Disclaimer: Please check with local authorities before a mission. This blog is not responsible for injuries and damages caused by building and using this platform.
This blog is intended to investigate and understand the performance of extreme robotics for better safety planning for cases in the following news.
The general platform built is in the previous blog, build-notes; the general operation note is in operation-notes. Our single-rotor platform with collective pitch has one extra degree of control for precision target diving, compared to fixed-pitch crafts with unplanned displacements, as discussed in the video on the right. We build this new extreme robot based on the endurance build but divert 21 grams of the mass from the battery pack toward crash resilience and computing, GPS (5.3g) tracking, thicker flexible wires (3.1g extra) for crash resilience, titanium main shaft (extra 2.7g), higher crash-resistance rotor grips (extra 2.5g), silent (thiner) rotor blades (2.2 g extra), thicker motor construct (1.8g extra), extra power VTX and antenna (1 + 0.6 g extra), soft mounting battery (1g extra) and thicker landing skid (0.8g). 5.3+3.1+2.7+2.5+2.2+1.8+1.6+1.0+0.8=21g. The battery pack is 21 grams lighter 87.2g+2.1g+0.8g-69.1g=21g. The build is pictured below; the bill of material follows.
The progression of the R/D process started with the prototype endurance build, testing unsuccessfully with asymmetrical airfoils, raising the original prototype's RPM for fast travel, and finally determining the production build with a smaller rotor with symmetrical airfoil. Summary table here on the right.
For the prototype build, the solution was RPM at 3100, setting the hovering pitch to slightly lower than 5 degrees but higher than 4 degrees, trading off 8% fuel efficiency as seen in operating note of cL/cD 23 versus 25. This angle between the orange and green lift curves so that the lift slope doesn't turn steep, which would have translated to more difficult altitude management. RPM of the new hovering pitch is 19% higher, 3100, versus 2600 of attitude mode. The RPM change from accelerometer mode to gyro mode has a ratio of 3100/2600=1.19. According to the NASA education page in the operating notes https://nocomputerbutphone.blogspot.com/2018/09/converted-iot-drone-operation-notes.html, the gyro mode should require the inverse of the square of the 1.19 ratio on the collective pitch, 1.19**2=1.42, because the lift is proportional to the airfoil pitch; in contrast, the lift is proportional to the second power of RPM-airspeed. The new pitch angle should be 6.2/1.42=4.37 degrees. However, the Reynolds number changes with RPM, shifting from the aqua-colored curve toward orange and green-colored curves, suppressing lift at a sub-6-degree angle but augmenting lift past 8 degrees. So, I experimented hovering to see that the mid-throttle collective pitch point needed to be 22 points, 22 / 29.9 x 6.2 degrees = 4.56 degrees of the collective pitch in the channel 1 curve. Notice that the mid-throttle is scaled by 0.98 in the transmitter and shown as 22x0.98 = 21.56 in the LCD display. However, the angle is 4.56 because the display of 21.56 points refers to the 989-2011us PWM range. The 0.98 scaling sets the PWM signal range 1000-2000 microseconds for 200 points for "83 degrees" as measured as the full servo horn travel angle. 21.56/200x(2011-989)+1500=1610us is the actual PWM signal. (1610-1500)x50%+1500=1555us is the mixer output toward the servo. (1555-1000)/1000x83=46.0 is the angle from the position where PWM is 1000us in the servo. 46.0-(83/2.0)=4.56 is the angle from neutral.
The prototype was subjected to terminal speed fast travel (diving) as the video on the right shows. The free fall from the antenna tip to the church spire, 0:08 to 0:19, is about 200 m. The dive started next to the building, but the craft relented its position and drifted behind the building at the bottom of the dive. The craft's body provides drag and gives the craft the equivalent of a minute elevator down torque. Trying to improve the dive precision by keeping the lowest collective pitch at 1-2 degrees to provide compensation by using single-rotor helicopter dynamics and converting collective pitch force to craft elevator tilting at high forward speed, resulted in difficult-to-pilot, swinging motion, as tested in the video on the lower right, with the compensation with 6 points of collective pitch in the -100 to 100 RF transmitter point range.
During the pre-prototype build with the substitute camera Insta360 Go, it was discovered that moving CG forward stabilized the diving, as seen here. When using the substitute Runcam Hybrid2, which weighed the same as Insta360 but distributed weight rearward 6cm on the recording board that weighs 5.4g and without the 3.5g custom bracket and without the 2-gram Caddx Ant camera, and with the 49-gram, 450mah, battery front close to the battery cavity front edge, the dive swung as shown in videos here.
The weights of the substitute components are in the pictures below. The loss of head-down torque with the Runcam Hybrid2 setup was 5.4gx6cm+(2g+3.5g)x9cm = 81.9g-cm, equivalent to having an 81.9gram-cm/30cm=2.7gram heavier tail motor.
In the solution picture, the loose mounting incorporates a Velcro loop tape cloth on the roof of the battery bay. The roof cushion is for craft attitudes when the battery touches the roof, such as inverted or diving vertically down. Without this cushion, the battery knocking on the roof produces yet another vibration, as shown in the video on the right.
PID tuning and tightening the battery logically can also divert the craft's whole mechanical system resonance frequency. However, testing with downshifting PID to the equivalent of 60 degrees F colder temperature's PID did not shift the frequency enough, as shown in the following 2 videos. The video on the left is raw FPV footage; the video on the right is Gyroflow stabilized but still shows fluid vortex vibration during vertical dive.
For gyro-only-stabilization, straight-line traveling (the b and c terms in pid2 of Matlab are canceled by zero steering), we convert and cross-reference CC3D PIDs with Betaflight PIDs by applying the vintage scaling as follows.
The action cameras logically use undisclosed motion blurring algorithms that may work better for specific vibration frequency profiles but worse for other frequency profiles. The action camera Runcam Thumb Pro in the prototype build was discovered to need careful PI values scaling together in conjunction with compensation for air density conditions (temperature), as tested and recorded in the following graph. The production build's FPV camera with soft-mounting battery tolerates deviations from the tabulation calculations. The dump_all_converged config file has 40 degrees F as profile 2 and is the default. The dump_all_converged config file has 1 profile for every 30 degrees F change between 0 degrees F and 100 degrees F.
According to NASA's education page, an airfoil's lift is proportional to air density, which is linearly proportional to absolute temperature; an airfoil's lift is proportional to attack angle, which is first-order propotional to P gain. To fit the PID-temperature data, the temperature is given a 1.3th-order power to account for attack angle's non-purely-linear power on lift and exaggerate the PID range in the tabulation, with -5°C (268K) as the calculating temperature as in the comparison video at the beginning of this discussion section,
The swapping needs to restore the rotational symmetrically of curved blades because our rotor hub does not have a cord-wise balancing bolting like the Bell 222 rotor, as highlighted in the picture on the right. The 2 blades with up-down warpings can be none-mirroring as the right side in the above diagram when subjected to 3150 RPM's centrifugal force. The solution is to pick and match a pair that dynamically match the warping to each other.
The first loop has the crossing beneath the DFC bolting and excess wire trimmed. Then, pinch and turn the wire for a few turns. In the example on the right, the 7 loops on one side are the correct balancing because 14 loops were tried on one side, and zero loops on either side were also tested to be lesser balance. This example ballast weighed 0.2 grams with 7 loops. However, this level of ultra balance is not required for smooth HD video shooting.
