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Autopilot Servo Calibration Procedure and System Troubleshooting

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ℹ️ Overview: This guide covers the complete autopilot servo calibration and test procedures required before your SkyView autopilot system can be used. Proper calibration identifies servo orientation and range of motion, while the test procedure verifies correct control surface movement. This guide also covers common troubleshooting scenarios including broken shear screw identification, calibration confusion, and AP panel mode requirements.
SkyView Network Status with Servos and ADAHRS

Prerequisites

Before beginning servo calibration, ensure the following requirements are met:

  • SV-ADAHRS-200 installed and configured – The system requires a functioning ADAHRS to operate the autopilot.
  • All servos properly networked – Servos must be detected on the SkyView network (verify in SETUP MENU > SYSTEM SETUP > SKYVIEW NETWORK SETUP)
  • IAS tape colors and V-speeds configured – Airspeed limitations must be set before servo calibration (see SETUP MENU > PFD SETUP > AIRSPEED LIMITATIONS)
  • Dedicated AP Disconnect/CWS button installed – A momentary, push-button normally-open (PBNO) switch must be properly wired and functional
  • Aircraft properly secured – Ensure the aircraft is in a safe environment for control surface movement during testing
⚠️ IMPORTANT: Adjusting autopilot settings while the autopilot is engaged is not recommended, as some settings changes may cause the autopilot to react immediately and counter to the pilot's immediate expectations.

Servo Calibration Procedure

The servo calibration procedure identifies the orientation and range of motion of each servo and must be performed before the servo test procedure. SkyView uses this procedure to automatically differentiate between the pitch, roll and yaw servos.

ℹ️ NOTE: SkyView supports single-servo autopilot configurations (roll only, pitch only, or yaw only) as well as dual-servo and triple-servo installations. During calibration, the system automatically identifies which servo controls which axis based on the control movements you make. For proper identification, the calibration must observe appropriate control surface movement from each installed servo.

Step 1: Enter the Calibration Wizard

Navigate to the Servo Calibration Wizard using the following menu path:

SETUP MENU > HARDWARE CALIBRATION > AP SERVO CALIBRATION > CALIBRATION

Access the Setup Menu by simultaneously pressing and holding buttons 7 and 8 on your SkyView display.

Autopilot Servo Calibration

Step 2: Follow On-Screen Instructions

The calibration wizard will present step-by-step instructions on the screen. Tip: Use the on-screen buttons to navigate through each step rather than pressing physical AP Disconnect buttons, unless required. Inadvertently double pressing AP Disconnect button may cause you to skip important servo identification steps or fail the calibration process.

During the calibration, you will be prompted to:

  • Center the aircraft controls
  • Move the controls through their full range of motion
  • Confirm the servo movements match the expected behavior
⚠️ CAUTION: Excessive servo throw can cause calibration failures. Before calibrating, verify the servo installation allows proper range of motion without binding or over-travel. If you experience calibration failures, try limiting control movements – you do not need to move controls to their absolute mechanical stops for successful calibration.

Step 3: AP Disconnect Button Check

During AP servo calibration, SkyView automatically checks the status of the AP Disconnect/CWS button. If SkyView detects that the button is pressed (the input is grounded) upon entering calibration, it assumes the button is stuck or incorrectly installed.

If this occurs, you will see the following message and the calibration will abort:

The servo disconnect switch appears to be pressed and may be
installed incorrectly. The servo disconnect switch should be
a type Momentary, Push Button Normal Open (PBNO).
Press Cancel below to return to the servo calibration menu.

If you encounter this error:

  • Verify the AP Disconnect button is not physically stuck or binding
  • Confirm the button is wired correctly as a normally-open switch
  • Check for short circuits or improper grounding in the button wiring
  • Be sure the AP Disconnect wire isn't chafing and shorting to ground
  • Ensure you are using a momentary push-button switch (not a toggle or latching switch)

Step 4: Complete Calibration

If the servo calibration procedure is successful, SkyView will automatically prompt you to run the servo test procedure. Do not skip this step – the test procedure is required before the autopilot can be used.

