[Canberrauav] flying this weekend

Andrew Tridgell tridge at samba.org
Sun Nov 4 15:26:24 EST 2012

Hi All,

We flew the X8 again today at CMAC, launching first with Stans bungee,
then with the one Chris brought.

We first flew with one battery, same as at Lake George. The aim was to
get an idea of endurance, given we ultimately want to fly for over an

The bungee takeoff went well after we stretched it out enough, and Steve
helped with the APM tuning from the ground station while we dialed in
the navigation parameters. The X8 flew for 25 minutes doing a simple
circuit auto mission before the battery reported 20% remaining and we
brought it down for an easy landing.

The next test flight was with 2 batteries, giving us 10Ah of 4S
LiPo. That requiired a bit more bungee stretch (with the bungee from
Chris this time), and the takeoff went fine.

After a minute or so of flying OK it started to lose altitude quickly in
AUTO mode. I put it into FBWA and found that it was still losing
altitude! It kept going down and crashed quite hard a couple of hundred
meters from the runway. Damage includes some dented leading edges, and a
broken wing spar.

The wing spar looked to be the main issue, and we had a long discussion
on how to fix it. Once I got home I found that inserting 3 pieces of
narrower carbon fiber tube hard up against each other inside the spare
repaired it nicely, so the X8 is ready for another go.

I'm still analysing the logs, but thus far it looks as though we had
very marginal GPS lock (losing lock completely several times), and that
had a huge impact on the GPS velocity measurements used to correct the
accelerometers. The result was a huge pitch error, which caused the
plane to dive hard. If I had switched to manual it would have been OK.
I'm planning on adding some some code to the AHRS to use both estimator
methods for acceleration correction in parallel, as a way of detecting
poor GPS velocity numbers.

Cheers, Tridge

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