And discuss how inexpensive and capable modern components are with a sub-30 dollar motor.
The general platform built is in the previous blog, build-notes; the general operation note is in operation-notes. Our single-rotor platform with collective pitch has one extra degree of control for precision target diving, compared to fixed-pitch crafts with unplanned displacements, as discussed in the video on the right. We build this new extreme robot based on the endurance build but divert 21 grams of the mass from the battery pack toward crash resilience and computing, GPS (5.3g) tracking, thicker flexible wires (3.1g extra) for crash resilience, titanium main shaft (extra 2.7g), higher crash-resistance rotor grips (extra 2.5g), silent (thiner) rotor blades (2.2 g extra), thicker motor construct (1.8g extra), extra power VTX and antenna (1 + 0.6 g extra), soft mounting battery (1g extra) and thicker landing skid (0.8g). 5.3+3.1+2.7+2.5+2.2+1.8+1.6+1.0+0.8=21g. The battery pack is 21 grams lighter 87.2g+2.1g+0.8g-69.1g=21g. The build is pictured below; the bill of material follows. 
Blade Linear Velocity And Angular Momentum For Fast Mission Travel
| Prototype High Endurance Build | Prototype Fast Travel Build | Production High Endurance Build | Production Fast Travel Build | |
| RPM | 2640 | 3100 | 3250 | 3430 |
| Rotor Diameter | 18.6 in/472mm | 18.6 in/472mm | 17.2in/438mm | 17.2in/438mm |
| Hover Blade Angle | 6.2 degrees | 4.8 degrees | 6.1 degrees | 5.5 degrees |
| Blade Mass | 14.6 grams | 17 grams | 13.4 grams | 15.6 grams |
| Moment Of Inertia | 0.00036388 | 0.00040843 | 0.00029416 | 0.00032933 |
| Angular Momentum | 0.10 | 0.13 | 0.10 | 0.12 |
| Blade Tip Speed | 65m/s | 77m/s | 74m/s | 79m/s |
Reducing rotor diameter and increasing blade velocity from the endurance build logically should improve wind resistance and increase top speed. In the endurance build chapter page, it was discovered that the small-diameter Sokolov-twisted and Clark-Y-slanted foils could not be used in single-rotors and could not be fixed without deteriorating efficiency and motor overheating/overclocking. But, even disregarding efficiency, Sokolov-twisted and Clark-Y-twisted foils have reduced blade tip speed relative to wind or travel. 12-inch and 14-inch Sokolov-twisted blades rotate at 3250 and 2550 rpm for a 250-gram lift, as designated and extrapolated in the graph below. Their blade tip speeds are 3.14*(12*25.4/1000)*3250/60=52m/s and 3.14*(14*25.4/1000)*2550/60=47m/s, respectively. For comparison, the symmetrical airfoil we use rotates at 2640 rpm at the lowest for endurance with an 18.6-inch diameter had blade tip speed of 3.14*(18.6*25.4/1000)*2640/60=65m/s.
To patch up the velocity (before improving upon the prototype build), 12-inch and 14-inch Sokolov-twisted blades would have to rotate at 4100 and 3500 rpm, respectively, with slight motor overheating. Remember, as tested in the endurance build, the slightly negative pitch affording the 4100 and 3500 RPM has more drag than a positive drag in Sokolov-twisted and Clark-Y-slanted foils.
But the biggest problem, as shown in the endurance build note, is the lack of angular moment, much lower than 0.1 kg⋅m^2/s of the prototype endurance build. When Sokolov-twisted and Clark-Y-slanted rotors were spun to match the angular momentum of the prototype endurance build, even without improving upon the prototype endurance build, the overheating became a risk of fault point.
A prototype rotor with 77 m/s blade tip speed was built to refocus on straight blades, which performed successful terminal speed divings. But was 77 m/s overkill and unnecessary? It was discovered that for a prototype with 210mm blades, the high-fuel-efficiency setting RPM2640 was sufficient for both straight diving and cruising for both the orange (nylon) and black (graphite reinforced nylon) Oxy210 blades, 2.7mm and 2.5mm cord thickness (not blade root thickness), respectively. The first two diving videos below show the blade tips for using orange and black rotors with an ESC governor. The third video shows the pre-prototype RPM2640 setup without an RPM governor during the "motor selection" with our pre-prototype builds. However, RPM2640 with 2.5mm blades was prone to forward travel stall, blade tip velocity 2640/60*(210*2+52)/1000*3.14 = 65m/s, as shown at 2:02 and 2:12 of the first video, due to the helicopter physics, which tilts the craft's head upward when traveling against the wind. RPM2640, with 2.5mm thin blades, caused several flyaways in high winds. It is well known that a thicker airfoil allows a higher attack angle without stalling because the thicker convex surface exerts higher pressure on the gas to press it onto the airfoil firmer, except at the very tail tip where thickness approaches zero regardless of airfoils, to prevent de-lamination and stall. It is also well known that the lift coefficient does not change when airfoil thickness changes. Also, the stall angle rises when Reynolds's number increases with the airspeed. In short, this recapitulates toward a separate operating mode at 77m/s or higher velocity as the solution for production builds.
For the prototype build, the solution was RPM at 3100, setting the hovering pitch to slightly lower than 5 degrees but higher than 4 degrees, trading off 8% fuel efficiency as seen in operating note of cL/cD 23 versus 25. This angle between the orange and green lift curves so that the lift slope doesn't turn steep, which would have translated to more difficult altitude management. RPM of the new hovering pitch is 19% higher, 3100, versus 2600 of attitude mode. The RPM change from accelerometer mode to gyro mode has a ratio of 3100/2600=1.19. According to the NASA education page in the operating notes https://nocomputerbutphone.blogspot.com/2018/09/converted-iot-drone-operation-notes.html, the gyro mode should require the inverse of the square of the 1.19 ratio on the collective pitch, 1.19**2=1.42, because the lift is proportional to the airfoil pitch; in contrast, the lift is proportional to the second power of RPM-airspeed. The new pitch angle should be 6.2/1.42=4.37 degrees. However, the Reynolds number changes with RPM, shifting from the aqua-colored curve toward orange and green-colored curves, suppressing lift at a sub-6-degree angle but augmenting lift past 8 degrees. So, I experimented hovering to see that the mid-throttle collective pitch point needed to be 22 points, 22 / 29.9 x 6.2 degrees = 4.56 degrees of the collective pitch in the channel 1 curve. Notice that the mid-throttle is scaled by 0.98 in the transmitter and shown as 22x0.98 = 21.56 in the LCD display. However, the angle is 4.56 because the display of 21.56 points refers to the 989-2011us PWM range. The 0.98 scaling sets the PWM signal range 1000-2000 microseconds for 200 points for "83 degrees" as measured as the full servo horn travel angle. 21.56/200x(2011-989)+1500=1610us is the actual PWM signal. (1610-1500)x50%+1500=1555us is the mixer output toward the servo. (1555-1000)/1000x83=46.0 is the angle from the position where PWM is 1000us in the servo. 46.0-(83/2.0)=4.56 is the angle from neutral. The prototype build was subjected to maximum climbing (punch) test with an overall collective curve from 6 points in the first quarter and increasing by 17 points every quarter of the entire throttle range, ending at 57 points, 6.2 x 57 / 30 = 11.8 degrees maximum, as pictured on the right. But the high-end punching has craft yaw lapse, gradually spinning to the left while ascending, as shown in the first video of this section. The workaround of increasing the P gain of the tail motor could not completely remedy the problem due to the near verticle drag slope at 11 degrees, as seen in the operating note's NASA foil data.
