Saturday, September 1, 2018

Converged IoT Drone Build Notes




Topics are sorted by significance. Mandatory procedures come first.

Power-Tran Setup

To prepare the motor for gear-less direct drive, first remove the setscrew(s) of the shaft and clamp the shaft down until the shaft is flat on the motor's top plane. The Wera 1.5mm hex screw driver is chosen for its tight fitting to all parts in this build to prevent stripping parts. Then, attach a 3mm stainless steel rod as a pusher on top of the shaft with double sided tape. Any grease on the rod and shaft needs to be wiped with alcohol for proper adhesion. The 3mm diameter rod is cut to slightly longer than the shaft's depth in the motor bell.


Clamp the shaft down the second time with the 3 inch vise to complete the removal of the original shaft. The jaw gaps, as highlighted in the following picture, need to have smooth close gliding by adjusting the bottom holder tab of the vise before applying clamping force. The double sided adhesion can slip due to imperfect right angle contact. 3-4 attempts rotating the contact surface is needed before full force clamping.
The 3/8 inch socket is used on the 2808 motor; the 1/2 inch socket is used on the 4004 motor.

Before using the 2808 motor bell with the craft's main shaft, stick a layer of tape on the opposite side on the shaft wall from the set screw. This is to center the bell to the axis when the set screw is cranked in.


When the main shaft is driven into the bell, friction draws the tape into the shaft hole leaving a flap of tape outside as pictured above highlighted in square. The lower square highlights the shadow of the flap of tape.



Trimming the 4004 motor stater saves 36.1-34.8=1.3 gram as seen in above pictures of the 4004-300kv. The stater needs not always trimming pending on combination of the build. For example, if replacing the 53-gram(including heatshrink tubes) 2808 motor with 4004 400kv motor, which weighs 47.4+1.3=48.7 grams untrimmed in the worst case, it saves 4.3 grams, resulting in 249.4-4.3=245.1 grams at takeoff. Or, if replacing the 2808 motor with 4004 300kv motor, which weighs 34.8+15.1+1.3-48.7+0.1(battery extra weight)=2.6 grams heavier, untrimmed, than the 400kv motor untrimmed, and it still saves 4.3-2.6=1.7 grams, resulting in 249.4-1.7=247.7 grams takeoff.




Trimming either 4004 motor or 2808 motor's stater base needs first preserving the outer ring as a guard against accidental rotary tool slips. Trimming the 2808 motor also requires pre-drill perforations on the base plate with 2mm tungsten carbide bids as in above picture, and also radial pre-cuts. For the 2808, desolder the original 3 lead wires and rebuild it with one of the inner conductor threads split into 3 equal portions. Then heat shrink 1.5mm tubes to reseal the wiring. This procedure saves the craft 0.8 grams. The 3-portions of strands can be substituted with the scrap wires from battery pack build without detectable weight change as in the following pictures. This is because the original AWG 18 wire has cross section area of 0.82 square mm, compared to the AWG 22 battery wires of 3 x 0.33 square mm, resulting in 17% weight difference with the quarter-gram weight of the combined core strands. 17% x 0.25 gram = 0.0425 grams, less than the graduation of the scale.

In all cases, any rotary tool cuts are pre-cuts that don't go through the plate. Instead, 6-inch long nose pliers bend along the pre-cut edges and metal fatigue breaks the material. In all cases, the outer ring does not need rotary cuts, instead, the pliers bend and pull out the ring sections one by one.





After stater trimming, the 4004 300kv motor can substitute the 400kv motor if the craft itself has 2.6-0.3(head room)+0.1(battery extra weight)=2.4 grams weight reduction. Be careful not to snag the motor's hub winding with the zip tie during installing the motor. The hub winding is loose and can be wedged between the zip tie and the stater base. Below picture is the correct installation where there is nothing between the zip tie and the stater base.
 
The tape insert between the motor bell and the shaft can be verified unbroken after uninstalling the motor and removing the shaft. The above picture shows that the tape is inserted into the shaft hole and not merely cut by the shaft during installing the shaft and extruded out of the motor.


To start the dual ESC build, remove original wraps by using the cuticle scissors to open them from the sides of the ESC circuit board. Then shorten the tail ESC's battery wires so that they neatly reach the main ESC. Pre-tin the short battery wires and tie the battery wires with wrapping wires as in the picture for the triple-junction soldering jobs. Solder the short wires to the inner side of the main ESC's battery wires. It is OK for the short wire leads to touch the capacitor between the 2 electrical poles because the capacitor is electrically wired to the 2 poles. Tail ESC build needs desoldering the motor wires of the tail ESC and replace them with the silicone insulated patch wires. The patching wires need to be long enough for soldering to the tail wires after the ESC is already installed in the battery-motor cavity. Take care not to leave solder streak-spikes that may puncture the insulating clear tape. Lap out the original solder and add fresh solder if needed.

The soldering iron temperature is 280 to 300 degrees. Any higher temperature causes instant oxidation of solder.


After soldering, apply clear tape. 2 layers of tape on each ESC on the side facing each other. So, 4 layers of tape insulation sandwiched between the 2 ESCs. 1 layer of tape on the outside surfaces.

