Imagine 15 mins flight time on a 3″ FPV drone using just a single 18650 Li-Ion cell. HGLRC and Dave_C collaborated and released a pre-built model – the Rekon 3 Nano Long Range FPV drone.
I actually attempted to build this from scratch a while back but with little success. It’s very picky about the choice of components and they are very tiny and hard to work with. The good news is that HGLRC is now offering this as a BNF (bind and fly) kit.
Where to Buy?
You can get the Rekon3 from:
You will also need a 18650 Li-Ion cell to fly the Rekon 3, ideally something with high discharge rate. The recommended battery is Sony VTC6, VTC5A also works but with slightly less capacity.
The Rekon 3 comes with the following accessories in the box:
Rekon 3 Features
The Rekon 3 is a light weight 3″ FPV drone designed around a single 18650 Lithium-Ion cell as its power source.
Making this work is quite remarkable because Li-Ion cells have very low discharge current for powering quadcopters, not to mention it’s only using one single cell.
Notable features of the Rekon 3 are:
- Compact and light weight, 63g without RX and battery
- Powered by a 18650 battery, offers 15min flight time in ideal conditions
- You can get some serious range with the 350mW VTX and Crossfire setup
- You can configure Betaflight wirelessly using Speedybee App over WIFI, a built-in feature of the Zeus5 AIO F4 flight controller
- Carbon fibre frame (NOT 3D printed)
- Zeus5 F4 AIO 1-2S FC (Integrated 5A BLHeli_S ESC)
- Zeus nano VTX (350mW) with dipole antenna
- CADDX Nano ANT FPV Camera
- Rekon 1202.5 11600KV motors
- GEMFAN 3018 3 inch 2-blade propellers
- Weight: 62.5g (without receiver), about 115g including battery and RX
DJI HD Version?
Only analog FPV system is available for now. I checked with HGLRC and they told me there is no plan of making DJI’s FPV system to work on this quad, because the voltage is simply too low (I guess you could use a step up regulator), and it’s a bit too heavy for this quad to handle.
Due to the lack of UART on the Zeus5 AIO flight controller, GPS module is not supported out of the box. But you can try soldering it to the legs of the F4 processor if you insist :) Or swap the Zeus5 FC out to something with more UART’s.
The lightest GPS module is probably the NLRC TinyGPS.
Closer Look at the Rekon 3
A little bit of background. The Rekon 3 is basically using 1S ultralight build components (toothpicks):
- 1202.5 11600KV motors
- 3″ props
- 1S Whoop style FC
People have been experimenting with 18650 cells on these builds for a number of years now, but it was only recently made popular by Dave_C with his unique frame design that uses a 18650 battery holder.
The other feature of the Rekon3 is using a separate VTX that offers decent range. It can give you over 1km to 1.5km along with Crossfire Nano receiver and high capacity of the Li-Ion cell.
What I have here is the PNP version which doesn’t come with a receiver. Out of the box the Rekon3 has a cable for connecting to Frsky receivers.
I am planning to use Crossfire, so I’d have to take the thing apart to solder the receiver to the FC. They use a lot of screws for the bottom cage.
All the components are connected to the FC – an AIO whoop style board. There’s is no external BEC, capacitor or LC filter. In the original design, there was a 5V step up to power the VTX, however HGLRC told me they didn’t need it in the Rekon3.
It wasn’t easy soldering on the FC, I should have avoided the PNP version :)
Here’s the wiring / pinout diagram for the Zeus5 AIO F4 FC:
And the Zeus5 AIO FC doesn’t have a current sensor unfortunately, it would have been nice to see battery mAh usage.
I am mounting the Crossfire T-Immortal antenna on the rear arms like this.
Later I moved the antenna to the front of the quad, which is much better.
The arms are very skinny (1.5mm thickness) and not the most durable frame. But there’s a 3D printed frame design on thingiverse, so you can go ahead and print replacement frames when it breaks: https://www.thingiverse.com/thing:4769576
Motors are connected to the FC via connectors:
Beware of battery polarity before inserting or you could fry the FC. They mark this very clearly in the battery tray.
Many people tell me I should use a battery strap, but no, it doesn’t need one, the battery is not going anywhere.
FPV camera is well protected by the 3D printed mounting plates, I think it’s PETG.
USB connector is easily accessible from the bottom. The bottom cage is also 3D printed in PETG.
Here’s some flight footage (both FPV and LOS)
The Rekon3 is pretty light weight even with a single cell 18650 at 114 grams, but it doesn’t have much power at all and is quite slow. It hovers at 55% throttle, is just not meant for freestyle and acro. Imagine flying a tiny whoop with a 70% throttle cap, then add some more weight to it, that’s what it feels like.
It can do some simple flips and rolls, but really it’s designed for cruising around.
