Ardupilot contribution of the month, August 2019

Congratulations to Andy Piper (aka Andyp1per on this forum and on github) for winning the Ardupilot contribution of the month prize for August 2019!

Graphs from Bill Geyer

Andy was nominated by the dev team for his work on adding the possibility of using Harmonic Notch Filters to Ardupilot.

For those that may not be familiar with the term, a notch filter, as its name implies, eliminates frequencies in a narrow band. Using sound as an analogy, a notch filter at, say, 4,000hz would for example eliminate all sounds close to that frequency, and pass all others in the sound spectrum.

In the Ardupilot world, filters are crucial to clean up or eliminate gyro data noise (produced by vibrations) from data then passed to the flight controller. With a harmonic notch filter, noise occurring at multiples of rotor frequencies (which is typical, especially for helicopters) can be filtered out, resulting in better and more stable flying characteristics.

Andy has been one of the key people to highlight that the previous notch filter in Ardupilot was not implemented in the optimal place, and has worked to move it to consume full rate gyro data. He then went on to extend the Notch filter by adding a harmonic notch filter option and is the author of a current pull request to dynamically adjust the harmonic notch frequency based on the average output thrust value.

As part of his work Andy has been flight testing an on board FFT based method of setting the harmonic notch filter frequency. As part of his testing he has implemented a vibration test system that he used to demonstrate the effectiveness of the harmonic notch filter, on board FFT and has been reviewing the internal filter settings of some of the IMU’s Ardupilot is supporting.

A thread on this forum, started by Ardupilot helicopter lead Bill Geyer, sheds additional light on Andy’s contribution.

The prize for the month was $200 for the top contributor. Many thanks to those who donated to ArduPilot, including our Corporate Partners . If you are a company and wish to donate a prize for an upcoming month, please email the partners email list (

Congrats again Andy! Quoting Leonard Hall (Ardupilot’s control and tuning expert developer), who has also been test flying using the dynamic harmonic notch filter, “it will be an extremely significant step forward for the quality of Ardupilot’s attitude controllers”!