I'm doing this commercial project where reliability is a MUST. I'll be investing a lot of money on top-notch parts, but I had enough mishaps (and read about many more here) to know that even great motors get out of sync, and great ESCs fail, brownouts can happen, issues with the power module, GPS glitches, RX/TX glitches, etc, etc...
Given my background in IT infrastructure, I believe the only way to have any hope of real reliability is through redundancy (at least as far as the machine is concerned). So I set out to design a multirotor that can stay in the air if any of the parts fail (except of course for the Pixhawk or an Arducopter bug)
I thought I'd run this design by you guys and see if you can find any flaws with it or something I could improve.
- I'm thiking of going with a custom-built X8 frame with coaxial motors. That by itself should add considerably to the reliability, given that most hardware faults are ESC/motor related. To make up for some of the loss of efficiency on coaxial props, I'll use slightly larger diameter and pitch props on the bottom.
- As the diagram above the 4 top and 4 bottom ESCs will be connected to redundant power distribution boards, even if one of them fail (unlikely, I know) the X8 will become a quad and it can land safely.
- I'm also using redundant power supply to the Pixhawk via both a power module (connected to Lipo A) and a BEC from one of the ESCs (connected to Lipo B). This should prevent brownouts from causing crashes.
- I'll be using redundant GPS modules (one of them with a compass). This should give me redundancy in both the GPS and compass, since the internal compass was activated in 3.2.
- I'm also thinking of extending the redundancy to TX/RX by using both a regular FRSky TX/RX while having droid planner remote control connected and displayed on a Nexus 7 mounted to my TX. This way I can turn off the TX in case of glitch and use the droid planner virtual TX feature. This should also help me in case of bad interference on 2.4 Ghz, because the telemetry will run on a completely different frequency.
- Power everything through two high capacity lipos. One connected to the power module, and the other to the secondary PDB. Both with their balance leads plugged into a voltage alarm set to 3.6v.
I know this is a bit of an overkill for most applications, but this project will depend on the reliability of the craft.
So what do you guys think? What would you change about it? Looking forward to listen to your feedback :)