Motor Setup
| Prototype | Production | |
| Part | T-Motor or Sunnysky 4004 | MAD Components 2806 |
| Component | Bell Setscrew Or Kevlar Inserts | Kevlar Inserts |
| Working Mode | More Power Than High Fuel Economy Setup | High Fuel Economy |
| Failure Mode | No Failure Possible With Strong Tightening | Slip Clutch Absorbing Crash Energy With Shaft Sliding |
To prepare the motor for gearless direct drive, remove the C-clip of the shaft to remove the bell and clamp the shaft up with a wrench socket spacing above the motor bell until the shaft's bottom is flush with the bell bore's bottom plane. Use the broad open side, not the narrow ratchet shank side, because the collar of the shaft can be jammed in the ratchet's shank hole.
The socket spacer's orientation in the middle picture is incorrect and can catch the shaft by the ratchet attachment square borehole. The 4mm-diameter shaft itself can go through the square borehole, but the shaft has a toothed groove wider than the shaft's diameter that will jam.
The production build uses multiple Kevlar threads (dental floss) as an insert. The torque is 4.5 N · cm for a 250-gram craft lift according to MAD Component specs, likely 8 N · cm during climbing. The motor radius is 1.75 cm, so the friction force needs to be 8/1.75/9.8=0.46kg=1 lb at the motor edge.
A force gauge is not required for building. Instead, use sensation to gauge whether the force is sufficient. It should feel like pinching and holding a one-pound bag of frozen vegetables by the corner of the bag in the supermarket.
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. Carbon nanotube inserts should eliminate this hassle because carbon nano tubes are notoriously hard to cut trim, but the nanotube tow delivery has a lead time of at least 1 week in addition to shipping time. The MAD motor already has a 45-degree opening of the shaft borehole, but they need to be polished, and the burs still cut the Kevlar strand, so the scraping needs to be done twice on both the top rim and the lower rim of the 45-degree slope.
The production build uses multiple Kevlar threads (dental floss) as an insert. The torque is 4.5 N · cm for a 250-gram craft lift according to MAD Component specs, likely 8 N · cm during climbing. The motor radius is 1.75 cm, so the friction force needs to be 8/1.75/9.8=0.46kg=1 lb at the motor edge.
A force gauge is not required for building. Instead, use sensation to gauge whether the force is sufficient. It should feel like pinching and holding a one-pound bag of frozen vegetables by the corner of the bag in the supermarket.
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. Carbon nanotube inserts should eliminate this hassle because carbon nano tubes are notoriously hard to cut trim, but the nanotube tow delivery has a lead time of at least 1 week in addition to shipping time. The MAD motor already has a 45-degree opening of the shaft borehole, but they need to be polished, and the burs still cut the Kevlar strand, so the scraping needs to be done twice on both the top rim and the lower rim of the 45-degree slope.
The last picture above on the right shows 3/4 of Kevlar filaments severed without rounded work surfaces with the prototype 4004 motor. The Kevlar string had to be tied to form a loose loop that avoids the sharp edges of any setscrew holes inside the bell bore hole of a prototype motor bell. For the production build with friction-only fitting, there are no set screw holes to worry about, but the friction-only fitting requires multiple trials of different number of strands of Kevlar to achieve the desired friction.
Healthy hands with normal good strength are required to build it. Test insert the shaft outside the craft as pictured here. In this particular example of the production build motor, 3 strands of Kevlar were correct for the consistent, substantial friction when the main shaft is driven into the motor bell.
For a prototype 4004 400kv motor, one and a half strands of the insert were the solution for the titanium shaft with friction-only production installation for the particular batch of shafts I received. With that batch of motors and shafts, it had been tested with 2 strands of Keclar with different arrangement angles, as pictured with a green cross-out, to find them either too tight for even strong hands to insert the shaft, or Kevlar severed during the shaft insertion. Splitting the Kevlar string, as pictured below, is not hard because the fibers are held with wax.
