Saturday, September 1, 2018

Converged IoT Platform Build Notes

Alternative parts are not discussed in this general build note. Alternative buildings are discussed in specific topic posts.

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 with a wrench socket spacing beneath the motor bell until the shaft is flush to the motor's top plane. 3/8 inch wrench socket with the 2808 motor; 1/2 inch wrench socket with the 4004 motor. Then, CA glue a 3mm stainless steel rod as a pusher on the motor shaft. The 3mm diameter rod is cut to 7mm, pictured on the right, slightly longer than the shaft's depth in the motor bell. The shaft end surface is not always smooth and perpendicular to the shaft because the production of the shaft uses a saw to cut off the product. Adjust the glue to align the rod as straight as possible. In the following 3 pictures below, the push rod in the first picture needs straightening. The second picture is a good straight example. 

To fully remove the original shaft, clamp the shaft down the second time with the prepared push rod assembly, as shown in the 3rd picture. 

Trimming either 4004 motor or 2808 motor's stater base needs first preserving the outer ring as a guard against accidental rotary tool slips. In all cases, any rotary tool cuts are pre-cuts that don't go through the plate. The 2808 motor needs a combination of drills and pre-cuts while the 4004 motor needs only the pre-cuts. Then, 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. Trimming the 2808 motor stater saves 33.2 minus 30.6 equals 2.6 grams. Trimming the 4004 motor stater saves 36.1-34.8=1.3 gram as seen in pictures below of the 4004-300kv.

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 as pictured on the right for the triple-junction soldering jobs. Solder the short wires to the inner side of the main ESC's battery terminals. It is OK for the short wire leads to touch the capacitor between the 2 electrical poles because the capacitor is electrically connected to the 2 poles. To save about 1 gram of weight, tail ESC build needs desoldering the original thick motor wires and replacing them with 4cm of tail motor's lead wires. The soldering iron temperature for ESC working is 350 degrees. Any lower temperature lengthens contacting time. The newer BLHeli_S or BLHeli_32 with protruding motor solder pads, as seen in the crossed out picture on the right , can not substitute the original BLHeli because the newer ESCs of any model have no RPM governor.

After soldering, the ESCs need to be tied, naked, with a Kevlar string, to the fuselage for extra cooling.  The two ESCs sandwich the landing skid base as pictured above on the right. Without this extra cooling, ESCs overheat in summer as shown in the video on the right.

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. For weight accounting, 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, from cutting tail ESC battery wires, join XT30 connectors and the power distribution point, so that power distribution point doesn't need re-pre-tinning. This weight saving cancels out the weight of the added pre-tin solder at the beginning of this dual ESC build.
The XT30 connector needs to have a half cut in between the poles for Kevlar string to tie it to the main frame.
The 1.25mm connector that comes with buck converter has current rating of 1A, sufficient with power tapping by servos and RF receivers, plus the full HD camera system (either Raspberry Pi or Caddx Turtle consumes less than 0.5A) or the 0.8A max current to a video transmitter.  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 output of the buck converter, which powers 3 servos, a 70mA flight computer 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 flight computer consuming 70mA and receiver consuming 30mA, 70+30+15*3=145. During hard maneuvering, the reading is slightly higher than 250mA. So the math is 0.15Amp + 0.8Amp = 0.95Amp. 
When HGLRC FD411 flight computer is used, it taps power directly on the battery terminal on the tail ESC, and RF receiver and flight computer don't consume current from the DC buck converter, which further reduces Picoblade connector's workload. 

Flight Computer Setup

To wire up the flight computer, use the following diagrams.     
This general layout and orientation is applicable to multiple brands and alternative products because the manufacturers generally use the same orientation of quadcopter components, namely the ARM chip on top for better cooling away from one-piece quadcopter bottom plate and motor signal wires face forward in line with intuition and away from bottom plate to avoid short circuiting. 

The fixture wholes allow 4 1A(AWG 26) wires thru. And the bottom side of the FD411 has the soldering scheme when flipped.

