Elevator Filter

The elevator filter is a feature in the PID controller that attempts to prevent elevator bounce by slowing the transition of the elevator (AXIS_PITCH) near mid-stick (0 deg/s pitch rate). Elevator bounce is more noticeable on larger helicopters. 300-400mm blade helicopters will show a small bounce without the elevator filter, while 500mm+ size helis will show a very large bounce.

set elevator_filter_gain = 100

• Multiplier for the elevator filter feedforward offset
• This value is divided by 100 in the code, so start with a setting of 100 perhaps work up from there.
• Gain automatically scales with the elevator feedforward gain
• Set elevator_filter_gain = 0 to disable the elevator filter code

set elevator_filter_window_time = 75

• Time is milliseconds to apply elevator filter after entering the filter window
• Recommend 75 ms to start

set elevator_filter_window_size = 30

• Size of the filter window in deg/s
• Filter window is centered around 0 deg/s pitch rate
• Recommend 30 deg/s to start

set elevator_filter_hz = 15

• Cutoff frequency for the PT1 filter applied to the elevator setpoint
• Lower setting should give less bounce, but will slow the elevator stop response. Find a balance!
• Lower settings will require longer elevator_filter_window_times to be effective, and vice-versa.
• 5-20Hz is probably fairly appropriate for most bigger helicopters?

The 4th value of DEBUG_AC_CORRECTION that isn't normally used now holds the eleOffset value (elevator filter offset).