Servo Test Procedure

The servo test procedure requires a successful servo calibration. This procedure verifies that each servo is configured properly by moving the control surfaces while you verify the correct movement. SkyView will not display AP status on the Top Bar until after this test procedure is successfully completed.

✓ TIP: The servo test procedure verifies that control inputs move in the correct direction. Control surfaces will not move fully to the stops during testing – the test movements are intentionally smaller than the full range of motion observed during calibration. This is normal behavior.

Step 1: Enter the Test Wizard

If you need to run the test procedure separately (after completing calibration), navigate to:

SETUP MENU > HARDWARE CALIBRATION > AP SERVO CALIBRATION > TEST...
AP SERVO TEST

Step 2: Follow On-Screen Instructions

The test wizard will prompt you to verify servo movements match the expected control surface deflections. You will observe:

  • Roll servo test: The aileron or roll control surface should move in the correct direction
  • Pitch servo test: The elevator or pitch control surface should move in the correct direction

Confirm each movement is correct before proceeding. If any servo moves in the wrong direction or does not move at all, do not proceed – exit the test and troubleshoot the installation.

Step 3: Complete Test

Once the test procedure is successfully completed, the autopilot system is ready for initial setup and configuration. You should see AP status displayed on the Top Bar of your SkyView display.

✓ Next Step: After successful calibration and testing, proceed to the Autopilot Setup Menu SETUP MENU > AUTOPILOT SETUP to configure autopilot behavior, torque settings, and control modes. Certified aircraft users should utilize Dynon provided aircraft specific configuration files.
Additional in-flight tuning procedures are covered in the SkyView Autopilot In-Flight Tuning Guide.
screenshot-N976BB-SN13057-17.5.B0.24012-20260206-143553-449-en_US-gigapixel-text-shapes-2x.jpeg

Identifying and Replacing Broken Shear Screws

Autopilot servos include a shear screw as a critical mechanical safety device. The shear screw is intentionally designed to break under excessive load to ensure pilot safety: if a servo seizes or malfunctions, the broken shear screw prevents the failed servo from restricting movement of the flight controls, preserving the pilot's ability to manually control the aircraft. This sacrificial component also protects the servo motor, gearbox, and aircraft control linkage from catastrophic damage. When a shear screw breaks, the servo can rotate freely without transmitting force to the control surface – manual control authority is maintained, but the autopilot becomes inoperative and calibration or testing will fail with confusing symptoms.

Symptoms of a Broken Shear Screw

A broken shear screw creates a unique failure mode that can be difficult to diagnose without understanding what to look for:

  • Control surfaces move the servo, but the servo cannot move the control surfaces – When you manually move the flight controls, the servo appears to follow along and rotate. However, when the autopilot attempts to move the controls, nothing happens or the servo spins ineffectively.
  • Calibration repeatedly fails – The calibration wizard cannot detect expected servo movement because the broken shear screw prevents force transmission between the servo motor and output shaft. This may cause the calibration process to for the presence of a yaw servo, even if one is not installed.
  • Servo test shows no control surface movement – During the test procedure, the servo motor may audibly run, but control surfaces don't deflect. Sometimes there is enough friction to trick the calibration into passing while the motor shaft can still spin freely once there is resistance from the weight of the control surfaces.
  • Excessive play or free rotation at servo output – If you can rotate the servo arm by hand with very little resistance while the servo is powered off, this often indicates a broken shear screw.

Diagnosing a Broken Shear Screw

To verify whether a shear screw is broken:

  1. Power off the aircraft and ensure all servos are de-energized
  2. Attempt to rotate the servo output arm by hand – The arm should offer significant resistance and should not rotate freely. If it spins with minimal force, the shear screw is likely broken.
  3. Check for physical signs – On some servo models, you may be able to see or feel broken shear screw fragments, though this often requires partial disassembly.
  4. Perform a powered test – Carefully power the system, enter the servo test procedure, and observe whether the servo motor runs but fails to move the control surface. If you hear or feel the motor running but see no output shaft rotation, the shear screw is broken.
  5. Remove hardware – Carefully remove the retaining hardware for the servo control arm or capstan and see if the component comes free easily confirming the broken shear screw. The head of the screw will often remain with the control arm or capstan while the threads remain in the black collar attached to the servo output shaft.

