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Senior Heliman
Location: calif*, U know where
| After breaking way too many Gumstixes and many weeks banging on the extremely temperamental XBee's, got all the guidance moved to the ground station & only a dumb transceiver on the airframe.
  
That's all the computation on the airframe. It generates PWM, controls the 3 angular rates, & sends the rest of the telemetry to the ground.
Ground based guidance system locked & loaded.
First auto hover guided completely by radio telemetry.
Ground based autopilot is insanely complicated compared to embedded autopilot, but has huge benefits in computing power, crash damage, & configurability.
The safety pilot communicates over 72Mhz to the ground station & the ground station communicates in full duplex 2.4Ghz with the copter. It's crazy but it's much more comfortable than being tethered to a ground station & the airframe has the absolute minimum amount of gear.
Unfortunately it's hard to remember to point the antenna at the aircraft instead of the ground station. Also don't touch the 72Mhz antennas because that resets the USB serial dongles. Finally, don't forget to take pictures.
XBee's don't like running in full duplex. You'll spend many weeks figuring out a parameter set which doesn't lock up the Xbee's yet gets all those IMU samples down. The radios were range tested up to 600ft without too much IMU drift but no-one in this dumpy apartment is feeling lucky. 300ft feels like the limit.
XBee's in full duplex can do 19000 bits/sec reliably at close range. At 600 ft it's more like 9000. If you wire the reset pin & implement a lockup recovery, they can do 32000 - 16000 bits/sec in full duplex.
Then you have to encapsulate all that telemetry in such a way that minimizes IMU drift inducing dropouts, synchronizes the ground station with the battery swaps, kills the engine during loss of signal, imports configuration & PWM from the ground station, & flashes a meaningful status LED. |
