Strix Nano Goblin

Originally, I wasn't going to make a page for the Nano Goblin as it was bought as a PNP model. However, I have stuck a fair bit of kit in this plank, so thought that I'd go ahead and document it. My Nano Goblin is running a full iNav setup and has kept pretty damn light. I'm running 2 specs currently: the first uses a 3000mAh 2S LiIon pack for which the take-off weight is 259g, the other setup uses a 1500mAh 2S LiPo pack with a take-off weight of 253g, including 20g of ballast on the nose. I could probably get a 1300mAh 2S LiPo in there and get the weight under 250g, but I'm really not that bothered. I may however, look at trying a 1300/1500mAh 3S LiPo at some point.


Parts List

Build Overview

Image showing the overview of the Strix Nano Goblin iNav build..

The Nano Goblin build is a pretty straight forward iNav build, the biggest issues arise because of the access hole that you have to the back of the fuselage. There are, however, some aspects that you need to be mindful of when you're choosing your components; the biggest issue seems to be the selection of the VTx.

TX200 VTx

The Nano Goblin is designed to run on 2S LiIon or LiPo packs, which can go down to 6V and 7.2V respectively. This is fine if you're electing to use an all in 1 25mW FPV camera, but if you want to use a normal VTx or one that can push out more signal power, the choice is somewhat limited. The regular VTx power requirements seem to start at 7V, but I've seen a 7V VTx stop transmitting at 7.2/7.3V, likely due to the power being drawn by the motor. I hunted around for a while to find the best solution I could, and I came across the RunCam TX200. This is a stand-alone VTx which is designed to run off a 5V power supply, can output at 25mW or 200mW, and has access to all the frequency bands, including Race Band; they even make a version that can use SmartAudio. The only issue is that it has no audio and comes with a stock dipole. There's nothing I can do about the audio, but the TX200's dipole is connected using a U.FL connector. I ordered a TBS Unify Pro U.FL to SMA pigtail, which allows me to run any antenna I want. I chose the Lumineer AXII stubby due to its small size, low weight, and I've been pretty impressed seeing how it performed on other models.

Installing the pigtail was straight forward, just mark on the fuselage where you want the antenna and put a hole through the same size as the black shielding on the bottom of the SMA connector. Poke the pigtail through the hole and draw around the brass fixing plate so that you can cut a small recess for the plate to fit in. Once cut, and test fitted, glue the pigtail in place. Pay close attention to the orientation of the U.FL connector, see the close up image. With the pigtail forward towards the nose of the aircraft, I have my U.FL connector facing down. This is for 2 reasons:

  1. It makes connecting the U.FL to the VTx slightly easier.
  2. It orients the VTX the correct way around to still have access to the control button.

Attaching the VTx to the U.FL is one of the last things I did. It was easier to connect the cables externally and use the dipole for testing. With regards to connecting, the TX200 has a plug for 5V in and ground and a plug for Cam in, 5V out, and ground. I cut the 5V out and ground wires on the cam plug close to the VTx and made sure the would not touch anything (hot glue does the trick). I then took the camera in wire and attached that to the VTx port on the Matek F405, the 5V in and ground went the 5V and G of the Matek F405, between the VTx and Cam pads.

RunCam Micro Eagle FPV Camera

The Micro Eagle is almost a straight fit in the hole on the nose of the model; however, you will have to make a few tweaks. The Micro Eagle has a full size lens, which adds a bit of weight, but also gives a better picture. I knew that nose weight would be needed for this, so better to have useful nose weight than just a bit of lead. You will need to cut the lens hole to accommodate the bigger lens, and also remove a bit of material for the connector. I have chose to attach the cable for the OSD and leave it inside the model, that way I don't need to disturb the camera to change any settings; the cable is just loose inside the fuselage. Wiring the camera was much the same as the VTX; the Video out wire went to the Cam pad on the Matek F405 and the power and ground connections to the same 5V and G pads as the VTx. This ensures I have video all the way down to 5V.

Image showing a close-up of the overview of the Strix Nano Goblin iNav build..

Matek F405 Flight Controller

Initially I was going to use an Omnibus F4 V3 that I had spare, but I had issues getting it to work with my FrSKY receivers, so I'm suspecting the inverter may have issues. The F405 was actually supposed to go in my S800 Mk2 build, but got put in the Nano Goblin as I knew I'd have that finished sooner. Something else came over from the S800, I had some test flight controller stack holders lying around, so I cut one down as small as possible to glue in to the bottom of the Nano Goblin. There are 2 reasons for doing this:

  1. I wanted to mount the FC on rubberised stand-offs to minimise vibration.
  2. I could mount foam to the FC holder to cover the barometer when mounted.

I have also rotated the FC by 90° so that the USB port and SD card slot are facing forwards. I found that in iNav Configurator I had to add 9° to the roll axis (actually the pitch as the board has been rotated) to get hands off level flight in horizon mode. The holder is glued in so that the rear screws are just accessible behind the carbon spar.

For wiring everything up, I've directly soldered to the board. The ESC signal goes to pad S1 and the 5V and ground from the BEC goes to 5V and ground on the Matek. With the servos, the signal wires go to pads S2 and S3 (which are unfortunately on the opposite side of the board to the servo), and the power and ground goes directly to the BEC. I also have a pair of wires going from the XT30 connector to the VCC and G pads on the Matek F405.