For a different batch of shafts, however, 2 full strands of Kevlar were the right fit, and the pullout of the shaft showed largely intact 2 strands, as shown in the pictures below. So, products have a slight margin of error. It is not the more, the better when it comes to the inserts because the pull force is exerted on the motor bearing during maintenance removal of the the shaft. Too much friction can damage the bearing because there is no axial bearing, only radial bearings that can't handle too much axial force.
Before actually installing the motor into the craft, trim the shaft at the lower bore hole. The M3 set screw should be installed and CA glued half in and half out of the motor base plate as the torque point of the motor. This torque point is to be wedged in the aft section of the servo-holding truss.
The bottom retaining borehole of the shaft with sharp edges is dealt with by simply trimming the shaft from the bottom borehole down, and then the edges need to be ground to a smooth quarter-sphere rounded surface. The direction of the grinding sanding is to grind from the bottom of the shaft up so that any burs don't cut Kevlar. To install the shaft, use both hands to clamp. It has intense friction and only healthy hands with good strength can do it. It can be verified that the insert is unbroken after driving in the shaft and the string still retains the looping, as pictured below. Cut Kevlar is pictured below with a red cross.
Sticky motor bells can occur when the clamping by hand is too strong and harsh, or it can be due to shorted motor terminals by the PWM frequency off option of the ESC or just the ESC's unmodifiable programming, as discussed in the video linked by the right picture. If not carefully monitored, clamping too firmly is common in friction fitting. The motors are rated at 1 kg lift, so there is no thrust/axial bearing. Strong hands can easily clamp at 100kg, such as in bar exercises and chin-ups. When it occurs, it has the same sticky feel as the ESC shorted terminal feel when turning the main rotor with fingers. Just pull out the shaft a bit to loosen it up.
What happens if half a Kevlar thread fewer than optimal is used? My test resulted in a slipped shaft during rapid climb that raised the shaft by 5 mm midair. So the craft lost lift, and I applied full collective pitch for the craft to minimize the negative collective pitch, which resulted in a autorotation emergency landing. This means that the pre-install test insertions to determine the number of Kevlar strands to insert , as mentioned earlier in this section, is crutial for the success.
Electrical Setup
| Prototype | Production | |
| Part | CC3D Atom | HGLRC F722 Zeus Mini |
| Component | Needs a 5-V power supply | 5V power supply built-in |
| Soldering | Needs wire tapping | 5V and 10V outlets on-board |
| Wires needed | Picoblade 10cm connector set | Picoblade 10cm connector set |
During the prototype build with flight computer CC3D, for the 5-V power supply, the 1.25mm-pitch connector that came with the buck converter had a current rating of 1A, sufficient with power tapping by servos plus a Full HD camera system (either Raspberry Pi or Runcam Thumb consumes less than 0.38A or 0.28A, respectively, and an analog camera with its video transmission have 0.5A extra current). The vendors often mistakenly label the Molex Picoblade 1.25 mm-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 CC3D flight computer, and the 30mA 2.4GHz RF receiver.
When the servos were idle, the specification said each servo consumed 15mA, and indeed, the current reading was 145mA, with the flight computer consuming 70mA and the 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 did not use the 5-V power supply. So the unplanned current budget is 1A - (220mA - 70mA) = 850mA for all power consumption from/with the flight computer board, except the servos and the RF control receiver.
For the production build, the male half of the 10-cm set is for flight computer power tapping; the female half is for RF control receiver.
The production flight computer taps power directly from the battery terminal at the main ESC as pictured here on the left.
For both the prototype and production builds, to start the dual ESC build, remove the original wraps using cuticle scissors to open them from the sides of the ESC circuit board. Then, as pictured here on the right, remove the main ESC's power wires and instead tap the tail esc's power wires ahead 1 inch, not be shorter than 1 inch each because that would impregnate the entire wire with solder during soldering and solidify the wire, leaving no flexibility.