Nontheless, the prototype verified that the stable terminal speed that our build can handle is 24.5 m/s or 55MPH or 90 km/h. It is calculated graphically below. The speed-time plot of free fall with drag is well known to be a tanh function with terminal speed in the scaling factors. The integral distance-time plot shows 10 seconds of dive with 203 m travel at 24.5 m/s terminal speed. Assuming the pull-up force is 2.5 G, the craft stops within 1 second past the 10 seconds of dive with 12 m overshooting travel. The church's spire's height is about 50 m. The tower's roof is about 240 m above ground, and the antenna mast likely adds another 25 m where the diving started.
We refocus on the 77 m/s with an angular momentum of 0.1 as the solution for the production build. In the current off-the-shelf parts market, the prototype and the production build need a compromise of a fast-travel operation mode (RPM and collective pitch angle) with less fuel efficiency than the high-efficiency mode. The ideal solution (the skinny blade unavailable in the market) for straight, symmetrical airfoil or endurance improves wind resistance for fast travel because the blade tip velocity is high at 3340 RPM, all in the same mode of operation for high endurance. Blade tip airspeed is 3340/60*(193*2+52)/1000*3.14 = 77 m/s, the same as having 3140 RPM on the prototype blades of 210mm and broader hub span, 3140/60*(210*2+52)/1000*3.14 = 77.5m/s.
For the production build, the solution could be simply an RPM 3300 for the 193 mm blades because that is how a 193 mm blade can achieve the needed 77m/s and 0.1 angular momentum. Still, we increase RPM to 3430 instead of the ideal 3300 for the margin for the blade balancing RPM adjustments. Remember, the spinning linear blades with centrifugal force is equivalent of a musical instrument string in tension, with resonant frequencies to be tuned out. And the RF controller channel 5 bypass is 3430*7/50000*200-100 = -4.
Unlike the prototype build, there is no lift-curving because both endurance mode and fast traveling mode have a collective pitch above 5 degrees. The calculated hovering angle for fast travel is 6.1 (degrees high-efficiency setting) / (3430/3250)^2 = 5.5 degrees. The PWM servo signal for this angle is (5.5+(83/2.0)) / 83 * 1000 + 1000 = 1566.265us. RF PWM is (1566.265 - 1500) / 50% + 1500 = 1632.53 , LCD display point (1632.53 - 1500)/(2011-989)*200 = 25.935 . Pitch curve point for it is 25.935 / 0.98 = 26.46 . Hence the production build's pitch curve is set as 0, 13, 26, 39, 52, maximum collective pitch is 6.2x52/30=10.7 degrees. The zero collective pitch at the low end avoids the pre-prototype swinging motion.
The production craft's servo mixing is larger than the prototype craft's because the servo arms are shorter relative to the blade pitch arm width, the p-value in the following diagram. The high mixing also allows the overshooting of the servo-throttle to avoid flight software startup cyclic "rapid twitch" discussed in the build notes https://nocomputerbutphone.blogspot.com/2018/09/converged-iot-platform-build-notes.html.
The relationship between servo mixer attenuation and servo/swash/pitch/DFC arm spans is illustrated here.
Because the prototype's servo mixing used standard CC3D 50%/50% collective/cylic mix when the p value was 1, the extra attenuation of production build's p value at 1.5 means the production build's collective mixing, if and we do want prototype's throttle curves reused in production build, needs to compensate the 50% mix by the factor of 1.5, 50% x 1.5 = 75%.
Because the prototype's cyclic mixing occurred with p*(d/u)=1*(1.833/0.916)=2 while production build's p*(d/u)=1.5*(2.25/1.1875)=2.842. The extra attenuation of 2.84/2 = 1.42 is compensated as 50% x 1.42 = 71%, and (50*sqrt(3)/2)% x 1.421 = 62%.
Because we compensate the mixer difference in software, the pitch curve calculation in RF hardware controller based on the 50%/50% mix does not need recalculation.
The endurance build notes show the measurements of p, d, and u, where lightweight substitutes were considered
All these production-improved settings are part of the dump_all file in the operating notes.
The weights of the substitute components are in the pictures below. The loss of head-down torque with the Runcam Hybrid2 setup was 5.4gx6cm+(2g+3.5g)x9cm = 81.9g-cm, equivalent to having an 81.9gram-cm/30cm=2.7gram heavier tail motor.
What's worse was that the loss of head-down torque disrupts the level travel pitch holding, as shown in the following videos.
For the substitute Runcam Hybrid2, the solution was to modify the 450mah battery with double-sided mounting tape and Velcro to protrude 2-3cm (about 1.5-2.5cm in the horizontal component).
When tested with Runcam Hybrid2, there was no difference in flight characteristics between 2cm and 3cm protrusion. The solution for a 10.1-gram substitute Rumbcam Thumb with a 1.1-gram nano3 camera and a 55.4-gram battery needed similar protrusion. With Runcam ThumbPro, the head-down torque loss was less severe at (18Insta-13ThumbPro+1.1Ubracket+(2.0Ant-1.1Nano))*9cm-(55.4Batt-49Batt)*6=24.6g-cm.
So, the actual head-down torque was
4.3g(servo)*1cm + 0.7g(Guard)*3cm + 1.7g(VTX)*4cm + 0.8g(buck))*4.5cm + 0.7g(skid)*5.5cm + 1.2g(antenna)*6.5cm + 55.4g(Battery)*6.5cm + 12.7g(Camera)*9.5cm + 1.2g(FPV)*10cm = 521 g-cm
; the actual tail-down torque was
(5.6g(GPS)+9g(servos)+2.8g(computer)+4.2g(ESCs)+2.1g(skid))*3cm + 1.2g(RX)*(8.5cm+3.5cm) + 4.8g(boom)*(12.8cm+3.5cm) + 2.4g(fin)*(25.5cm+3.5cm) + (6.9g(motor)+1.5g(prop)*(25.5cm+3.5cm+1cm) = 485g-cm
. The original main gear radius was 3.5cm. The math is
4.3*1 + 0.7*3 + 1.7*4 + 0.8*4.5 + 0.7*5.5 + 1.2*6.5 + 55.4*6.2 + 12.7*9.5 + 1.2*10 = 521
(5.6+9+2.8+4.2+2.1)*3 + 1.2*(8.5+3.5) + 4.8*(12.8+3.5) + 2.4*(25.5+3.5) + (6.9+1.5)*(25.5+3.5+1) = 485
In the following diagram, the production build Blade Fusion 180 frame has a rotor and tail congruency as the prototype Blade 230 frame.
The congruent tail has the moment of inertia as
>>> 0.007*(0.3**2) + 0.0048*(0.25**2)
0.00093
The non-congruent motor, battery, and camera have the moment of inertia as the following calculations,
>>> #for production build
>>> 0.0438*(0.054*10/7)**2 + 0.0691*(0.092*10/7)**2 + 0.0023*(0.084*10/7)**2 + 0.00093
0.002417
>>> #for prototype
>>> 0.0501*(0.059*10/7)**2 + 0.0554*(0.083*10/7)**2 + 0.0137*(0.084*10/7)**2 + 0.00093
0.002262
So, the difference is about 7%.