BN-180 GPS Module

The Beitian BN-180 is connected to UART 1 on the Flight Controller. Tx to Rx1, Rx to Tx1, VCC to 5V, and G to G. On the BN-180, the cable closest to the G cable is the TX, this is also the closes non-power cable to the TX LED. On the lid of the Nano Goblin there is a circular moulding recess, this is the ideal size and place to put the double-sided foam pad that came with the BN-180. The orientation of the BN-180 doesn't matter, so long as the ceramic antenna is facing up. I chose to have the cable coming out the back.

FrSKY R-XSR Receiver

I decided to mount my R-XSR to the side of the fuselage, and have the antennae exit directly on to the wing. I have one antenna extending straight out and the other facing rearwards along the fuselage. I may change the rear facing antenna as I think it's a bit close to the carbon spar; I think I'll have it extent forwards towards the nose.

The R-XSR is connected on the SBUS pad and UART 4's TX. The SBUS wire from the receiver goes to the SBUS Pad, the SmartPort wire goes to Tx4, Power comes from the 4V5 pad, and ground to G. There's no need to do any hardware inversion hacks, just enable SoftSerial and Telemetry and you should be good to go.

Finishing Off

Finishing touches included using blenderm tape to tidy up some of the internal cable routing, using the tape with string in it along the bottom of the fuselage to add landing protection, adding Velcro to hold the batteries, and of course, adding the stickers. With the 2S 3000mAh LiIon pack (home made using LG HG2 cells) installed at the front of the nose, the Centre of Gravity is perfect. For using the NanoTECH 1500mAh 2S LiPo, I had to add 20g of weight to the nose end of the pack to hit CG.

iNav Configuration

27th of May, 2018

I'm using a pretty standard iNav setup with the usual Z84 wing preset used for the initial rates and PIFFs, then added the standard Fixed Wing CLI mods. I'm using iNav Configurator 1.9.3 and iNav firmware 1.9.1. I've had no problems with 1.9.1 so am happy to keep on this version. My procedure is to flash iNav (full chip erase), set the Z84 preset, calibrate the gyro, run my setup script, then setup the remaining configuration parts (UARTS, modes, servos, calibrate motor).

My base setup script

Here is the majority of my setup script. I've left out the OSD settings as they're all personal preferences.

# Features feature -TX_PROF_SEL feature PWM_OUTPUT_ENABLE feature AIRMODE feature OSD # Base settings set min_throttle = 1035 #You will need to change this when you calibrate your ESC and find the minimum smooth spinning position for your motor. set max_throttle = 2000 set min_command = 1000 set gps_sbas_mode = EGNOS #I set to EGNOS (Europe) for faster lock, but either set to your region or auto. set gps_ublox_use_galileo = ON #Only use if your GPS module supports Galileo satellites. # Fixed Wing set max_angle_inclination_rll = 600 set max_angle_inclination_pit = 600 set small_angle = 180 #Return to Home set nav_rth_allow_landing = NEVER #Never land when home point reached, the aircraft will loiter above. set nav_rth_climb_first = OFF #Turn towards home before climbing to the set altitude. set nav_rth_altitude = 7000 #RTH altitude of 70 metres. # General assisted navigation settings. set nav_fw_cruise_thr = 1400 #Will vary dependant on your aircraft, but 1400 is a decent starting point. set nav_fw_min_thr = 1200 set nav_fw_max_thr = 1900 set nav_fw_bank_angle = 35 set nav_fw_loiter_radius = 3000 #60 metre circle in the sky. set roll_rate = 54 #I measureed the roll rate of my Nano Goblin at 540 degrees a second in Manual mode. set pitch_rate = 22 #I measured the pitch rate of my Nano Goblin at 225 degrees a second in manual mode. #Failsafe set failsafe_recovery_delay = 10 #Allow 1 second to pass before using failsafe. set failsafe_throttle_low_delay = 0 #Never call for failsafe based on the throttle being low, allows for gliding. set failsafe_procedure = RTH # Auto Launch set nav_fw_launch_velocity = 200 set nav_fw_launch_accel = 1700 set nav_fw_launch_max_angle = 180 #Allows the craft to launch at any angle. set nav_fw_launch_detect_time = 30 set nav_fw_launch_thr = 1900 #This is the climb throttle setting and will change depending on the aircraft. set nav_fw_launch_idle_thr = 1000 #Idle throttle of 1000 will mean the prop won't spin until the launch has been detected. set nav_fw_launch_motor_delay = 300 #This will change depending on the aircraft, if there’s more chance of your hand hitting the prop, make this number bigger. set nav_fw_launch_spinup_time = 100 set nav_fw_launch_min_time = 0 set nav_fw_launch_timeout = 10000 #10 seconds, the time that auto launch will stay active, climbing the aircraft, before defaulting back to the currently selected mode. set nav_fw_launch_max_altitude = 0 set nav_fw_launch_climb_angle = 25 #The angle at which the aircraft climbs out. Copy CLI code

You can copy and paste this into iNav's CLI. Remember to enter SAVE afterwards.