As pictured above on the right, when tying a knot, make 2 same-orientation ties first because the 2 same-orientation loops allow adjusting length with slip. A 3rd loop should be a reverse orientation to lock the length, and then a 4th knot reverses the orientation again to double-secure the tie. The Kevlar string should snag the ESC by the electronic components.
Soldering temperature should be standard 300 degrees for ESC jobs. When accidentally dialed the temperature to 350, it resulted in melting the MOSFET components as pictured here on the left.
In the right picture, 2cm x 2mm clear mounting tapes sandwich the 3 poles, before installing the main motor, to create insulation. Then, after installing the main motor, the motor wires are soldered to the ESC.
The ESCs need to be naked for maximum cooling. Without this maximum cooling, ESCs overheat in summer as shown in the video below on the right.
The underside GPS wires require CA glue to the board itself.
Original M1-M4 signal socket faces rearward in our craft, and signal wires point out and rearward for accessible soldering jobs. The socket of the array of pins provides an even mounting surface.
The 1 mm acrylic sheet of 2.4x3 cm is CA bonded to the tail block as shown in the above diagram. The bonding can be visually verified as liquid wetting appearance. The front of the flight computer uses 3 layers of mounting tapes; the rear uses 1 layer. 
The prototype build had 210mm blades; for the production build, purchase the original Oxy2 193mm (nominally 190mm) blades or trim the 210mm blades to 193mm with a pair of office scissors. To eliminate tail strikes, the rotor is raised from the Blade180 smart fuselage's original positioning. The anti-rotation/GPS mount raises the rotor blades with this mount to match the raised rotor. The acrylic riser sheet is CA corner-bonded to the anti-rotation bracket. Use a soldering iron at 300F beneath (but not touching) the acrylic sheet to make a thermal forming bend of 90 degrees. Then the mount is installed and GPS attached with clear mounting tape. 
As shown in the picture above on the left. To install the DFC pin, add 4 layers of 1mm M2 plastic washers. Then, mark the position of the bolt that allows the free rotation of the DFC link. It can be verified that 2 DFC arms meet in the middle of their ball socket axis with a correct DFC pin installation. When installing the swash after all servo arms are installed and anti-rotation is installed, turn up the rear servo arm as pictured above on the right and tilt it to the side to allow the swash arm through the servo rod socket. To insert the swash arm into the anti-rotation slot, the top arch of the anti-rotation needs to be nipped cut with a wire cutter. The cutting also allows crash resistance because the opened anit-rotation allows the swash arm to escape a crash impulse and not break. Replacing the anti-rotation is much easier than replacing the swash.
The shaft collar bolting torque can not be too forceful with the thin and low profile bolt. Instead, the collar is designed to wedge the bolt into the shaft with wear and use and doesn't loose the grip for the lifetime of the shaft until the shaft fails and bent. See picture here.
Replacing main shaft also prompts replacing main shaft bearings (4 x 7 x 2 mm) but doesn't require opening the fuselage. The aluminum block serves as the pivot point for cantilever action to extract the bearings.
The plier cantilever goes in on the left side of the craft when extracting the bearings, both the top and bottom.
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's wiring, so it is normal to see a solder stub as circled out green in the picture.
, 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 raised rotor requires raised servo arms, which are done by rotating servos to make arms on the upper side of the servos. This raises the arms by about 10mm, and then they need to be lowered by 5mm with trimming of the servo rods. Here, pictured below, the servo rod is marked with the new servo arm position, and then the original banding (2 sections) is trimmed, and a new banding is made with a plier.
Flight Computer Setup
The servos tap the original VTX 5V power with a pair of 1A wires; the GPS and the RF control receiver use the manufacturer-designated power pads. So, the RF receiver is powered up via a USB connection to the configurator computer. The wires are threaded through the fixture bore holes, 2 holes per wire, to prevent tugging the solder pads during crash or during handling.
