I have an issue that has come up with my Trex 450L with a 3gx gyro. Both are less than 2 yrs old. All was working well until a flight last week. On landing the tail rotor made contact and dug in while it was idling down without power. It did just some minor mechanical damage, a slightly bent tail shaft. I replaced it and took it out today. The. heli flew fine with one exception, it wants to yaw right. I've looked everything over, seems good mechanically but it still would yaw right equally in all flight modes (70%&95% throttle). I used sub trim and the yaw stopped around -28 on my dx9. My question is can a gyro just go partially bad at any time or could the hard landing have messed up the gyro a little? I'm not sure what to check next.
FBL Gyro 3gx gyro
- Thread starter Eggy 71
- Start date
Smoggie
Well-Known Member
The 3GX can be a real pain in the neck, but having said that, if it was working before the little mishap then it should be working now. Gyros dont go 'partly bad' after a minor crash, they either work or they dont.
If you clipped the tail hard enough to bend a tail shaft then 99 times out of 100 you would also have chipped some teeth off the front torque tube drive gears. It's quite tricky to detect the damage sometimes, teeth may be chipped from either of the front bevel gears or the large auto gear or the small tail drive spur gear. If any teeth are missing the tail drive may be slipping.
The other thing to check is if the tail blades are chipped or the torque tube bent or bearings damaged (or damage elsewhere if the heli tipped over in the incident) which could cause vibrations. Vibrations can interfere with the oiperation of the gyros.
If you clipped the tail hard enough to bend a tail shaft then 99 times out of 100 you would also have chipped some teeth off the front torque tube drive gears. It's quite tricky to detect the damage sometimes, teeth may be chipped from either of the front bevel gears or the large auto gear or the small tail drive spur gear. If any teeth are missing the tail drive may be slipping.
The other thing to check is if the tail blades are chipped or the torque tube bent or bearings damaged (or damage elsewhere if the heli tipped over in the incident) which could cause vibrations. Vibrations can interfere with the oiperation of the gyros.
Tony
Staff member
Are you flying in Rate or HH mode? If the tail was working fine (as stated earlier), then it should still be working fine. If you are in Rate mode however, putting a new tail shaft in there, you could have clamped teh tail blade grips slightly off from where the other one was so you would have to readjust the control rod. But, you should fly in HH mode at all times which will counter this issue.
and on this gyro, you should never put any kind of trim into the radio. This gyro, and many others, HATE trim and will do all kinds of weird things. Subtrim in DIR mode is just fine to get the tail where you need it, but if you add trim, bad things happen.
and on this gyro, you should never put any kind of trim into the radio. This gyro, and many others, HATE trim and will do all kinds of weird things. Subtrim in DIR mode is just fine to get the tail where you need it, but if you add trim, bad things happen.
All the teeth are good. That was my first check, I have had problems there before. I'm always flying in HH mode. It's been around 40-45% gyro. I adjusted gyro settings as well but it did not affect the yaw. I didn't open up the tail servo but it seems to move freely. It's an idea to open it up double check and regrease it if nothing else. Its just weird as it acts like the gyro is seeing a positive subtrim and when I add negative all goes away.
Tony
Staff member
Make sure you have a green status light on the 3GX. This is what indicates HH mode. I know it sounds simple and more than likely you are doing it perfectly fine, but I have seen time and time again where people have an issue with the tail holding and it turns out to be the wrong channel in the Tx Gyro menu. If you are using satellites only, then it is channel 7, but if you are using a separate Rx, it is channel 5.
Last edited:
Update on this yawing issue.
I disassembled the tail and tail boom mount. All looked good cleaned up all bearings and replaced the front umbrella gear and tail drive gear assembly anyway as I had a spare on hand. Opened up the tail servo and cleaned it up and regreased it.sealed everything back up and checked all moved freely. Went outside and started it up. SAME THING. It hovered nicely, just wanted to yaw right and the only way to cancel it was to apply around -28 sub trim.
