So I lied by omission in my previous post; I’d assumed Zoe would fly better in the cold (it’s only just above freezing outside), but I posted before I tested. So I took outside, left her sampling without the props running to find her ambient, and flew her a couple of times. Both flights were about 5m drift forwards, compared to the indoors 1m drift with the same flight plan.
So once more temperature change is critical. I’ve previously done two different attempts at temperature control:
- the BYOAQ-BAT series uses the IMU temperature sensor, and a resistor to try to keep the IMU at a fixed temperature (40°C). This was a completely OTT approach and I think I fried my IMU at one point.
- The Butterworth IIR digital low pass filter extract gravity from acceleration, letting through linear changes but excluding spike – this only works for the DRI code as the filter is timing critical, and required ‘ an indeterminate number of samples for the filter to settle – this is the 20s ‘warm up’ in the DRI code. It also wouldn’t handle the rapid cooling when the props start up in cold-ambient conditions.
But there are two much easier ways to do this (trust me to do it the hard way first).
- The base level for gravity is currently taken when the props aren’t spinning and so aren’t cooling the IMU. But there is a one and a half second period before each flight where the props spin up to hover speed – the ready to fly (RTF) period. Sampling gravity during this period with a complementary filter will provide a much better base-level value for gravity due to the props providing the cooling air-stream.
- Even simpler, popping Zoe into a little cardboard box would shelter her from the cooling breeze from the props.
Option 1 is easier as it’s a simple code change; finding or making the box is hard because there’s little vertical space between the HoG and the frame, but I’ll be keeping my eyes peeled.
P.S. I’ve just taken Zoe out into the pitch black and freezing cold and flew her for 2 short flights with Option 1. The horizontal drift has vanished, but vertical was still there: the first flight descended during hover, and the second ascended. There’s clearly some tuning to be done, but it’s looking promising, and safe enough for further testing indoors tomorrow.