GePRC Darkstar20 WTFPV O3, the test of a 2S nano racer equipped with DJI 03


Here is the 5th representative of the 2S and HD nano racers under test, after the Pavo Pico from BetaFPV, Happymodel Mobula8 HD, theAcrobee75 from NewBeeDrone, and the Flywoo FlyLens85...Is it still possible for a manufacturer to offer a new version with enough strong points to set it apart from the competition? Answer in this column.

The version that I purchased and tested is the one sold ready to fly with an integrated ExpressLRS radio receiver, without a DJI O3 Air Unit but ready to accommodate one. The promise of GePRC? Getting started requires no soldering, just a screwdriver (provided) and software settings.

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Owner's turn

At first glance, the Darkstar20 looks a lot like BetaFPV's Pavo Pico, probably because its propeller guards take on a very similar look. But the Darkstar20 is larger: it is a device that measures 9 cm diagonally from motor to motor. It is based on a hard plastic structure stiffened by a system of hoops and propeller protections. The flight controller is attached to it, as well as the motors and the cradle intended to accommodate the camera and the DJI O3 box. 

The flight controller is a Taker F411 including an ExpressLRS 2,4 GHz radio receiver module and a 4A 1-in-12 ESC. The motors are SpeedX2 1102 brushless at 10000KV for HQProp DT51 four-blade propellers. They are presented in push mode, oriented downwards.

Continuation of the tour

The motors are soldered onto the flight controller, so you will need to arm yourself with a soldering iron to replace them. Note that the electronics are protected by a capacitor. An easy-to-access microUSB connector under the device provides access to the flight controller settings. 

The Darkstar20 WTFPV expects 2S batteries with an XT30 connector. The support to install them is rigid. This means you can use 2x17mm 12S batteries (regardless of length).

The 450 mAh LiPo from BetaFPV and Tattu are compatible, but they must be in good condition. If they are a little swollen, they no longer pass. The 450 mAh LiHVs from GnB are also available. But none of the 550 mAh I had on hand. Damage !

The assembly of the O3?

The procedure is very simple. You must remove the original dual connector antenna by removing the 2 screws from the plate that holds it. You must remove the O3 support cover on the Darkstar20 WTFPV with the 4 screws on the sides. Then, you must install the O3 box and connect the connector prepared by GePRC. 

The most difficult thing is to successfully connect the 2 dipole antennas (supplied with the frame and pre-installed) – but it only takes a few seconds. You must then close the hood. All that remains is to install the camera on the front of the support. Note that the original box to camera cable is a bit long, so you have to manage to hold it in such a way that it remains inside the support. And then ? That's all.

Actually, GePRC provides a protective plastic hoop to protect the top of the camera, but the screws are too short. In the end, I chose not to install it.

There is no rubber shock absorber or vibration reducer. So much the better because they are often components that are a bit painful to manage and replace. Will this impact image quality? We are going to see him. 

What to note?

Unlike the mounting of some competing devices, GePRC's O3 holder allows easy access to both the microSD memory card and the USB-C connector. Furthermore, the assembly of the device is particularly clean and neat, without any trailing or protruding cables, with the radio antenna guided towards the left side, with two short and rigid guides for the O3 antennas.

The weight ?

The bare Darkstar20 WTFPV weighs 50,2 grams. It increases to 87 grams with the O3 and its camera. Or a weight of 113,7 grams in flight order with a 2 mAh GnB 450S LiVH battery. 

Getting started?

The Darkstar20 WTFPV comes factory preset, flashed with Betaflight v4.4.2. GePRC took care of configuring all the UARTs for the ExpressLRS radio link and the O3. Actually, it's quite simple, since the flight controller only offers 2 UARTs! Be careful if you want to add a component, such as a GPS: there is no longer a UART available. Just in case, here is a dump of factory settings.

The ExpressLRS part is very classic, pairing is carried out with 3 successive power-ups... if the firmware version is compatible. On the copy I bought, ELRS was in 3.0.0 and my radio control was in 3.2.1. So I had to do an update.

With ExpressLRS configurator, you must prepare firmware in the “Generic targets used as a base 2.4 GHz” category and in the “Generic ESP8285 2.4Ghz RX” device. I took the opportunity to enter my Binding Phrase, which automates the connection to all my ExpressLRS radio controls.

Flashing ExpressLRS is easy via wifi: you just have to wait 1 minute of inaction from the receiver for it to create its wifi access point, connect to it, possibly with the expresslrs password, and start flashing. Practical and effective!

In Betaflight, I only modified the radio control channels, the combination of switches and the placement of the OSD elements. Everything is preset. Except for one element all the same: the barometer is not activated, and yet there is one on the flight controller. Simply check the Barometer box in the Configuration tab and add the item to the OSD to enjoy it during the flight.

flight behavior

Of all the 2S nano racers I've tested so far, the Darkstar20 WTFPV is the one that benefits from the most successful factory settings. It flies like it's on a rail in Acro mode, it's responsive without being too nervous, it doesn't vibrate, and it has a power reserve similar to that of Flywoo's FlyLens85 with an O3 Lite!  

