GravityKills

• the kit comes with a 10 tooth pinion (6mm)
• there are 4mm, 5mm, 6mm, 8mm, 10 mm screws, so better pay attention
• Most M3 screws use about five turns (count to check, whether the length is correct)
• The length of a button head screw is the thread, excluding the button
• The length of a countersunk head screw (those with a cone-shaped head and matching pre-drilled holes) are measured including the head, from end to end.
• The lowest main shaft bearing mount and the front bevel gear mounting block would probably work even if you put them in the wrong way. For a while, at least.
• I think the landing gear is supposed to point forwards, even though it looks different in the manual (might be perspective).
• Circlip pliers are needed to grease the one way bearing (grease is included).
• Frame post and CF anchor frame (page 9 upper picture): The tapered holes in the CF frame are slightly too deep and the countersunk head screw locks against the aluminium frame post. The CF frame plate will still be able to move. Solution, slightly extend the threaded hole with a drill bit so the screw can turn a little further. If this is not a bug but a feature, it is unmentioned in the manual.
• After tightening the final frame screws, the main shaft drops now by its own weight, almost without any friction by the 3rd bearing. I have been assembling the frame very carefully (and slowly) to achieve just that. Maybe it was just luck, or maybe the efforts paid off.
• Stuff some fast-lad packing foam into the ends of the tail support carbon fiber rods, so the epoxy can't get away inside the rod and gets pushed out instead.
• Before putting on the second cap, rub the rod so it gets hot. Reason, the warm air will contract and thus hold the caps in place. Otherwise, they might start to wander while the epoxy binds.
• Maybe this is paranioa, but filing down the screws for the torque tube ends might reduce vibrations a tiny little bit. They are about 1.8 mm too long.
• A slim 5.5 mm socket key is required for the nuts in the tail grips
• I think one of the 16.5x19x0.2 washers between main gear and crown gear was missing
• Gaui isn't Align, and a few things are different than a T-Rex veteran would expect. For example, the one-way-bearing grease tube turned out to be sealed at the tip. And even more surprisingly, leaking at the back end. Squeeze gently...
• There are different versions of the Scorpion 4035 HK-III motor, differing in hole placement and shaft length.
  The "standard" one can be mounted only with two screws and the shaft is too short. Here is a ---LINK--- to the longer upgraded shaft. The shipped price for the shaft from the manufacturer is $USD 58.80... this has become a very expensive motor.
  Note that there are two different "XL" shafts, one 100 and one 110 mm. Get the right one.
  It can be changed with a pipe wrench: disassemble the motor, loosen the screw, hold the shaft at the flat spot, twist against the bell and pull / twist until it comes off.
  Tedious but no special tools required.
• The mini V-bar was a mistake, should have gotten full-size instead.
• Why?
  
  • It's clumsy to wire in the limited space (wires may not be too tight to avoid passing vibrations, but must be carefully supported so that they don't get pulled out)
  • The satellite wires bend directly at the connector
  • most important: Adequate power supply requires quite a bit of soldering work. I use two servo extension wires, split in the middle and connected to an EC5 connector (direct 2s LiPo). In addition, one supply-only wire to the 2nd Rx port. Especially with power-hungry servos (Align DS 610 comes to mind), a 700-size FBL heli draws a lot of current. Mikado recommends two or three parallel power supply wires (link). Less important with more efficient brushless servos.
  