The 3-pin PicoBlade wire set is spliced for the RF receiver and for powering and signaling Raspberry Pi or for video OSD. 

With all options of the flight computer, the original M1-M4 signal socket faces rearward and signal wires points out and rearward for easy soldering jobs, and so that the array of pins provides an even mounting surface.
The front and rear of the board needs 3 layers of clear mounting tape on the bottom. The rear needs 1 extra layer on the signal pin array as clearance to prevent the pins touching the electronics bay floor, as picutered on the right. Mounting needs temporary foam tapes as a jig to align the board in the electronics bay, as shown below on the right. The mounting backing films are only removed after the board is placed firmly in position with the jig. 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.

Rotor Setup

The main frame kit comes with 2 different sizes of screw sets, Philips #1 and #0. If you receive the Philips #1 hardware, the screw driver needed to fasten main shaft cage is a 2mm slot driver, in stead of the official Philips #1 because Philips #1 screw drivers with 1/8 inch shaft to go into the small boar holes is very rare in the market. The screws go in from the left side of the craft(by the craft's first person perspective) 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 because the frame design tries to avoid the front servo's upper tab, which are on the left side of the craft, blocking the fastening job on the left.

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 v950's pre-drill hole is 9mm from the end, the hub's retainer hole is 1.6mm in diameter, 7mm from the top, so the excess 2mm of the shaft needs to be trimmed, and the holes on the hub needs to be stretch enlarged with the 2x10mm bolt first to ensure the centering of the hole. Then use a 2.0mm drill bit to scrape off the excess material from the hole's inner wall
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.
The video on the right shows the F411 startup servo twitch that travels down to only a few milometers above the base. This problem is unique to F411 software. It can not be fixed with latest version 4.2.11. Compared to alternative hardware, the software version 4.2.0 through out 4.2.5, don't have the twitch in the other hardware.
The generic zip ties of 3mm width, such as the DWF branded product, can not replace the HyperTough 3mm wide zip tie even though they have the same tensile strength rating of 18 lb. The generic zip tie simply breaks with a jerk of torque after the rotor spool-up and collective pitch suddenly change from negative to zero to positive, and the tail motor takes on countering the motor torque, all happening within a split of a second.

Tail Build

We need 2 nylon washers as spacers to give room to the protrusion of the motor shaft. As shown in the picture here, the space is tight between the shaft and the tail fin board. It is OK to mill a slight concave of the fin plate at the tight spot, but we shouldn't drill a hole through because that would weaken the fin structure.
Depending on the bolt length and fin plate thickness, we can use another 2 nylon washers to cushion between the brittle acrylic and the hard M2 screws' head, and also to stop the bolting from crushing the stater winding. The motor's 2400-2750 kv range requires Y termination of the motor stater wiring, so there should be a solder stub as circled out green in the picture.

Check for mislabeled sales of the 2400-2750kv motors especially those motors without color coding/differenciation. If the mentioned stub is missing, the motor has higher kv in delta termination and mislabeled. When mislabeled motor in combination with misconfigured Low RPM Power Protection in BLHeli Configurator in combination with high wind, tail lapse occurs as shonn in video on the right.

The diagram above of the fin has the coordinates of the corners, such as  (3.4 , 8) and (17 , 11.6), unit mm. It is to the scale when printed out with 60 pixels/cm. The tight corner in the middle is hard to cut with a rotary disk, and it will be easier if following the arrow in the diagram of cutting sequence to make 2 cuts meet in the middle. Use rotary 1mm drill to make 2 adjacent holes on the 4 corners of the attachment square for the zip ties, then break the 2 holes to form a oblong whole. Use CA glue sipping between the fin and the carbon tube. Pinion gear is meant to be a fitting spacer and has a very tight fit on the motor shaft, so you need to place the gear on a surface then press onto the motor shaft. CA glue is applied to prop's lip before attaching it to the motor bell. 

