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Knowledge base Quark Common problems

Question #83
The helicopter tail wags / flutters / kicks / twitches.

Rapid wag / fluttering (continuous or during specific manoeuvres)

If the tail wag is continuous and rapid it is most likely the result of high gain. The overall gain of the tail is a combination of the gyro gain plus the mechanical gain of the tail.

  • Lower the gyro gain until no wag is seen at any time in flight.
  • In some cases you may also need to lower the mechanical gain by moving the tail servo ball link closer to the centre. See [topic 84] for information on the mechanical gain and how it affects your gyro.
  • The Trex 250 has excessively high mechanical gain by design. Use the shortest possible servo arm length.
  • For 450 size helis you may need to place the servo ball link at the shortest possible distance. If using a Futaba servo try the small servo horn disk.

Irregular random wag with drift

If the tail wag is random and a stepped drift is seen each time the cause may possibly be electrical noise, static discharge or faulty bearings affecting the gyro's rotation sensing. Try repositioning gyro wire keeping it away from the high current battery, ESC and motor wires. Also avoid getting close to the tail belt pulley as it is commonly an area of static discharge.

Irregular random wag/kick with no drift

If the helicopter continues to maintain the correct heading it is a good indication that the gyro is aware of where the tail should be but other factors momentarily preventing the gyro from holding it there. This will will result to the tail momentarily drifting off until the gyro manages to regain control and bring it back. This will appear as an occasional wag.

  • Check that all linkages operate smoothly without excessive backlash (play).
  • If your transmitter has a servo test function connect the servo directly to the receiver and perform a few test sweeps. Observe the servo arm for any point where it may momentarily pause indicating problems with the servos gear train or potentiometer.
  • Most small electric helicopter use only radial bearing in the tail grips. These are not optimal for the sideways forces that they are subjected to and can sometime become gritty and momentarily lock up. Keep in mind that bearings may appear ok during bench testing but will behave different under load when the tail rotor spins.
  • Check the gyro and tail servo wiring for any loose connectors, wires damaged by robbing on the sharp edge of the carbon helicopter frames or severe wire kinks which may have resulted to internal wire damage (often the wire insulation appears white on severe kink points). Slowly flex the wires at different places to check for internal breakages by observe if the gyro changes behavior (servo moves or the light flashes) or the tail servo stops workings as you flex the wire. Pay particular attention close to connectors and where the wires enter the gyro and servo.
  • The built in governor of some ESCs does not provide smooth response thus resulting to rapid and random changes in torque. Disable the governor and observe if the problem persists while using throttle/pitch curves only.

Unfortunately in some cases a persistent wag may continue to exist despite following all the best practises for building a new helicopter kit and installing the gyro. Tracking down the faulty part can be difficult, time consuming and will require having the helicopter in front of you. Spartan RC can not help in this process but we will be happy to test your gyro free of charge subject to the conditions of our free repair service.

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