Flight Software With Stabilization Precedence
The problem of erratic, forceful PID Integral over-correction is common throughout nearly all helicopter flight computers. An example of the same problem is with Blade 230, in the video on the right, during the spool-up, the error rolling to the right is at 0:14 . This is because the PIDs are tuned for flying in the air when rotor RPM is sufficiently high, but the ground contacts force the craft attitude out of the planned flight envelope. To overcome this problem, we cancel the PID process and use passthru-manual mode during spool-up. The spool-up RPM should be controlled by the pilot by the throttle proportion on channel 5 to ensure safety, and the pilot's control should not be relinquished without the pilot's explicit input on the channel 6 switch, even when the throttle position reaches full spool-up. The reason for this specific channel switch assignment and the alternatives are discussed in the in-depth spool-up note. The spool-up throttle channel setup is pictured here on the right.
Toward complete solving the problems of the previous two paragraphs, we configure the flight computer to give the pass-thru mode a channel switch, and this channel switch for the pass-thru mode is tied with a constant negative collective pitch. The negative pitch prevents a takeoff while the pilot spools up the rotor with the CV1 curve. We highlight the disabling of the accelerometer and/or gyro sensors in blue. The flesh color underneath all flight modes is for the same set of PID coefficients throughout all modes.
When the first mode does not set the collective pitch to -23(that prevents liftoff) via an extra channel one mixer page in a faulty improvised setting, the pilot may forget to switch channel six to the middle position when attempting to reduce time to takeoff to save battery life in the midst of enabling video recordings and operating other equipment. The result is forceful crashes due to the high power applied for takeoff and the high-speed drift of the manual mode. The video of such a crash is on the right.
When the transmitter and flight computer setups are improvised out of sync, the takeoff can happen in gyro-rate mode. This happens even after a hand-tethered hovering test because the rate mode hovering can be successful without the pilot knowing that the modes are out of sync, for that gyro-rate mode does have stabilization characteristics. Then the actual takeoff will, again, crash badly due to the high craft momentum nature of the gyro-rate mode. The video of this gyro-rate mode takeoff is on the right. This field fault occurs when we are tempted into setting a single 2-position switch on Aux2-channel6 for a cruise-only mission. In the field, you may think that the PWM for profile switching needs more than 33%, say 40% or 50%, weight to expand over the 1/3 spool-up region at a low position. And that is true for a 2-position switch, but Betaflight would interpret the high position (2000-1500)*0.4+1500=1700, in the gyro-only setting because the weight scaling is centered at 1500, not 1000, as depicted in the diagram on the right.
Motors Use Multi-Rotor Software
To configure the ESC, we use the FD411 computer's passthrough USB-to-UART connection program with BLHeli Configurator. To access USB tty device, the program needs to be started as root user. For the passthru program to work, MOTOR 1 pin needs to be temporarily assigned to the SERVO pin of main motor(SERVO 5 in CLI) or tail motor(SERVO 4 in CLI). Safety precaution dictates that ESC battery power should be applied last after all connection/software are set up, and ESC battery power should be first one to be torn down after any configuration/software flashing. With that in mind, power on flight computer by connecting micro USB cable, start the BLHeli app and click "Connect" with default baut rate and auto-detected tty port. The computer now reboots into USB-to-UART adapter program. But, wait, there is sometimes a 1-minute delay for the reboot to occur if the BLHeli program determines that the Inernet connection is available but software web site unreachable, so the best is to ensure Internet access of the laptop PC. Now connect ESC's craft battery power, then click "Read Settings" to actually connect to the ESC computer. If the "Read Settings" button is not available, it is still in the 1-minute period. After flashing ESC with motor software, tear away ESC's craft battery power plug first, as the safety precaution. Then tear down software/other connections. If you don't tear away the power, when the program switches back to BetaFlight software, the motors will spin up to compensate craft orientation or spin up to match unintended RF transmitter command signal, posing great danger.
Yet another question is whether to use fixed-RPM governor. The configuration for the main rotor motor using MULTI code takes advantage of the RPM governor instead of alternative channel 5 mixers that need to compensate voltage drops, scale with collective pitch, and match up cyclic maneuver demand for torque. The governor needs small P-Gain 0.50 to prevent oscillation (yes, motor RPM can oscillate producing audible noise), I-Gain needs to be high at 3.00 to track RPM precisely, Startup Power needs to be the lowest so that spool-up does not capsize the craft with unbalanced(blades not stretched fully) high torque. Overall as screenshot.
In production, with RPM PID computer, without ESC capacity scaling, the craft with the 12-node 2808 motor needs 2640RPM / ( 50000RPM / 7 ) x 200poionts = 74 points level in the 0-200 scale of the transmitter for the same RPM as the pre-protytpe. Here the 200 point scale is assumed to perfectly corresponds to 1000us to 2000us RF transmitter output, and if RF transmitter uses 989us to 2011us range, such as Frsky's X9 Lite or QX7, RF transmitter needs scaling the channel by (2000-1000)/(2011-989)=97.8%. The 50,000 max RPM is seen in the above github page of ESC source code. 1/7 fraction is attributed to the 14-pole brushless motor compared to elementary 2-magnet motor. In the production model, the battery pack is further reinforced to 4S, giving 25% extra power budget for future improvements on fuel-economy/G-force-performance optimization. This battery change does not need RF throttle signal change with governor'ed RPM control. However, in either battery setups, without tuning and verification, incorrect RPM can cause craft instability and/or vibration because the flight computer PID gain is tied to rotor angular momentum and proportional to rotor RPM. For the 24-pole 4004 motor, to use the same throttle curves from transmitter, the PWM needs to be scaled from the original span to 1000us x 7 / 12 = 583us. The scaling is performed in GUI.


