Cutting it Close

Last week I took the new copter out to test the GPS functions. Everything was going well; the GPS locked and could hold a loiter fairly accurately, simple mode was working well meaning the compass was not being interfered with by the high current lines running right below it.  Then I switched it to RTL (Return To Launch) mode.  The copter started ascending as it should but just kept going.  I started getting concerned when it passed 60 meters and I decided to bail.  I later realized that I never changed the default RTL height of 100 meters! When I switched it back to manual mode I made the rooky mistake (it was my first time after all) of not setting mid throttle and the copter started to drop.  Being 60m high I had plenty of time to recover, I gave full throttle and it stabilized for a second but then all the motors cutout and it started to drop again! I backed off on the throttle and it love tapped the ground but seemed fine. I continued flying but about a minute later one of the motors popped off and the whole thing turned into a deranged nylon-clawed implement of tumbling destruction.2013-08-25 motor mounts  I had mounted the motors with the same zip ties I used on my other builds but the difference here is that this copter is twice as heavy and twice as powerful and the thin plastic couldn’t hold on.  I now have them hard mounted with aluminum plates.

2013-08-22 crash_smThat moment when weeks of hard work started to fall out of the sky I realized just how out of place this over weight piece of flotsam is in the sky and how badly it wants to be back on the ground that is the origin of the wood and metal it is made from.

The only damage was the landing gear and one arm were smashed and of course the props.

Technically speaking I’m pretty sure the battery couldn’t deliver enough current thereby sagging its voltage below the ESC cutoff threshold.  The battery I was using at the time was a 5000mAh 4S 30-40C so it should be able to push 150-200 Amps.  The current sensor said 147 Amps but everything happened so fast I may not have seen an additional spike or it may have happened too fast to register or the sensor I was using couldn’t handle it (it was the Chinese clone of the 3DR 90A current sensor). I have since upgraded the current sensor to a genuine 180A AttoPilot board.

Here’s the new and improved version with lighter, folding landing gear.

This new design weighs in at 2.1kg with the battery but without the camera.

Preflight checks at the field:
setup 2013-09-02

And it’s up!
flying2 2013-09-02

Hands free Return To Launch (RTL) set at 20m/2m this time.
hands off RTL 2013-09-02

On board camera.
aerial1 2013-09-02

I had quite an audience!

The carry case:
2013-09-02 carry box

The case is hideously ugly, inside and out, and smells like evil dinosaurs.  But it was free so I’ll just break out the Febreze and maybe line the thing with dryer sheets.  On the up side, everything fits, but just barely.  I timed myself setting it up and from closed box to flight ready including mounting the camera and preflight checks it clocks in at 12min.  Break down is about 6 min.

Still left to do:

  • Finalize the preflight checklist
  • Finish ground station / FPV box.
  • Tune camera gimbal
  • Tune ArduFlyer PIDs
  • Give the copter a name (it’s tentatively called Zippy after the Ziplock canopy)

I have one week, that’s cutting it close.

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