Over tightening the tail motor bolts and/or the fin zip tie pre-load the fin with stress, resulting in premature break of the fin , as shown in the picture. The PVC insulated, low-voltage wires is not used because the low-voltage, 30V, light wires are not available for retail from and other vendors. Above picture has 60cm of it cut from a Picoblade 3-pin connector set. It is the lightest in the market but still weighs 0.88 grams extra for 111cm. 0.8x(111/60) - 0.6 = 0.88.
HGLRC 1106 kv2400, HGLRC Aeolus 1303.5 kv2400, and Happymodel EX1404 kv2750 are all interchangeable. The video on the right is with Aeolus 1303.5 kv2400.

Mounting Radio Receiver For Reduced Interference

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, resulting in "Failsafe Mode free fall", when the receiver was mounted on the rear pedestal of the main frame. The spacing is sufficient about 3 inches behind the pedestal. 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.

The 2 antennas of MX+ are encased by the mounting tape square.

The spacing between main motor and the receiver is as the following pictures.
The closeup of the mounting and the option of TBS Crossfire Nano receiver follow.

Custom Servo Bracket

The alternatives of using larger servos would add 7 grams. The option used in this part is blade 230's landing skid set for struts, which have the same diameter as the Plastruct MS-160 Square Rod.

To create rigidity of servo control, the rear side of the servos are aligned to the axis of the rear fixture hole as pictured above so that the servos can not be twisted and depressed into the servo cage by the screw standoff stopper. In the diagram above, the curious number 1.25mm of he fixture 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 custom bracket at the front lower mount is a scrap from trimming the main frame's lower front protrusion. Use CA glue and double layer wall to reinforce the thread.

To compare the rear servo geometries, as shown on the picture on the right, the servo fixture system is forwarded on the 230 by 1.2mm. So, the 230's servo setup has a slightly more vertical servo rod toward swash. This can not be improved because we need to prevent servo from caving into the servo cage with BSR frame, so we can't move the rear left servo forward 1.2mm in relation to the cage geometry.

When the servo is positioned as so to prevent caving into servo cage, the servo tab is 10mm behind the BSR frame's servo cage's upper front wall surface as measured in the pictures below. The placement of the 1.25mm half holes are 10mm+2mm=12mm behind the upper front wall surface because the struts have a 4mm diameter, 2mm radius. The counter part of the 1.25mm half holes on the bottom plate is 12mm+1.4mm=13.4mm behind the lower front wall surface as indicated in the picture below. The 1.4mm shift is due to the thickness of 4mm of the upper wall. The fixture hole diameter is 1.2mm. The extra thickness from the edge of the fixture hole to the wall's surface is (4mm-1.2mm)/2=1.4mm . The lower Wall's thickness is the same as the fixture hole diameter. The lower wall's surface is tangent to the fixture hole's edge and hence no extra thickness.

The servo fixture holes geometry, namely the width/height/depth, of the 230 frame is congruent to that 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's inner surface is tangent to the hole; in the BSR frame, the wall is aligned to the hole. The 14.6mm distance coincides with pressing the upper bracket rod on the rear of the antirotation bracket base, as pictured below on the right. In either case of BSR or 230, the axis-to-axis distance between original fixture hole and the hole for custom struts is 14mm. The math is 13.4+0.6=14=14.6-0.6 . 
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.

Wiha Philips #1 screwdriver or another driver with 3.5 inch shaft or longer is used to penetrate the conduit. The conduit to allow the long screw driver is about 5mm in diameter. Before any drilling, pre-treatment to smooth the injection seam line bump is needed to prevent slip. 

The drill bit for the holes on the craft is 1.4mm as seen in picture below on the right, and the drilling can be done using a chuck to pinch and twist the drill bit.

