My quad is once again functioning after my last crash! f450 frame replacement arrived in about a week, but the replacement motor took over 3 weeks. Hard to wait for. So as soon as I got it in the mail, I flew the next morning at a beach in laporte - got some nice footage! html5 video link 1, and html5 video link 2.
Despite the platform being flyable, I am still concerned due to RX/TX reliability, low voltage performance, and vibration.
RX/TX reliability:
In order to test range of my FS-TH9X, I went out to the field across my house, powered up my copter, and left it disarmed. I then left my transmitter on the ground and walked out into the field holding my quad. Viewing telemetry data with my phone using andropilot, I found that my throttle dropped to failsafe value consistently at 400ft.
When I got home, I opened up both the TX and RX to check for antenna continuity, which looked OK. Therefore, I'll be picking up a 9X compatible FrSky TX and RX module to increase my range.
Low voltage performance:
Due to the divebomb performance (in RTL mode due to loss of transmitter) during my last crash, I thought that it might be due to low battery. In order to test, I flew until a low alarm buzzer at 3.6v/cell. Then I changed the buzzer to 3.5v/cell, and hovered for 60 seconds after the buzzer engaged. While it required an increase in throttle to maintain hover, it did not cause any unpredictable behavior, so I am not too worried at the moment. In the future, I plan on picking up an attopilot so that I can view live battery voltage and current.
Vibration:
The swerving behavior in an automatic mode (RTL), also could have been caused by vibration in the internal measurement unit, as arducopter software actually uses acceleration to calculate altitude, and then uses barometer and GPS data to compensate for any errors. So today I turned on IMU logging, and flew a quick hover session indoors. The arducopter wiki article on measuring vibration states that an acceptable vibration level for Z is between -15 and -5 m/s/s. The following graph shows raw data (X and Y at the top, Z at the bottom), and I do fall in that criteria.
However, the vibration damping page states that "You should strive to get in the region of + and – 1/10 G in all axes". In order to check, divide the raw IMU accelerometer data by 9.8 m/s^2 (1 G) and add 1 to calculate variation from standard gravity. My results are shown below - I've reached the 'required' vibration levels of +/- 0.5 G, but about 20% of the time I have vibration greater than 0.1G.
Obviously, I can do a lot better than a bootleg F450 frame and one piece of stick 3M foam as a mounting platform. Until I do a complete platform revamp, I will be staying away from any automatic modes.
I've copied over this content which I posted on my site, http://wrlab.com