The ESC and DC buck converter tap on to the power distribution point from battery output that is the scrap from the tail ESC battery wire pair. There is no added weight of solder to the dual ESC build because the factory pre-tins the leads and the soldering pads. Here the scrap battery wires join XT30 connectors and the power distribution point so to merely relocate the pre-tin solder to the power distribution point, so that power distribution point obtains tinning. That cancels out the added pre-tin solder weight at the beginning of this dual ESC build.


The Y-cable can be substituted with simple tapping as above 2 pictures without changing any craft weight because the simple connector weighs 0.1 grams, 0.1 grams less than Y-cable, substituted by solder and insulations. Picoblade 1.25mm connectors with Y-cable are chosen because the current rating of 1A is sufficient with CC3D with power tapping by servos and RF receivers, plus the 0.25A current to the 0.2W video transmitter and 0.65A to the full HD camera system.  Notice that the vendors often mistakenly label the Molex Picoblade 1.25mm-pitch connectors as JST connectors. Here, the actual trade name is used throughout this build. In the following video, the current is measured on the power tapping of CC3D, which, in turn, has its power tapped by 3 servos and the FrSky R-XSR receiver.
When the servos are idle, the specification says each servo consume 15mA, and indeed, the current reading is 145mA with CC3D itself consuming 70mA and receiver consuming 30mA. During hard maneuvering, the reading is slightly higher than 250mA. So the math is 0.25A + 0.25A + 0.6A = 1.1A , or 1.1A x 5V = 5.5W . This power consumption is about 20% of the main motor, and about twice as that of the tail motor. This also means that the hovering time increases about 10% when video transmitter and camera are turned off. This also means that the hovering efficiency of the main motor is about 30% less than the manufacturer specified efficiency of the motor itself, which excludes all  electronics power consumption. For example, when the main motor is operating at 13g/W efficiency point, the battery mission budget needs to treat the craft as operating at 9g/W .




The XT30 connector needs to have a half cut in between the poles and a marker paints the color code on the casing before installation to reduce operating errors.

The main ESC output is soldered to the main motor as one chained unit.  The chain is installed from the bottom of main frame up. ESC signal wires, XT30 and Picoblade connectors go in first through the opening in front of main shaft cage and come back down in the main frame, exposing only the main motor wires on the outside on top of the roofing of the battery-motor housing. The 5 volt y-cable is attached to the side column of the frame.

Then, the ESC signal wires, XT30 connector, and buck converter go into the lower compartment of the rear electronics bay. XT30 and buck convert exit out of the bottom before the landing skid; ESC signal wires exit behind the landing skid. The buck converter meets the y-cable up on the side of the body.

The XT30 connector can be substituted with EC2 connectors without adding weight, but it needs clamping tools.


ESC RPM Setup

The ESCs comes pre-loaded with multi-rotor software for direct drive systems and is appropriate to be used in gear-less setup for main rotor. It is not necessary to change the pre-loaded software, and in fact, changing it to MAIN rotor software results in a "spool up" delay of roughly 3 seconds whenever throttle-up and resistance is detected. That means that when you descend too fast approaching an obstacle, you can't punch up the craft immediately because the ESC senses blade foil drag with throttle-up and gives small increments of torque over 3 seconds to prevent damage to the helicopter pinion/gear. In the gear-less helicopter, there is no resistance reduction gearing, so the ESC needs to apply the torque regardless of resistance, just like a multi-rotor system.
The default ESC configuration parameters are good in the above screenshot for main motor. For the tail motor, the quadcopter firmware has a sloped power output, causing momentary PID resets with large deviation of tail attitude when you make a left yaw during cruising or correcting a diving trajectory. The momentary reset and crash videos are here,

The firmware needs to be changed to TAIL for helicopter tail. And most ESCs under 12A do not have TAIL firmware, so we use 20A ESC for the tail. To reflash the firmware, we use Omnibus F4 controller's passthrough USB-to-UART connection. And we use BLHeli configurator on Chrome browser.

The configurator is not listed in chrome web store, instead, google it "chrome web store blheli" and add it. To access USB tty device, chrome needs to be restarted as root user with command "google-chrome --no-sandbox", then browse chrome://apps to start the app.

Safety precaution is 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 Omnibus controller by connecting micro USB cable, connect only the tail ESC's signal cable to a PWM out header of controller, which is on the 2nd to 5th rows. Start the app and click "Connect" with default baut rate and auto-detected tty port. The controller now goes into USB-to-UART adapter program. Now connect ESC's craft battery power, then click "Read Settings" to actually connect to the ESC computer. After flashing ESC, tear down ESC's craft battery power plug. Then tear down software/other connections.

Incorrect RPM is the first cause of the 3 equally significant sources of craft instability and/or vibration because the flight controller PID gain is tied to rotor angular momentum and proportional to rotor RPM. Here we control the RPM by stipulating and scaling the PWM signal output from CC3D. The scaling in CC3D with the factory ESC software needs positioning the slider to the high position after first sliding it up-and-down sequence, then the ESC makes a questioning tone(you will perceive the tone as asking you to give another input), and you position it to the low point to finalize the configuration. 

It is discovered that, without ESC capacity scaling, the craft with 2808 660kv motor hovers, immediately after battery full charging, at 80 points in the 0-200 scale. The LiPo technology has steep voltage drop toward quarter discharge. So the hovering at 80 points only lasts for a few seconds.