Fluid Vortex-Mechanical Resonance Diversion
Action cameras logically have proprietary motion blur and other features that consumers cannot control, making them difficult to be a converged solution with high levels of control for a wide range of applications. The following two videos compare the prototype built with the Runcam action camera and the production build with FPV onboard recording, which shows more detailed raw-resolution pictures.
When the prototype's action camera block was removed from the front battery bay roof, it was discovered that the fluid vortex-induced oscillation's frequency matched the craft's mechanical resonance frequency. This results in high straight headwind velocity vibrations, as shown in the video (first dive) below on the left. When the battery pack's mounting was strengthened, the resonance became stronger and more persistent, as shown in the video below on the right.
The solution is to use loose battery mounting, as pictured below on the left. The multiple tests in the video below show that the solution diverted the craft's resonance frequency, effectively eliminating the resonance.
Main Rotor PIDs
It was discovered that the physical P-to-I ratio of 1:20 is suitable for straight-down terminal speed diving.
In the video, the left side is controlled by Betaflight (our production build) with the vintage scaling numbers set by a racing champion robot or an anonymous human defector as the following,
PTERM_SCALE 0.032029
ITERM_SCALE 0.244381
DTERM_SCALE 0.000529
PID_MIXER_SCALING 1000
ITERM_SCALE 0.244381
DTERM_SCALE 0.000529
PID_MIXER_SCALING 1000
PID_SERVO_MIXER_SCALING 0.7
. More than 3 different racing controllers in the market follow such a "define" of scaling in their pid.h file. Pitch PIDs at -1°C is 45/118/0 on the left side. The prototype CC3D flight computer used physical PID parameters on the video's right side. Pitch PIDs 0.002/0.04/0, tail yaw PIDs 0.0015/0.0034/2.1e-5 at -9°C. Both sides had identical main blades, RPM, swash mix, servos, tail motor, tail prop, weight, and weight distribution.
For gyro-only-stabilization, straight-line traveling (the b and c terms in pid2 of Matlab are canceled by zero steering), we convert and cross-reference CC3D PIDs with Betaflight PIDs by applying the vintage scaling as follows.
pCC3D / 0.032029 / 0.7 * 1000/2 = pRacing
, i.e. 0.00200 / 0.032029 / 0.7 * 1000/2 = 45
, i.e. 0.0015 / 0.032029 / 0.7 * 1000/2 = 33
iCC3D / 0.244381 / 0.7 * 1000/2 = iRacing
, i.e. 0.0400 / 0.244381 / 0.7 * 1000/2 = 117
, i.e. 0.0034 / 0.244381 / 0.7 * 1000/2 = 10
dCC3D / 0.000529 / 0.7 * 1000/2 = dRacing
, i.e. 2.1e-5 / 0.000529 / 0.7 * 1000/2 = 28
In our production build, which uses racing quadcopter controller, the 1000/2 factor emulates PWM 1500+/-500 servo travel of helicopter. The 0.7 factor is another racing controller scaling in the developers' mind to protect servos from perceived overrun.The action cameras logically use undisclosed motion blurring algorithms that may work better for specific vibration frequency profiles but worse for other frequency profiles. The action camera Runcam Thumb Pro in the prototype build was discovered to need careful PI values scaling together in conjunction with compensation for air density conditions (temperature), as tested and recorded in the following graph. The production build's FPV camera with soft-mounting battery tolerates deviations from the tabulation calculations. The dump_all_converged config file has 40 degrees F as profile 2 and is the default. The dump_all_converged config file has 1 profile for every 30 degrees F change between 0 degrees F and 100 degrees F.
physical Ppitch=0.002*(tempK/268)^1.3
physical Ipitch=0.040*(tempK/268)^1.3
physical PI for roll is 1/3 of those for pitch
, and the resulting tabulation for racing PIDs on the right table.
However, even with exaggeration, the PIDs in the right table does not cover the full range of PIDs needed to compensate for the variation of the swashplate slop. For an old swashplate with many crashes, the video shows the play between the outer and inner rings of the swashplate's bearing.
The swashplate is prone to slop because the bearing is designed to bear lateral/radial forces, but crash forces can be longitudinal/axial. For example, the brass inner ring of the swash can bite into the titanium shaft during impact, and the DFC link simultaneously pushes the outer ring of the swashplate bearing upward. The swashplate and the grip bearings are the only two metal-to-metal grinding points in the rotor of this craft, but the grip has thrust bearings designed to withstand longitudinal crash forces.
When gauging the slop degradation, hold the craft vertically to drape the blades and gently tug the DFC links up and down to see the scissoring movement's end position, as pictured here, which is with the swashplate with considerable slop used in the first video of this chapter page.
Tugging up produces a 2mm gap between the front blade on the left and the hind blade on the right; tugging down produces an 8mm gap between the front blade on the right and the hind blade on the left, as pictured above.
With a brand-new swashplate, tugging up produces no gap, while tugging down produces a 3mm gap, as pictured below.
For swash centering and gauging purposes, the tuggings must make the blade tips switch places or perfectly align with a tugging direction while producing a gap with another tugging direction. The gaps need to be summed because the swashplate is not perfectly centered due to the limited precision of servos, which is 0.83 degrees, as discussed in the operating notes https://nocomputerbutphone.blogspot.com/2018/09/converted-iot-drone-operation-notes.html. In the examples, the old swash has a sum of gaps of 2+8=10mm, while the brand-new swash has 3+0=3mm. Our tabulation uses a 5mm gap sum for the calculated value. The loose swashplate example in the first video of this chapter page requires and uses cyclic PIDs 10-5=5 entries above the calculated values in the tabulation; the brand new swashplate with a 3mm gap sum requires cyclic PIDs 3-5=-2 entries below the calculated values in the tabulation. When brand-new DFC links are used with brand-new swash, the slop will be too small to gauge using the sum-and-difference method because you can't always find a swash position to make the scissoring of blades switch directions. This happens when the slop sum is smaller than 3mm - the limit of servo precision. To understand this limit, using the brand-new swash pictures as an example, the perfectly centered swash should produce (3+0)/2=1.5mm gaps either tugging up or down. The example picture shows the servos lower the blade tips by 3-1.5=1.5mm from the ideal perfect center. The servos are arcsin(1.5mm/207mm)=0.415 degrees too low. 207mm is the length of the blade's leading edge as viewed on the ruler. But adding 0.83 degrees would make the servos 0.83-0.415=0.415 degrees too high, producing a 207mm*sin(0.415)=1.5mm deviation of swash center, the same deviation as before, just a different place. When the slop is too small to gauge, the required PIDs can only be assumed to be 3 to 4 notches below the tabulation calculated entry.
The following 2 videos show the prototype build diving with PIDs setting of the brand-new swashplate at 2.5 entries below 60°F, at the 35°F setting. The raw footage is on the left, and the post-production stabilized video is on the right.
The following two videos show the production build diving with the PIDs setting of the brand-new Blade Fusion 180 stock rotor at 0.5 entries below the 20°F row at the 15°F setting. The ground temperature was 20°F. The raw footage is on the left, and the post-production stabilized video is on the right.
