450 Trex 450 Pro/BX & Align DS520 tail servo

[Bruno]

So, i switched from the 3GX to the AR7200BX. I switched since my tail has been spinning clockwise after a stable hover of about a minute with the 3GX. I couldn't find anything else wrong that would cause the tail spin. Setup the BX, tail compensation direction is correct (opposite tail movement), tail slider is correct (right rudder stick left tail leading edge movement).

I take her out today for a maiden BX flight with 5mph wind. I hover and do some slight cyclic movements mostly to compensate for the wind and she holds good for about a minute. I then hear a "click" after a few seconds the tail starts spinning clockwise. Too familiar I bring her down as easy as possible and hit throttle hold. Bent shaft, broken main blade, few teeth striped on main gear. Tail boom and gears are OK.

I am thinking this may be a broken tooth in the tail servo from an earlier crash despite tail servo travel on the bench seemingly without issue.

I'm gonna take apart the servo and take a look.

Any other suggestions would be appreciated.

Any recommendations for a different tail servo (the Trex 450 pro is stock)?

 

[Tony]

I would do just what you are going to do. Take the tail servo apart and check it out. Maybe time to upgrade to the DS525 to get some more speed and torque. They may actually have another one out now that I don't know about. But I would definitely take that one apart.

 

[Bruno]

Just took the servo apart. No Evidence of Broken Teeth. No evidence of servo motor issues. This is getting really frustrating.

What could be causing the clockwise tail spin if it's not the tail servo, not the tail rotor compensation direction, not the tail servo direction, tail mechanisms are smooth as butter, tail spins with leading edge up and counter clockwise from tail rotor side view.

I am using the AR7200BX and I am familiar with successful the settings it is my third heli with the BX (changed this heli to the BX when I had this problem using the 3GX thinking it was the 3GX).

TT bearing is smooth. No chipped gears in tail gears front & back.

Any ideas??

 

[Tony]

without any rubber on the skids, set it down on concrete, asphalt or another hard smooth surface, and do these checks.

First off, you should have NO trim on teh rudder. Subtrim is okay, but ONLY if you did it in DIR mode. Wait, you are running a BX, you should have NO subtrim or trim, everything is done in the gyro on that unit. So make sure you are at 100% travel both ways with no DR or expo in the tail.

Go into the gyro and set your trim in the gyro it's self until your servo arm is 90º to the linkage rod. Once that id done, make sure your slider is centered on the tail shaft.

Now, put the helicopter in RATE mode (yes, you heard that right, RATE mode!) and spin it up. If the helicopter, at your flying head speed, is spinning around, adjust the linkage rod to counter this spin, then test again. Keep doing this until you can hold the tail in one spot at your regular flying head speed with no stick input. Once that is done and it's stable, put it back into HH mode and test it out.

 

[Tony]

Oh, and you should be on 1520µs and if you are on 333Hz, and you are having issues, lower that down to 250Hz and see what it does. The Hz is just how many time a second it corrects. 250 is still fine for sport flying.

 

[Bruno]

without any rubber on the skids, set it down on concrete, asphalt or another hard smooth surface, and do these checks.

First off, you should have NO trim on teh rudder. Subtrim is okay, but ONLY if you did it in DIR mode. Wait, you are running a BX, you should have NO subtrim or trim, everything is done in the gyro on that unit. So make sure you are at 100% travel both ways with no DR or expo in the tail.

Go into the gyro and set your trim in the gyro it's self until your servo arm is 90º to the linkage rod. Once that id done, make sure your slider is centered on the tail shaft.

Now, put the helicopter in RATE mode (yes, you heard that right, RATE mode!) and spin it up. If the helicopter, at your flying head speed, is spinning around, adjust the linkage rod to counter this spin, then test again. Keep doing this until you can hold the tail in one spot at your regular flying head speed with no stick input. Once that is done and it's stable, put it back into HH mode and test it out.

Tony, I am using a DX6i and I am not able to determine how to " Go into the gyro and set your trim in the gyro it's self until your servo arm is 90º to the linkage rod." Please clarify.

Otherwise, I will give your recommendation a try ASAP. Thanks.

 

[Tony]

Okay, it turns out that you can't adjust tail subtrim in the gyro. There is a way around this however. If you dial in the subtrim into yoru Tx BEFORE connecting your gyro, the gyro will think that is the factory setting. This is not suggested, but can be done if all other steps fail.

And I had a typo, I should have put 270Hz up there, and not 250Hz.

 

[Bruno]

Well, I put enough of the heli back together to spool her up on the bench without the main rotor housing/blades. I had the tail rotors on and was prepared for some force/torque from the tail. The tail rotors seem to spin normal however, they had little torque. The tail of the heli failed to move despite giving her full left/right rudder. It seems something has come loose/broken associated with the torque tube. I will delve a bit deeper tomorrow and keep you posted.

Hopefully this will help someone else.

 

[Ken Jackson]

Re: Trex 450 Pro/BX & Align DS520 tail servo

Sounds to me like the front gear set of the torque tube tail is slipping. If it hovers OK then weirds out I would for sure check it but I'd probably replace it anyway. No point in crashing. It will get worse if that is what is going on.

Ken

- - - Updated - - -

Bruno I had the same problem but blamed it on my IKON.

- - - Updated - - -

Check out this video, I got very frustrated myself. I eventually but this HK500 back in a box and its been sitting ever since.

http://youtu.be/G0ET9iC4imM

 

[Bruno]

Re: Trex 450 Pro/BX & Align DS520 tail servo

As I suspected the one metal/gear rotor tail end of the TT came loose of the tube itself. I will replace with a new TT and epoxy the old one for future use. Seems this should not have happened.

- - - Updated - - -

Sounds to me like the front gear set of the torque tube tail is slipping. If it hovers OK then weirds out I would for sure check it but I'd probably replace it anyway. No point in crashing. It will get worse if that is what is going on.

Ken

- - - Updated - - -

Bruno I had the same problem but blamed it on my IKON.

- - - Updated - - -

Check out this video, I got very frustrated myself. I eventually but this HK500 back in a box and its been sitting ever since.

Tail Problems - YouTube

Yea, I share in your frustration. I thought it was my FBL however it was a loose gear end on the TT which reduced the tail speed causing a loss of control and clockwise rotation.

Did you discover a mechanical problem as well?