Progress report

Although the blog’s been quiet, I am still tinkering with both Zoe and Phoebe.

Zoe’s drift is better with 3 changes:

  • I’ve changed my 0g offset calibration so that it’s now done standing on her feet, and an average of 4 readings are taken with her rotated 90° each time and an average used
  • I’ve changed the double sided foam sticking her HoG to the frame – it’s all a bit of a balancing act between having her held down firmly, and yet also providing buffering against vertical prop vibrations
  • I’ve change the code which controls how many samples are per motion processing – there was a minor bug in the timing I knew of, but until now had not thought it worth the effort fixing it.

Here’s the result.

I don’t think it’s going to be possible to get things much better – my guess is the 0g offsets are the dominant contributor to the reduced drift, and they vary. Here’s the output from three runs – the first with her resting on her props, and the other two on her feet; the entries with the Z axis set to 0 are the averages of the preceding 4 calibration test entries. 8000 is roughly 1g to give you an idea of the size of these offsets.

0g calibration results

0g calibration results

The progress with Phoebe is less positive; with the SRF02 rangefinder installed, the code blocks during initializion; i2cdetect can see the sensor so I presume it’s because the sensor is only rated to 100kbps I2C baudrate.  There is a similar URF from a different manufacturer which does support 400kbps, but only if the I2C master (the Raspberry Pi) supports clock stretching; sadly the RPi I2C driver does not, although that may be fixed soon apparently.  However, until that happens, height control using the URF is blocked.

Without the sensor, she’s flying, but occasionally seems to decide to drift; it’s not a steady drift, it suddenly kicks in as though she gets a dodgy reading from the sensors.  I then have to kill the flight before she gains too much height.  It’s not clear to me yet what, if anything I can do about this.

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