up problem, works on rudder stick but not on Gyro. I have had this before and my usual work around has been to boot up with the gain wire disconnected and reconnect after booting up, not this time though, but left it for an hour ,went back and it works fine. No daylight left so will have to complete another day.

Got as far as setting up in rate mode, gain and set up mechanically for no drift, reset end points and started increasing PID I. but I can tell it will be good.

Thanks again for all the help from this thread and will let you know how the 500 performs.
Apr 26, 2012, 08:18 PM
Registered User
Thanks OlliW and ElectoPete,

I have removed the unnecessary resistors, but I still could not connect to AVRootloader. I was trying to press and hold Left button (and all others) on power-up, but to no avail .
However flashing the firmware directly - as ElectoPete has done, fixed it all .
Thanks again guys.

not sure if it is your case, but I was initially using Rudder trims and sub-trims to get servo arm centered (as I have been doing before). However the gyro stopped booting up after I've exceeded the limits (red LED was flashing slowly - waiting for valid input). Zeroing trims and subtrims and using provided parameter "Servo Mid" instead fixed my problem.

Apr 26, 2012, 09:54 PM
Thread OP
Hey Ray,

COOL report, thanks, much appreciated

It seems you really like the alternative firmware better than the original GA250 and the LH GY520 Glad to hear that it works out well for you.

The rudder-only-no-gyro problem is really strange. Several of you have reported it now. Would be interesting to know if this could be avoided by software (I have no clue how though) or whether it's entirely a hardware issue.

Cheers, Olli


A questions to anyone who experienced the rudder-only-no-gyro problem:
Did it occur (so far) ONLY after a programming step via the USb adapter and the Windows program, or did it even happened at start up also with the last programming a couple of flights back?

(I wonder whether I should implement a security feature of the kind that if the rudder-only-no-gyro case is detected some signals such as a constantly sweeping tail servo or such is emitted, to avoid that someone takes off in such a state, which I guess could easily cause damage to the heli).
Apr 26, 2012, 10:14 PM
Thread OP
Hey Jan,

IMPRESSIVE work your programing box! In particular as it's only single-sided layout and you don't seem to have many bridges, excellent wiring job.

(one suggestion: except of the reset resistor R12 all other resistors are actually not needed, as well as C4,C6-C8,C15, and the voltage regulator circuitry (the LCD-vo circuitry you removed already), so a future layout might be simplified). EDIT: voltage circuitry is not needed if BEC voltage is below 5.5V.

I see the pads for a ceramic oscillator, but they are unoccupied. Since the communication is serial (usually frequency accuracy to within something like 1-2% is recommended) it may happen that sometimes the connection doesn't work, could e.g. depend on temperature etc. EDITII: OH SORRY, got it, its the blue thing below the LCD

I am glad the box is working now for you, but am dissapointed that the bootloader option didn't work out. I have no idea what the problem could be, but would be curios to know what's going on here.
You did power the box from an external source when using AVRootloader? How is your USB adapter built? You have tried different baud rates?

So I should implement the buzzer function, hugh? Would be sad if your efforts to integrate the buzzer wouldn't be good for anything...

Again, excellent work!
Last edited by OlliW; Apr 26, 2012 at 10:48 PM.
Apr 26, 2012, 10:22 PM
Thread OP
Jan's work motivates me to post my efforts on a totally-through pin DIY prog box. Cheap and simple. It uses a Atmega8L and 8MHz ceramic. The LCD, the most expensive part, can be obtained on ebay for 3-4$. Needs an adapted firmware though (can provide it).
Apr 26, 2012, 10:50 PM
Registered User
Hi OlliW,

thanks for the kind words, the board is actually double sided (top tracks are covered by the LCD). You can also see the ceramic resonator next to the buzzer (through wires) EDIT: I see you've noticed. I use a simple laser printer toner transfer method to 'print' my PCBs.

Regarding the bootloader, my chip is '88PA so I've flashed it with the provided BL_4RobbeProgger_m88pa.hex. I have tried both, the diode serial adapter and FTDL USB to serial adapter with different speeds and power-on sequences, also direct RS232 port and USB to RS232 cable converter. I've had no response.

I think it does not matter anyway, because soldering 6 wires and flashing with 'Dude' is quick and simple and it must be done at least once (unless you plan many future firmware revisions )

On another topic, does anyone use 'Chinese weights' on the tail rotor to significantly reduce rudder servo loading? I was intrigued, see
and have tried. It really works and is really easy to do. Don't know yet if the tail rotor is not going to suffer from the additional weight.

Last edited by JanRy; Apr 26, 2012 at 10:59 PM.

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