3GX on Trex 250DFC - Heading Hold not working?

[ephilang2]

The light changes color from red to green but nothing changes in flight characteristics. While setting mechanical trim in the tail I switched it to HH to feel how locked in it was and the tail continued to wander the same as it did in rate mode. NO CHANGE IN FLIGHT CHARACTERISTIC AT ALL! Tobe honest, it doesn;t feel like the rudder is doing much in either mode!

I don't have a USB plug for it so I can't exactly scrutinize the settings. The tail seems to wander around no matter what the gain is set too. The only setting that seems to make any difference in the tail (bouncyness) set up menu is the delay while setting it to the small heli and I can't give any exact value with out that stupid cable!

I have went through the tail and it feels like butter, no binding on any movement. The cyclic appears to be good but the way the tail wanders I can't take it too high for now. I am running at a 100-90-100 throttle curve. IDK...

Any thoughts? I am almost thinking that this 3GX unit that I bought second hand is a problem child (came on the second hand 250). I am using the DX7s, DSM2 Sat, stock 15a ESC and Servos.

BTW, does any one have an extra USB cable that they are willing to part with $$??

Thanks for your thoughts
-Eric-
__________________

[dwdw910]

I don't think the 3GX unit is bad. They are finicky and a pain sometimes, but they are basically bullet proof.

I have heard of many 250 Pro's that would not hold in the tail. Many people have decided that the Align servo is at fault and replaced it with an upgraded servo.

If it were my helicopter- I would keep the Align tail servo and instead- wire up an external BEC. Something like the CC BEC with 10A.

The internal BEC in the align speed control is not capable of the demands of the 3GX. Period.

It is a linear BEC 3A continuous and 5A max.

There have been many posts and articles across the internet that a linear BEC on a 3S battery is super weak.

I just put an external BEC on my 450 and I can tell you the servos move lightning fast compared to how they moved on the stock ESC BEC.

[ephilang2]

I hear you, I already ordered the CC10A BEC. However, I don't believe that is my problem. The unit acts fine except there is nor rudder corrective respone (or very very little). The end points were set up in rate mode properly. It feels like there is no tail gyro at all.

The tail servo is extremely responsive and fast, the rudder output of the 3GX is what seems to be lacking.

Even on the bench the tail doesn't really respond. the cyclic seems fine but I havn't really flown it yet.

[dwdw910]

I think it is the problem.

Especially when you say very little corrective response. I'm guessing you have firmware 3.0. The 3GX is power hungry and without a good power supply- its going to act funny.

The gyro is very active and needy for power- between feeding all the servos and calculating flight corrections on 3 axes- there's just not enough power to keep the gyro adjusting and tail servo whipping around like it should.

Given that you setup everything correctly- there's not much left that could be wrong. Its almost impossible for the 3GX to be broken. I've never heard of that. I even made a thread about it and asked the forum...

You may get some more specific 250 experience in the 250 forum, but I am quite sure that the system is just underpowered.

My external BEC brought a new life to Trex. I swear by it. :-)

If you have 3.0.... one other thing you can try.... is turn down all the flight gains... this can help alleviate the power strains on the system. All of those gains increase the demand for power for the 3GX.

[ephilang2]

I hear you, but I would ask why just the tail and why on the bench. I will find out soon as I have one coming.

On the bench the head acts fine but the tail doesn't.

[dwdw910]

I don't have a technical answer for why... But I'm pretty confident that's the problem.

Keep us posted.

I had the greatest surprise ever when finally wiring up my external BEC.

The servos were turbocharged- I could turn up the flight gains ALL the way- I could really feel a difference in how the 3GX behaved. It acted a lot less mysterious.

[ephilang2]

Will do! I ordered the BEC early this morning so as soon as I get, I will throw it on and let you guys know the results!

[krauley]

Originally Posted by ephilang2

The light changes color from red to green but nothing changes in flight characteristics. While setting mechanical trim in the tail I switched it to HH to feel how locked in it was and the tail continued to wander the same as it did in rate mode. NO CHANGE IN FLIGHT CHARACTERISTIC AT ALL! Tobe honest, it doesn;t feel like the rudder is doing much in either mode!

