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7.5 Gram Super Sub-Micro Digital Prog Servo, DSP75

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Preventing Servo Oscillation DSP60/ DSP75

High precision digital servos like the Spektrum DSP60 and DSP75 feature a narrow deadband and high gain offering accurate centering and powerful holding torque. In some applications these servos can cause the control surfaces to oscillate (vibrate at neutral) when the servo should be at rest. This is caused by the servo attempting to aggressively return the control surface to its desired position and the mass and inertia of the control surface causes the system to overshoot and oscillate when the servo should normally be at rest. Following are tips on how to prevent this over shoot oscillation:

• Linkage Geometry
By changing the linkage geometry (the attachment point of the linkage on the servo horn and on the control horn) changes the mechanical advantage the servo has over the control surface and this greatly affects oscillation characteristics. Generally if oscillation occurs move the linkage on the servo arm inward one hole and or move the linkage on the control horn outward one or more holes. The geometry change will improve the mechanical advantage and in most cases with reduce or prevent control surface oscillation. This may require that the travel adjustment in the transmitter be increased to regain the total control throw.

• Dampening the Control System
If you have a surface that oscillates note that buy simply lightly touching the control surface the oscillation will cease. In fact in flight the air flowing over the surface will have a similar dampening effect that also causes the surface to stop oscillating. Effective methods of dampening the control system includes applying heavy grease to the gear train in the servo or to place a light rubber band on the control horn that lightly loads the servo.

• Programming
The DSP servos are programmable for three specific applications: airplane, helicopter and tail rotor for helicopter. In airplane mode the DSP servo has the widest deadband and gain making it least prone to oscillation. When using the DSP servo in airplanes be sure the servo is programmed in the airplane mode (which is the default setting.