The dump_all config file has 4 PID profiles for 100°F, 75°F, 50°F, and 15°F settings. 50°F being the default.
For the prototype build with an action camera tightly bound to the frame, oversetting PIDs with high-temperature settings produced craft vibration that completely destroyed the video, as shown in the following 2 videos for comparison. The 2 tests were only 1 day apart with identical craft setups. But the second day's morning temperature was uncharacteristically low for summer and caught me off guard.
The production build's camera takes raw video pictures without processing and tolerates vibrations of wider frequency profiles. Oversetting PIDs with high-temperature settings in the following tests produces less obvious vibration differences from setting on-target PIDs for the production build with a soft-mounting battery.
During prototype builds it was observed that changing RPM does not influence fast-travel stability as long as the rotor is balanced. This is shown in the 2650 RPM discussion earlier and here, using the same old, loose swashplate.
So what happens when PIDs are set from the lookup as-is without adjusting for swashplate slop? The PIDs are 3 notches too high for a brand-new swashplate with a 3mm slop gap sum. The video below on the left has such an as-is PIDs setting, and the shaking of the craft at 0:22 and 0:27 is unnerving to the pilot because the craft is making a smooth turn, equivalent to 0:22 of the previous video of optimal PIDs setting with 3650 RPM. In the video below on the right, the PIDs are 5 notches too high for the same brand-new swashplate, and viewers, not just the pilot, can see that the craft is shaking itself apart.
On the other hand, with the old loose swash, the lookup PIDs are 4 notches too low in the following video. The left side is the raw video, and the pilot can see shaking at 0:15-0:16 during a smooth turn. The right side is the stabilized version, and the footage sees twitches throughout the level traveling.
The shakings for insufficient and overshooting PIDs appear similar in the raw videos. But piloting can feel that the shaking with insufficient PIDs has a bigger rolling banking component while the shaking with overshooting PIDs has a bigger pitching, up-and-down component.
The shakings for insufficient and overshooting PIDs appear similar in the raw videos. But piloting can feel that the shaking with insufficient PIDs has a bigger rolling banking component while the shaking with overshooting PIDs has a bigger pitching, up-and-down component.
Tail Rotor PIDs
| Prototype | Production | ||
| Part | Gemfan straight 4025 prop. | HQ Prop slanted 4025 prop. | |
| PIDs | 33, 10, 28 | 48, 10, 29 | |
| High-wind PID | 33, 8, 34 | 48, 10, 29 | |
| Reference Temperature | -9°C , 15°F | 4°C , 50°F |
The production build's all-weather tail PIDs are improved based on the prototype's PID set that needed a separate high-wind set of PIDs. This improvement was possible because the HQ Prop's slanted prop design allowed a faster reaction.
The prototype tail with a glued straight propeller was tested and shown that, with Kd=0, at the bottom of the dives or whenever the main rotor torque has rapid, sudden increases, the direct drive tail lapses while the motor spins up with finite acceleration. The high integral produces winding resulting in "collision with thin air" bounces at 0:57, 1:16, and 1:41 of the video below on the left. One solution was to use a high torque tail motor of 1306 size and Kd=0, such as the video below on the right. But the CG setting was incorrect with the heavier tail motor, so the general solution was to set Kd to around 2.1e-5 in CC3D, or equivalent D=28 in Betaflight, with a small Ki with 1106/1303.5 motor.
The fact that whenever a control axis has ample, instant corrective torque, the Kd should be zero acknowledges that our rotor attitude control PID with Kd=0 is a correct setting because the variable pitch rotor can produce the desired corrective torque utilizing the considerable spinning momentum of the main rotor within half a revolution of the rotor without speeding up or slowing down any propeller. This also explains the contrast of why multi-rotor systems need Kd tuning for roll and pitch control.
Yet the general solution needs to consider wind conditions. With the prototype's glued straight tail propeller, in high winds, the I term should be lowered by 30%, D term should be upped by 20% for Betaflight to prevent wind-induced oscillation, as the following 2 experiments show.
The dump_all configuration is shared between the racing drone and the utility drone. The previous section's tabulation gives temperature 0.5th-order power to scale PIDs because tail PIDs control tail RPM with a 2nd-order power on thrust.
The production build's bolted slanted propeller requires 40% extra P gain and is in the dump_all configuration. The production build's single PIDs handle both low and high winds.
Higher Rotor Balancing With Angular Momentum Higher Than 0.1
In the platform's operating note, we visually make sure the rotors are symmetrical. For the prototype build with RPM 3140 and the production build with RPM 3420, the rotors has imbalances not visible to the eyes
. The first thing to take care of is the tightness of the rotor grips. For consistency, we set the blade draping angle to ideally 90 degrees, as the video on the right shows.
If the blades are over-tightened, imbalance easily results in mechanical vibration; if the grips are too loose, such as in the video on the right, the P-I ratio is different from usual and unpredictable.Going from 2650 to 3100 and higher RPM requires fine-tuning the rotor with hand-tethered hovering. Here the R/D test retained the original decal of the blades. And the tuning took 3 tries in the research process, as pictured below. First, I fixed the tremoring by cutting out a corner of a decal. When aggressively trimming the corner, it was over-corrected, and tremoring reoccurred. The balance was restored by cutting the corner of the other decal. Once the amount of taping was determined, all decals were removed, and the clear tape was put in place for the required balancing. The balancing progress during the research is the 4 pictured below from left to right. The conclusion is that one square centimeter of tape makes all the difference because the rotor is stretched by centrifugal force like a musical instrument wire, and the 3143 RPM is on one of the resonance frequencies of the device. The thickness of tape 0.002-0.003inch = 0.005-0.0075cm, weight (assuming density 1g/cm-square) 0.005-0.0075 grams. This means RPM3150 needs a precision balance of 1/100th of a gram.
However, during multiple test builds, it was discovered that most builds could not achieve smooth balance and that blade swapping was needed. One of the successful blade pairings was pictured above on the right with a green checkmark. The 2 distinct symmetries, rotation and mirror, for balancing the rotors is diagramed here.
The swapping needs to restore the rotational symmetrically of curved blades because our rotor hub does not have a cord-wise balancing bolting like the Bell 222 rotor, as highlighted in the picture on the right. The 2 blades with up-down warpings can be none-mirroring as the right side in the above diagram when subjected to 3150 RPM's centrifugal force. The solution is to pick and match a pair that dynamically match the warping to each other.The match needs not take blade ages into account. In the above example good match with a green checkmark; the older blade's color fades, but it is the best match picked out from 3 different sets of purchases. And the static warping mismatch is also disregarded. One warps up, and the other down, but they balanced up when spun up to 3150 RPM. All the other blades from the 3 sets fail to match the lower blade in the picture. The only way to check the pairing is to spin them up to full speed. And each pairing test needs to be checked with 2 different orientations of the grip installation. In the pictured example, only one orientation can produce a smooth spin. The other orientation always has vibrations that can't be tuned out with scotch tape.
Before the pairing process of a purchase, mark each blade with a unique serial number you manage, then weigh each blade individually and note the heaviest blade. The following pictures show an example of the heaviest blade, blade 3, of 7.301 grams. Then use scotch tapes spread evenly on each blade (except the heaviest one) to patch all the blades in the purchase to the heaviest weight. This ensures that the pairing process focuses on matching the the warpings of the blade material.
