Monday, November 28, 2011

Introducing the Inflight ACC Calibration


I programmed a feature that allows to find the perfect hovering zero point for the ACC sensor while inflight.

At the Shreddiquette community I took part in programming the same procedure after an idea of a fellow programmer and I ported the idea to Multiwii.


  • In reality there is no flat surface, so calibrating the ACC on ground will bring you close to a good value but you still have to find the perfect trim by trial and error.
  • Every copter is different so a perfectly flat surface does no recognice the inaccuracies in a copter, COG, bent arms, askew pylons etc.
Doing this inflight makes sure you are defining the zero point while in a perfect stable hover


  1. Arm the function with a stick combo (see below)
  2. take off and find the point of no drift (in acromode or in hovemode with TX-trimming)
  3. disarm via Aux1 and Aux2 (Aux disarming is a requirement) while flying, fon't worry there is a failsafe that prevents the engine from turning off while yu still have throttle > minthrottle. The offset is measured.
  4. Land and redo the combo to save the measured values. (be sure to undo the TX-trimming you did while flying in hovermode)
  5. Take off again and be happy ;-)
  6. You can do the combo again if you do not want to start the calibration anytime before taking off and do the measurement, to disarm the measurement. If you do not want to save the meausred value just do not do the combo. The values are lost after you cut power. You can always repeat the processover and over again  if you are unhapy with the result.

Stick Combo to arm/disarm the calibration.
You can find the code here:


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