Wednesday, January 23, 2008

Crash Gordon and the Helicopter(s).

My Son came down from the bay area to visit this weekend so I did not get much unreasonable work done.

Crash #1 On Sunday we were going to a play in balboa park and I had 30 minutes to kill. so I was flying the little fully manual trex 450 in the driveway. While I was doing this my wife came out and started moving the garbage cans toward the curb. I was in the way so I landed the trex next to the truck, shut down and preceded to take off the neck strap on the transmitter so I could help with the trash, in the process of doing this I hooked the throttle hold switch with the neck strap and the helicopter spattered itself all over the side of the truck. Its a good thing the trash cans were not yet at the curb, I had additional material!

Background for Crash #2.
On the last reported test flight altitude hold worked very well, but I had not yet tested clmb and descent. So I made two minor software changes, I added limits to the vertical velocity. (Vertical velocity had just been the differential term in the alt hold PID, but I spluit that in half so I could explictly limit vertical velocity. )I reprogrammed the mode switch to facilitate testing this. The Mode switch has three settings mode 0, 1,2 Mode 0 has always been manual.
Mode 1 was rudder heading hold, mode 2 was Altitude and Rudder hold. I changed this so both Mode 0 and Mode 1 were manual and Mode 2 was automatic Rudder and altitude.
I also recorded the target Altitude , Heading and initial collective value when going from mode 0 to mode 1. The idea being that I could set my target altitude by toggling from 0 to 1 then manually deviate from this position and go to it when switching to mode 2.

I went and test flew this combination on Tuesday Morning. In the process of adding the velocity limits I'd changed a feed back sign and altitude hold went the wrong way... I started above my target and when engaged the helicopter accelerated up at ever increasing rates. I tried this twice and figured out what was wrong and called it a day after 45 seconds of flying.

I changed the software sign last night and went out this morning to test the change.

Crash #2
I did my usual preflight routine I made sure that all the controls on the helicopter moved in the correct direction. (In past S/W version this was also a test to insure I was in mode 0, because in mode 1 rudder would not respond) So I brought the helicopter to a stable hover about 30 feet in front of me at about 15 to 20 feet of altitude. I then proceeded to flip the mode fro0m mode 0 to mode 1, alas it was already in mode 1 and I went to mode 2. Realize that while manually flying a helicopter you can't look down at the transmitter to check switch positions. It must have gotten bumped into mode 1 while I was hooking up the main propulsion battery or starting the video camera. So when it went from Mode 0 to Mode 1 it was at altitude 0 and full down collective. So when I went to mode 2 its target altitude was 0 and its initial guess for the collective position was full down. This is a fully acrobatic helicopter so full down collective is at least 3 negative gees. Before I could react the helicopter was on the ground, hard.

Broken parts: Both skids,flybar, flybar paddles, both blades, GPS antenna mount, one blade grip ball end, battery tray and the Jesus bolt. (the bolt that holds the main rotor to the airframe is called the Jesus bolt) total damage about $120.00 with the majority of that being the blades.
I had spares of most of the parts. Tonights task was to reassemble the helicopter. Its done, but not tested yet, I'm letting the glue on the GPS antenna mount dry while I type this.
(After glue dried tested all electronics and systems all check out ok, ready for blade tracking in the AM weather permitting.)

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