Radiomaster GX12 with ELRS Gemini: a review

Radiomaster GX12

The GX12 is a compact EdgeTX radio from Radiomaster with a number of interesting features. 

First of all, it has native support for ELRS Gemini Xrossband/GemX which suggests that it’s targeted primarily at the drone/video market. That being the case, I was initially sceptical about its application for sailplanes and electric gliders (my area of interest).

However the GX12 also supports the Ranger transmission modes which makes it compatible with PWM receivers like the Radiomaster ER6G, Matek 24R P6V etc., and these are popular with fixed wing line-of-sight pilots. The GX12 also has some innovations of general interest. 

With my scepticism diminished, here is my review. I hope you enjoy reading it!

Style and build quality 

First impressions are good: the GX12 comes packed in a lovely little carry case, with internal padding moulded to shape, and an internal pocket for accessories. Open the case, and there it is, ready to play!

The styling is quite striking - a mixture of soft corners and edgy angles. It looks functional yet also a bit radical. (Does this herald a new direction for Radiomaster, I wonder?)

Fit and finish are good, with the exception of the trims which are a little rattly. 

There's no carry handle, instead there’s a smart fabric strap with the Radiomaster logo. It does the job and keeps the unit compact. One nice detail is that the GX12 is perfectly stable when standing on its base. 

Top view. Centre ports are headphone jack, USB-C and DSC ports

Case design and ergonomics

The GX12 is short and wide, and rather less stable in the hand than the taller TX16S which I'm used to. Using a neck strap improves stability. On the positive side, the sticks are well positioned and the stick spacing is generous for a compact set, being identical to the TX16S. 

The switch legends are engraved in white and are easy to read - a welcome improvement on previous Radiomaster offerings. 

There's a comprehensive selection of widgets, comprising two momentary pads, two momentary buttons, two rollers, and four swappable switches. Included are two spare switches. There's also an array of six illuminated buttons. More about these later.

The programming controls follow the usual RM convention. The programming buttons have a nice feel. The click roller is quite small, though.

Programming controls

A high-contrast OLED monochrome display is located near the top of the case. 

OLED monochrome display

The display itself is small and resolution is just 128*64, so any programming is best done using EdgeTX Companion.

The antennas are short and rigid and may be folded flush when not in use - just like the antenna on the the Zorro.

Configurable buttons

Along the bottom are six buttons with built in RGB LEDs.  These offer a number of interesting possibilties.

Configurable button array

The buttons are configured in the Model Setup menu:

• A button can act like a momentary, or push-on/push-off. 
• A button may be 'independent', or part of a group where only one button is active at any time. 
• The startup state of an 'independent' is configurable to On/Off/As-last
• The startup state of a group is also configurable
• The LED colours for the on/off states can be set individually for each button. 

Very clever and flexible. Below are some possible applications:

• Arming gesture: push the end buttons together for n seconds to arm.
• Two sets of triple rates (or three sets of dual rates), with a designated default at startup. 
• Flight mode selection

Note that you can't change the state of a switch programmatically, only by physically pressing it. So for example, you can't use their LEDs to indicate the state of something else. 

A full evaluation of the buttons' usefulness will await flight testing.

Swappable switches

There's another surprise in store… the clue being the Allen bolts in the switch panels.

RH panel showing momentary (SH), 3-pos (SF, SC) and roller

Undo the bolts and lift off the panel, and voila you have full access to two switches, the roller and a momentary button. These all connect to a small PCB. 

The roller and momentary button are soldered directly to the PCB, while the switches are connected via cables.

Panel removal

Each switch can be a 3-position, 2-position or momentary. Swapping a switch is just a question of removing one and plugging in another. A slight niggle is that no tool is provided for the switch retaining nuts (fortunately I already had one).

As delivered, all the installed switches are 3-position. In addition, a spare momentary and a 2-pos are provided separately in a bag. 

Fixed momentaries (SH and SG)

SH and SG are momentary buttons (as opposed to switches) and their location is fixed. Unfortunately they're located on the front shoulders, where many pilots will expect to find a 3-position switch. This for me is the weakest aspect of the radio. 

It would be nice if Radiomaster could address this with an alternative panel, however it would likely necessitate a different design for the daughter board.

Also included is a pair of panels without slots for the roller. I can't see much use for these as it involves disassembly of the roller unit - it's simpler just to ignore the rollers.

Alternative panels (without roller slots) and extra switches

Now here's a nice detail: the plastic posts which receive the panel bolts have threaded metal inserts. No worries about stripping the threads!

The pots near the bottom of the case are commendably smooth, with a positive centre detent. Good for secondary functions like speaker volume. 

Cute little pots!

Gimbals

The gimbals are top quality CNC units with multiple ball bearings and 3D Hall effect sensors. 

And there's a useful mechanical innovation: pull smartly on a stick, and a hinged joint is exposed, allowing the stick to be folded flat. Straighten the stick, and a spring pulls it back in position ready for use. No need for gimbal protectors!

Fold-flat sticks!

The gimbals themselves are silky smooth, with a satisfying ‘clack’ on hitting the end stops. Very much like AG01 gimbals. 