So, what happens if the rotor is axially off-balance by more than 1/100th of a gram in the field? In the videos below on the left, with perfect balancing, the PIDs are 2 notches lower than required because the swash slop is 10mm, the largest. The diving loses its heading hold about 2 seconds before pull-up at 0:11, but video stabilization patches up the insufficient PIDs below on the right.
But, when a 2 square-cm balacing tape is intentionally removed and immediately performing another test, the dive has loss of heading hold at 0:08 and 0:09, and the stabilization result is sub-par, with blurring at 0:07 and 0:09, to the above good video.
When inspecting the gyro data, both good and sub-par dives are 11 seconds between 2 green pitch-up dips in the following 2 pictures. The first picture is the good dive; the second is the sub-par one. And the blue-band noise level of the sub-par dive is about twice as thick. The good dive has a long period of quietness between 05:49 and 05:55, while the sub-par one has no quiet period.
When inspecting the gyro data, both good and sub-par dives are 11 seconds between 2 green pitch-up dips in the following 2 pictures. The first picture is the good dive; the second is the sub-par one. And the blue-band noise level of the sub-par dive is about twice as thick. The good dive has a long period of quietness between 05:49 and 05:55, while the sub-par one has no quiet period.
The ultimate smooth balancing has a lateral (on the side) ballast, in addition to the axial balancing, as follows with 24 AWG copper wires.
The first loop has the crossing beneath the DFC bolting and excess wire trimmed. Then, pinch and turn the wire for a few turns. In the example on the right, the 7 loops on one side are the correct balancing because 14 loops were tried on one side, and zero loops on either side were also tested to be lesser balance. This example ballast weighed 0.2 grams with 7 loops. However, this level of ultra balance is not required for smooth HD video shooting.
Electronic calibration to fix aborted/diminished dive
The example on the right is of diminished dive happened with 1495us center pitch PWM output. The full deflection of the stick is 720 degrees per second. The 5us from center 1500us is 5 / 500 x 720 x 0.25(exp) x 6(sec) = 10.8 degrees tilted dive at the bottom of the dive. And this tilting is also very obvious when tethered hovering in hand.
Hardware Modification
First, to trim the motor's stater base, preserve the outer ring as a guard against accidental rotary tool slips. Any rotary tool cuts are pre-cuts that don't go through the plate. Then, 6-inch long nose pliers bend along the pre-cut edges, and metal fatigue breaks the material. Trimming the 4004 motor stater saves 36.1-34.8=1.3 grams, as pictured below of the substitute 4004-300kv motor. The 2 pictures also reveal that the 300kv motor is about 2.5 grams heavier than the 400kv motor.
The good dives are reproducible consistently using Oxy2 grips, which have thrust bearings pictured here.
When installing the Oxy2 grips, watch out for factory assembly mistakes that occur about once every 10 pieces by the tentative(without washers and without hard cranking) installation of the feathering shaft and pulling, as shown in the following video on the. But, first use a marker to mark a dot to make sure, if the pulled grip rotates smoothly by itself or by rotating the shaft and the other grip's bearing provides the smoothness. A correctly assembled grip set should feel surprisingly and pleasantly slick in the pulling test on both grips.
The technique in the following left-side video is incorrect because a good grip on one side can ensure a smooth rotation on the other side, masking the problem of one-sided manufacturing mistakes. The following right-side video shows the entire assembly process.
To use substitute Blade Fusion 180 stock rotor, turn the "dog bone" 8 half turns after purchase (4 full turns) to shorten the DFC link so that it is identical to the production build's Blade Infusion 180 DFC link length, which was used in the video with word "stockrotor" in the title in this chapter page. When turning 6 or 10 half turns, the resulting swash center test showed obvious deviation. The 193 mm blades' root needs to be thinned using a Lego planning sled, as shown in the following 6 pictures. The router's sled is made of 2 long, thin Lego bricks glued to the front plate of the rotary cutting tool.
The thin flat Lego brick that the blades are glued on can be reused after scraping the glue off. The final assembly, as tested in the "stock rotor" video, was without the hub-grip-gap washer because a test with the stock washer proved it too tight.
On a high-wind day, the throttle may need to be kept high throughout the mission, and that causes the fly-away. The actual fly-away video footage shows traveling over roads and people, which was unlawful. It is only resolved when the throttle is lowered. The solution is the canted angle same as the Seahawk helicopter's design. The fix can be verified line-of-sight, on the right, and the maximum throttle punch-up at 0:30-0:33 happens rather uneventfully, straight up.
, and the craft appears to move from the left side of the road to the ball park on the right side of the road more than 210 feet between 2 frames of 0.033 seconds illustrated in the satellite photo on the right.
In the third frame to the camera failure, the camera points toward the south east corner of the park; in the second to the last frame, the camera points toward near straight north.
The apparent mach-6 hypersonic movement optical illusion needs to be re-fitted into pilot's mental picture for the craft's actual movement. Due to the near-170 degree wide angle lens of either Goqotomo or Caddx Turtle, the camera can display overlapping objects after craft turning 160 degrees. In the above first and second frame, the area at the overlap of line of sight is the actual position of the craft. In the last frame, the battery pack is seen thrown off the craft, and the craft crashed on to the right curb of the road as circle-highlighted in the satellite photo. The craft's actual position is closer to the right curb of the road on the peripheral of the thrid and second frame than it appears.
All objects in the FPV feed are "squeezed" toward the center of the screen from all angles, and the pilot needs to know that the craft is actually positioned closer to the objects on the screen's periphery than they appear. This is the same principle of wide-angle rear mirrors where car manufacturers warn, "Objects in mirror are closer than they appear." The same principle applies to the footage of the mission leading to the tailspin in the video on the right.
At exactly 1:00 mark, the craft appears to be outside of the ballpark over the row of pine trees lining the south side street on the peripheral of the screen, but the craft is actually closer to the pine trees, likely right above them. 12 seconds later, at the 1:12 mark, the apparent position of the craft has moved the improbable 1000 feet to the northwest side of the curved road, even though the actual position is still in the confine of the park because the view is exactly the same as the third frame to the camera failure video picture frame. Between the 1:34 and 1:36 mark, the craft appears to move the impossible 600 feet from the southeast side outside the park to the curved roadside crash landing point within 2 seconds. The craft moved from near the park's center to the curb of the road, 80 feet at most, within 1 second.
The conclusion is that the craft has been within the confine of the ballpark all though out the entire mission doing very small maneuvers.
and the go-around at 0:06 results in a steep increase in craft speed and altitude drop, resulting in a crash. A seemingly smooth touchdown in gyro mode can still capsize due to the general high speed approaching the target in the last video on the right.
Forgetting about switching to attitude mode can occur during high workload situations such as combating high wind while locating an obstacle landing patch impromptu.
So, the trick is to flip SwitchC to use accelerometer-assisted leveling mode for the final approach, and that should be trained into the pilot's reflex because attitude mode landing is appropriate in nearly all circumstances. And there should be a time to familiarize the wind conditions after changing to attitude mode before the actual touchdown, as shown in the footage here
As pictured, this dive also uses a dedicated battery pack for the full HD camera.
