Multiwii Trimming Accelerometer for Auto-level Flight


Before following this tutorial make sure your transmitter is properly trimmed out using normal (Gyro/Acro) flight mode and adjusting the trim dials on your transmitter. Without properly trimming your transmitter to neutral your transmitter will be commanding the quadcopter to move when you intention is for the copter to maintain a level attitude.

What is auto-level mode?

The Quadrino contains an accelerometer sensor which the copter can use to maintain a level attitude. This means without any stick input, and without wind, the copter will stay perfectly still in the air. Auto-level is not position hold, if there is wind it will still blow the copter away. However, even in wind the copter will continue to maintain a level attitude and will not flip or otherwise blow over at an angle. (Imagine the behavior of a hovercraft floating on a pillow of air.) You can still fly around in auto-level mode as the amount of roll or pitch stick input will slant the copter’s attitude accordingly and maintain it for as long as you maintain that amount of stick input. Release the stick and the copter will return back to level flight. This is in contrast to gryo/acro flight mode where a neutral stick will try to stabalize the copter’s current attitude, but will not return to level position.

Prerequisites to this Guide

Before following the steps in this tutorial you should have already done the following:

  1. You’ve verified your accellerometer is properly calibrated using the Calibrate Accellerometer tutorial.
  2. Trimmed your transmitter in gryo/acro mode. Once you can hover the copter in gyro/acro mode and the copter maintains the hover (for the most part) you are ready for auto-level trimming. An untrimmed transmitter will be commanding the copter to move thus defeating the purpose of auto-level.
  3. You’ve assigned the LEVEL flight mode feature to an AUX channel (AUX1 or AUX2) and into one of the channel positions (LOW, MED or HIGH). You do this by clicking the appropriate checkbox in the MultiWiiConfig GUI.

Perfecting auto-level performance / How to trim auto-level mode

Auto-level flight requires a properly calibrated accellerometer. The Quadrino’s accellerometer is calibrated at the factory but you can also repeat the calibration process in the MultiWii GUI. In any case, a desk or a floor is not perfectly level so some adjustment of this calibration will have to be done in-flight. There is a method to tuning the accellerometer (auto-level) in the field. This must be done after trimming the transmitter though otherwise you are just trying to correct one error with another. So with acc pre-calibrated and your transmitter already trimmed previously in gyro/acro mode do the following:

multiwiicopter-acc-calibrate2

Accelerometer (Acc) Calibration – The PARIS is calibrated before shipping, at 25°C – However  if you Ops are at a different temp a temp bias can be introduced need a re-cal, so for your Ops temp set the Copter level 0.00° – Press CALIB_ACC – (after first Flying the Copter in ACRO mode – Trim out any YAW using motor tilt (3-5°) – Dont use Tx trim – all Tx trims must be 0) – – Land – Switch over the HORIZON or ANGLE mode – hover STILL air (no wind)  – if the copter is drifting by more the 2° tilt the calibration is effected by temp and you need to do a field Acc Cal -> land – – 

Disarm the copter (see above) ; ensure the Copter is on a perfectly LEVEL LZ – it must be completely static – 
 Confirm the DISARMED LED is OFF – Hold Full THRO/YAW LEFT and the Cyclic stick Back for 1 Sec ;  

release – you will see the GREEN LED blinking fast for a few secs then go out – The Acc is now calibrated for LEVEL mode (at this ambient temperature) – The ACC on a PARIS/warthox board is the Nunchuk®.  

 MultiWiiCopter-Acc-trimming
Accelerometer (Acc) 2° Trimming – Also called auto-LEVEL trimming – FIRST do after the GYRO & ACC calibrations and normal ACRO trimming (see above).  LAND.  

Switch over to LEVEL mode (Gear Switch).  

Take off and mentally note the way the copter wants to drift – DO NOT TRIM THE TX 
– Land – The final ACC trimming procedure (below) is this -DISARM (see above – the Green LED will go OFF) Move the THRO to the ‘Learn Position – full up) – in this example the copter was moving back and right – so ; using stick-banging – move the cyclic (right stick) up once (led blinks) – then left once (led blinks) – these alterations are saved to the CPU memory.  ARM again – hover and repeat the process until the copter hovers ‘level’.  Each Stick-bang = 0.1°

 

  1. Enable LEVEL mode using the aux switch on your transmitter. You should have already setup LEVEL mode on one of your AUX channels/switches.
  2. Arm the copter and take off. Try to maintain level flight, if level is not perfect you will have to counteract the error with some stick input.
  3. Same as with acro try to keep the copter level and note how much roll/pitch stick you need to put in to correct the error.
  4. Now land the copter and disarm motors (throttle all the way back, roll all the way left)
  5. Now with motors disarmed, slowing move throttle all the way to max (motors will not spin if copter is properly disarmed). Move throttle slowly just in case motor disarm failed. With the throttle at maximum, the copter is waiting for command input to adjust the ACC level.
  6. If the copter was pitching forward (going away from you), then:
    • a. Pull full back on the pitch.
    • b.Then return to center
    • c.Repeat a number of times, the more times you repeat the more correction it will make but it only does it in a single small increments for each “full back, and return to center” sequence. Repeating 3-4 times is not really noticeable (only a slight correction). I often have to start with 10-12 increments for the first correction. Then test fly, and repeat the process with another 3-5 increments.
  7. Now you can do the roll, same process:
    • a.All the way left or right, then return to center
    • b.Only do a correction for a single direction at a time…diagonal correction input does not work.
  8. After doing a number of increments for Roll and Pitch. With the P/R stick at center, return the throttle back to full low. Rearm the motors and test fly. Repeat until the copter maintains level.
  9. Do not do the ACC calibration from MultiWii again or you will lose this calibration. The copter will remember your calibration settings so once trimmed your auto-level should perform perfectly and you won’t have to repeat this tutorial until you upgrade your copter Firmware.
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