Collective Curve For Maximum Efficiency

Level swash plate to prevent tip-over during spool-up and the technique
Input s-bus PWM signal does not need calibration because it is calibrated in transmitter with stick calibration to ensure high precision.
Indoor Hovering With RF Receiver With Proximity Cutoff
Takeoff Procedure With Safety Checks
Failsafe Setup
We have to keep the betaflight internal arming signal high during failsafe because it is the reason the flight was recovered at 0:18 . Further more, to prevent accidental disarming mid-flight, , arming signal from the radio transmitter needs to be also stay high during most of the flight with any mode-PID-profile switch position when throttle position is not zero.
https://www.youtube.com/watch?v=yOUkg2uYwlA
Accidental Manual Mode
Accidental Disarming
Landing Procedure
Aborting landing in rate/acro+ mode also often results in crash due to altitude drop with the big maneuvering nature of rate mode. Rate mode spot landing is often nearly impossible even fly line of sight. Here in the following video, the landing approach, trying to avoid the fence, is deemed to high at 0:05 in the video here below,
and the go-around at 0:06 results in steep increase in craft speed and altitude drop, resulting in crash. Seemingly smooth touchdown in rate mode can still capsize due to the general high speed approaching to the target in the last video on the right.
Forgetting about switching to attitude mode can occur during high work load situations such as combating high wind while locating a obstacle'd landing patch impromptu.
Flipping SwitchC to attitude mode for final approach should be trained into the pilot's reflex because attitude mode landing is appropriate in nearly all circumstances even the most unlikely ones, such as the following example.
To summarize, with all alternatives considered, the montage of 42 screens of created/edited/confirmed pages after installing OpenTX 2.3.10 is here below. The whole-transmitter-receiver configurations are in the first 2 columns and need to be reconfigured ever time a new transmitter or receiver is added. The whole-transmitter configuration pages for file browsers, global functions, and PWM alteration are skipped. The actual per-model configuration pages pertain to non-computerized helicopter setups are skipped. Navigate-thru pages without needing to click Enter are skipped. Pages with all automatic generated known defaults(such as rudder) or no content modifications are skipped. Repeated pages with identical contents are skipped. Notice that the SF switch is the Frsky QX7's equivalent of X9Lite's SD switch, and that QX7's SA and SC are the same as X9Lite's SA and SC, respectively.
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Video Monitoring
Linux raspberrypi 5.4.51+ #1333 Mon Aug 10 16:38:02 BST 2020 armv6l GNU/Linux
pi@raspberrypi:~$ cat .bash_profile
sh /home/pi/stream.sh
pi@raspberrypi:~$ cat /home/pi/stream.sh
raspivid -t 0 -rot 180 -b 1700000 -w 640 -h 360 -o - | gst-launch-1.0 -v fdsrc ! 'video/x-h264,width=640,height=360' ! h264parse ! queue ! rtph264pay config-interval=1 pt=96 ! gdppay ! udpsink host = 192.168.1.1 port=9000
pi@raspberrypi:~$
Rotor Balancing For RPM 2650


The permanent solution is to use a 1 inch clear tape about 5cm square area, which weighs about 0.03 grams, to test weighing the blades near the tips and find the most balanced configuration.
The Tarot replacement blades for Trex250 have wildly uneven bending and are hard to find balanced pairs even with multiple purchases.
Change Rotor RPM And PIDs With Weather


Weather temperature and pressure deviates air density from normal condition by 7%+2%=9%. Our normal condition is gas chemistry standard condition at 25C temperature. So, at cold temperature, such as -9C , the RPM needs to be reduced with factor 1 - (1 - 264 / 298.0) / 2=0.943 , 2492 and 3058. So, RF transmitter point should be roughly 0.943x74=70 and 0.943x88=83 points.
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