Another 3GX Success But Weird Ground Behavior

[skyhigh]

Today, I am happy to report a successful maiden of my old T-Rex 500 ESP upgraded with 3G head and the Align 3GX FBL unit! This old bird flew in the air crisp and clean like never before. Tail was locked in just as good or better than the old Align GP750 tail gyro.

But I have to say the ground behavior of the 3GX unit was very unnerving! During spool up, the swashplate often was leaning quite a bit to the left. I expected the swashplate to level out during spool up like the manual says it would. But on several occasions, as the rotor RPMs came up, the swashplate still did not level out. I had to abort these takeoff because it was clear the helicopter would likely roll and blade strike on the ground or, at best, takeoff but shoot itself to the left!

I believe I am careful not to touch the cyclic controls during power on initialization or during spool up. Has anyone else experienced anything similar to what I described? Others at my field seem to think that this is common for the Align FBL units. But I'm not so sure. Vibration on the heli is normal.

I would like some opinion and thoughts on what could be causing this. Because its quite scary. Its bad enough to crash from the air but crash just before takeoff has got to be the worst . No such thing happens even remotely at all on my Logo 600 V-Bar even if I touch the cyclic on the ground. What 3GX settings can I look at to reduce this ground behavior? I'm using the T-Rex 500 ESP expert settings and my AIL and ELE pots on the 3GX unit itself is around 40 each.

I am using the 1.2 firmware on an Align T-Rex 500 ESP with 3G head. DS510 plastic gear servos with DS520 tail. I had the rubber feet on my landing gear and was taking off from pavement but off a thin sheet of carpet from Home Depot.

[dave creighton]

Ditto - just had the same problem - waiting to see if its me or the unit?

[Magnum80]

I had a similar problem with my 450 pro. Turned out to be tail blades. Blades flew fine with 3g unit. When I installed the 3gx, I saw the same as you describe.Remove your main blades and spool it up. Remove or change tail blades and check. Seems the 3gx is more sensitive to vibrations. Check for other posts on this. I have read other posts on this. If your heli is belt drive, some are saying static electricity is casing similar behavior. If yours is torque tube, tail drive support bearing can cause this. Some have gone to two bearings on the tail drive. Some have moved unit from anti rotation pad to the frames under the mainshaft. Also, when you do the settup in dir, make sure your trims are 0 on the movement screen. If it's flying ok, when off the ground, I suspect some resonant vibration during spool up. Check all your bearings.

[wifeorheli?]

most FBL units do this while on the ground still. when still on the ground if the unit feels the heli is going right it will try to correct to the left and with it on the ground obviously its not gonna goto to left so unit will keeep trying to tilt left. Thats why its best to get the heli off the ground as soon as possible.

[skyhigh]

Originally Posted by Magnum80

I had a similar problem with my 450 pro. Turned out to be tail blades. Blades flew fine with 3g unit. When I installed the 3gx, I saw the same as you describe.Remove your main blades and spool it up. Remove or change tail blades and check. Seems the 3gx is more sensitive to vibrations. Check for other posts on this. I have read other posts on this. If your heli is belt drive, some are saying static electricity is casing similar behavior. If yours is torque tube, tail drive support bearing can cause this. Some have gone to two bearings on the tail drive. Some have moved unit from anti rotation pad to the frames under the mainshaft. Also, when you do the settup in dir, make sure your trims are 0 on the movement screen. If it's flying ok, when off the ground, I suspect some resonant vibration during spool up. Check all your bearings.

Thanks for the tips. Sounds plausible. I'm heading out to the flying field later in the morning. I have a lot of different tail blades for the 500s. I'll bring a few pairs out for testing. If it doesn't work, I'll look into extra padding and the metal plate trick for the 3GX. Failing that I'll check the torque tube bearings...

[skyhigh]

Originally Posted by wifeorheli?

most FBL units do this while on the ground still. when still on the ground if the unit feels the heli is going right it will try to correct to the left and with it on the ground obviously its not gonna goto to left so unit will keeep trying to tilt left. Thats why its best to get the heli off the ground as soon as possible.

Yes, I also came to this conclusion when I heard of people having these problems at my field and from reading the online forums. It would be similiar to the heading hold mode on the tail and why the tail pitch slider doesn't return to center like in rate mode.

But I'm not touching the cyclic and this problem occurs. Even so, I have tried pushing the cyclic right to try to level out the swashplate. It worked some of the times. Other times the 3GX still migrated the swashplate back to the left. All this while the blades are stationary so there's no chance of vibration issues.

No such problems on the V-Bar for myself or others at my field. Mikado's got some nice software on theirs.

[skyhigh]

Originally Posted by Magnum80

I had a similar problem with my 450 pro. Turned out to be tail blades. Blades flew fine with 3g unit. When I installed the 3gx, I saw the same as you describe.Remove your main blades and spool it up. Remove or change tail blades and check. Seems the 3gx is more sensitive to vibrations. Check for other posts on this. I have read other posts on this. If your heli is belt drive, some are saying static electricity is casing similar behavior. If yours is torque tube, tail drive support bearing can cause this. Some have gone to two bearings on the tail drive. Some have moved unit from anti rotation pad to the frames under the mainshaft. Also, when you do the settup in dir, make sure your trims are 0 on the movement screen. If it's flying ok, when off the ground, I suspect some resonant vibration during spool up. Check all your bearings.

UPDATE: Today's flights at the field with this new 3GX were awesome. I changed the tail blades from the KBDD plastic blades back to the Align stock carbon fiber blades and now I can't even replicate the problem at all.

I've tried strange things intializing the helicopter with it tilted like 30 degrees, or moving the cyclic while on the ground before spool up. In both cases, the swashplate levels out.

