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. 2 Kevlar inserts is the solution for the titanium shaft with friction-only installation. Use both hands to clamp. It can be verified that the insert is unbroken after uninstalling the motor and removing the shaft. If you don't have strong hands for friction-only installation, use a motor with setscrews.

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. The front uses 3 layers of mounting tape, the rear uses 1 layer. 

Anti-Rotation-GPS Mount

The mount raises the rotor blades with this mount to ensure maximum manuveuring without tail strike. The 1cm x 3cm Kydex sheet is sheered by a pair of scissors because Kydex is flexible enough at 1.5mm thickness. Then the sheet is CA corner bonded to anti-rotation bracket. The drill hole is marked 4mm below the original mounting bore hole and drilled. Then  use a soldering iron at 300F beneath (but not touching) the Kydex sheet at pictured below to make a thermal forming bend of 90 degrees. Then the mount is installed and GPS attacked with clear mounting tape.

Rotor Setup

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.

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

The holes on battery try avoids studs as pictured below. The holes for camera zip ties is 15mm from the front edge. The side zip ties require drilling of the carbon fiber side wall beneath the original bolting hole because the original bolting hole is too close to the side wall's material edge.

Battery Mount

A strip transversely cover the upper front as a stopper to prevent battery pack being pressed into fuselage. A 5cm long velcro with loops and with backing goes on the top, 2.5cm bond to the battery tray, 2.5cm hangs over. Then a 6cm long hook velcro without backing sticks to the overhang, and it goes around the battery pack, wrapping the front bottom as a cushion for landing on battery.

Raspberry Pi Setup

A generic zip tie goes around the right servo and wire lead is preserved for a quarter inch on the lower part. Similarly, the battery tray's zip tie on the right aft also has the wire lead. Raspberry pi's fixture hole goes to these 2 leads.