Monday, August 6, 2012

Failure is always an option.

Well there it was this morning, looking pretty good. There was one more plate to be bolted on over the KK2 for the battery to be velcroed to. Everything seemed pretty solid and all the electronics powered up and tested fine. The KK2 was an pleasure to setup and do the initial ESC and sensor calibrations. So I strapped on a battery and went outside to do some flight testing on it; now my RC flying skills or lack thereof are a bit rusty. And well some of my design choices could have been better so what the quad looked like after the flight...

Yeah... and specifically:

 Bad material choice bites me in the ass

The carbon fiber tubes split nicely along the seams after a few hard landings and eventually came apart. Well lesson learned cheap carbon fiber from China has some issues. Tube was a 10mm square with an 8mm circle running through it so the walls were only 1mm thick on each side; and all the fibers running in one direction... With the rails completely useless I disassembled the quad and cleaned off the dirt from it and planned out revision 2. Now the few tries I was able to get the thing in the air successfully and it seemed to work pretty well; I had issues with it drifting around but I think that was my lack of control over the craft and the gusty wind.

So after tearing it apart revision two started:

Solidworks <3

So the carbon fiber has been replaced with .5 alum box stock 1/32 wall thickness, roughly the same weight but stiffer and 6061 doesn't suffer cracking issues. I do however need to check if I have any .5 box, if not other solutions will be sought but probably not going to touch carbon fiber. Thinking about it, using clamps with round stock carbon fiber instead of drilling though it would have probably worked out well. But I digress, the booms are also now .5 inch shorter and the landing legs moved closer to the center. In the last iteration they were all the way to the edge which acted as a lever amplifying forces from hard landings. Also the landing legs will be made longer so the blades are father from the ground, broke 2 already on the last bad landing...

So as soon as I can go back to the shop more laser-ing and CNC-ing the above should happen. "These kinds of parts are really simple and quick to fabricate especially with CNC gear. So hopfully the rebuild should be done in a week or two at the most.

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