Tail wobble

[Gerald01]

I installed the new 7210 beast x on my trex 500 dfc pro. Before I changed it the heli flew and hovered very smoothly. Now I have tail wable. It's twitching back and forth about 1/4 inch... it seems to operate well but it never had that wable before. I did bang one of the main blades on the corner of the bench during the rewiring project and it did put a little chip on the leading edge of the blade so I replaced the main blades. I took off the main and tail blades and spooled it up and I can't feel the main shaft wobble but I can feel a vibration when I'm holding the tail boom... not sure where it's coming from. Would that make the tail wobble?.... just not sure where to start...
Any ideas?

[Solmanbandit]

What did you have on it before?

[Gerald01]

Naza h with gps.

[learnedthehardway]

Lower your tail gain, or your gyro gain in your tx if the 7210 works like the AR7200BX. Little bit at a time till the wag goes away.

If it was flying fine before and all you changed is the fbl controller then there shouldn't be any mechanical issues

[johncblacker]

On the other hand, it sure wouldn't hurt to re-check the balance of the tail blades and make sure there is absolutely no binding from tail servo all the way through to the blades. Also, some waggle might be due to low head speed.

[Felix the cat]

Originally Posted by Gerald01

Would that make the tail wobble?.... just not sure where to start. Any ideas?

Is it a wag (sideways left to right - on the yaw axis)
Or a bob (nose up and down - on the pitch/nick axis)

If it's a wag, follow other posts to ensure mechanicals are be buttery smooth. Also, remove main blades, free tail pushrod at the servo end, spool up and manually actuate the tail pushrod, this will provide an idea on the tail bearings or thrust bearings reaction under load.

Low HS will seldom make it wag but rather drift to one or the other side with very little tail authority. Mushy.

If it's a bob, usually is related to un-lubed, worn out head dampers.

If all checks out, have your HS properly set for the type of machine, increase tail gain till it wags in a hover, then decrease till the wag is gone and no further.

Hope this helps some

[learnedthehardway]

Have you tuned the tail in since installing the 7210?

Small chip in the main shouldn't matter much, just fill it in with CA if it's not too big and you could try the old blades out if that's the only thing you changed mechanically. Doubt it's from the mains though, they would make your bearings chirp and give you cyclic wobble if they were way out of balance and not tail wag. Anything's possible though

Those are all good suggestions and it sounds like you may have some tail vibes but if it was flying good before then it should still fly good.

You always have to tune the tail when you setup a new fbl unit so having a wag at first wouldn't surprise me at all. I got a huge tail wag just by swapping the esc on my old Trex, short fast wag is almost always too much tail gain or too much gain in the esc.

Mechanically, chewed up gears or slop/binding in the tail linkage like others mentioned are the main suspects

[Gerald01]

The movement is left to right and I rechecked the tail blades and they weigh exactly the same. I do feel a vibration when I spooled it up with no blades on it, just can't tell what's causing it. I'm thinking of replacing the main shaft and if the vibration is still there may the torque tube. I wouldn't think that the bearings are worn-out because it's only got about 30 flights on it.... light flights, no 3d, but I'm still new at this so I'm not sure.

[learnedthehardway]

You will always get some vibration from the tail, especially on a torque tube driven one. Hard to tell how much is acceptable when you're first starting out though, usually if the tail fin doesn't look blurry when it's running then you're okay. My Trex is loud and a bit more vibey than my other nonBlade helis and it has a belted tail so I could see a TT tail Trex having a decent amount of vibration even when it's running just right.

I would definitely put a drop of oil on the tail shaft and mess with gain before swapping any parts since it's still new and was working fine before. Unless you had it working with the 7210 already and the wag developed afterwards. Always try the cheapest/easiest things first, even swapping the tail blades between the grips can reduce tail vibes sometimes.

Way too much gain can make the tail vibe itself to shreds

[Gerald01]

Thanks so much for all the information. Can't wait to make some adjustments and see how it turns out.... if it would just stop raining..lol
I had 2 days of mostly clear weather now that's gone... In north Louisiana, no floods but lots of rain... will post how things work out in a few days, hopefully...
Thanks again and happy flying.

[Gerald01]

Is the tail gain the gyro? It was set at 77, the same as my 450x with the beast x. I'll turn it down to 65 and see if that makes a difference.
The dx7s also has tail curve.... all the values are set to 0. My dx6i didn't have that or there was no setting for it in the manual. Any advice on that?

[Solmanbandit]

Typically I say that the gain number is just a number, but that does seem a bit high. Lower it down to 50 and see if that makes a difference.

[Gerald01]

The wobble stopped at 60.... should I still turn down the gyro to 50?... I also set the d/r on the rudder to 100. It's hovering well but the real test will be at the field this weekend. Not enough room to fly in the yard... too many trees.
One more thing... I was told not to oil the gears on the torque tube... is that correct?

[Solmanbandit]

I don't oil umbrella gears. As far as the gain goes, fly it and adjust as needed.

[peteski]

Originally Posted by Gerald01

Is the tail gain the gyro? It was set at 77, the same as my 450x with the beast x. I'll turn it down to 65 and see if that makes a difference.
The dx7s also has tail curve.... all the values are set to 0. My dx6i didn't have that or there was no setting for it in the manual. Any advice on that?

77 seems very high to me, but I don't know what the mechanical geometry is like on your 500. My G380 is down in the mid 30s although I'm still tuning it. If you are not doing 3D you could get away with a very low gain and not see any practical issues. Too high and you will get the fast wagging you experienced, especially in fast backward flight. Too low and the hold will be weaker, but probably not an issue until you start stressing it more with harder moves.

If the wobble stopped at 60, I would go down to 55 and fly it. If no issues in your normal flying routine, then job done. You can always re-tune it as you start flying harder if the tail hold feels weak.