The boreholes on the bracket rods themselves should also be 1.4mm to prevent material warping with high pressure. The struts should be drilled from both end surfaces progressively to the center in the material. Drilling from one surface through often results in mis-aligned servos, which are hard to gauge the play. Before final assembly, the screws need to be filed of their protrusion because the  splinters of the lower bracket prevents a snug fitting of servos. For the Blade 230 main frame, file and carve the upper strut 1mm along the contact surface with the cage roof wall. However, the upper strut for the BSR frame should not be cut to prevent warping. Instead, for BSR frame, the anti-rotation bracket's groove needs to be carved, and the bracket sit on the flat surface of the anti-rotation bracket as shown in the picture below on the left. This is because Blade 230's servo cage ceiling is 1mm higher than BSR frame's. The final assembly uses the same Phillips #1 screw driver to fasten the bottom custom rod from underneath the craft. Then use M1.7 screw, or the landing skid's fastener screw, as the stopper to prevent the servo from sinking into the servo cage. The servos are fastened without washers to allow self-centering by the tapered screw heads. The M1.5 fasteners on the servo tabs need to be tightened evenly and progressively, checking the play in the process by shifting the servos up and down and probing for a snug fit.

The alternative nylon landing skid rods weighs exactly the same as ABS struts, which should not be a surprise because the density of ABS is known to be lighter than nylon, and the nylon part is smaller, more compact in volume. 
When building the frame, do not omit any screw, as omitted screws creates weak spots during a crash, as pictured blow on the left. The crash would not have been a total loss of the frame if not for the omitted screws that allowed the middle plate to break. Also in the picture, the frame is Blade 230s V2 frame. This frame's vent window for the USB port is about 1-2mm lower than the BSR frame's. This requires trimming of the vent window, which is also shown in the picture.


Servo Clutch Setup

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

The ball head screws are M1.6 threaded and needs 1.6mm drill bids to enlarge the servo arm's last hole. 
Summary of the torques used in the build.

Camera Mount

Drill 3 holes flush and parallel to the ceiling of the front battery bay through the ceiling stud using a 1.5mm drill bid.
The 2 holes on the right side of the craft (from the craft's perspective) should be closer to each other, shifting the middle hole from the center by about 5mm to avoid drilling beneath the seamline that would weaken the fuselage's strength. Then the zip ties need their corresponding holes through the ceiling to thread through as pictured above on the right. 

Battery Mount

The top mounting velcro loop strip is split into two, and the thin strip (about 2-3mm) goes between the narrow gap between the closely placed zip ties. The split loop strips then wrap around the ceiling plate down into the battery bay, and the excess head and tail bond to each other rearward at the ceiling opening.
On the bottom bar, the loop strip also warps around and joins rearward. Then the hook strips fasten onto the loop strips. The battery pack has loop strips and is "grabbed" with the hook strips from the craft.

Raspberry Pi Camera Setup

Frame Option Trimming

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 thick rear corner needs the middle-speed setting on the rotary tool with a cutting disc, which often splatters hot plastic lava.

To ease the work, the middle speed should be only used halfway from the rear on the sides, and use middle lower speed to just score the rest of the cut, and then use pliers to tear the plastic, as in the following picture.   
Cutting out the rear pedestal on 230 V2 saves 0.5 grams.

Cutting the enforcement extension plate needs the cutter disk axis to be mounted with spacing as in the picture here to allow clearance between the bay and the rotary tool chuck nut. 

The cutting needs the rotary tool shaft 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 the front lateral studs on both BSR and 230 V2, saving 0.3 grams, for installing thicker battery packs is a mistake because thinner battery cells are available even for capacities higher than 900mAh. Reinforcing the seamline with bots and plates would add more weight than the original stud and screw weight.

Carving the shaft cage sides saves another 0.7 grams. The carving avoids wall studs along the pencil marking before carving. The residual pencil lead is shown in the following picture. But, first, the studs for the original canopy peg need to be drilled out with a 5mm drill bit.

 It can be done manually without an 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,

The final weighing after all trimming is 21.6g as shown on the weight breakdown page.
The bottom plate has a sharp join that is often the very first fracture the build encounters with a crash. The sharp join can be smoothed with the rotary sanding drum as the lower example. But such modification doesn't improve the crash characteristics. The broken joint is repaired with a scrap patch from carving the main frame.

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