To wire up the flight computer, use the following diagrams. The 4-pin 10cm PicoBlade wire set male half is for the RF receiver and S5 (main motor), and the female half is for powering and signaling Raspberry Pi or VTX and OSD.
Original M1-M4 signal socket faces rearward in our craft, and signal wires point out and rearward for accessible soldering jobs. The socket of the array of pins provides an even mounting surface.
The GPS bracket is 12 mm high from the bottom of the anti-rotation bracket to the 100-degree angle. The graduations are spaced 1 mm between.
The battery power tapping points are on the left side of the boom stuck to the clear mounting tape (alien tape).
The servo power and main motor signal tapping points are on the right side of the boom. The servo power tapping loom should not have twisted conductors because twisted solder makes replacing wires hard.
The positive and negative junctions are naked and only separated by longitudinal spacing. As pictured above, the carbon plate at the tail section needs a piece of tape to provide insulation and cushioning.
Rotor Setup
The prototype build had frequent fuselage breaks, requiring rebuild and leaving the main shaft intact; the production build's strong fuselage can not break in all crashes and instead allows infrequent main shaft bending to absorb energy. The servo sequence of the production build is marked in the picture here.
The height from the upper edge of the upper bearing block to the hub bolting hole axis shall be 30mm to prevent a tail strike during forceful maneuvering and crashes. As pictured below on the left, for the 30 mm height rotor setup, the shaft dent of the V950 shaft coincides with the upper bearing block, and the collar's screw wedges to the dent's upper corner in the picture after installing the collar. When friction-fitting the main shaft, the retaining collar's bolting needs dents because the extra friction used to fit the main shaft above the friction resistance can be greater than an undented collar bolting's friction can handle. More importantly, during the pull-out of the main shaft, the entire main shaft friction on the motor bell is countered by pulling the collar with a pair of pliers, as pictured on the right. The stator rotation stopper is an M3 setscrew CA-glued and bolted on halfway. Be careful not to wedge the bolt in between the strut for the fuselage and the strut for the servo because that space is not enough for free-vertical pressing of the stater onto the bearing block. The bolt should be between the 2 struts toward the two sides of the fuselage plates.
The DFC pin requires a bushing section without threads with the DFC arm. Factory partial threaded M2-15mm bolts with 3mm end threading take multiple weeks to deliver, and even then, the non-threaded section isn't a high-quality fit because a bolt is never meant to be a bushing axix. For fast production, use copper tape of 1/4 inch to wrap the section in contact with DFC arm bushing. The copper foil tape and M2 fully-threaded bolts are part of the essential supplies of the science and art industries and so the delivery is the fastest among all parts of the build. As pictured here, the 1/4 inch copper tapes generally have a similar thickness as very thin clear stationary tape. The example needs 2 layers of the tape, so the length to use is 2mm x 3.14, about 6 mm. The product description of the copper foil tape often indicates "double-sided" adhesion, but, depending on product picture, the adhesive is double-sided while the copper foil facing outside can not be double-sided with adhesives, so the outside face is without adhisives and with low friction. The wrapping doesn't need to be very neat or tight because it can always be compacted after inserting into a DFC arm, just by use a screw driver to tun and rub the foil against the DFC arm's inner wall for a couple minutes.
In the example picture, the wrapping of the copper foil may seem very tight and not increase the bolt's thickness at all, but the actual installation is very tight and requires the technique of turning the screw against the DFC arm inner wall for a few minutes to compact the wrap to make a proper fit. When the DFC pin is correctly made, the DFC arm can fall by itself when held and released, as shown in the video.
The main shaft anti rotation setscrew is in the aft truss section, additional 1 3/4 zip tie insert is on the left. The zip tie insert should be short so not to allow it to be bent during insertion with pliers and nicking the motor stater. See pictures here.