 


. That means that when hovering the craft at 0.50 throttle stick position, PWM output from CC3D at 1400us (or 400 based off zero), ESC RPM will be at 400/1000=0.4 capacity. 

By scaling with motor KV value, it can be calculated that a 400kv motor will need to scale and stipulate the full ESC RPM capacity at 1000x400/660=606 us PWM output (or 1606 based off 1000). And when using 300kv motor at 4S, the stipulation will be at 1000 x 300/660 x 4/3 = 606 (or 1606 based off 1000).

The technique to quickly slide the PWM to exactly 1606 in LibrePilot GUI is to tentatively set the maximum throttle at 1606 without saving the configuration to CC3D flash, and then drag the PWM slider to that maximum before clicking on "Test Output". No need to save the configuration to CC3D flash for the ESC PWM change. Instead, use the CC3D default PWM range of 1000us-2000us for all crafts.  

The next step in setting a consistent RPM is to compensate voltage drop during battery discharge.  Lipo batteries discharge voltage cuves from 4.2 to 3.7 volts. At the end of discharge cycle, the hovering point will be 80points x 4.2volt / 3.7volt = 91points, or 11 points boost. The hovering point of 80(based off 0) scale for 250 gram target weight means that every 3.3 grams deviation needs 1 point of throttle to compensate. Hand-wound motor stater has extra RPM and needs -5 point to +3 point compensation. The compensation for voltage drop and craft weight deviation is adjusted with addition of mixers in Taranis QX7. The mixers are listed on top of throttle cut mixer using the same transmitter switch. That means that, at takeoff to 10 minutes into the flight, the switch changes  position to 6 points boost, then, after mid discharge, the switch changes position again to add 11 points boost.



Control System

The CC3D UAV config files for LibrePilot 16.09 are at 
. The Pitch fields gain numbers are twice the numbers of Roll fields because the helicopter has very long longitudinal axis compared to its lateral axis. The configuration needs to be Import'ed then Save'ed to the CC3D's flash.

 All credit and copyright belong to airfoiltools.com , NACA, and Xfoil , for the following picture.


Our rotor RPM is 2645/minute = 44.08/s , diameter 0.5m , speed at 80% blade span is 0.5m x 3.14 x 44.08/s x 0.8 = 55.36m/s . Our Reynolds number is 55.36m/s x 18mm / 1.46 x 100000 = 68,260 . So, between the aqua and orange curves are our curves for attitude mode.


 

Optimal lift-to-drag ratio blade 6.2 degrees, DFC arm raise sin(6.2 degrees) x 12mm = 1.296 mm
Swash plate raise 1.296mm
Servo arm rotate sin-1(1.296mm / 12mm) = 6.2 degrees
Servo PWM 6.2 degrees x 1000us / 84 degrees = 73.8 us
Doubling PWM for CC3D halving and shift centering for collective pitch 73.8us x 2 + 500us = 647.6 us
Transmitter Flysky 0-100 point system 647.6us x 100 point / 1000us = 64.8 points
          Taranis -100 to 100 point system 647.6us x 200 point / 1000us - 100 point = 29.5 points

The pitch curve is as following pictures.


. The equivalent pitch points are
  Taranis           0      20       30       40       50
  Flysky         50      60       65       70       74
.

Endurance test for the optimal fuel economy lift-to-drag ratio,



The Roll/Pitch PIDs of the attitude mode bases off acro+ mode's PIDs,

. The lower RPM of attitude mode, 2670 versus 3115, 2665/3145=0.856 requires increase of the PIDs to compensate the lowered lift of corrective pitch angle changes. According to NASA education,
lift depends on speed squared ratio,

But, the lower RPM itself also lowers the rotor's angular momentum, requiring linearly less force of correction. The result is that the PIDs for acro+ mode are compensated by between the ratio of the RPMs squared, 0.733, and linearly for attitude mode. 8/0.7945=10, 16/0.7945=20, 160/0.7945=200, 320/0.7945=400.

The PIDs in attitude mode allows precision, tight spot hovering.
Mount the CC3D controller with 3 layers of clear mounting tape at the front and 1 layer on the back, and another strip on the servo pins.

The actual mounting starts with pushing the USB plug against the inner wall of the main frame cavity and lowering the the rear mount edge keeping the vertical strip on the servo leads pressed onto the rear edge of the main frame. The vertical mounting strip's backing should stay on the mounting tape at this time so that it can slide up and down freely until the rear mounting strip touches down on the cavity floor.

The front mounting strip's backing film is not yet removed at this time. If the CC3D board is not aligned properly, abort the operation to replace the rear strip to start over. If all is aligned properly, mount the front edge, then remove the vertical strip's backing film. The premise of being able to remove the sticker backing in very tight gaps is that the backings are partially lifted at the corners during preparation.

Main Rotor Setup

The screw driver needed to fasten main shaft cage is Walmart item "Hyper Tough TS99818A 44-Piece Precision Screwdriver Set". The driver needed is Philips #1 with thin shaft to go in the small holes, which is very rare in the market. The screws go in from the left side of the craft on the BSR main frame. The front 2 screws of the cage on the 230S main frame go in from the right side of the craft.

