Converged IoT Platform Build Notes

Alternative parts are not discussed in this general build note. Alternative buildings are discussed in specific topic chapter posts. The parts listing is in https://nocomputerbutphone.blogspot.com/2017/12/converged-drone-developers-platform.html . Here below is the listing of tools to build it.

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 with the motor's top plane. Use a 1/2-inch wrench socket with the 4004 motors. Then, CA-glue a #6 flat-head 1/2 inch machine screw as a pusher on the clamp. Clamp the shaft down the second time with the push rod assembly, as shown in the picture, to remove the stock shaft of the motor. The main shaft is not pressure-fit to the motor but slightly thinner than the original motor shaft. The video here shows that the short bell shaft hole amplifies the thinned diameter, resulting in wobbling.

The solution is to use a Kevlar thread (dental floss) as an insert. But the Kevlar material can be cut by the sharp edges of the bell shaft hole and the shaft itself. So, the rim of the shaft needs very subtle, delicate scraping, and the shaft's end needs a 45-degree grinding. 

The last picture above on the right shows 3/4 of Kevlar strands being cut without  proper finishing of work surfaces. The kevlar string should be tied to form a loose loop that avoids the sharp edges of the set screw of the motor bell, as pictured on the right. Pull the loop after the main shaft is inserted into the motor stator, and you can verify that the thread is unbroken. You can feel the consistent, intense friction when the main shaft is driven into the motor bell from the craft top with your thumb and middle fingers. I have tested using a twisting motion of less than 45 degrees while driving the shaft into and out of the bell and verified that the insert is unbroken after uninstalling the motor and removing the shaft.

For the 5-V power supply, the 1.25mm-pitch connector that comes with the buck converter has a current rating of 1A, sufficient with power tapping by servos plus a Full HD camera system (either Raspberry Pi or Caddx Turtle consumes less than 0.38A) and analog camera with its video transmission (0.5A max current). 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 30mA RF receiver.

When the servos are idle, the specification says each servo consumes 15mA, and indeed, the current reading is 145mA with the flight computer consuming 70mA and receiver consuming 30mA, 70+30+15*3=145. During bursts of heavy loading of servos, the reading is slightly higher than 250mA, an average of 220mA. The production flight computer and RF receivers do not use the 5-V power supply. So the unlikely maximum current usage is 220mA - 30mA - 70mA + 380mA + 500mA = 1A. 

When the HGLRC FD411 flight computer is used, it taps power directly on the battery terminal on the tail ESC, and the RF receiver and flight computer don't consume current from the DC buck converter.

To start the dual ESC build, remove original wraps using 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.

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. 

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 XT30 connector needs a half cut in between the poles for Kevlar string to tie it to the main frame, as pictured on the right.

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 choices of the flight computers, the original M1-M4 signal socket faces rearward in our craft, and signal wires point out and rearward for accessible soldering jobs. The array of pins provides an even mounting surface and is flush to the edge of the electronic bay floor. The clear mounting tapes are 12x7mm, with 4 pieces on the front and 1 piece on the array of pins. The 7mm-wide USB socket protrusion will be our guide to fit the flight computer into a temporary soft jig. The soft jig is made with foam mounting squares, as pictured below. Also, in the inside picture of the jig, you can see that the electronic bay floor has only a 2mm strip overlapping on the front of the flight computer board. So, the 4 pieces of clear mounting tapes need to be staggered with 1mm protrusion per layer.

However, the vent window needs to have the USB socket carved out. When you look at the jig from the outside, the oblong carving overlaps our soft jig by 1.5mm to tolerate errors during mounting. And the diameter of the oblong carving is 7+1.5*2=10mm. The carving uses a 1/16 or 1.5mm inch milling bit with our rotor tool. And the carving will destroy our soft jig.

Once the oblong hole is carved and the soft jig destroyed, set up the jig the second time with 3 layers of foam on the opposite side of the USB socket to finally install the flight computer.

