Reptile S800 Sky Shadow V2

As this is the first RC plane that I'm building, I thought I'd document the build along the way. Here I'll share my thoughts behind my decisions on what I do and the components I'm using.

Parts List

I'll put a complete list of the parts that I'm using here. If I change a part, I'll update the link to the latest product I'm using in the built aircraft, but will keep the links to original parts as some people may prefer to use them after seeing my reasons for changing. For clarity, some links are affiliate links.

3D Printed Parts

I'm also designing some 3D printed parts for the S800. This is my first attempt at designing and printing my own parts, so please bear with me. In fact, I didn't even have a 3D printer when the S800 arrived, so it's all very new. As I'm working on the parts, I'll put links up to the Fusion 3D models so that if people are interested, they can check out my progress. As I finish parts I'll put the Thingiverse link here too. Please note that the files in the Fusion links are completely untested, so don't download them and print them. Once I have a proven, printed, and fitting design, I will post the Thingiverse link and feel free to print them as much as you like.

Building the S800

Trimming the foam

Image showing the trimmed components of a Reptile S800 kit Image showing the trimmed components of a Reptile S800 kit

The first step is to trim all the excess foam from the edges of the parts. Some parts have large lumps that need removing, but most just have a thin seam along the edge where the mould joins; I removed all the excess with a scalpel. The first image is the fuselage after trimming. The second images shows the rest of the parts after trimming them the next day.

Image showing the modified ESC bay of a Reptile S800 Image showing the fitted rc plane ESC in a Reptile S800

Adding the ESC

Seeing a few build videos on the S800, I knew that the BNF kit comes with a quadcoptor ESC, and also that these aren't really desirable in a plane due to the lack of airflow. I looked on a HobbyKing for the smallest, lightest 30A plane ESC I could find on a reasonable budget. I eventually settled on the HobbyKing 30A Blue Series ESC, which is only 24 × 25 × 9mm and weighs 28g.

To fit this in the bay, I had to trim the side edges and make a deeper recess at the front. It fits in pretty snugly, but I plan to 3D print a new cover for the ESC compartment with an air scoop to aid cooling. The heat sink of the ESC is facing the bottom, where the air scoop will also be situated.

Image showing the glued carbon rods in a Reptile S800's wings

Carbon up the wings

Next I glued the carbon spars into the wings. Following some damn good tips from Matt from the YouTube channel Rag the Nuts Off, I used pins to hold the spars in while the UHU POR set.

Image showing the laid out components for a Reptile S800 build

Test the parts layout

Next I wanted to lay out the parts over the S800 to get an idea of placement and cabling. I'm not too keen on the GPS module, so have decided to change it for a same spec part that will sit on the FC stack. This will mean that one wing will be heavier than the other, so I will make the heavier wing the left wing which may help counter torque roll a little.

Image showing the built motor mount of a Reptile S800

Building the motor mount

The next job was to assemble the motor mount, which involves gluing 2 pieces of balsa together, and then gluing a piece of carbon fibre to the balsa assembly. The next step is to attach the optional motor mount extension. The reason I went for this is 3-fold.

  1. Changing the motor does not involve cutting the motor mount from the body, just remove 8 screws
  2. Being further away, the prop is quieter
  3. Being further away, the air getting to the prop is cleaner and therefore it can spin faster, meaning a faster wing

I used Loctite to secure the rear screws to the red stand-offs of the extensions kit, then attach the carbon X piece to the motor. The final step is to screw the carbon x piece to the red stand-offs, but I'm not doing this til after I've sorted out the ESC wiring.

Image showing the to be glued in a Reptile S800 build Image showing test fitted servos in a Reptile S800 build

Servo test fit

Next I temporarily mounted the servos. The holes in the wings needed to be cut out slightly to accept the servos and cable.

I also sanded all the edges that are to be glued together, including the wing, winglets, and carbon spar covers.