The 4004 motor and 2808 motor are interchangeable providing that the 4004 has 2.8mm shaft protrusion while the 2808 motor has 0.5mm shaft protrusion at the bottom of the motor. The difference of 2.8-0.5=2.3 mm matches the motor height difference of 21.3-19=2.3 mm. The shaft is inserted up-side-down from the original Microheli Blade 230 Carbon Main Shaft's intended orientation.





The bottom side of the shaft has larger distance from the end of the rod to the retaining hole for the original rotor hub. The larger distance ensures that the said hole is placed in between the motor's 2 bearings to re-enforce the weakened shaft due to the hollowed structure. The collar is flipped up-side-down so that the lip of the collar faces down in contact with the main bearing's inner tube so that the outer tube of the bearing does not scratch the collar adding resistance. The Philips #0 screw driver from Walmart item Hyper Tough 6-Piece Precision Screwdriver Set is use to tighten the collar because most other #0 screwdrivers on the market have thicker shaft than the main frame allows . Use all your finger's strength to crank the collar. The thread of the collar's bolts are not likely stripped due to the small diameter of the screwdriver producing weak torque. 

The hub retainer hole is 1.6mm in diameter, 7mm from the top. The smaller than the original hole preserves the integrity and strength of the shaft material.

The screw retainers on the hub needs to be torqued as hard as the collar with the thin shaft precision screw drivers #0 and #1. In the case of loose torquing in the following video, the punch-up was unusually weak, the shaft was free-spinning in the rotor hub's hub when the dive has a sudden elevator-down indicating the hub shifted. 



After the crash, the hub is found to be free rotating, and the shaft has been ground thinner by the retainer screws. The following picture's green line is the original retainer screw's position. The red line marks the new elevation of the retainer screws after the crash
The repairing requires that the shaft be evenly thinned around the fault point as shown in red circle in above picture so that the retainer screws will not slips to the thinned area by previous damages. Failure to smooth out the repair surface results in more slips and failures in the following video.





When properly torqued, in nearly all crashes, the shaft is not damaged. In below video, the pull up was too little and too late resulting in crash. But the main shaft is totally unharmed, and the craft can take off in 5 minutes after the crash.

The swashplate fits the 230 main frame unmodified. For the BSR frame, trim the antirotation bar, first grind the top to form a flat surface. Use the cutting disk/wheel with the slowest rotary tool speed for this job. Then slice the 2 sides 45 degrees from the top to form a rough final shape.


Once the rough final shape is formed, draw a mental line vertical from the upper left corner down. The plastic material on the left side of the line needs to be preserved. Grind out the lower right corner material to finalized the trim. 



After the trimming, shorten the bar so that it can escape the antirotation bracket in the event of crash.
 

Shortening the anti-rotation bar is done for both BSR and 230 frame.


For the DFC swash control rods, The original Blade 180CFX hub has 2 swash-driving arms that need to be removed to make way for DFC links.
A set of servo links includes 1 long steel rod and 2 short steel rods. The long rod, after cutting out the center, non-threaded area, has 2 short segments, each for 1 rear servo link. One of the original short rod is used for a DFC link. The second short link, unmodified is used as the front servo link. The extra ball socket pair from a second purchase of servo link set has 1 rod for another DFC link. The extra ball socket pair from the second purchase has 2 ball sockets for the 2 DFC links.


 
The short rods are still too long for the DFC link and needs trimming out 2mm with the rotary cutting wheel. Once trimmed, the DFC link and the ball socket join tightly giving a uniform length, and no swash tracking needed. 

Rotor Stabilization

Balance rotor to stop high frequency vibration, which is the second cause of craft instability-vibration, by swapping blades and tugging the blade grips to either direction of the blades. This means that the rotor head is built without the rubber dampener washers. Here one craft requires tugging the grip toward the side of the hub with larger hole of the original retaining screw of the hub, and the gap is visibly larger than the other side of the hub.

Yet, another craft has no difference in stability either tugging the grips left or right. So, this tugging diagnoses the weight imbalance between the 2 blades. And the permanent fix is using Walmart item "Fiskars Premier 8" Straight Scissors" to trim the blade tip of the heavier blade. As little as a grain of rice's volume of plastic is enough up upset the balance. Such weigh difference is less than 1/30 of a gram and can not be detected accurately with common scales.
After all visual corrections of blades fix imbalances not visible to the eyes. When you hold the craft for hovering in attitude mode, it feels deliberate vibration on the fingers, and you hear the air beating sound. This subtle imbalance causes cyclic swinging motion makes it unflyable. Swap the 2 blades between the 2 grips. The margion of errors in the root hole positions can be corrected with margin of errors of the grips.

This build uses the spare screw of the main frame as a retainer on the larger hole on the side of the hub. The spare screw's pointy tip needs to be trimmed out to allow the thread more gripping area on the hole's wall. And one of the anti-rotation bracket's screw is used on the smaller hole. The anti-rotation bracket uses one of the landing skid's screws. Rotor imbalance is the first reason among the 3 equally significant sources of craft instability and vibration.

The third source of craft instability with low frequency twitches is blade pitch trapping . Fix it by inserting packaging tape slips in between linkage balls and sockets at the swashplate.


