In the deep mid winter…

Zoe can’t be flown…

I took her out this morning, controlled by the accelerometer and gyro, but with the LiDAR and Camera running in parallel passively so I could do a comparison.  But she could hardly drag herself off the ground.  However, in her world, she thought she way climbing throughout:



The props span up to hover speed for the first 0.1s, then she ‘climbed’ for 3 seconds and then “hovered” after 3 seconds.  By 5 seconds she was on the ground with the props spinning at the minimum setting.

Throughout (orange line) she thought she was climbing, which is why she struggled to take off.

If you look at the IMU temperature plot, as she starts to climb, it seems the propeller wind cools off the IMU, and that’s shifting the scale of the accelerometer significantly.  The problem is caused because a snapshot of gravity is taken before takeoff, and then is used throughout the flight to extract net acceleration.  That works fine when the temperature is in the teens, but it’s about 5°C today outdoors.

I’ve seen this in the past, and tried lots to do it either by calibrating the accelerometer against temperature – all I got from that was a beer fridge in the office – and using a butterworth low-pass filter to extract gravity dynamically during the flight – I can’t remember how well this worked but I assume “not well enough” since I dropped it from the code a while back.

What she really needs is a wind-proof jacket or scarf to shield her from the draft from the props.  I might try a duct tape wrap.  Alternatively, I could just bring her indoors into the temperature range where the accelerometer doesn’t drift; I’m just a little nervous as I’ve just popped into the lounge, and the scars on the ceiling are quite revealing of past exploits! Finally, I could take Hermione and her salad bowl lid to see if that helps.

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