RadioMaster GX15 review

Back in January I reviewed RadioMaster's new flagship radio, the TX16S Mk3. I found it to be a fine general-purpose radio, for both FPV and LoS (line of sight) applications. However, I felt it was a little over-specified for LoS, and it comes with a few usability compromises.

Enter the new GX15, another high end radio from RadioMaster... but this time specifically targeting LoS users.

RadioMaster GX15

So, is the GX15 the answer to glider flyers' prayers? I've had several weeks with a review unit, during which I’ve done extensive flight testing... so read on to see how it performs!

Full disclosure: RadioMaster provided me with a review unit to keep. They have not imposed any conditions or seen this review prior to publication. All views expressed are my own. Finally, there are no affiliate links in this review.

GX15: one transmitter, two versions

The GX15 is a full feature transmitter running EdgeTX. It's equipped with a 2.4 GHz RF module with twin SX1281 chips for ELRS Gemini support. 

Physically, the set is characterised by its top-mounted screen, internal antennas and relatively light weight.

GX15 MAX - review unit

The GX15 is available in two versions

• Standard, with regular gimbals and plain finish in a choice of colours. 
• MAX, with AG02 CNC gimbals, faux carbon finish, leatherette side cheeks and anodised metalwork (five colours available).
  

This review is for the MAX version.

Compared with TX15, TX16S Mk3

Before going into the detail, let’s do a quick comparison of the GX15 and its relatives the TX15 and TX16S Mk3. All comparisons are for the MAX versions. 

Left to right: TX15, GX15, TX16S Mk3

The GX15 is shorter and wider than its siblings. It also has a top mounted screen. In terms of switches and knobs, it's equal to the flagship Mk3:

• GX15: 8 switches (+2 optional), 2 pots, 2 sliders, 6 programmable buttons, 2 aux trims
• TX16 Mk3: same as GX15
• TX15: 6 switches, 2 pots, 6 programmable buttons

The RF capabilities are different between all three radios.

• GX15 (2 x SX1281). 2.4 GHz. Supports Gemini (simultaneous dual path) and F1000  (ultra-fast/low latency). 250 mW max.
• TX16S Mk3 (2 x LR1121). 900 MHz and/or 2.4 GHz. Supports  Gemini as well as Xrossband  (simultaneous dual band). 1 W max.
• TX15: (1 x LR1121). 900 MHz or 2.4 GHz, single path. 1 W max.

The GX15’s 250 mW max output is more than enough for LoS flight. However, for long range FPV the TX15 and TX16S Mk3 are better choices.

Weight is an important factor when flying for long periods. The weights below are for the MAX versions, without batteries (for the standard versions, subtract around 60 g).

• GX15: 725 g
• TX16S Mk3: 864 g
• TX15: 672 g

The GX15 is 140 g rather lighter than the TX16S Mk3 - a useful saving.

Unboxing the GX15

The GX15 comes packed in a smart carry case. The case's semi rigid foam chassis offers adequate protection while being commendably lightweight. There's an internal zipper pocket for stashing a neck strap and other small items.  All in all, it's perfect for the intended job of storage and transport.

External dimensions of the case are 245 x 245 x 115 mm.

Carry case

Provided with the set are a neck strap, alternative shoulder panels, USB-C cable, screen protector and various other bits and pieces:

Accessories provided with the set

Also provided is a quick start leaflet and a sticker sheet:

Quick Start Guide and sticker sheet

The radio is supplied in mode 2 configuration. Swapping to mode 1 can be done via holes in the front of the gimbal.

Build quality

The GX15 MAX is nicely made and has a quality feel. There's no sign of creaking when it's squeezed or twisted. That said, there was one hiccup on my unit: the navigation pad was a bit rattley.

The side grips on the MAX add a bit of class! They're made of rubber with a leatherette finish, and have decorative stitching in the same colour as the CNC items.

Remove six screws, lift off the back and hey presto everything is beautifully accessible. Should you need to remove the PCB there are icons showing which screws to undo.