In practice, the Darkstar20 WTFPV recovers from a dive without propwash, it holds movements a little hard and flies quickly on demand. All things considered, of course: it’s a 2S device. 

Outdoors ?

It is outdoors that the Darkstar20 WTFPV expresses itself best: it is capable of flying quickly almost in contact with the ground, it is perfect for skimming the canopy in the forest, it can climb a beautiful cliff and slide down it.

Wind is the enemy of featherweight racers, but this machine performs quite well even when buffeted by gusts. To a certain extent, obviously. Can we try freestyle tricks? Without a doubt. I don't have the level for that, but the resources of the Darkstar20 WTFPV are sufficient to have fun with committed flights.


The aircraft is slightly over-powered for indoor flights, but the GePRC settings allow very fine throttle management. In practice, the Darkstar20 WTFPV allows nice flights indoors, at very low speed between 4 walls, or with good speed gains in parking lots. Very interestingly, it allows you to switch from outdoor to indoor flights with ease…

The video ?

As we have seen, the camera and its integrated gyroscope do not benefit from vibration dampers. Is it serious doctor ? No, clearly the Darkstar20 WTFPV does not vibrate more than other competing devices. No less either. Indoors or outdoors with little wind, the stabilization of the DJI O3 Air Unit completely eliminates vibrations. In the presence of wind, a little remains. The solution to remove them is to use an ND filter, chosen according to the brightness. The Darkstar3 WTFPV's O20 camera mount allows you to install any O3 or Avata compatible ND filter. 

The Rocksteady stabilization applied in real time is satisfactory. If you prefer more GoPro-style images, you can force the FOV to Wide and disable Rocksteady (EIS), then stabilize the images in post-production with the help of the open source software gyro flow. The result is convincing, and it even allows stabilization on the roll, perfect for obtaining beautiful images on indoor sequences. 

If you like to control your images?

Be sure to choose your settings manually, especially if you're flying in low light – as the O3's electronics tend to automatically brighten images by introducing noise and blur. It is also recommended to film in 10-bit D-Log M to be able to adjust the colorimetry with post-production software such as Premiere Pro from Adobe or Da Vinci Resolve from Blackmagic. The O3 Air Unit is capable of filming in 4K/120, which allows for 4x slow motion.  


This is undoubtedly the main weak point of Darkstar20 WTFPV. I obtained the best results with Gaoneng's 450 mAh LiHVs: allow around 2 minutes for fairly aggressive flights, or with sustained throttle inputs, and up to 3min30 max when flying smoothly. It's not great. 

Too bad the battery holder doesn't allow you to install 550 mAh or even 750 mAh models. Too bad since the engine is compatible with excess weight. By tinkering with a mount for a 750 mAh under this support (it's not practical), I exceeded 4:30 minutes in gentle flight – that's already more interesting.

The scope ?

Pay attention to the regulations: I remind you that it requires flying with an observer who keeps the drone in direct view – and the Darkstar20 WTFPV is very small, you quickly lose sight of it.

In practice, I have never been limited by radio range, I have never even had a weak link warning. I also wasn't limited by video during unobstructed flights between headset and drone.

What limited the range... was the battery! In the undergrowth or indoors, I went far enough to have fun... and never found the device after a crash.

Solidity ?

This is a strong point of Darkstar20 WTFPV! I hit tree trunks and walls head-on several times. The battery was ejected, I lost ND filters, but the propeller guards held up and the camera came out without a scratch. Very good mention, therefore, for the material of the structure and for its architecture which seems to absorb shocks very well. 

The ends of the propellers are far enough away from the propeller guards to prevent them from breaking when the structure deforms during an impact. The block containing the O3 Air Unit has never been torn off either, even with somewhat hard crashes. The antennas are well protected in their rigid guides. Finally, the Flip Over After Crash function works correctly to flip the device if it lands on its back. There is no beeper, however.

The price ?

I bought the Darkstar20 WTFPV directly on the GePRC website with the ExpressLRS option for $130 (excluding shipping, excluding taxes). It's a very reasonable price, but don't forget that you have to add the €250 for a DJI O3 and some batteries.

Should I buy it?

For the moment, this is the O3 2S nano racer model that has impressed me the most, both for its very successful factory settings both for indoors and outdoors, its very decent power for a device 2S, and its resistant structure. The combination of these three qualities makes the difference against the competition. 

With the O3 Air Unit, you can return from a flight with superb 4K images that you can also boost in post-production. The main drawback of the Darkstar20 WTFPV is its very low autonomy, which must be compensated for with the purchase of several batteries and possibly a charger that can be used in the field.

Other pictures

Other screenshots

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  1. Hello Fred, a (stupid) question. why take the drone with the ExpressLRS option, since the dji also allows you to pilot it? Is there such a glaring difference?

  2. Hello Fred, thank you for the great test!
    Question: the small flexible antennas are not supplied with the drone?
    If not, which ones should you take?
    Thank you!


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