TV1: Thrust-Vectored Coaxial Copter, vehicle 1
Lifespan: May-June 2021, disassembled on June 06th.
Since single-stage-to-orbit rockets are nonsense on Earth - and a Starship is to be assisted by a Super-Heavy Booster - it is also tempting to design a “booster” coax copter that would deliver a smaller coax copter to interesting altitudes. And while the smaller coax is to be flown FPV, the booster looks best to fly missions:
- First, arm the second stage.
- Command the first stage to reach the specified altitude, supposedly at maximum throttle and depleting maybe 70-90% of the battery.
- Stage separation: take-off the second stage from the first stage.
- The first stage understands that its job is now done, so it starts a controllable free-fall to the ground, with minimum throttle to control the attitude.
- At a specified altitude it reorients itself and performs a usual ArduCopter’s soft landing, draining the rest of the battery.
While it is still a batch of bold ambitions, one thing is for sure. A coaxial copter for the first stage needs to cope with a relatively heavy load, so instead of flaps for pitch and roll, it possibly needs thrust vectoring. ArduCopter has seen a concept build of separate engine tilting, a similar thing has been recently investigated in INAV and by Nicholas Rehm in his Starship model. All these implementations have various problems related to highly asymmetric mixing, so I decided to go a way that (still) seems more appealing to me: engine section two-axis gimbaling.
This concept needs testing, as this is a kind of vehicle ArduCopter has not probably seen. This was what TV1 was born for.
This vehicle underwent a series of tests, none of which resulted in actually flying. Most of these tests have been continued until something broke. The broken parts were printed once again (with a stronger design) or, in the case of propellers, replaced with new ones, until the next test.
This is the last testing day of this vehicle, more are on the same channel.
The vehicle was, of course, too brittle to carry a real payload, and too fragile overall. The right PID values seem to be really difficult to come up with, and the existing control algorithms do not seem to cope well with the nonzero mass of gimballed engines, not even counting in the gyroscopic forces. But the idea continued to take its place in my brain, so the successor of TV1 was imminent to come…