Mikado 550 SE Tail Wag

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I’m currently trying to identify the cause of the tail wag. This is a newly built heli with Mini vBar, YGE90LV speed controller. All Savox servos (the tail one is a Savox 1290) running on 5.7V (from the Speed controller BEC)

So far, the tail has been rebuilt completely 3 times, bearings checked for correct orientation and have been well greased. The tail shaft has been lightly polished with a fine grit wet + dry paper, the slider has had a slightly rough edge removed from inside the edge of the brass tube. I have added a slightly longer bolt to hold the 90 deg pushrod arm allowing a lock nut to be used, this means the bolt isnt quite as tight on the arm. All done, the tail pitch mechanism is really smooth and operates with hardly any resistance. However, after a flight, we have noticed some fine metallic residue on the tail shaft and the mechanism seems to have some resistance evident until cleaned. I have tried a BLS251 tail servo (cheers Ian) which did reduce the wag but did not eliminate it completely so I don’t feel that is currently the solution.

Aside from the wag, the helicopter is flyable and the tail responds well to input, yaw stops when told to and the tail doesn’t drift at all.

The wag frequency appears to match exactly the belt rotation frequency (in the video, you can just make out the white print on the belt as it passes the drive pulley).

Update – 21st Aug

Looks like this may now be solved. Although still some work to do. This video taken earlier today show how the heli flies now…

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I found that the pre-assembled pitch slider had a small amount of play which has now been tightened. In addition, the ball link under the slider that connects to the pitch arm was also a little loose (0.4mm difference between the ball diameter and the hole diameter) this may have been down to me in trying to achieve a smoother operation of the tail. Both added together were probably contributing a degree of play at the tail blades. I will replace the arm as soon as I can get hold of a replacement and to see if it just makes that last bit of difference.

 

 

About Richard 6 Articles
Been flying since the late 90's. Hope I'm still flying when I'm in my late 90's

    • I think its an iPad thing. I thought I had uploaded an IOS compatible video but it seems not, unless the recent IOS 10 update has affected things. I’ll see if I can get it recoded so it works on Apple devices again.

  1. Hi Richard,

    I have the exact same problem with my new 550sx. I’m using the Savox 1290MG and can see quite some play in around the tail pitch slider ball. Did you manage to eliminate that play?

    I can’t see your second video.

    • Hi Roger,

      Sorry for the late reply. Are you still having problems? Mine had excessive play in the pitch slider bearing. This was eliminated by tightening the inner brass tube, be careful not to over tighten it though. In addition, it took some work to ensure the whole tail pitch slider moves as freely as possible when disconnected from the servo. Including cleaning the machined ends of the brass slider tube and loosening the ball links etc. Mikado also suggested improvements to the mounting of the V-Bar receiver to eliminate as much vibration transfer, specifically not having the cables connected to it attached too firmly to the frame close to the v-bar (hope that makes sense) not sure if this helped but their explanation made sense and I did have everything packed into a small space at the time.

      If you still have the issue, let me know and I’ll see if I can help more

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