  
• The canopy mounts are flimsy and break at the slightest touch. They could be 10x as strong and wouldn't stand a chance of damaging the frame in a crash. If you ask me, I'll call it either design flaw, intentional rip-off or boutique heli that isn't meant to be flown.
  And, of course, they are sold out.
  A sawed-off T-Rex 700 frame bolt comes to the rescue (the hex end fits into the canopy rubber, or grind it down using a power drill and a file. A poor man's lathe...).
  IMG_2702.JPG
• The canopy paint is brittle and doesn't stick very well to the glassfiber body.
• On the bright side, the most annoying part of a T-Rex 700 build is missing (the 700 has 7 more pushrods than the X7)
• The stabilizer fin on the tail boom has to go, and the clamp will be mounted upside down as it results in a more obtuse angle on the tail support rods. Also, the open mounting holes disappear.
• The manual (V1.2.1) apparently does not mention the countersunk head screw between the divider frame and the back tail boom clamp:
  IMG_2704.JPG
  The only remaining screw in the kit is 8 mm long, but it will cut into the tail boom. Allowing this, or drilling a hole into the boom, would weaken it at the point where stress is greatest. I'm not that fond of boomstrikes, so I decided to shorten the screw.
• Judging from the feel on the bank (not flown yet), I'd use JR DS 8915 on 2s LiPo next time, instead of the Outrage Torq 9180 I've got now. They are advertised as "the fastest in response time", but side-by-side with the lightning-fast JRs in my 700 they seem a almost sluggish. Looking at the specs sheet, it becomes clear that those would benefit from longer servo arms than an 8915 in the same place.
• The V-bar geometry calculator is happy with 19 mm swash servo arms, but I might increase this a bit to make this heli crack... if I could find compatible servo arms...
• "3D masters club" on the swash plate: Maybe the heli is a member, I'm not there yet, so I decided to paint it over with a black pen
• It flies very nicely. So far running a very low headspeed to get the most flying time out of it. Nice low head, it likes to roll, and it achieves amazing cyclic rates and accurate stops even at the low headspeed, with an ominous growling of blade flutter.
• Pictures: Here (link)
• There are multiple sets of washers with different thickness for the feathering shaft. After a couple of flights, I had to switch to thicker ones. Probably the dampers got squeezed a little.
• After a couple of flights, the nyloc nuts inside the tail blade grips had to be tightened slightly
• I "upgraded" to Align 700-size torque tube bearing mounts. The stock parts sit too tight, and the torque tube doesn't easily settle so that it doesn't push into either gear box and causes friction (especially the tail end is quite sensitive. Even a small amount of friction will waste lots of power as the torque tube spins at about the same RPM as the motor). I haven't test-flown yet, but they fit nicely.
• I'm not planning to pay €28 to equip each battery pair with a mounting plates. Using conventional adhesive velcro tape, it is straightforward to attach the battery directly to the frame and there is no need for the plates.
• If you break a canopy mounting pin, cut it off and use as improved battery holding pin (the rounded aluminium pin on the rear where the battery plate is held). The battery will stay in place even facing downwards without straps when I turn over the heli to insert the other pack.
• Check the swash guiding bracket when adjusting cyclic limit. At the upper end, the swash arm may come very close to the point where it jumps free. I added a washer below the bearings to extend the arm by 1 mm, now it's safer. Before, I had it come off in transport (not sure, but I'd probably have noticed.during the flight..)
• Here is my solution, using a 450 SE V2 washer (it's not as thick as it looks)
  IMG_2721.JPG
• Blade control links and "washout arms" (see picture). This part of the puzzle isn't as easy as it looks. For a start, the washout arms are asymmetrical, while the manual shows them as symmetrical. IMG_2719.JPG
• In my opinion, the beveled side should go UP, as the control rods lean slightly outwards on the upper end (next picture)IMG_2720.JPG
• Depending on the length of the blade control links, there may be a sharp edge...
  IMG_2722.JPG... that can get stuck as follows:
  IMG_2723.JPG
• I rounded the edges with a file (both inside the washout arm and the metal edge), now it won't get stuck anymore.
• Why the washout arms have ball bearings is beyond me. In my opinion, they aren't supposed to move at all => tighten the screws until they stop moving.
• Servo mounting: It is usually preferable to put a single ball to the inside of a servo horn (not "on top"), as it reduces the moment of tilt on the servo shaft. With my servos (Outage Torq), this is possible for the two swash servos in front.
• The elevator servo is mounted on top of some leftover servo plates from another heli to get the pushrod exactly vertical.
• My servo arms are ~18 mm, and the geometry is spot-on (a little longer might still be OK, but they shouldn't be shorter, IMO).
• The 10 stock tooth pinion for the Scorpion HK III 403 (kV 500) is a quite balanced setup. You won't deep-discharge any Lipos with this setup, as the decrease in headspeed at the end of the pack is obvious.
• I'll probably upgrade to an 11 tooth pinion at some point.
• Chinese weight mod (picture): Use M3 x 20mm bolts
  IMG_2730.JPG