Rotor Setup

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 on the left side of the craft, blocking the fastening job on the left. The 4004 has a 2.8mm shaft protrusion on the bottom when cyclic control servo arms stretch horizontally as in their neutral position. In the picture on the right, the motor's stator has been trimmed to clarify the view, and the general build should not trim the stator for weight saving. 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 the excess material from the hole's inner wall.
In the upper right corner of the picture above, you can see that the gap for the anti-rotation zip-tie to thread through is very narrow. So, the zip tie must be pre-bent and pre-twisted, as pictured on the right, to fit the narrow gap. 

The main frame kit comes with 2 different sizes of screw sets, Philips #1 and #0. If you receive the Philips #1 hardware, the screwdriver needed to fasten the main shaft cage is a 2mm slot driver instead of the official Philips #1 because Philips #1 screwdrivers with 1/8 inch shaft to go into the small bore holes is very rare in the market.  

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 need trimming out 2mm with the rotary cutting wheel. Once trimmed, the DFC link and the ball socket join tightly, giving a uniform length. Before installing the DFC swash control rods, the original Blade 180CFX hub has 2 swash-driving arms that must be removed to make way for DFC links.

 

The video on the right shows the F411 startup throttle reset to the lowest level, and servos travel down about 4.2mm=12mm*sin(83.0/4) to only a few millimeters above the base. This problem is unique to F411 software. It can not be fixed with the latest version, 4.2.11. Compared to alternative hardware, the software version 4.2.0 through 4.2.5 don't have the twitch in the other hardware. For this reason, our build uses Microheli Blade 130x's shaft collar that is thin enough to avoid colliding with the swash. 

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 nominal tensile strength 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. The higher kv doesn't improve handling of tail lapse, as shown 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 digikey.com 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.

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 vertical servo setup is the shared knowledge and industry trend for rigidity of servo control. However, the typical trend frame is overweight, as shown in the pictures below, where the 180-sized main frame is over 27 grams, approaching 30 grams. 

The 230s frame's front servo is already vertical, so, the front servo's lower tab is CA glued to the fuselage's corner without any fastener. For the rear servo, we align the rear side of the servos to the axis of the rear fixture hole, as pictured below on the left, so that the servos can not be twisted and depressed into the servo cage by the screw standoff stopper. The upper strut, coincidentally, needs to be placed onto the corner of the anti-rotation bracket base, as pictured below on the right. For the rear servos, we have 2 options to make the custom bracket; below on the right, blade 230's landing skid set is used for struts, which have the same diameter as the Plastruct MS-160 Square Rod.

The screwdriver 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. 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 nylon landing skid rod option 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 USB port. This requires trimming of the vent window, which is also shown in the picture.

Servo Torque Clutch Setup

To make the servo arms resilient to crash, cut the spline and partially split the arm to make a torque clutch. That way, whenever the impact force is larger than the gears can handle, the clutch slips, relieving the gears from damaging forces. When dialing the spline position, loosening the arm's fastener screw is unnecessary with such a servo clutch modification. 

The ball head screws are M1.8 threaded and needs 1.6mm drill bits 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 bit.

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 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 the 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, 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 carving should reserve 2-3mm edges from the straight stud walls. 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 pictured below.

Carving the shaft cage front needs a small diameter cutting disk, as in the following picture. The small diameter is obtained after a disk is worn out or trimmed. Carving the middle panel and shaft cage front saves another 0.7 grams.

Cutting the bottom panel extensions saves another 0.3 grams. 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. However, such an extra step doesn't improve the crash-breaking characteristics. The broken joint is repaired with a scrap patch from carving the main frame.

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

Cutting out the lips of the lower shaft bearing holder and final cleaning saves another 0.2 grams, including caving a dent in the vent window. 

The final weight after all trimming is 21.6g, including the erroneous cutting out of the front lateral studs that reduced by 0.3 grams, as shown on the weight breakdown page.