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Knowledge base Quark Common problems

Question #10
The tail bounces when it stops.
Answer

High performance gyros expect equally high performance from the helicopter mechanics. If the helicopter tail does not decelerate as fast as the gyro anticipates it overshoots the intended stop position; then the gyro brings the tail back. The end result is bouncy stop. Since the main rotor torque assist the stops in one direction, bounce is often observed in the other direction only.

To eliminate bounce you can either improve the mechanical setup to keep the gyro happy in line with default gyro configuration tailored for high performance 3D helis. Or, using the PC software lower the gyro's deceleration rate to match the particular heli.

You can try the following:

  • Gyro and heli setup
    • Ensure the gyro gain is correctly adjusted and the optimal gain value has been reached.
    • Adjust the tail linkages (mechanical trim) so the heli can fly with the gyro in rate mode.
    • Change the position of the servo ball link. Try moving the ball link 1-2 holes further out first and observe if stops are getting better or worst. If stops don't improve try moving the ball link further in. Note that every time the ball link is moved the [mechanical gain] of the helicopter is also affected, thus the gyro gain also needs to be re-adjusted.
    • In case of electric helis disable the built in governor of the ESC. Sharp stops require a sudden surge of power. Many cheap ESCs commonly found in combo kits have poor governor function which reacts too slow and then over-speeds. The variations of RPM affect tail authority and as a result the stopping performance.
  • Improve the performance of the helicopter's tail.
    • Try increasing the head speed a bit which in turn will increase the tail RPM and thus available tail thrust.
    • Try different, slightly larger or higher performance tail blades.
    • Try a faster tail servo. The Futaba S9650 servo has been a popular choice in past as it was the only available small size digital servo. However its intended use is for 1/12 scale cars and thus it is not an ideal match for modern high performance gyros. It is possible to increase the speed of this servo by replacing the gear train with S9257 gears.
    • Ensure that the radio power system (regulator and/or battery) can supply current. If it can't keep up under load the voltage will dip and as a result the servo speed will drop too.
    • Ensure that all tail lineages run smoothly and with minimal friction.
    • Ensure that the servo endpoints have been set correctly and allow all the available tail pitch to be used.
  • Using the gyro's PC software you lower the gyro's deceleration rate to match the helicopter. However note that stops may start to feel very soft if the deceleration is dropped too far.
  • If the wag is aggressive you may try lowering the stop gains using the PC software . If the stops are too soft you can try increasing the corresponding stop gain.
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