I’ve finally found and almost resolved the instability problem with Zoe. Zoe is a Pi0W compared to Hermione’s B3. As a result, she’s a single CPU at lower frequency and she’s struggling to keep up. In particular the LiDAR / Video distance increasing lag behind the IMU:
As a result, once fused, Zoe is reacting to historic movements and so drifting. The IMU data processing takes priority and by slowing it down to 333Hz (from 500), that allows enough space to process the LiDAR / Video distance to stay in sync with the IMU. Here’s the result for a simple 10 second hover.
There is still lagging drift but much less than seen previously; this drift is still cumulative; hence my next step is to reduce the video frame size a little more.
While this might not be the reason behind the RC drift, it cannot have been helping.
By the way, the fact the incrementally lagging drift is consistently left / right suggests strongly that I need to reduce the port / starboard PID due to the weight balance, primarily the LiPo battery aligned fore / aft in the frame. On the plus side, without this flaw, I’d never have been able to diagnose the drift problem so clearly and quickly!