Easily accessible internals

Styling and ergonomics

The MAX features a faux carbon pattern with a gloss finish. 

The glossy surface is easy to keep clean, however it does suffer from unwanted reflections. I suspect many pilots will prefer the matt finish of previous MAX radios.

Glossy surface

I like the styling details, for example the top mounted screen blends smoothly into rest of the shell. It's rather more elegant than the bolt-on look of the Jeti DS-series and FrSky X20.

Elegant treatment of screen extension

The stick spacing is 120 mm, that's 10 mm wider than the TX16S. I had no problem adjusting during flight tests.

Grip and balance

Having used a TX16S Mk1 for five years the GX15 took a little getting used to! But I now find it very comfortable to hold.

Compared with the TX16S the grip of the GX15 is quite short. On the other hand, there's a recess under the slider for the middle finger, and this provides some extra stability. I also like that all edges are rounded. 

With a neck strap and 18650 batteries the screen tends to tip down a little, however I didn't notice this while flying. The balance will of course be more neutral if larger batteries are used. And, if you're really picky RadioMaster offer a balance bar as an accessory. However, this will partially obscure the on/off switch.

Antennas

The GX15 features dual internal 2.4 GHz antennas. These are mounted at 90 degrees to one another.

From a practical perspective, the change to internal is most welcome. No longer do you have to fiddle with antenna orientation,  and there’s no risk of damage while in transit.

Dual internal antennas

Switches and controls

Okay, so let's have a look at the twiddly bits:

Switches

The switches follow the format of the TX16S:

• SA, SB, SC, SD , SE and SG are all 3-position. 
• SF (left side) is 2-pos, SH (right side) is momentary.

The four farthest switches (SB, SF, SC, SH) have taller stems.

There is also provision for two user-fitted switches SI and SJ.  These plug into the 'EX1' and 'EX2' sockets on the PCB.

Pots and sliders

The S1 and S2 pots have a smooth action with positive centre detents.

S1, S2 pots

The sliders LS and RS are rear mounted with a vertical action. Personally, I find the action a little unnatural - I prefer the sliders on the TX16S Mk1/Mk2 which are shoulder-mounted and with a horizontal action. 

Rear mounted slider

The stock levers are short and some may find them tricky to manipulate. I've printed some longer levers (levers designed for the TX16S Mk3 will also fit the GX15).  

For pilots who don't use sliders, RadioMaster provide spare shoulder panels with the slots blanked out.  

Trims

The trims for the main flight controls are logically positioned, if not quite as easy to reach as those on the TX16S Mk3. 

Primary trims

There are also two auxiliary trims designated T5 and T6. These are typically used to adjust mixers in flight, with the bonus of being flight mode aware, and saving their position between sessions. Or they can be configured as dumb two-way switches.

Auxiliary trims

Programming controls

In a departure for RadioMaster, the GX15 doesn't use buttons and roller for navigation. Instead, there's a 4-way navigation pad on the left side, and a scroll dial on the right side. 

Navigation pad

Most pilots will welcome the new scheme. It's quick and intuitive, and there's no more fumbling for the right button. In fact, I found myself using the new controls instead of touch much of the time.

Last but not least, the controls are far enough from the edge not to be operated by accident.

Function switches

Above the pots is an array of six RGB LED buttons. Each is independently programmable.

• A button can act as a momentary switch, or push-on/push-off switch.
• A button may be independent, or part of a group where activating a button deactivates the others.
• The startup state of a button can be configured 'On', 'Off' or 'As-last'.
• The RGB colours for the on/off states are individually configurable for each button.

The buttons are a little tricky to identify by feel, so are best suited for ground-based functions such as motor arming,  enabling logging etc. 

Function switches

Finally, the buttons can be used as dumb LED indicators, by means of the PushCS special function in EdgeTX (this simulates the push of a button).

The gimbals

The MAX version features AG02 CNC gimbals.  These are high quality units, already well proven. However there is an issue with the friction strap which I describe below.

AG02 gimbal internals

Centring spring options

The gimbals come with regular springs installed. Spring tension is adjustable from the front of the gimbal.

