Barometric altimeter for AR.Drone
Channel: szulat
Date: 2011-09-29

I'm presenting an unusual way to interface a barometric altimeter with the drone - by sending artificial ultrasound echo (received by the drone ultrasound altimeter). The prototype turned out to be not very useful but it is still interesting to see that the drone navigation algorithm managed to hold the altitude and position quite well.

Conclusions:

- Adding a single pressure sensor is enough for rough altitude stabilization and solving the infamous "flyaway" problem. Seems like a good guess of what Parrot could add in their next generation drone.

- The drone can be forced to use additional altitude sensors even without changing the firmware. This is nice, because it makes such modification compatible with all firmware versions, all control applications and all other mods.
Theoretically, such "artificial echo" add-on could be even acoustically coupled, like the ancient modems, without any electrical connection to the drone.

- If we wanted to stick with the presented interfacing method, we need more accurate altitude measurement. Averaging multiple sensors? Laser ranging? Using accelerometer for sensing short term altitude changes? Anyway, it becomes too complicated, compared with the "regular" method, that is inserting some additional logic between the control application and the firmware or even modify the firmware. This way the newly added information on the atmospheric pressure can be inteligently combined with other sensors, instead of pretending it is the ultrasound measurement.

Components for the barometric altimeter:
- Bosch BMP085 pressure sensor
- Atmel ATtiny85 microcontroller
- few resistors and capacitors
- total cost ~ $15

Software used for making this video:
- Synfig Studio (animated sequences)
- GIMP (image editing)
- Cinelerra (video editing)
- ffmpeg, mencoder (video conversions)
- Flight Record (recording drone video)
- Eagle (schematic capture)

Music:
  "Burned" by Astat (from Jamendo, CC-BY-AS)

Thanks for watching!  :-)

Update:
schematic diagram of the interface circuit - https://plus.google.com/photos/114553380922202925452/albums/5685674168207202129