How to Centre Servos (without losing your trim settings)

by Mike Shellim

This article describes the MPX way of re-centring your servos. It is much more effective than 'sub-trim' on most other sets, because it leaves your trim offsets intact.

Calibration Mode

The key is the Evo's 'calibration' mode which is not properly documented in the manual. In Calibration mode the Tx ignores the current stick and trim positions, and sends a 'calibration' signal. This calibration signal is adjustable, so that you can make your servo line up with any convenient reference. For example, ailerons would line up with the fixed trailing edge.

Calibration mode is entered by pressing the key in the Servo/Calibrate menu. Here are the steps in centring a servo:

Step 1 - choose calibration positions for control surfaces

First decide on a consistent reference for your control surfaces. This will normally be the neutral position of the control surface, i.e. with no trims dialled in. For example, ailerons are normally aligned on the trailing edge, so use this as your calibration reference.

Step 2 - calibrate servos

For each servo:

  1. Go to the Servo Calibrate screen.
  2. Select the middle point P3
  3. Press the digi-adjuster
  4. Press button to enter 'calibrate' mode.

    The servo - and vertical bar - will now jump to the centre, i.e. the servo will see the calibration signal.
  5. Adjust the digi-adjuster to re-align your control surface with your chosen reference position.
  6. Press the button again to release. This exits calibration mode, and trim and mixer settings are restored.

Subsequently, if your servo drifts or you bend a linkage, simply re-calibrate the servo(s). Any trims you have set will automatically be restored when you exit the calibration screen.

Comparison with SubTrim

Most Far Eastern sets provide a 'Sub-Trim' menu for centring servos. However, Sub-Trim does not normally enter a special calibration mode, so it's impossible for the user to distinguish between trim offsets applied by the user, and inaccuracies (mechanical or electrical) in the R/C command chain. The Evo way is SO MUCH BETTER !!

Note

Unlike using the REV/TRM adjustment, this method of centring only affects the centre point on the servo calibration curve - the other points are unaffected.