I don't have a USB plug for it so I can't exactly scrutinize the settings. The tail seems to wander around no matter what the gain is set too. The only setting that seems to make any difference in the tail (bouncyness) set up menu is the delay while setting it to the small heli and I can't give any exact value with out that stupid cable!

I have went through the tail and it feels like butter, no binding on any movement. The cyclic appears to be good but the way the tail wanders I can't take it too high for now. I am running at a 100-90-100 throttle curve. IDK...

Any thoughts? I am almost thinking that this 3GX unit that I bought second hand is a problem child (came on the second hand 250). I am using the DX7s, DSM2 Sat, stock 15a ESC and Servos.

BTW, does any one have an extra USB cable that they are willing to part with $$??

Thanks for your thoughts
-Eric-
__________________

im not familiar with the dx7 but on a dx8 with just sats running on a 3gx you have to have the gyro on the aux2 channel. not on the gear channel like you usually setup the gyro. if your dx7 is the same check out to make sure you are on the right channel or the gyro will act just as your describing.

[ephilang2]

I will double check those settings this weekend but the light is going from red to green as it should with the switch I assigned to change the gain with, so?

[Argypak]

I'm having a similar issue where the tail is not holding. I thought it was in particular moves, but testing today showed that a breeze would make the tail blow out. Tonight I added a bec to the mix and on first inspection the tail seems to lock in.
More testing tomorrow morning and I will report.

Running ver 3.1 3GX with hitec 5084 on the tail

Argy

[ephilang2]

OK, I finally got the CC10A BEC installed and the tail is not responding at all (other than rudder inputs). I think that I got a lemon...

My only thought is, as I do not have the USB to access the software, is it possible that there is a setting that can make the tail none responsive??? I am not enjoying throwing money at this...

[dwdw910]

You need the CC BEC plugged into the Batt Port on the 3GX and the red white black jumper goes from the SBus Port to power the receiver.

If you hooked up backwards, sometimes the servos twitch and will not respond or act funny. To remedy this, I had to reset the model data in the transmitter.

You also will need the Castle Link to Program the BEC to output at 6.0 Volts.

[ephilang2]

I am using a Satellite Rx and the BEC is plugged into the correct port with the correct polarity and the ESC has the middle BEC power supply wire removed from the plug.

The 3GX is simply giving absolutly no input to counter act any unwanted tail movement. Answer me this, when powered up on the bench, in HH mode, if you twist the helicopter the servo should respond and stay there until the original heading is achieved, right? In my case, I get no response to the tail EVEN IF I SHAKE IT BACK AND FORTH!

The BEC fixed any under achievement of the stock ESC/BEC but did nothing for my tail (Although I still havn't really flown it enough to find out if that would have been a seperate problem).

Can anyone tell me if there is any 3GX setting that can affectively 'mute' the gyro-rudder response that I can quadruple check?

[dwdw910]

Oh sorry, I didn't think if you had Sat or not...

I'm thinking your rudder servo or connection is bad. Are you sure its plugged into the 3GX right side up?

Yes, the gyro should counter act you moving the tail back and forth.

[ephilang2]

The servo responds just fine (and really quickly) to my stick inputs. I can fly it, it is just like flying with out a tail gyro and I don't recomend that with this little guy (maybe for a Szabo or similar). When I hold the rudder stick on my radio and let it go, the servo is so fast that it twitches with the stick flickering to a rest. I am impressed with the servo so far.

[dwdw910]

Interesting... So you see what I mean... the servos and 3GX come alive with a direct power supply :-)

As far as your rudder gyro not working... and everything else is? I've never heard of that.

I would try to update the firmware... regardless if you have the newest version or not... Upgrade the firmware again, reset the model data in your transmitter!, and go through setup all over again.

I know it seems redundant, but these things are super finicky... almost haunted at times.

I had a similar problem where my cyclic servos wouldn't move or respond after the BEC install.

I reset the model data... and voila

[dwdw910]

Also, be aware the CC BEC is still not at 6.0 Volts yet.

You will need the Castle Link and program to set it at 6.0 volts.

So the servos will have even more power :-)

[ephilang2]

I may go to 6V if I square this thing out. Anybody want to buy a 3GX for $50?

[ephilang2]

BTW, the servo was responding extremely fast BEFORE the BEC was added.

[dwdw910]

Did you reset the model data in the transmitter?