GT-5 on OLD Trex450XL

[sbc]

Hi all, I just want to share some infomation that I have just discovered when I upgraded my old Trex450 to FBL.

On normal flight-mode, the heli will take off, hover and land very well. However if I switch on idle-up, it will roll violently to the left. Needless to say, after a couple of blades changes and repairs, I was losing confident fast.

Reading up on some postings about beastx problems on the web, it was suggested that it had something to do with high frequency vibration in the region of 20kHz. That set me off thinking,,,what could vibrate so fast on the heli? It should not be the main blades as they only rotate at about 3200 to 3400 rpm. Besides there are many people flying Trex450Pro with even higher head speed.

First I tried to dampen the vibration by using 2 layers of tape instead of 1. BIG BIG MISTAKE!!! The little heli can't even take off without drifting strongly to the left.

Then it dawned upon me that it could be related to the tail rotor. I remembered I still had the 109T/22T tail drive assembly. I changed it to the later 106T/25T assembly, dropping about 15% on tail RPM. I was desperate enough to try anything.

Like magic, the problem is gone! I could switch to idle-up 1 and 2 and back to normal without the heli committing sucide.

So now I am a happy flyer, even though I am still thinking about it - how can a 15% increase in tail speed causes the gyro to go crazy?

[Stolla]

easy what can happen is the tail shaft starts oscillating and cause severe vibrations, had this with my furion, you can see it easily side on view on the bench.

[sbc]

So did your furion have the rolling problem too?

When I had the flybar on with the Futaba 520, it flew ok. The whole tail assemby - boom, belt, shaft, grip, blade, etc is brand new.

Is the GT-5 that sensitive?

[Stolla]

nope didn't have a rolling problem, maybe you had some trims in one of idle ups our perhaps different total gain? ace is less sensitive than vbar on vibes.
If vibrations aren't bad something in your setup is wrong

[jockstrap]

Did you try changing the vibration filter setting?

The original manual says 5 is the highest vibration resistance but actually 1 is - the newest doco has been changed to reflect that..

Out of interest - can you check what your vibration filter is currently set to and if it's 5 that means it's basically "off" and try lowering it.. if it is lower - then probably was mainly the tail..

[sbc]

Originally Posted by Stolla

nope didn't have a rolling problem, maybe you had some trims in one of idle ups our perhaps different total gain? ace is less sensitive than vbar on vibes.
If vibrations aren't bad something in your setup is wrong

There is no 'trim' in idle up mode. I checked it like 50 times on the bench, running at 100% throttle (without blades of course). The trims are linked, meaning it will be the same setting for ALL flight modes. Likewise, all gains are linked, meaning the settings will be the same for ALL flight mode.

Anyway, changing the gain up or down DOES NOT solve the problem. The heli will roll to the left in idle up mode no matter if the gain is 10, 20, 60 or 80, or any other numbers.

There is nothing wrong with the settings. It flew well in normal mode. When I downgraded the gear ratio, I changed nothing else - the settings remains the same.

[sbc]

Originally Posted by jockstrap

Did you try changing the vibration filter setting?

The original manual says 5 is the highest vibration resistance but actually 1 is - the newest doco has been changed to reflect that..

Out of interest - can you check what your vibration filter is currently set to and if it's 5 that means it's basically "off" and try lowering it.. if it is lower - then probably was mainly the tail..

Yes, I tried that too. The default is 2. I tried 0 which is the max filter. It does nothing. Anyway, I read in another forum that someone played with the filter settings and the heli felt the same regardless of the setting. I think I can agree with him.

Yes, it is probably the tail. But the thing is, the whole tail is brand new. I upgraded the heli with the latest Trex450 Sport's tail. On the bench I could not feel any abnormal vibration. If the experts over at the beastx forum is correct, it would be some super high frequency signal or vibration coming from the tail. I guess the tail acts like a tuning fork, sending out a high frequency signal that somehow interferes with the gyro's operation.

This is of course just a speculation on my part.

I hope Thunder Tiger/Ace RC will fix it with a firmware upgrade. I have people at the field running 4000 rpm head speed, which mean the tail blades will be spinning at incredibly high RPM. Pity him if he tries the GT-5!

