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I am trying to create the following set up as a project in education:

  • QAV250 quad with CC3D controller
  • 2xBBC Micro:bits used as the receiver, giving out 50 Hz PWM signals to the CC3D controller - one does throttle and yaw, one does pitch and roll.
  • 2xBBC Micro:bits sending out controlling signals

I can get past the receiver setup wizard and even arm the quad, however I'm getting erratic behaviour, particularly for the throttle. Despite commanding it low, the throttle sometimes remains high.

I don't know if this is linked but on the receiver calibration page of LibrePilot, the input values only update every second (PC plugged into the CC3D). Should these update more frequently? Also, the image of where the sticks are during calibration rarely moves.

Possible reasons I have thought of are:

  • BBC Micro:bit runs at 3 V. Is this insufficient for the PWM signal (although I just tried with a Raspberry Pi and Adafruit PWM adaptor and the same laggy behaviour shows on LibrePilot)
  • Is there a syncing issue in the PWM? (i.e. two Micro:bits outputting PWM signals which aren't synchronised). Unfortunately the Micro bit doesn't reliably cope with four simultaneous PWMs, hence the need to use two.

My goal is to show the power of the Micro:bit, despite the fact it's aimed at children, but is this just too much for it?!

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Ok I think I'm getting somewhere. Two issues found:

  • When the Micro:bit runs off two AA batteries the 3v output can drop significantly as the batteries run down. The CC3D wasn't liking the even lower voltage. I've now cut a USB cable up and wired it to the ESCs' BEC output at 5v. Much better signal now.

  • When the throttle is raised above the neutral detent, I was expecting a gentle increase in motor power. Instead you get a power a little below take off power. This scared me before even fitting the props! Now I've got some more confidence in the system, I've managed to sustain a good hover.

Still need to improve stability but that is normal use of LibrePilot.

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