120S gyro problem?

[smdub]

Background: Have a couple wk old 120S. Using DX6i. First heli. Have had a couple minor crashes in the grass as expected. I can move around ok in beginner mode so I've switched to advanced mode and am hovering and starting to move around again. Warning: I am a power electronics engineer that does motor control and control systems. I might be my worst enemy

It has developed a worsening uncontrollable tail rotor. At first it would just twitch yaw one in a while (20-30deg, even in beginner mode.) As of a couple days ago I can't fly more than about a minute before it wildly spins to the ground while in a steady hover. Its rotating CCW so the tail rotor may have an intermittent open. But I have a few observations that make me think its a gyro problem and hoping to pick the collective brain trust here.

1) If hold the heli by the skids and bring the throttle up a little then rotate it slightly (yaw) the tail rotor will start to spin up as the gyro tries to correct. At that point if I hold it still, the tail motor sometimes briefly goes nuts - from full power to off - and then recovers and runs normally. It it was an intermittent open in the motor/wires/controller it would just go off and not full speed. It does both. Makes me think gyro.

2) When hovering, turning the heli w/ the tail rotor causes a LOT of direction change. I understand some forces will couple but it seems REALLY coupled. If I put it on a table, throttle up slightly to get everything working but not enough lift to take off, and then rotate it CCW 360deg in place using my hands on the skids, at the end of the rotation the pitch and roll servos will be maxed out in the upwards direction. Why does rotating it on a level surface cause MAX servo travel on the other axes that are not moving? Again, seems like the gyro.

It still hovers fairly level in beginner mode so I don't think the gyros need to be recalibrated again.

3) I think unrelated to gyros but maybe not. It doesn't have consistent main rotor speed. In a good hover it occasionally gains/looses ~20% rotor speed. That can be duplicated when holding it by the skids stationary. Say at 50% throttle after a minute or so the speed will change noticeably. Anywhere between a couple seconds and a minute later it will go back to the original speed. I can only think this is some sort of intermittent a control board problem. Thinking about it now I should hook a scope to the motor leads and log the voltage at constant throttle input...

Help?

Considering that a control board/gyro is <$40 and sending it back to HH for diagnosis/repair will likely cost that between shipping and their labor, should I just order a new one and DIY?

[Floyd4223]

I had one flight of my 120 S and the right servo went. Replaced the servo and the Gyro was doing similar things to what you describe, Sent the heli back and they gave me a new one.

If there is another problem other than the servo the SAFE function makes the Gyro unstable. So problems are harder to diagnose with SAFE.

.

[HeliLust]

The tail rotor maybe slipping on the motor shaft. A friend got one of these and that was a problem we had to sort out on it after a few minor crashes. A little super glue in the hole on the rotor blade fixed it up.

[BrokeDad]

Originally Posted by Floyd4223

I had one flight of my 120 S and the right servo went. Replaced the servo and the Gyro was doing similar things to what you describe, Sent the heli back and they gave me a new one.

If there is another problem other than the servo the SAFE function makes the Gyro unstable. So problems are harder to diagnose with SAFE.

.

If you are talking about the 120S and not SR I had the exact same thing happen. Second flight the right servo went. They were OOS until Sept. and when HH called me back I got told if it flew fine once out of the box there is NO WARRANTY. Fortunately I found a crashed 120S for $25 and got the part. That one is now also repaired and waiting for the servo to be in stock. I'm glad you had a better experience with HH. They didn't even offer to have me send mine in. I guess I should have waited and called to get another rep and maybe a different response. With both servos being OOS I feel there is definitely a known problem with them or a batch.

[smdub]

Seems I had 3 problems:
1) gyro was bad. I replaced the control board and I can now rotate the heli (w/ the main motor unplugged), throttle at 50% (so it 'thinks' its running) and the roll/pitch servos don't go to maximum. Yay, go to fly and still have an intermittent/odd tail motor Must be the tail motor going bad too...

2) Order a new tail motor. Came in yesterday and I just replaced. Same intermittent problem on the table. WTF! HAS to be an open in the tail boom wires I'm thinking. So Im getting ready to pull the tail boom out and notice I can make the motor freak out. wiggling the wires carefully, it turns out there is an intermittent open on the red wire where its under the heatshrink to the magnet wires that run into the boom. So I pull that off and there appears it was NEVER soldered. Just pressed together w/ heatshrink on top Im an EE by day so broke out the soldering iron and added a TINY bit of solder. Yay, go to fly and just as I get into hover...

3) it spins wildly into the ground as if the tail motor appears to turn off. After looking it over the tail rotor isn't pressed on well. Press it back on and try to repeat hover and it goes nuts again.

Originally Posted by HeliLust

The tail rotor maybe slipping on the motor shaft.

Yup. The tail rotor is slipping off the new motor shaft (it was very firmly attached on the orig motor shaft.) I will add a tiny bit of glue per suggested. Left my glue at work so HOPEFULLY I will have a running heli on Mon.