Spring tension and throttle friction are adjustable with an allen key through holes under the side cheeks.  Switching between modes 1 and 2 is accomplished in a similar way.

Soft springs and allen key

Each stick's vertical travel can be altered via adjusters on the front face (remember to re-calibrate the sticks after adjustment).

Access holes for gimbal adjustment

RF module with ELRS/Gemini/Xrossband

The feature most touted by Radiomaster is the internal module which supports a number of transmission modes from single channel ELRS, to dual-band Gemini Xrossband. 

Compared with single band/single-channel ELRS, Gemini Xrossband offers better link quality (but not necessarily greater ultimate range) in areas of high interference. However, it's unlikely to offer any significant benefit for sailplane pilots given the relatively short ranges that we fly. 

If you would like to know more about Gemini, please see the links at the end.

Hello, bunny rabbit!

RF power is 1W max per band. The module is equipped with a heat sink (just visible inside the case) and cooling fan. For line of site flying with 100mW is more than sufficient, and will not trigger the fan.

Battery

A battery box is provided for two 18650 LiIon batteries. Alternatively it will accept a 21700 2S pack. Batteries are not provided with retail units.

Radiomaster stipulate the use of batteries with a nominal voltage of 3.7V and end voltage of 4.2V for compatibility with the internal charger.

Batteries compartment incorporates a reset switch

Charging is via the USB port at the top of the radio. The port is also used for data transfer.

EdgeTX

My set came with a development version of EdgeTX 2.11.0 which is not compatible with the latest version of Companion at the time or writing (version 2.10.5). 

Because of this, a little trickery was required to transfer my F3F setup from my TX16S to the GX12. After extracting the yaml file from the TX16S, I replaced the header and footer with corresponding sections of a setup already resident in the GX12. I also installed my crow aware trim script. It's all working fine. 

If you're an early adopter, I would advise flashing the latest version of EdgeTX.

Technical note: EdgeTX 2.11 promises some neat enhancements which will finally differentiate it from OpenTX. For example Diff, Weight and Offset can be number, or a GV, a channel or various other elements. 

Flight testing

Unfortunately LBT firmware is not yet available for the module (it's planned for ELRS 4) so flight tests will have to wait. When the time comes, I will use my Sting F3F slope racer equipped with Matek 24R P6V receiver (schhhh... it works on the bench!).  

Conclusion

Reviewing the GX12 has been an interesting exercise - it's not often you get a set with so many new features.

While the Gemini and GemX capability mainly interest drone pilots, there are some nice features for sailplane pilots such as the plug-in switches, configurable LED buttons and the folding sticks. 

Nothing is perfect of course. A bit more height on the case would I feel improve the comfort and balance for pilots who are used to the TX16S. And it's disappointing that the momentary buttons (the ones on the shoulders) are fixed. Hopefully somebody will find a workaround.

All in all, the GX12 is a highly capable transmitter and its compact form factor make it ideal as a sophisticated holiday radio, and for drone work. Whether line-of-sight pilots will benefit from its dual band capability is not so clear cut, however it still plays nicely with single channel ELRS.

The price in the UK is just under £170, which is remakably reasonable considering its capabilities.

Once ETX 2.11 is stable and LBT firmware is available I plan to do some flight testing, and will update this review accordingly.

EU/UK users note: LBT firmware for the RF module is slated for ELRS V4, no release date available as yet.

Radiomaster GX12 specifications

• Size: 183*148*78mm
• Weight: 573g
• Frequency: 2.400GHz and Sub-G 900MHz
• Internal RF: ELRS 2.4GHz / Sub-G 900MHz
• Supported Protocols: Express-LRS
• Cooling Fan: Yes
• Antenna: Dual folding 2.4GHz/ Sub-G 900MHz omni directional
• RF: (Dual 1,000mW | Dual band XROSSBAND ELRS)
• Voltage Range: 6.6 - 8.4V DC
• Current: 390mA - 1000mA (Depending on Rf output)
• Radio Firmware: EdgeTX (Transmitter) / ELRS (RF module)
• Channels: Max 16 channels (Receiver dependent)
• Battery: 7.4V 2-cell Lithium-Polymer / Two 3.7V 18650 Lithium-Ion cells (batteries not included)
• Charging: 2s Smart Balance Charging
• Connectivity: USB-C
• Display: 128*64 Monochrome OLED display
• Gimbal: GX01 1000Hz, 3D Digital CNC Hall Effect Gimbal with folding sticks
• Gimbal Sticks: 3mm
• External Module: Nano / Crossfire compatible
• Upgrade Method: USB / EdgeTX Companion PC software
• Memory: 512Mb Integrated Flash 

Package includes

• 1 * GX12 Radio Controller
• 1 * Signature Carry Case
• 1 * 18650 Battery Tray
• 2 * Replacement Switch Panels
• 1 * Type-C Cable
• 1 * Screen Protector
• 1 * 1.5mm Hex Wrench
• 4 * Low Tension Gimbals Springs
• 1 * 2 Position Switch
• 1 * Momentary Switch
• 1 * RadioMaster Sticker Set
• 1 * GX12 Manual

Links

• Radiomaster 
• ELRS Gemini - explainer
• EdgeTX Clinic - pro quality sailplane templates for OpenTX and EdgeTX