So mechanically I'm sure it was good. I plugged it into the computer to go over the settings and powered up the heli. It did have a green light, I'm in HH, 40% gain, all settings look right. I noticed that there was no tail compensation when I moved the heli and that the linkage was if I was applying left rudder. I could operate the tail sevro but after centering it, it would creep back to full left rudder. I did not change anything in the gyro and unplugged the heli. I thought about things for a bit and plugged it back in again to check. After initializing all seemed to be back to normal. I unplugged it and took it outside, it flew fine, no yaw and zero sub trim.
So in recap it seemed to go screwy a total of 5 different times after initializing and then fixed itself on the sixth time. The only thing that seems slightly off now is that when I fired up the heli and spooled up , I launched into a hover.Once in the hover it seemed to increase throttle a little more to its preset position. It's like it went to 60% throttle and only went to it's preset position of 70% about 10 sec in. It did an instant jump to 95% throttle and back to 70% when switching from stunt 1 to stunt 2 and back. I landed and hit throttle hold and then restarted, same thing again. It's not the normal soft start that normally happens, it's like there is a 10 sec lag.
Anyone have a thought of what this gremlin is that I'm chasing?
I disassembled the tail and tail boom mount. All looked good cleaned up all bearings and replaced the front umbrella gear and tail drive gear assembly anyway as I had a spare on hand. Opened up the tail servo and cleaned it up and regreased it.sealed everything back up and checked all moved freely. Went outside and started it up. SAME THING. It hovered nicely, just wanted to yaw right and the only way to cancel it was to apply around -28 sub trim.
So mechanically I'm sure it was good. I plugged it into the computer to go over the settings and powered up the heli. It did have a green light, I'm in HH, 40% gain, all settings look right. I noticed that there was no tail compensation when I moved the heli and that the linkage was if I was applying left rudder. I could operate the tail sevro but after centering it, it would creep back to full left rudder. I did not change anything in the gyro and unplugged the heli. I thought about things for a bit and plugged it back in again to check. After initializing all seemed to be back to normal. I unplugged it and took it outside, it flew fine, no yaw and zero sub trim.
So in recap it seemed to go screwy a total of 5 different times after initializing and then fixed itself on the sixth time. The only thing that seems slightly off now is that when I fired up the heli and spooled up , I launched into a hover.Once in the hover it seemed to increase throttle a little more to its preset position. It's like it went to 60% throttle and only went to it's preset position of 70% about 10 sec in. It did an instant jump to 95% throttle and back to 70% when switching from stunt 1 to stunt 2 and back. I landed and hit throttle hold and then restarted, same thing again. It's not the normal soft start that normally happens, it's like there is a 10 sec lag.
Anyone have a thought of what this gremlin is that I'm chasing?
Tony
Staff member
I just read my post where I said something about the tail gyro channel above. I had is bass akwards. If you are using satellites only, then it is channel 7. But if you are using a separate Rx then it is channel 5. I learned this lesson the hard way just today lmao. And I'm supposed to be the "expert" with these gyros hahahahaha.
I just replied to your other thread. I wasn't running a satelitle and never did any actual changes. The only thing I can think of was that when I was initializing I was touching the heli a little too early and the gyro wasn't recalibrating properly. I got a great deal on a Microbeast 4.2 and swapped the gyro out 2weeks ago anyway. The 3gx is a nice gyro but the new microbeast is so much nicer, rock solid tail.
Tony
Staff member
The BX is a much better gyro all around. The ONLY reason I have a 3GX in my Devil 450 is because I needed a 3GX helicopter in case someone needed some settings or something. So I had Banggood send me one and I put a 3GX in it since that is the only gyro that will fit inside the frame of a Pro 450 Align lol. My other 450 now has a Dominator Frame on it, and has the AR7200BX in it, and the Align 600N and the Goblin both have Ikon gyros. The Goblin has the Ikon2 to be exact. Have not flown that helicopter though. Not sure if I will. Interest for it kind of just died.