Shear Screw Replacement Procedure

⚠️ IMPORTANT: Shear screw replacement requires partial servo disassembly and must be performed carefully to avoid damaging internal components. If you are uncomfortable performing this repair, contact Dynon Technical Support for guidance or return the servo for factory service. For certified aircraft, a licensed A&P mechanic is required to handle the inspection and repair. 

Required tools and materials:

  • Replacement shear screw (obtain from Dynon Avionics)
  • Appropriate hex wrenches or screwdrivers for servo case disassembly
  • Clean workspace, or access to the installed servo with good lighting
  • Optional: Digital camera or smartphone to document disassembly sequence

General replacement procedure:

  1. Remove the servo from the aircraft if necessary – Disconnect all wiring and control linkages. Label connections and photograph the installation for reassembly reference. Leave the servo in place if able to work with as installed.
  2. Locate and remove broken shear screw fragments – Carefully extract any remaining pieces of the broken screw.
  3. Install the new shear screw – Insert the replacement shear screw according to the kit-provided instructions. Do not over-torque the screw, as it is designed to fail under excessive load.
  4. Reassemble the servo – Carefully reassemble the control arm or capstan hardware, ensuring all present and reinstalled in the proper order.
  5. Reinstall in the aircraft (if removed) – Reconnect control linkages and wiring per installation documentation.
  6. Recalibrate the servo – After shear screw replacement, you must run the complete calibration and test procedures again.
🚫 CRITICAL: After replacing a shear screw, investigate why it failed. Shear screws break due to excessive mechanical loads, which may indicate: improper servo installation with binding linkage, over-travel of control surfaces hitting mechanical stops, obstructed or frozen control surfaces, or incorrect servo mounting creating misalignment. Address the root cause, if able, to prevent repeated shear screw failures.

When to Contact Dynon Technical Support

Contact Dynon Technical Support if:

  • You experience repeated shear screw failures even after correcting installation issues
  • You are uncertain about servo disassembly procedures for your specific model
  • You lack the proper replacement shear screw hardware
  • The servo shows other signs of damage beyond the broken shear screw
  • The black collar tied to the servo output shaft has no more available threads
  • The black collar tied to the output shaft spins freely from the output shaft.
  • You prefer factory service rather than field replacement

Troubleshooting System and Calibration Issues

The following table covers common autopilot servo calibration and system issues with recommended solutions. Use this as a quick reference guide when encountering problems.

Issue Symptom & Likely Cause Solution
AP Disconnect Button Error During Calibration Symptom: Calibration aborts with message stating the servo disconnect switch appears to be pressed

Cause: Button stuck, wired incorrectly, or wire shorted to ground		 Verify button is momentary, normally-open (PBNO) switch. Check button is not mechanically stuck or binding. Inspect wiring for short circuits or chafing causing ground shorts. Test button with multimeter to verify normally-open state.
Calibration Asks About Yaw/Rudder When Only Pitch and Roll Installed Symptom: Calibration wizard prompts for rudder inputs (full left/full right) despite only having pitch and roll servos installed

Cause: User accidentally double-pressed AP Disconnect button, or dirty button contacts caused contact bounce, skipping positional updates during calibration		 Exit calibration and restart the procedure. Use ONLY the on-screen menu buttons to advance through calibration steps rather than pressing the physical AP Disconnect button. Clean AP Disconnect button contacts if bouncing suspected. Ensure smooth, single button presses when required.
Calibration Fails Repeatedly Symptom: Calibration wizard does not complete successfully, or servos do not respond correctly during calibration

Cause: Broken shear screw, binding servo installation, excessive throw, poor control linkage, or servo failure		 Check for broken shear screw: Verify servo shear screw is intact – broken screw allows flight controls to move independently from servo rotation. Replace if broken. Check servo installation: Verify adequate range of motion without binding or hitting stops. Inspect control linkage: Ensure servo arm and linkage allow full travel without excessive resistance. Use on-screen buttons: Always use on-screen menu buttons to advance calibration rather than physical AP Disconnect button to avoid skipping steps. Contact Tech Support if all else fails.
Excessive Throw or Control Movement Symptom: During calibration, control surfaces move too far or hit mechanical stops, causing calibration to fail