The acro+ mode PIDs that the attitude mode PIDs bases off has this characteristics video,

Servo PWM Signal

It is well known that servos accept PWM range 1ms to 2ms, or 1000us to 2000us. But, the consensus is that manufactures specify margin of error of 250us, while the signal differs less than 115us , typically below 50us, between CC3D and ESC when viewed in BLHeli configurator. So, it is safe to give servos PWM between 1000-250+115=865 and 2000+250-115=2135. In the following example, servo 2 happens to have PWM range 1ms to 2ms, purely by chance. 

The spline count of the servo arm is 15, the servo arm travels 90 degrees for 1010us. So, each spline change is equivalent of  270us PWM change. That means that when attempting to set the high PWM to larger than 2135us, you might as well dial the arm position up 1 spline and increase PWM on top of 2135-270=1865us, which will settle the high PWM in the safe zone. 

When dialing the spline position, there is no need to loosen the arm's fastener screw with the following servo saver mod. 


This servo modification, combined with the un-geared main rotor, give the craft crash resilience , as see in this video,
, which the craft is totally undamaged. Only the splines need to be dialed back. No repairing of rotor hub or any part. Not even a screw driver to re-tighten the hub is needed.
Should I use servo rods or servo signal PWM to adjust the leveling and centering of swash? 
The M1.4 servo rods has a pitch of 0.3mm, 0.15mm per half turn. PWM change needs to be bigger than 10us to reflect on servo arm. Also changing 10us PWM needs power recycling to take effect. sin(10us / (1000us/85degrees)) x 12mm = 0.178mm movement granularity. So, PWM is almost as good as mechanical thread turning. PWM adjustment should be used. 

The technique to level the swash plate is to put the craft on manual mode cyclic control and keep the transmitter off so that all servos are at neutral positions, then visually check the 90 degree angle between swash plate and the main shaft beneath the swash plate.

The technique to check the swash plate center is to hang the blades vertically, then grab and move the DFC links up and down in the craft's perspective. The scissoring action of the blades needs to be evened on the 2 direction of movement. In the following video, the swash plate is overly high because the far end blade is pitching up more than pitching down, which means that all 3 servo PWM center value needs to be lowered. 


Once the center values of servo PWM are adjusted to level the swash plate. The extreme ends of the PWM range are +- 500 of the center values.

Input s-bus PWM signal does not need calibration because it is calibrated in transmitter with stick calibration to ensure high precision.


Tail Build

The LHI 1306 motor and Amazon item HobbyMate 1306 motor, with Sea Jump 5030 props, and Gem Fan 5030 props, are all interchangeable. The fitting is quite tight and needs a 5mm drill bit to scrape the prop shaft hole's opening to allow CA glue to sip in freely. A tight fitting can mask a underlying improper glue bonding resulting in crash.
  
 
The scraping is performed with an angle, and so it mostly scrapes on the 2 open ends of the hole and does not alter the center balance positioning. In either case with LHI or HobbyMate motor, the shaft cut needs a 45 degree filing at the top of the shaft for smooth insertion of the prop.

Tail wires with ESC patch wires span 30cm. 25cm to span from tail to the main motor zip tie.


Substituting silicone wires with enameled wire saves 1.2 grams because 75 cm of enameled wires, weighing 0.5 grams, combined with 5cm silicone patch, weighs 2.1g x 5cm/30cm  + 0.5g = 0.9g .


The PVC insulated, low-voltage wires can also can save weight, but the low-voltage, 30V, wires are not available for retail from digikey.com and other vendors. Above picture has 60cm of it cut from a Picoblade 3-pin connector set.
After soldering and testing tail motor direction with CC3D output page, anchor the joins to the main motor's zip tie.


It has been tested and shown that, at the the bottom of the dives or whenever main rotor torque has rapid, sudden increases, the direct drive tail lapses while spinning up with finite acceleration. The high integral (60) gives overly large force to counter the lapse resulting in "collision with thin air" bounces at 0:57 , 1:16 , and 1:41 of the following video.


The solution is to lower the integral term.
The integral for rate mode is lowered to 8, the same value as the proportional term. And actually the attitude mode's yaw PIDs are derived from the rate mode PIDs but integral term doubled to 16 and the proportional term halved to 4

The low integral allows the craft's heading to deviate more than 90 degrees from zero torque to hovering torque and it is disorienting during takeoff. The reason for the attitude mode's doubled yaw integral as seen previously is to reduce disorienting the pilot during takeoff.

The last step in setting the tail motor is to stipulate the ESC PWM signal range to 0-1550us , instead of the default 0-2000us. This scaling up is needed to compensate the non-linear relationship between motor thrust and throttle and RPM. A large gyro gain at low thrust can induce oscillation while the same gain is not enough to counter the main rotor's torque at high main rotor throttle. The high end 1550us-1615us is chosen because the CC3D and ESC has PWM discrepancy below 115us, typically below 50us,  and ESCs only accept PWM high end above 1500us during configuration. The margin of error of 115us is used through out the entire build note.

Main Frame Modification

The main frame is modified to hold the battery at the lower position to allow FPV camera installation. At the same time, it trims and carves 4.5 grams out from the Blade 230s V2 frame and 0.9 grams out of the BSR frame.