[1004ron]

Have you spooled it up without main blades and watched to see if the swash tilts at the same RPM you've been experiencing it at with the blades on - if it does, then rest assured it is a vibration issue.

[1004ron]

Originally Posted by sbc

Yes, I tried that too. The default is 2. I tried 0 which is the max filter. It does nothing. Anyway, I read in another forum that someone played with the filter settings and the heli felt the same regardless of the setting. I think I can agree with him.

jockstrap has done a fair amount of experimentation with this, and I value his input.

Yes, it is probably the tail. But the thing is, the whole tail is brand new. I upgraded the heli with the latest Trex450 Sport's tail. On the bench I could not feel any abnormal vibration. If the experts over at the beastx forum is correct, it would be some super high frequency signal or vibration coming from the tail. I guess the tail acts like a tuning fork, sending out a high frequency signal that somehow interferes with the gyro's operation.

This is of course just a speculation on my part.

I hope Thunder Tiger/Ace RC will fix it with a firmware upgrade. I have people at the field running 4000 rpm head speed, which mean the tail blades will be spinning at incredibly high RPM. Pity him if he tries the GT-5!

As you noted, the BeastX also has the tilting tendency when adversely effected by vibration, and both Align and BeastX did not "fix it with a firmware upgrade [update]".
I fixed my 550/BeastX by addressing the vibration, selecting a preferred mounting location, and using the 3M mounting tape.

[sbc]

Originally Posted by 1004ron

Have you spooled it up without main blades and watched to see if the swash tilts at the same RPM you've been experiencing it at with the blades on - if it does, then rest assured it is a vibration issue.

Yes I did. See post #6. Without main blades, the swash did not tilt. With main blades on, the swash will tilt when the throttle is above 85%.

How many layers of 3M tape did you use. 3M has two types of tape - a thicker one for rough surface and a thin one for smooth surface. Which one did you use?

[1004ron]

Originally Posted by sbc

Yes I did. See post #6. Without main blades, the swash did not tilt. With main blades on, the swash will tilt when the throttle is above 85%.

How many layers of 3M tape did you use. 3M has two types of tape - a thicker one for rough surface and a thin one for smooth surface. Which one did you use?

On my BeastX, 3GX and GT5, I use one layer of the thin gray 3M (4011) outdoor mounting tape.

Excuse me for not going through the whole thread again, but can you tell us where you have the GT5 mounted - mine is mounted on the side of my 450 - I avoid mounting near or on the tail boom mount after the bad experience with vibration induced tendencies.

http://solutions.3m.com/wps/portal/3...glGSZXQMXY91bl


http://www.uline.com/BL_6574/3M-4011...-Mounting-Tape


PS. - there's many here with the expertise to help you, and have already offered sound advice. They also have patience and perseverance, but might withdraw if your tone leaves them with an impression of rebuttal.

[sbc]

It is mounted on the top of the boom at the rear of the frame - the old location for gyros, before Align shifted it into the frame as per Trex450Pro.

Because I have been mounting gyros there for years, I thought it is safe to mount the GT-5 there too. It never occur to me that it is a bad place for it.

1004ron, thanks for the insight. Next time when I have a chance I will try the side frame mounting method that you prefer.

[rexxigpilot]

ace is less sensitive than vbar on vibes.

Can't agree you you on that statement! The G-T5 is more sensitive than V-Bar in my experience. Neither is great for vibration rejection. Best to use a Futaba CGY750 on nitro IMO. The PinPoint/Silicone Sensing sensors in the 750 seem to tolerate vibs much better than anything else on the market. It could be that the Futaba MPU works better too. It seems the Invensense sensors (in beastX and perhaps in G-T5 too) have a harder time with vibs.

[swalko]

Originally Posted by rexxigpilot

It seems the Invensense sensors (in beastX and perhaps in G-T5 too) have a harder time with vibs.

G-T5 have sensors from Silicon Sense. Silicon Sense offer too PinPoint sensors and G-T5 must be hard mounted, then G-T5 may have PinPoint sensors:

The G-T5 uses latest MEMS gyro sensor technology with internal temperature and drift correction algorithm.

All types of sensors may be blinded by vibrations at certain frequencies.