Replacing main shaft also prompts replacing main shaft bearings (4 x 7 x 2 mm) but doesn't require opening the fuselage. The aluminum block serves as the pivot point for cantilever action to extract the bearings.
The plier cantilever goes in on the left side of the craft when extracting the bearings, both the top and bottom.
Tail Build
| Prototype | Production | |
| Part | Gemfan 4025 straight edge | HQ Prop 4025 slanted edge |
| Component | 081.5A gear spacer CA glued | M2 bolting |
| Weight | 1.5 + 0.1 grams spacer | 1.5 + 0.3 grams bolts |
Our production build is based on improving on the prototype's glued tail propeller, which was 0.2 grams lighter. The prototype setup is pictured below. The video on the right shows the prototype's tail failure due to the slip of propeller glue adhesion, which goes into a left-turn tailspin at 2:00 and continues until the crash. There was no crash in the 11 minutes between 18:32 and 18:43 . The prop slip is distinguished from the radio loss free fall video in the Failsafe Setup section by a characteristic left turn instead of a right turn with an initial jerk due to Failsafe's sudden zero-collective-pitch setup.
The problem is solved in the production build with bolting the propeller onto the motor bell.
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's wiring, so it is normal to see a solder stub as circled out green in the picture.
The diagram on the right 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.
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.
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 tail boom insert and close-up of the mounting and the option of TBS Crossfire Nano receiver follow.
Servo Setup
To make the servo arms resilient to crash, cut the spline and partially split the arm to make a torque clutch. That way, the clutch slips whenever the impact force is larger than the gears can handle, 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.
When making the slit, do not be conservative. As shown in the picture below on the left, when one of the servos' cutting was very conservative, the clutching was overly strong, and a crash damaged the servo's internal gears. The correction was liberal cutting to thin the remaining material and make the opening approach the servo rod, as pictured below on the right.
The raised rotor requires raised servo arms, which are done by rotating servos to make arms on the upper side of the servos. This raises the arms by about 10mm, and then they need to be lowered by 5mm with trimming of the servo rods. Here, pictured below, the servo rod is marked with the new servo arm position, and then the original banding (2 sections) is trimmed, and a new banding is made with a plier. The trimming of the 5 mm excess needs to be conservative because of a trick we use to mitigate a bug unique to the FD411 flight computer. With the prototype fuselage build, it was discovered that when the FD411 was booted up without RF control turned on on the transmitter side, a pulse of the lowest collective pitch signal, as stipulated by the servo range configuration, was sent to the 3 servos. That made a rapid twitch down and up motion of the rotor blades, which added unwarranted wear and tear to the servos, as shown in the video on the right. But there was a solution discovered subsequently.
It was accidentally discovered during the production fuselage build that when the servo upper range was higher than 2080 us, the twitch motion disappeared, which meant that the servos ignored PWM commands higher than (include) 2080 us. In the production build, the servo range direction is in inversion, so the lowest collective pitch signal pulse translates to the highest PWM signal to the servos. To ensure that the high-end signal is higher than 2080 us, the servo arm rods need to be tall enough so that the high end needs to be raised 80 higher than (include) 2000 to oppress the tall servo arms. To keep the servo arm rods tall enough, the trimming of the 5mm excess needs to be conservative. The first servo arm hole, at 8 mm, is used with the servo rods. M1.5x6mm screw (#0 American gauge screw) fastens the servo arms to the end turn and the arm turns. Then, back off a half turn. The thread width is 1/32 inch, so half a turn allows about half a mm for servo clutch relief and ease of clutch slip.
Summary of the torques used in the build.
Battery-Camera Mount
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.
The holes on the battery tray avoid 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 margin.
The Velcro on the battery should only have a slip opening to allow the front wiring to go through. No need to crop the Velcro as the hole only allows the material to stretch and distort.
The underside of the craft's protruding Velcro strip needs a backing of another hook Velcro strip to mount the 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.
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