The Rekon 3 could be a good training quad for beginners, because it’s small, not powerful and safe. It’s very quiet and stealthy, it doesn’t bother other people.
With that said the arms are very thin (1.5mm thick), so they are not made for crashing. It will take a few hits on grass because it’s light weight, but it won’t survive much abuse on concrete.
Flying with Li-ion 18650 in the Rekon 3, I have been told you can let the voltage to go down to 2.5V in order to use all the available capacity.
I know it goes against what we were taught, to land when the voltage reaches 3.5V, but that’s for LiPo. For Li-Ion it’s allowed to go lower, and because it’s under load, you are going to get some voltage sag especially for batteries of such low C-rating like Li-Ion cells. When you see 2.5V-2.6V and land, it’s going to recover to around 3.1V-3.3V (or even higher). Anyway, you should experiment with the battery you have, and determine what’s the minimum voltage you should land.
Surprisingly it flies okay even with some of my low performance 18650, like Panasonic NCR18650B, these have 6A discharge current only. I don’t get the full flight time though with these, because voltage drops way too low before it can be completely discharged. When voltage drops below 2.3-2.4V the quad will just drop out of the sky and you will lose video also, I think that’s the limit for the BEC on the FC.
HGLRC’s recommendation is to get the Sony VTC6 for best performance.
Flying the Rekon3 out of the box, I was randomly losing video. It appeared that the VTX restarts whenever I move throttle too quickly. I checked with HGLRC and they told me they didn’t have such issue in their testing. But another tester of the Rekon3 is also having the same issue and he was using the recommended Sony VTC6 battery.
To troubleshoot, I tried using a LiPo instead, no more video drop-out, so that points the issue to the power source.
Since they are not using a 5V step up voltage regulator, I decided to try adding one for powering the VTX. And guess what? That fixed the issue! No more VTX restarting, video was good the entire flight. This is the BEC I am using: https://oscarliang.com/product-rqbl
But I was getting a bit of interference which appears to be electrical noise, so I added a 10V 1000uF capacitor to the power. It didn’t completely clean up the noise, but it’s much better.
Optionally you can also try adding an LC filter in between the 5V BEC and VTX to further clean up the video feed: https://oscarliang.com/product-r24p
Rekon 3 Setup for First Flight
You will have to dig through the settings and configure it pretty much from scratch.
Out of the box, Betaflight and BLHeli settings are not optimized. Obvious things like voltage warning and minimum voltage should be set much lower (2.7V, 2.5V), but they were all left at default. And they should have flashed the ESC to 16.9 and use 48KHz PWM frequency which is more efficient, since this quad is all about flight time.
To give HGLRC some credit though, Bi-directional DShot and RPM filter are already setup, PID seems to be tuned out of the box as well and it flies alright. And SmartAudio works flawlessly for changing VTX channels and power.
Note that camera is NTSC so make sure to put OSD elements in the correct portion of the screen so they don’t get chopped off.
When attempting to flash the ESC to BLHeli_M (v16.9), the ESC’s somehow got bricked (not responding anymore) after a “Flash Failed” error. So I had to re-flash them via C2 interface and it was laborious. Sometimes when I “Read Setup” only two or three ESC show up, so it seems those ESC aren’t the most reliable in the world. Maybe just a bad unit I received.
And for some strange reason, it just doesn’t work well with 16.9 firmware, it randomly drops to the ground. I spent a whole day troubleshoot to no avail. Totally fine with 16.7 firmware (the version it comes with), that means I can’t run 48KHz and RPM filtering. But the other tester has no such issue, so that’s a weird one.
Update (27th May 2021) – Good News
I think the first Rekon3 I got from HGLRC was just faulty, so I got myself a brand new one from Banggood, and it flies MUCH BETTER!
Here’s some uncut flight footage from today with my new Rekon3:
I no longer get video loss during flight, so I didn’t add the 5V step up BEC this time, and didn’t use additional capacitor and LC filter since video is pretty clean.
But because of the lack of 5V step up BEC, VTX and FPV camera just turn off when battery voltage drops to 2.8V, so you have to land around 2.9V. It’s totally fine, but after you land, the battery voltage ends up at 3.3V -3.4V which means there’s still some unused capacity. With a 5V step up BEC, you can probably fly until 2.6V or even 2.5V, giving you an extra 2-minute flight time.
Anyway I am still getting almost 15 minutes of cruising time, so I am pretty happy without soldering the 5V BEC.
The Rekon3 has potential flying mid range (1.5km to 2km – about a mile), however the stock antenna is a huge bottleneck.
Video quality is pretty unreliable with the stock dipole antenna, I was getting lots of multipath interference and breakup as you saw in my first video. I replaced the stock VTX antenna with the TrueRC Singularity, it’s a light weight CP antenna, only 1.1g! And huge improvement to video quality. Buy here: https://oscarliang.com/product-feh0).
These are other cheaper options: