[Autopilot-announce] Hovering the helicopter under computer control works!

[Trammell H. <hu...@ro...>]

After a year and a half of effort, the autopilot system finally works!
Yesterday, Dennis, Will and I hovered Dennis' Nova for entire tanks
of fuel, with only the collective/throttle under manual control.
All control loops except altitude were closed and tuned.  We should
write a detailed guide to tuning the PID loops, which took the better
part of two full days.

Onboard the Nova was our IMU / Magnetometer / Servo controller,
a Cerfboard with 802.11 CF, and our new u-blox TIM-LP / IO board.
I'll be checking in the code that was used later today with the
exact gain constants.  These should be good starting points for
other folks for tuning to their helicopters.

Will filmed the entire flight testing and we'll have MPEGs of
the interesting bits soon.   I even "flew" the helicopter and we
have it on film!

The helicopter stayed in about a 1 m CEP during calm winds and about
a 2 m CEP when the wind gusts would hit it.  It flew in slow circles
while under computer control, which post flight analysis showed that
our hard iron calibration for the magnetometer on the bench did not
include the engine.

This resulted in about 20 degree offset between our heading and the GPS
north value, so when we would go "north" based on our magnetometer, we
would actually be flying north west.  It is a testament to the stability
of the inner attitude loops that this only caused minor position problems
instead of a catastrophic crashes.

As always, this could not have been done without the combined effort of
everyone involved.  Especially big thanks go to Aaron Kahn for all
of his code and assistance flying; to Dennis D'Annunzio for risking
his helicopter and being an incredible test pilot; and to Will Barger
for long hours of helping us build assemblies and spending countless
hours at the field with his camera.

We'll hopefully have MPEGs and charts from the flights available
very soon.  I'll send another announcement with URLs when they
are online.

Trammell
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