The factory assembly sometimes misplaces a high-error inner thrust disk instead of the low-tolerance outer thrust disk, as explained in the video above on the right. Discard the bad grip. The outer thrust disk needs to hug the feather shaft tightly because the radial bearing's inner tube needs to rest on the outer thrust disk without sinking into the crevice between the shaft and the disk, which would result in transferring centripetal, axial force onto the junction between the outer radial bearing's inner and outer tube. The general IoT platform build uses Align250 main grips without thrust bearings to avoid the added build complexity.
The general build's Align main rotor grips without thrust bearings can also dive at terminal speed properly, as in the following video, but only with brand-new grips if without modifying PIDs, as seen in the previous section about calibration of electronic PWM. Unless you trim the rotor blade roots, the Align250 grips are too short to accommodate a thrust bearing on the far side, like the Align300 grips. With wearing, the feathering friction is more significant without thrust bearings, so the physical P-to-I ratio differs from 1-to-20 (as seen in CC3D, or, unscaled) for terminal speed traveling,as shown in the following video.
To use substitute Blade Fusion 180 stock rotor, turn the "dog bone" 8 half turns after purchase (4 full turns) to shorten the DFC link so that it is identical to the production build's Blade Infusion 180 DFC link length, which was used in the video with word "stockrotor" in the title in this chapter page. When turning 6 or 10 half turns, the resulting swash center test showed obvious deviation. The 193 mm blades' root needs to be thinned using a Lego planning sled, as shown in the following 6 pictures. The router's sled is made of 2 long, thin Lego bricks glued to the front plate of the rotary cutting tool.
The thin flat Lego brick that the blades are glued on can be reused after scraping the glue off. The final assembly, as tested in the "stock rotor" video, was without the hub-grip-gap washer because a test with the stock washer proved it too tight.
When using the stock rotor, the weight saving from Oxy2+Infusion180 parts is (6.2 + 0.8 + 0.9) - (2.934 + 0.806 + 0.889 + 2.441) = 0.83 grams. The grips are 1.57 grams lighter, but the DFC links are 0.74 grams heavier.
Highly Reliable RF Control
In the general operating notes https://nocomputerbutphone.blogspot.com/2018/09/converted-iot-drone-operation-notes.html , we showed that 4004 motors need the toned-down governor P-gain of 0.13 for proper RF control lost recovery. But, a high P-gain of 0.5 is needed for high-performance "punch up." In the RF control signal loss and recovery exercise in the video on the right, the 4004 motor's high torque with sudden high throttle breaks the motor anti-rotation zip tie when the ESC governer P-gain is 0.5. The wreckage of the crash has main motor power wires twisted due to anti-rotation zip tie failure. A common strategy is to increase the RF range to increase reliability. The TBS Crossfire RF control transmitter and receiver setup follow.
Canted Tail Rotor Setting
The build's helicopter tail rotor is not on the rotation plane of the main rotor. It has a small right-roll torque on the craft, and the gyroscopic precession makes it tilt backward and fly backward. The parasitic torque increase as the throttle increases. The pullback problem can be discovered in gyro mode travel with sudden maximum throttle, the tilt backward happens between 0:31 and 0:33. Just 2 seconds of pullback already sends the craft away from the car where it hovers initially. Then a forceful pitch down is applied in a panic at 0:33. At the end of second 33, the car is seen in front of the craft, compared to it is on the side of the craft at the beginning of the punch-up. Please notice that the tilt angle is barely perceived, lowering horizon for about half an inch when viewing this video on computer monitor. That means FPV pilot can not notice the problem is occurring.
On a high-wind day, the throttle may need to be kept high throughout the mission, and that causes the fly-away. The actual fly-away video footage shows traveling over roads and people, which was unlawful. It is only resolved when the throttle is lowered. The solution is the canted angle same as the Seahawk helicopter's design. The fix can be verified line-of-sight, on the right, and the maximum throttle punch-up at 0:30-0:33 happens rather uneventfully, straight up.FPV Fishbowl Optical Illusion
A 30-frame-per-second FPV feed of a tail-spin, craft shaking itself apart, has the following 3 consecutive final frames,
, and the craft appears to move from the left side of the road to the ball park on the right side of the road more than 210 feet between 2 frames of 0.033 seconds illustrated in the satellite photo on the right.In the third frame to the camera failure, the camera points toward the south east corner of the park; in the second to the last frame, the camera points toward near straight north.
The apparent mach-6 hypersonic movement optical illusion needs to be re-fitted into pilot's mental picture for the craft's actual movement. Due to the near-170 degree wide angle lens of either Goqotomo or Caddx Turtle, the camera can display overlapping objects after craft turning 160 degrees. In the above first and second frame, the area at the overlap of line of sight is the actual position of the craft. In the last frame, the battery pack is seen thrown off the craft, and the craft crashed on to the right curb of the road as circle-highlighted in the satellite photo. The craft's actual position is closer to the right curb of the road on the peripheral of the thrid and second frame than it appears.
All objects in the FPV feed are "squeezed" toward the center of the screen from all angles, and the pilot needs to know that the craft is actually positioned closer to the objects on the screen's periphery than they appear. This is the same principle of wide-angle rear mirrors where car manufacturers warn, "Objects in mirror are closer than they appear." The same principle applies to the footage of the mission leading to the tailspin in the video on the right.
At exactly 1:00 mark, the craft appears to be outside of the ballpark over the row of pine trees lining the south side street on the peripheral of the screen, but the craft is actually closer to the pine trees, likely right above them. 12 seconds later, at the 1:12 mark, the apparent position of the craft has moved the improbable 1000 feet to the northwest side of the curved road, even though the actual position is still in the confine of the park because the view is exactly the same as the third frame to the camera failure video picture frame. Between the 1:34 and 1:36 mark, the craft appears to move the impossible 600 feet from the southeast side outside the park to the curved roadside crash landing point within 2 seconds. The craft moved from near the park's center to the curb of the road, 80 feet at most, within 1 second.
The conclusion is that the craft has been within the confine of the ballpark all though out the entire mission doing very small maneuvers.
Navigation With GPS
The GPS connection needs baud rate 115200 , for HGLRC F411, on UART1(TX1/RX1) as the following.
All these configurations are part of the "dump all" file in operating note https://nocomputerbutphone.blogspot.com/2018/09/converged-iot-platform-build-notes.html .Softserial, as the 3rd serial line, controls the video transmitter and is already soldered on the S5 lead as shown in the build note. This arrangement is based on the technical note from HGLRC.
The navigation depends on the 3 digits of coordinates as highlighted in the following video. The historical definition of the metre dictates that the biggest of the 3 digits correponds to about 1km distance (actually about 1.1km on latitude and 0.9km on longitude). And diving requires 10m precisition, which is the smallest of the 3 digits. The heads-up display also shows the distance home, which is about 180m as shown in the thumbnail screen of the video. And the corresponding home latitude 3 digits is close to 021+(180m/11m) = 037, as shown at the landing of the video.The OSD elements' locations in the dump_all configuration https://drive.google.com/file/d/1_asy-pvVoEm3Tlr_Lams4AKPT4plXA37/ are pre-configured to be more centralized to the center of the video picture so that multiple substitute FPV cameras can see all the information elements. So, the exact element locations must be adjusted to align the latitude and longitude digits for each locale, except with the Nano3 camera in North America. For example, in the Eastern hemisphere, the missing negative sign of longitude pushes the decimal point one place to the left. The VTX setting does not use Pit Mode because the extremely low VTX power renders the video picture distorted and can be mistaken as hardware failure. The VTX setting is meant for SmartAudio VTX with 4 power levels, "powervalues 14 20 26 27" with the TBS Unity Pro32 Nano.