In this example, the frame starts out at 26.1 grams. Rotary wheel cutting front protrusion for both BSR and 230 V2 frame saves 0.4 grames. And carving side walls on the 230 V2 saves another 0.5 grams. Carving uses the 1/16 cutter through out the entire build because it has smaller contact area with the material and needs smaller force and thus more precise work. Also highlighted in the picture is the subtle bump of the wall stud of the servo concave. It needs to be identified and pencil marked to be avoided when installing fixtures for electronics or further carving.


Cutting the corner curve requires a small diameter of the cutting disk. For BSR, the vent window for the receiver plug is slightly higher than 230 V2's. Carve out a dent on the lower edge to allow easy access.



Cutting out rear pedestal on 230 V2 saves 0.5 grams.

Cutting the thick rear corner needs the middle speed setting on the Hypertough rotary tool with a cutting disc, which often splatters hot plastic lava. To ease the work, the middle speed should be only used half way from the reat on the sides, and use middle lower speed to just score the rest of the cut, and then use pliers to tear the the plastic, as the following picture,
 

Cutting the enforcement extension plate of electronic bay on the 230 V2 needs the cutter disk axis to be mounted with spacing as the above picture to allow a clearance between the bay and the rotary tool chuck nut. And the cutting needs the axis sinking into the hollow part of the electronics bay plate.

Cutting out side enforcement and electronics plate extension saves another 0.6 grams.

Cutting out front lateral stubs on both BSR and 230 V2 saves 0.3 grams.

Carving the shaft cage sides saves another 0.7 grams. The carving avoids wall studs along the pencil marking before carving. Residual pencil lead is shown in the following picture.

But, first the studs for the original canopy peg needs to be drilled out with a 5mm drill bit. It can be done manually without electrical drill with a chuck holder as in the following picture.




Carving the shaft cage front needs a small diameter cutting disk as in the above picture. The small diameter is obtained after a disk is worn out or trimmed.

Cutting the middle panel and shaft cage front saves another 0.7 grams.

Cutting the bottom panel extensions saves another 0.3 grams.

Cutting the front servo mount extension and rear servo cage enforcement double saves another 0.3 grams.

Cutting out the lips of the lower main shaft holder and final cleaning saves another 0.2 grams, including caving a dent on the vent window of BSR, for both BSR and 230 V2,



Battery Pack Build

The cells are cleaned to the bear foil wrap, which takes out quite a few grams.



The ground wire leads are cut to the middle point of the lateral width of the cells. The lead positive wires are cut to extend to the top side and at the same middle point. The first piece of tape binds the cells at the far side from wire leads before soldering jobs start. The soldering point at the bottom ground lead needs to be as close to the center as possible, otherwise the junction between the hardened solder and the soft wire will be bent with a sharp right angle and breaks quickly shortening the pack's life span. After soldering, tape the cells longitudinally top and bottom first, then make the lateral binding on the near side with the lead wires. Then apply the 7cm Velcro on top of the lateral binding tape. The lateral binding tape is cornered and anchored right at the edge of Velcro so that it doesn't come loose as easily as the longitudinal binding tape. The tape used is Walmart item "PEN+GEAR Transparent Tape 0.75 IN x 1300 IN", which is lighter than Scotch's tape.


The 53.1 gram cells build up to be 56.4 grams; the 50.8 gram cells build up to be 54.1 grams.


The 50.8 gram cells are from Amazon item "sea jump 6pcs 3.7v 800mAh 25c Upgrade Lipo Battery with JST Plug + 1pcs 6in1 Charger for MJX X400 X400W X800 X300C Sky Viper S670 V950hd V950str HS200" , but its actual capacity is close to 600mAh when discharged to 10.74V in the following picture. The Tattu 800mAh's capacity is close to 800mAh when discharged to similar level in previous video's description.

The 600mAh Tattu cells is a substitute using 4S with 300KV motors.

The 3/4 inch velcro used on the battery itself is 7 cm long, 6 cm on the battery plate, and 5 cm on the landing skid beam, totally 18 cm.


Custom Servo Brackets


The custom bracket rods are cut from unused landing skid round bars. The upper rod has 2 holes to attach to the craft,  spaced 5mm for both the 230 and BSR frames. Before any drilling, the bumps along the seam lines need to be smoothed as the following picture.

Substitution for the rods is the 4mm square plastic rods from Amazon itemPlastruct MS-160 Square Rod.



Also in the first picture, the upper rod is cornered to the anti-rotation base of the Blade 230 frame. For the Blade BSR frame, there is no anchoring corners, and the location of the holes on the anti-rotation bracket is 12mm from the front wall of the bracket. This distance is chosen so that the original servo cage becomes stoppers so that the servos can not be pressed and twisted into the cage. Coincidentally, this distance is chosen so that both BSR and 230 builds have congruent servo geometry. The following 2 pictures show this arrangement. The first picture also shows the bracket marked at the based of the servo tab.