Cause: Servo installation geometry creates excessive throw, or user moving controls to absolute mechanical limits		 Review servo mechanical installation and linkage geometry for safety. Adjust servo arm length or control rod attachment points to reduce throw if needed. Ensure servo is installed per aircraft-specific kit instructions. Verify control surface travel limits are appropriate. Limit control input during calibration if installation is correct – you do not need to move to absolute mechanical stops.
Servo Not Detected on Network Symptom: Cannot access servo calibration menu, or servo is not listed in network configuration

Cause: Servo not powered, network cable disconnected, damaged, or not wiring correctly, network not configured, or servo failed		 Verify autopilot power switch is ON (if installed). Verify servo is powered (check fuses/breakers). Verify presence of power and ground at servo connectors. Confirm servo connectors are pinned per installation manual. Confirm network cable is properly connected and not damaged or chafing. Run network configuration wizard: SETUP MENU > SYSTEM SETUP > SKYVIEW NETWORK SETUP > CONFIGURE... Check servo firmware is compatible (newer servos may need rollback with FORCE NETWORK LOAD).
Calibration Works But Test Fails Symptom: Servo calibration completes successfully, but test procedure fails or shows unexpected behavior

Cause: Controls not centered, mechanical binding, broken shear screw, power supply issue, or wiring issue		 Ensure aircraft controls are centered before starting test. Verify no mechanical binding or interference with control surface movement. Verify servo shear screw is intact – broken screw allows servo to rotate from control surface movement without being able to move surfaces. Check servo power supply voltage is within specifications. Verify power and grounds are not tied to the SkyView Network. Re-run calibration and test procedures from beginning. Confirm network cables are securely connected and not damaged.
SV-AP-PANEL Does Not Function Symptom: External autopilot control panel (SV-AP-PANEL) is installed but does not control autopilot or appears inactive

Cause: Autopilot configured for SIMPLIFIED mode instead of EXPERT mode – SV-AP-PANEL only functions with EXPERT controls		 Navigate to SETUP MENU > AUTOPILOT SETUP > AUTOPILOT CONTROLS and verify setting is EXPERT. The SV-AP-PANEL requires EXPERT mode to be active. If you have both pitch and roll servos installed, EXPERT mode is available. If you only have one servo (pitch only or roll only), the system can only be set to SIMPLIFIED mode and the SV-AP-PANEL will not function.
Single Servo Installation Not Recognized Symptom: System does not properly identify single-servo installation (roll only, pitch only, or yaw only)

Cause: Calibration did not observe appropriate control surface movement to identify servo axis		 During calibration, ensure you move the correct control surface that corresponds to the installed servo. For roll-only installations, move ailerons. For pitch-only, move elevator. For yaw-only, move rudder. The calibration must observe proper control movement to automatically identify which servo controls which axis. If calibration continues asking for other axes, you may be moving the wrong control or the servo is not properly connected to the control surface.

After Successful Calibration and Testing

Once both the calibration and test procedures are complete, you can proceed with autopilot configuration:

  1. Configure Autopilot Controls: Choose between Simplified or Expert control modes SETUP MENU > AUTOPILOT SETUP > AUTOPILOT CONTROLS
  2. Set Servo Torque: Adjust roll and pitch axis torque settings for appropriate override force SETUP MENU > AUTOPILOT SETUP > ROLL AXIS / PITCH AXIS
  3. Test Override Force: Engage the autopilot using LEVEL mode and verify you can comfortably override the servos manually. Only do this occasionally to avoid premature wear on the shear screw or servo motor
  4. Perform In-Flight Tuning: Use the SkyView Autopilot In-Flight Tuning Guide to optimize autopilot performance for your specific aircraft
ℹ️ NOTE: The Autopilot Setup Menu SETUP MENU > AUTOPILOT SETUP is only accessible after a successful servo test procedure. If you cannot access this menu, verify that both calibration and test procedures have been completed successfully.

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