All these configurations are part of the "dump all" file in operating note https://nocomputerbutphone.blogspot.com/2018/09/converged-iot-platform-build-notes.html .Softserial, as the 3rd serial line, controls the video transmitter and is already soldered on the S5 lead as shown in the build note. This arrangement is based on the technical note from HGLRC.The navigation depends on the 3 digits of coordinates as highlighted in the following video. The historical definition of the metre dictates that the biggest of the 3 digits correponds to about 1km distance (actually about 1.1km on latitude and 0.9km on longitude). And diving requires 10m precisition, which is the smallest of the 3 digits. The heads-up display also shows the distance home, which is about 180m as shown in the thumbnail screen of the video. And the corresponding home latitude 3 digits is close to 021+(180m/11m) = 037, as shown at the landing of the video.The OSD elements' locations in the dump_all configuration https://drive.google.com/file/d/1_asy-pvVoEm3Tlr_Lams4AKPT4plXA37/ are pre-configured to be more centralized to the center of the video picture so that multiple substitute FPV cameras can see all the information elements. So, the exact element locations must be adjusted to align the latitude and longitude digits for each locale, except with the Nano3 camera in North America. For example, in the Eastern hemisphere, the missing negative sign of longitude pushes the decimal point one place to the left. The VTX setting does not use Pit Mode because the extremely low VTX power renders the video picture distorted and can be mistaken as hardware failure. The VTX setting is meant for SmartAudio VTX with 4 power levels, "powervalues 14 20 26 27" with the TBS Unity Pro32 Nano.
FPV Landing Procedure
Gyro-only mode landing often results in capsizing due to the drifting nature of the gyro mode, as seen in the last few seconds of the video on the right when the pseudo touch down at 1:43 has a remaining altitude, maybe 1 foot, and the drift scraped the grass at 1:45 resulting in capsizing.
Aborting landing in gyro-only mode also often results in a crash due to altitude drop with the large maneuvering nature of gyro mode. Gyro 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 too high at 0:05 in the video here below,and the go-around at 0:06 results in a steep increase in craft speed and altitude drop, resulting in a crash. A seemingly smooth touchdown in gyro mode can still capsize due to the general high speed approaching the target in the last video on the right.
Forgetting about switching to attitude mode can occur during high workload situations such as combating high wind while locating an obstacle landing patch impromptu.
So, the trick is to flip SwitchC to use accelerometer-assisted leveling mode for the final approach, and that should be trained into the pilot's reflex because attitude mode landing is appropriate in nearly all circumstances. And there should be a time to familiarize the wind conditions after changing to attitude mode before the actual touchdown, as shown in the footage here
Diving Pullout
4-series lipo is required in this procedure.
When pulling out of a terminal velocity dive, first cyclic pitch up from negative 90 to negative 45 degrees, then add a collective pitch. Do not add a collective pitch first because helicopter physics dictates that the craft pitches upward, resulting in stalled movement with a collective pitch. The negative 45-degree attitude is enough to slow down the dive and make a horizontal movement because there is lift due to relative air movement that gives a small equivalent collective pitch (not enough to have a "receding blade stall").If, without a careful zero-collective-pitch maneuver, in the video below on the right (with Sunnysky v2806 400kv motor and 20A ESC), the pullout had stalled, stumbled movement.
3-series lipo is discussed in the substitute parts chapter page.
When pulling out of a terminal velocity dive, first cyclic pitch up from negative 90 to negative 45 degrees, then add a collective pitch. Do not add a collective pitch first because helicopter physics dictates that the craft pitches upward, resulting in stalled movement with a collective pitch. The negative 45-degree attitude is enough to slow down the dive and make a horizontal movement because there is lift due to relative air movement that gives a small equivalent collective pitch (not enough to have a "receding blade stall").If, without a careful zero-collective-pitch maneuver, in the video below on the right (with Sunnysky v2806 400kv motor and 20A ESC), the pullout had stalled, stumbled movement.
3-series lipo is discussed in the substitute parts chapter page.
Motor, ESC, Shaft, and Battery Substitute
In addition to the prototype motors, the T-Motor MN2806 400kv works, as shown in the following diving. This dive uses a 10A 1-3S DYS ESC and a carbon fiber main shaft, the same as in the endurance build. And this dive uses a brand new Align 250 Sport grip set.
The 4 substitutes is the standard of the endurance build.
Do Not Use Rolling Shutter Correction And Do Tilt Camera Slightly Down With Gyroflow
The bbl gyro data file from the flight computer is loaded into blackbox.betaflight.com, as seen in the Hardware Modification section, to verify the right bbl file for Gyroflow processing. The FPV onboard recording video is also loaded into blackbox.betaflight.com to facilitate the verification of the bbl file for a video file.
Also, the rolling shutter correction, which should have been disabled, and the turning blades in HD footages with Gyroflow cause all jello/twitches in this chapter's videos wherever jello/twitches are present. It sabotages all videos, whether the original raw video is smooth or shaky, as shown in the following side-by-side comparisons.
The default settings in Gyroflow are all good except the rolling shutter correction. Disable it as follows.
Sources of jello are often related to shutter, as reported by Valley FPV below. A source of tremor is newer BLHeli_32 ESC that uses the same working frequency of 24kHz as the action camera's gyro sensor's working frequency, as reported by Valley FPV. But, according to the original BLHeli's manual, our ESC can not be (mis)configured to use the 24kHz working frequency.
When the helicopter blades are prominently visible in the HD camera's view, Gyroflow is confused, as in the video below on the left. Gyroflow's auto-sync shows yellow and orange flags of camera timing offset. The fix is to tilt the camera slightly down and away from the rotor blades, as in the video below on the right.
Using the same craft build, the dive on the right was done one hour after the bad Gyroflow problem in the video on the left. There was no balancing work in the rotor in between. The FPV feed of the good dive is https://www.youtube.com/watch?v=1ryHxWiM1qU, which is similar in stability to the bad dive's FPV feed.
Sunnysky 2806 Motor On Carbon Fiber Shaft
It uses 3 Kevlar strand inserts for the Sunnysky 2806 motors on a worn carbon fiber shaft.
The substitute 2806 650KV motor doesn't produce noticeable excess heat compared to a 2806 400KV motor. But, as expected, a 2806 motor has noticeable extra heating compared to a 4004 motor. This 650KV was tested in the previous section's HD camera tilt-down test.
Software Gyro Noise Filter Does Not Rescue PWM 50Hz And Oversetting PID
The gyro data time series shows the Betaflight 4.3+ notch filter dramatically reduces the motor vibration noise in the following 2 screenshots. The comparison test was done with overturned PID and PWM 50Hz. Normally, PWM is set to 480Hz. All the prototype video tests on this page are done with PWM 480. There is no noticeable video improvement by the notch filter.
The actual video corresponding to the top gyro data time series (without notch filter) screenshot is at 0:29 here,
The actual video corresponding to the bottom gyro data time series (has notch filter) screenshot is at 0:28 here,
There is no subjective difference between piloting with and without a software notch filter with the T-Motor F722 Mini flight computer, which has a BMI270 gyro chip. However, the dump_all config file includes a notch filter for compatibility with other flight computers with different gyro chips that may need it.
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