Both Phoebe and Zoe now rocket up to the sky at at least 3ms-1 when they should be climbing at 0.3ms-1.
The main relevant change is that both were flying with alpf 0 – 460Hz. Reducing this to 2 (92Hz) with Phoebe yesterday got the vertical climb rate under some level of control, but the horizontal drift was back. I’m assuming Zoe will show the improved behaviour at alpf 2 also.
Clearly there’s something in the accelerometer readings that’s integrating (after gravity is removed) to lower velocities than expected. Then it dawned on me: sampling at 1kHz with the minimal low pass filter set to 0 means that >2g spikes could get picked up; with the range of the sensor set to ±2g, the value could overflow, resulting in the <0g values I’d been seeing.
A very quick test with Phoebe in a howling wind proved me right. I tried it with Zoe and the result was better but a long way from perfect so more work required there, including fixing her broken arm before tomorrow’s engineering conference. Oops!