"Shower Concerns" -- so called because they often come to you whilst in the shower. I had a few come to me today:

• Propeller nuts. I've got opposite-pitch propellers that are mounted 180 degrees off from each other, so the motors will be rotating in opposite directions. The nuts are both the standard right-hand type, and I've also taken the liberty of chopping off the part with the little hole (which I assume is for a safety cable). They're technically a kind of collet, so this may not be a concern; but I'm a bit nervous about one of the nuts spinning off during operation. If this happens, my current plan is to hit it with some Loctite Blue.
• Rho control. Newton's second law: every action has an equal and opposite reaction. In this case, assuming the rotating gimbal and the main frame weigh the same amount (and gyroscopic/aerodynamic effects are negligible, which they surely aren't), rho actuation would actually cause the frame to rotate in the opposite direction compared to the gimbal. That means if the angular change between the two subassemblies is x, the actual rotation compared to a reference plane in space would be x/2. Three ways I'm considering handling this issue:
  • Bottom-up redesign of GimbalBot, probably ending up with a more traditional gimbal design that uses two 'hinged' axes. That would also do away with the expense and complication of the slip ring and power inverter.
  • Develop a rho coefficient table that increases delta-rho values beyond their initially calculated values to 'overshoot'; this would continuously rotate the GimbalBot frame, but would point the thruster in the right direction.
  • Correct for the frame rotation by modulating the relative propeller speed. This would essentially add a layer to the motor speed control loop, taking another input from the IMU system.

I've realized that the main reason I'm hesitant to redesign the 'bot is because I've spent so much time on the current iteration. However, moving towards an X/Y gimbal from the current polar design would save me lots of money and headache: no more power inverter ($250 + 74 grams), no more slip ring ($200ish + 50ish grams), and better battery/motor options (no longer constrained to a 50-60vdc supply and a 1100-1300kv motor).

Thoughts? Should v07 be a clean sheet design, given that I haven't pulled the trigger on any of the aforementioned pricey components? Either way, I'm still going to do thrust tests using the setup I've (mostly) built.