Third ‘Flight’

I glued everything together, it seems to work so far. I also moved back the CG and tuned the PWM frequency and max value. I didn’t measure it, but I think I’m around 3-4 A at 5 V, which really is the limit for, well, pretty much everything. This would give me a thrust-to-weight ratio of around 60 W/kg, which should just barely be enough for a slow flyer. I also estimated the speed it needs to generate lift (by running around with the plane in my hand), and I think that at 10+ km/h I should be well flying.

Sadly, it did not really fly. But! It almost did, and it stayed in the air for around 5 seconds! It also crashed landed a lot smoother. The video recording unfortunately decided not to record anything this time, maybe because my laptop had some issues. But the telemetry logging did record, so I analyzed it using the Ardupilot website – interestingly, the PX4 website doesn’t take TLOG files:

Maybe I’m interpreting too much into it, but it clearly shows that I was not just doing an assisted crash this time. I also remember trying to pull up the nose mid-flight.

I have a growing suspicion that the motor/prop I’m using is to blame for the bad performance. It does move a lot of air, and it has a static thrust of maybe around 30-50 g, but it came from a quad copter that mainly just hovered around. I don’t have any evidence, but I think the air velocity (effectiveness when in moving air? I have no idea, I’m an IT/EE guy ¯\_(ツ)_/¯) is quite low. Or, to put it the other way around, the people who put it together never thought it would move at more than a few m/s. If this turns out to be true, I might have a problem.

Anyway, the way forward is pretty obvious: More Power!

Maybe I can chain a MOSFET after the motor driver, as some kind of ghetto Darlington circuit. Let’s see what I find in my “misc electronics” box.

Update on the MOSFET idea: Yes, it kind of works. But the motor does not like 20 W. Also, whenever I plug in the motor now, my rudder and elevator servo decide to move on their own. Looks like I built an antenna. I could probably work around that, but I’m starting to lose patience with this whole powertrain. Also, the MOSFET would probably use a heat sink, and those tend to be heavy. I decided to get a whole new powertrain, see here for details.