This week, before I declare the problem fixed, I'll need to put the old KBDD blades back on and see the problem appear and then disappear again with the Align tail blades.

[jamesb72]

Just to add my 500 3G I first flew with Align tailblades, switched to KBDD and hovered fine in normal ~2200rpm, when I flicked to idle ~2400, heli would tilt dramatically right and even if I corrected would 'sway' back and forth alarmingly. Back to normal it was fine again, I scratched my head, then realised last thing I changed was the tailblades. Put the align tails back on and it flew perfectly.

Checked KBDD tail blades and they were out of balance, I sanded the heavy blade trailing edge to balance and everything was fine.

With the kbdd blades, the heli looked fine flying, no vibration I could see anywhere, tail fin was solid etc, so if I hadn't just swapped tailblades, this would have puzzled me for ages.

Made me realise that vibration can have weird effects on 3G, and sounds like all gyro's/FBL units, I wonder how many people have vibration problems without realising.

I bet if you check/balance the KBDD blades, they will fly perfectly.

[Magnum80]

Great, sounds like your on the right tract. Seems the 3gx is more sensitive to vibration and mounting than previous 3g units. Skyhigh, if yours is moving by itself with nothing turning, your gains are too high or your trims are not zero on the settup screen. You've got a setup problem not related to vibration. Some people forget to center the throttle stick during setup. This will cause all sorts of weird stuff, when you try to lift off. Asphalt or any hard surface, can give you problems on lift off. Dirt {not recommended}, short grass, or carpet is much better. Check your movement screen in normal and idle 1 & 2. Trims can be different in each mode. You didn't mention what radio, but I think all are basically the same.

[Riff]

I had similar problems with a Turnigy V-bar and what I found out was that tail blades were not so evenly balanced, caused vibrations. When I changed the tail blades similar problem was solved, maybe 3GXhas the same problem. Also what I changed was the tail boom to a carbon fiber boom that is thicker and more rigid from the aluminum one, reduced resonance vibrations and made it even better.

Now I am about to buy a 3GX and I'm reading inf about ppl experience.

[NUMBA]

Originally Posted by skyhigh

This week, before I declare the problem fixed, I'll need to put the old KBDD blades back on and see the problem appear and then disappear again with the Align tail blades.

Did you have a chance to try this? Your initial results are really intriguing. Cheers.

[Ninjaboy]

I just had the same problem.... In my case everything happened so fast. I tried to counter the movement with zero effect. Stripped main gear, 3 servos stuffed, main shaft bent, feathering shaft bent & main blades in pieces.... I grazed one of my tail blades on the last flight and forgot to replace them. This tail vibe thing seems very plausible to me. It just kills me to crash on spool up... I hope it never happens again. Makes me want to convert to fix wing.

[skyhigh]

Originally Posted by NUMBA

Did you have a chance to try this? Your initial results are really intriguing. Cheers.

Yes, I put on the old KBDD blades and tried a spool up in my living room on hard wood floors. Couldn't reproduce the problem. The only way I could get the swash plate to be unlevel is to push hard on the cyclic but it would gradually return to level.

So still inconclusive. The problem has never occurred even during all of last weekend's flights. I'll still got my eye out for it though because it clearly was a problem on the first day witnessed by myself and other flyers at my field.

[skyhigh]

Originally Posted by Ninjaboy

I just had the same problem.... In my case everything happened so fast. I tried to counter the movement with zero effect. Stripped main gear, 3 servos stuffed, main shaft bent, feathering shaft bent & main blades in pieces.... I grazed one of my tail blades on the last flight and forgot to replace them. This tail vibe thing seems very plausible to me. It just kills me to crash on spool up... I hope it never happens again. Makes me want to convert to fix wing.

Sorry to hear about that unfortunate crash on the ground.

I'm still trying to reproduce this problem on my T-Rex 500 but have been unsuccessful in doing so. It has only happened on the day I maidened this 3GX system. The one thing I could recommend is to be extra vigilant for this problem because you can easily see it during spool up. I still am nervous about it myself.

Another thing I'm doing, just be extra cautious, is to plug in the batteries to the T-Rex 500 but with my transmitter radio off. I know this can be dangerous but just make sure your fail safes are set. But, on my Hitec Aurora 9 system, both the receiver and 3GX are off and the ESC doesn't even initialize until it senses the receiver is on. So, with the batteries plugged in, I put on the canopy and place the T-Rex 500 right on the takeoff area. Only then do I turn on the radio where the entire system comes to life as normal and the receiver and 3GX do their intializations. This gaurantees the 3GX's intialization phase is exactly the same level for take off because the 3GX never moved before spool up and take off.

[jamesb72]

Originally Posted by skyhigh

Another thing I'm doing, just be extra cautious, is to plug in the batteries to the T-Rex 500 but with my transmitter radio off I know this can be dangerous but............This gaurantees the 3GX's intialization phase is exactly the same level for take off because the 3GX never moved before spool up and take off.

As you clearly know, this is a very bad idea (so is spooling up a heli you know had a problem outside in your house!!), and not good advice to put on a forum

Surely plugging the flight battery in on the take off pad, is not only much safer (and is considered best practice) but also guarantee's 3GX is initialised at the correct level - SAFELY.

My experience is that as long as the heli is on the ground still when plugging power in so the FBL unit initialises, it doesn't matter if it moves afterwards, as long as the heli is on the ground for spool up (hard to imagine anything else).

[helimaddness]

I had exactly the same problem as Ninjaboy. Spooling on the heli (Trex 500EFL) rolled to the right too fast for me to do anything. Come to think of it the tail did graze the ground very briefly on the previous landing. I was totally unaware of this problem and not looking out for it. Rebuilding now. I think I will at least put the second pad under the 3gx. Very frustrating to crash before you even take off....