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The  "Gold Standard" Servo

Capstan Servo                                               Crank Arm Servo

The Intelligent Servo

The Gold Standard servo is unique in the industry.  When Trio introduced the altitude hold systems, we did so only when we felt that we had designed a "safety-conscious" servo that we were comfortable connecting to an aircraft elevator system.  (It is used for both aileron and elevator systems).

The Gold Standard servo has inherent "intelligence" capability acquired by the two internal microprocessors that govern its operation.  It has full authority to disconnect itself from the controls if it senses anything that deviates from normal operational conditions.  It watches motor driver currents and temperatures (both servo and auto-trim) as well as short circuits.  It monitors crank arm positions and will disconnect (and alert the pilot) in abnormal circumstances - i.e. extreme elevator/aileron positions.  It obeys the "G" force limitations dictated by the A/H control electronics and it will disconnect itself if it detects a communications error.   It has a slip clutch to allow pilot override in emergency situations.  It fully disconnects the internal gears when not engaged and the pilot will not feel any "system drag".

In short, the Gold Standard servo borders on being paranoid about your safety.

  •  All digital electronics for accuracy and reliability

    The servo communicates, via a high-speed bidirectional data bus, with the altitude hold control module.  This unique capability allows it to inform the control module (and the pilot, via the LCD switch screen) of any unusual activity within the servo.   For instance, it can notify the pilot if the clutch is not properly adjusted.  If critical activity is reported, the control module will immediately remove all power from the servo, releasing the elevator and (if installed) automatic trim system.

  • Dual microprocessors monitor all functions for safety (an industry first!)

     The Servo Main Processor (SMP) controls all servo functions.   It also monitors communications from the motor and trim drivers, and it constantly listens to the "heartbeat" signal from all other processors in the system.  If it detects any anomalies it will provide an alarm and disconnect from the aircraft controls.

    A Supervisory Processor continuously monitors the Servo Main Processor to ensure it is executing its program as designed.  It looks for the “heartbeat” signal from the SMP each 10 milliseconds.  If for any reason the processor does not provide a “heartbeat” signal to the supervisory processor for a period of 65 milliseconds the supervisory processor will unilaterally cut power to the safety disconnect solenoid and the trim and servo motor drive circuits.

  • Triple protected motor drivers continuously report their condition to the microprocessors

    The integrated circuits used to drive the servo and trim motors are internally equipped to detect and report to the SMP a variety of fault conditions including:

         1.  High side (supply side) short to ground (low side)
              Low side short to high side
         2.  Under voltage lockout
         3.  Over temperature condition

    The SMP will immediately disconnect upon receiving any of these fault messages.

  •  Complete motor and gear train disconnect when not engaged - free from system drag

    The servo contains a solenoid that allows a complete disconnect of the servo gear train whenever power is removed from the solenoid.  Power can be removed under program control of the System Main Processor (SMP), the supervisory processor or whenever power is interrupted by the AH module.  In addition, it is advisable to always install an easily accessible circuit breaker or switch in the aircraft power line to the system.

  •  Reliable slip clutch (adjustable to your airplane) provides immediate pilot override

    The servo employs a clutch, which allows the pilot to override the servo by applying moderate force to the control stick.  Even though the solenoid will hold the gears in place, the clutch will then slip and allow the control surfaces to move.  In the event of strong turbulence, or an altitude anomaly, the pilot can thus override the servo to control the airplane. 

    The slip clutch may be employed freely without any damage to the system.  The clutch function does not rely on a shear pin failure mechanism as is sometimes employed on  other autopilot servos.

    Servo Dimensions are here