FrSKY R-XSR quarter wavelength mod

I had a delivery turn up, and one of the items was an X4R-SB for another aircraft, so I thought it was the perfect time to do the 1/4 wavelength mod on the R-XSR. Like the regular XSR, the R-XSR has a 1/5 wavelength antennae. By converting them to a 1/4 wavelength, you gain signal strength, and therefore range. For a proof of concept range test on this, check out this video with StingersSwarm & Mr Steele. With the XSR there is only one way to perform this mod; however, with the R-XSR you also have the option of buying X4R antennae and replacing the R-XSR stock antennae. I went down the XSR route ...because I'm cheap, but also like the shorter antennae.

Image showing the steps in a FrSKY R-XSR quarter wavelength mod Image showing the steps in a FrSKY R-XSR quarter wavelength mod

In the image on the left, you can see a comparison of the X4R-SB antennae and the R-XSR. I have already modded one of the antennae of the R-XSR in the photo, but the antenna nearest the X4R-SB antennae is un-modded.

In the image on the right, you can see the first step of the mod. I held the X4R-SB antenna next to the R-XSR antenna, making sure the antennae are straight and the tips are level. The next step is to carefully remove the black outer casing of the R-XSR so that the exposed inner antenna is the exact same length of the X4R-SB. I gently cut mine with a scalpel, but whatever you use, go slow and gentle, you don't want to lop the whole thing off.

Image showing the steps in a FrSKY R-XSR quarter wavelength mod Image showing the steps in a FrSKY R-XSR quarter wavelength mod

Next (left image) you want to un-plait the shielding all the way down to the black casing. Once un-plaited, carefully cut the excess shielding away with small, sharp, precise snips. Again, be very careful not to cut the antenna.

Once you've done that, repeat with the other antenna and the mod is complete (right image). If you are unfortunate and snip off the antenna by mistake, you can try again by cutting the black casing off by the length of the required exposed antenna. The length of the final black encased part of the antenna doesn't actually matter.

Finishing up the build

Unfortunately I got pretty slack with documenting the build, mainly due to the limited time I had in the day to do the building and wanting to get as much done as possible. However I thought I'd use this section to bring you up to speed on the build, then go in to more detail below on certain aspects.

The aircraft is now complete, other than some fine tuning, and has had a single maiden flight; no, it didn't crash. There have been some changes to my plans; the main change being the removal of the OLED display. The reasoning behind this was 3 fold.

  1. I bought the wrong OLED panels and iNav couldn't communicate with them
  2. I wanted to get a bit more space back under the hatch for the battery cable
  3. I could fit LEDs to the rear of the aircraft, which other than looking cool would also tell me all the information that I needed to get flying (Satellite fix status).
I printed myself a new FC stack holder (V1) and got to work. Unfortunately this decision had been made after completing all the soldering and almost finishing the build. The following sections will detail some aspects of the build that I think may be useful. All of it is retrospective, and some of the images will be taken from the completed aircraft. Please ignore the empty place holders, the content will arrive shortly.


SmartPort and SoftSerial

Vortex Generators


Right, the first thing I'm going to mention, before I forget, is that if you're using an Omnibus F4 Pro from Banggood or the like, the LED signal is not in the specific LED 3 pin header! When the board was produced, they made a bit of a cock up with the circuitry. Instead, you have to wire it to the PWM 5 pin (not so good if you have something that needs more than 2 servos, like a plane) and use the specific OMNIBUSF4PRO LEDSTRIPM5 source. This had me confused for ages, so thought I'd get that out the way first.

For the LED mod, I used 2 of the CJMCU strips listed at the top of the page. The process involved holding the strips against the back of the fuselage and marking where they sat. I then cut a recess in these marks so the LED strips would sit flush with the motor mount. I wanted the wiring to be completely hidden, so I found the longest drill bit I could, and drilled a hole in through the EPP. If you look at the motor mount, there is a circle cut in the middle where you can see the vertical wood support and the EPP either side. I drilled in the left side of this hole and aimed down and to the left. When it came time to poke the wires through, I taped them to a piece of carbon rod and pushed that through the hole.

With the wiring, again I wanted it neat, so I tried to make all the connections in the centre, near where the wires will go through the fuselage. This works fine for the 5V and GND, but the signal needs to be in serial. So in the left trench, I cut a little deeper, enough for the signal cable and ran that along the back of the LED strip. Here's a diagram for the wiring to make it easier to follow.

Image showing the wiring diagram for 2812 LED strips with an Omnibus F4 Pro