. The ruler in the above picture of the BSR frame shows 10 mm from the wall to the said mark with servo tab. The holes on the bracket rod are drilled at the center of the 4mm diameter/width rod. So the distance from the wall to the holes is 10mm+2mm = 12mm.  This is because the BSR servo cage's upper wall has the 4mm thickness while the lower wall has 1.2mm thickness that is the width of the original servo fastener hole's diameter. 4mm/2 - 1.2mm/2 = 1.4mm extra space. 12mm+1.4mm=13.4mm . For the BSR frame the holes on the anti-rotation bracket are actually half-moon dents of 1.25 mm depth because the screw we use is 1.5mm in diameter, and the bracket's width is 6mm. So, the center of the 2 half moons are 0.5mm from the bracket's side edges. 0.5mm+(1.5mm/2)=0.5mm+0.75mm=1.25mm .

The screw driver to install and service the upper custom rod needs to be inserted from the bottom of the craft through the middle plate. So, a conduit is drilled on the middle plate beneath the custom rod.



Use the Wiha Philips #1 screwdriver for this job, or another driver with 3.5 inch shaft or longer.

The conduit to allow the long screw driver is about 5mm in diameter as seen in the first picture row of this chapter. In the second picture below, the same pre-treatment of smoothing the seam line bump is shown. The drill bit for the holes on the craft is 1.3mm as seen in below picture, and the drilling does not need tool, instead there is room to use finger to pinch and twist the drill bit,

.

The servo cage geometry of the 230 frame is congruent to the servo cage geometry of the BSR frame. And the mentioned 13.4mm distance of the BSR frame is equivalent to having 14.6mm on the 230 frame from the wall to the fastener holes. This distance has 14.6-13.4=1.2mm increase because the new 230 frame moves the wall forward 1.2mm, which is the diameter of the servo fastener hole's diameter. In the 230 frame, the wall is aligned tangent to the original servo fastener hole while the BSR frame's wall is aligned to the center of the original fastener hole. The 14.6mm, or 14mm from axis to hole, distance coincides with the distance from wall to the cornered upper rod's fastening holes.

For verification of the BSR-230-servo-geometry-congruent theory, the 14mm distance is indeed 13.4mm+0.6mm=14mm, the distance from the BSR frame's lower rod hole to servo hole axis. And the 14mm distance is indeed the same distance from the BSR frame's upper rod hole to the servo hole axis, 12mm+1.4mm+0.6mm=14mm.

Before final assembly, add 3 m1.6 0.3mm thickness washers to each side of the bottom fastener for the Blade 230 main frame. This is because the 230 main frame's servo cage is raised 1 mm on the top wall. Alternatively, file the upper rod 1mm along the contact surface with the wall. Use the same Phillips #1 screw driver to fasten the bottom custom rod from the underneath the craft. 2 washers should be used on the bottom side with installing the lower rod on the BSR frame because BSR frame's plastic material is softer than that of 230 frame.




The final assembly uses one of the landing skid's fastener screw as the stopper to prevent the servo from being twisted and depressed into the servo cage. 


The replacement ABS styrene rod weighs the same, 0.3 grams, as the rod cut from landing skid. The holes on the custom rod for servo fastener screws are drilled with a 1.2mm bit in the following picture.

The servo's original screws are not used. The servos are fastened without washers to allow self-centering by the screws. The tab at the lower mount is a scrap from trimming the main frame's front landing skid area. 

Summary of the torques used in the build.



Mounting Radio Receiver For Reduced Interference

The spacing between main motor and the receiver is as the following pictures.



The rear half of the antenna of R9M Mini receiver is bent to the side perpendicular to the first half to create receiving diversity.

For the FrSky XM Plus receiver with a repairing replacement antenna, the replacement is about 1 inch longer and it coils around the boom stick for 1 turn. The 2 antennas are encased by the mounting tape square.




The last photo shows the original antennas without coiling around the boom.


. Without proper spacing between main motor and radio receiver, the interference can disconnect the radio locking with Flysky XM+ when the craft is well within the expected range, such as in this video, happened when the receiver was mounted on the rear pedestal of the main frame, 
.  

The spacing is sufficient with the wire that comes with the CC3D. If the receiver is further extended to the rear, the receiver is struck and destroyed by tail strike in a crash, as occurred multiple times on the 2 tail booms pictured here,

, and the 3rd case,

. In the last picture of the 3rd case, the tail strike also detached the receiver's antenna but no damages, which means that the mounting tape should be placed as far as the last picture's, at 85mm or less from the front end of the boom.



Mounting Cameras

For the Goqotomo camera, the mounting holes are spaced 6mm from the hollowed front plate of the frame. Then use gardening wire through the holes to tie down the camera. For the Caddx HD camera, either version 1 or version 2 comes with the same accessory pack, with a vertical mount.






The maximum mounting holes spacing is 15mm from axis to axis. The holes on the main frame are placed on the original location of stud that has been carved out. Drill the holes to maximum spacing so that the bracket's tension reinforces the main frame.



It is required to temporarily hold the bracket in place when installing the fasteners with one hand on the screw driver and another holding the bolt with long nose pliers.It is required to drill the bolt holes to 1.8mm, no larger, for the bolts to stay in place when installing the bracket with one hand on the screw driver and another holding the bolt with long nose pliers.  The last step before actually fastening the camera on the bracket is to shorten the 2 side hex screws because they are longer than the thickness of the bracket and the depth of the tapped holes on the camera combined. Shorten it by 1 to 2mm.

