The battle for rigidity with laser cut quad frames by enivid
I've been trying to design a 100% laser cut frame. The goals were ease of build, low cost along with an optimal use of ponoko materials (which is my laser cut supplier). As my designs progressed, I have never been satisfied with the rigidity of the booms/arms of the quads I built. When I held a blackout (carbon fiber) in my hands at the local meetup I knew right away that I needed to find a way to improve rigidity.
My first design had very narrow bamboo arms which were not rigid enough, to correct for the lack of rigidity I played with PIDs on low end KK (low frequency) flight controller board and it flew.
I then reworked it a little, simplified it but also tried to make the arms more rigid by widening the booms.
Again with the basic low frequency flight controllers I lowered the PIDs and it flew quite well. But lack of rigidity also meant that these things were very fragile and not at all crashproof.
Bamboo and Delrin
I decided to move away from bamboo booms and try out delrin. This time with a more modern multiwii FC.
I sandwiched the delrin booms (3mm) in between some bamboo center plates. This flew, but the flex was still there (became worse in hot conditions). The new FC didn't help, it has high frequency corrections that triggered crazy oscillations (felt like I was flying a little bee) on throttle up. The only way I could eliminiate some of the oscillation was by enabling the low pass filter features in the multiwii software.
I went back to the drawing board. Do I laminate or do I spar? I knew a spar would work but it would make my build more complex so I've tried lamination and here it is.
I decided to sandwich delrin in between a bamboo core. Since gluing delrin is near-impossible, they're bolted together.
The rigidity has improved a lot from some manual tests. I plan to maiden it soon without the low pass filters to see how I did.