Camera System Setup

The front hole is placed at the front edge of original main gear cage. Use a pointy tool to punch the axis for precision drill. Use the 1.9mm drill bit to drill the hole for the m2 screws. The m1.6 washers' hole needs to be enlarged also with the 1.9mm drill bit. 4 washers needed, 2 on each side of the main frame wall.


The fixture arm is cut from the tail fin's upper part. The tieing hole on the main frame is drilled with 1/16 inch Dremel carving bit. Finger screw driver with very thin shaft for Philips #1 is needed to fasten the screws at a small tilt. Pictured here is Walmart Hyper Tough Precision Screw Driver. The washers act as lubricant so that the bolt is not seized after tightening and securing the nut to position. A second nut on top of the module board can then be tightened when the driver continues to turn the bolt after the first nut is secured. The m2 washers are not used because the m2's hole is larger than m2 bolt's diameter and allows the first nut to seize before the second nut is lowered. The fixture arm also use 2 nuts to secure, but the fixture arm does not need washers because the carbon fiber is hard enough by itself as opposed to the soft wall plastic material.

The washers act act lubricant so that the bolts don't seize when installing the outer nut.

Do not drill holes on the other side of the main frame wall for screw driver shaft to go through because that will weaken the structure and damage the camera wire connectors during crash.  Experiment shows a complete break off of the upper main frame when the left side wall is weakened with the extra conduit for screw driver.

Use gardening wire, stripped of plastic wrap, to tie the fixture arm. The tieing is similar with Caddx Turtle V1 and V2, but the rear hole on the arm is 2.5mm recessed with V2 because the board mounting hole is forwarded with V2. 

The last step before plugging in the camera wire plug to the socket is to chip away the lower left corner of the plug using a wire cutter. The corner gets in the way of the fastener as seen in above picture.

The FPV transmitter is attached with a 5mm width Velcro strip, and the camera taps its power on the transmitter's 5V output or directly on the battery as seen in previous post https://nocomputerbutphone.blogspot.com/2018/08/converged-drone-at-edge-of-space.html . FPV feed has slightly more interference when tapping the 5V directly on the buck converter's output, though not as bad as tapping the battery. The transmitter taps its power on the buck converter output with the Picoblade connector socket.

Before the first flight with the camera, adjust the HD camera focus by twisting and loosening the lens retaining ring with finger. No tools needed. Then turn the lens wile monitoring the video feed on FPV goggles.


Tie the fixture onto BSR frame needs first making the gardening wire into a 135 degree hook, then insert and lay the wire on the anti-rotation column to thread the hook.


A pencil marks the stud location of the servo concave curve. The pencil also marks around the right face of main shaft cage. And the front tie hole is drilled right in front of the pencil mark after the rear tie is installed.

Substitute Cards Turtle with Runcam Split 3 nano saves 3.7 grams.
The board hardware dimensions are the same. The nylon standoffs can only tolerate twisting with fingernails. Using tools on the nylon standoffs strips the threads. Nylon nuts are used as spacers for the camera. Long bolts needs to be trimmed for the camera mounting on the common 15mm bracket.

Canted Tail Rotor Solving High Throttle Pullback 

The helicopter's tail rotor is not centered up on the rotation plane of the main rotor. It creates a small right-roll torque the craft, and the gyroscopic precession makes the craft tilt backward and fly backward. The parasistic torque increase as the throttle increases. The result is craft fly-away when high throttle is used without other corrective measures. The actual fly-away video footage shows craft flying over roads, people, which is illegal. It is only resolved when throttle is lowered. In a high-wind day, the throttle may need to be kept high through out the flight, and that causes the fly-away.

The solution is the canted tail rotor , same as the Seahawk helicopter's design,

.

The pullback problem can be discovered in rate mode flight 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.

The fix can be verified line-of-sight,

, and the maximum throttle punch-up at 0:30-0:33 happens rather uneventfully, straight up.

Tail Repairing/Replacement

The replacement e-clip is from Amazon Prime Traxxas E-clip 1.5mm . The replacement is silver white, versus black of the original LHI motor's e-clip. The tool needed to install the e-clip is a pair of regular long-nose pliers. However, the pliers need to be removed of magnetization so that the pliers don't pull off the clip before it is clamped on. That can be done with Walmart Hyper Tough Magnetizer/Demagnetizer , or by heating the tip of the pliers, soaked with solder, with soldering iron for 3+ minutes continuously. The residual magnetism does not need to be 100% removed, it just needs to been weakened to less than the shaft's own magnetism and excess lubricant motor oil's capillary force combined. The shaft's own magnetism is inducted from the motor's own magnets. The pliers' residual magnetism is accumulated when the pliers in a tool beam stays in contact, for a prolonged period, with screw drivers that do need a magnet attached to work with small screws. 
  

The original Lynx Blade 230 tail boom has length 255 mm. The replacement 8x7x500mm carbon fiber tube from ebay xzw791 can produce 2 250mm booms each. The weight of the replacement is expected to be 4.8g x 250mm / 255mm = 4.7 grams. But the actual weighing has 17.6g / 4 = 4.4 grams. So, the replacement has 0.4 grams weight reduction.

 

Raspberry Pi Wiring



No comments:

Post a Comment