For those who prefer a soft feel, a set of weaker springs is provided. 

Tip: don't try to change the springs in situ - there's a risk of deforming the spring when unhooking from the rocker. Instead, remove the rocker first, then it's easy to unhook the spring.

To remove a rocker: remove the (tiny) tensioner limit screw on the inside of the gimbal (take care that that it doesn't drop under the PCB!). Then slacken off the tension until the rocker is free.

Adjustable throttle straps

The throttle axis has both a ratchet and friction strap. Both straps are adjustable, however the adjusters are hidden:

• For mode 2, the adjusters are under the left hand side cheek. 
• For mode 1, the adjusters are under the right hand shoulder switch panel.

There is a known issue with the friction strap - when tightening for maximum friction, a screw can interfere with the strap. The effect is to reduce the travel at one end. I dealt with this simply by relaxing the friction, and relying more on the ratchet. 

Adjustable travel limits

Both the horizontal and vertical travel limits are externally adjustable. The sticks should be recalibrated  after adjustment (via System>Hardware).

Sight, sound and tilt sensor

RadioMaster have listened to their users - the screen on the GX15 is located at the top of the unit! 

Compared with bottom mounted screens, it's both easier to read, and - crucially - it's located well away from wandering hands and therefore safer against accidental swipes.

The panel itself is a 3.5-inch touch-sensitive IPS device, with a resolution of 480 x 320. It's the same spec as the  TX15. Both are rather smaller than the massive screen on the TX16S Mk3 (5-inch, 800 x 480). 

I had no problems reading the screen in bright sunlight. 

Tip: if you find the EdgeTX graphic confusing, you can easily hide it:

1. Open the System>File Manager menu
2. Navigate to the Themes/EdgeTX folder. 
3. Scroll down to the file background.png
4. Rename the file to, say, 'background_xxx.png'
5. Cycle the power 

Voila, a nice clean background.

Sound

Sound quality is excellent - at maximum volume the speaker is commendably loud with no distortion.

Tilt sensor

The GX15 features a 2-axis tilt sensor. Sensor values can be read via mixer sources TltX and TltY. Unfortunately, there is no built- in way to detect shake gestures (tilt acceleration) which rather limits its usefulness.

Batteries and charging

A battery box is provided for 2x18650 LiIon cells (batteries are not included). For those who need greater duration, there's lots of space for 21700 LiIon cells or a 6200 mAh LiPo pack.

Battery compartment

Charging is via the USB port at the top of the unit. RadioMaster state that the charging circuit is only for cells with a fully charged voltage of 4.2 V/cell. If using LiIon cells, that means only cells with a nominal voltage of 3.7 V can be charged through the tx. (LiIon cells with nominal voltage of 3.6 V must be charged via an external charger.)

RadioMaster quote 'intelligent battery management' but there are no further details.

Sockets L-R: headphone, USB charge+data, pupil/trainer

RF module

The RF module is equipped with a heatsink and fan, though I suspect most LoS users won't see the fan working as the default threshold is 250 mW.

RF module with heatsink and fan

The RF module operates on 2.4 GHz only and supports the following ELRS modes:

• 'Standard' (single transmission path)
• Gemini (simultaneous dual transmission path)

Let's take a deeper dive:

'Standard' ELRS mode

The GX15 is compatible with RadioMaster's popular ERx, ERxG and ERxGV 6 and 8-channel receivers. For these, a single transmit path is used. In this mode the module can use Antenna 1 or Antenna 2 or it can alternate between the two.. 

Gemini mode

The module also supports Gemini mode, where each packet is transmitted simultaneously over parallel 2.4 GHz transmission paths. Currently RadioMaster do not offer any Gemini receivers, however these will be appearing soon.

External modules

The GX15 accepts JR-style external modules, for example the iRangeX 4-in-1 MPM and RM Nomad micro. Note that some modules, like the Nomad, can interfere with the folding handle.

External module bay with IRangeX MPM 

Module firmware

The module came with ELRS v3.6 FCC firmware. I have since flashed v4.1 EU and this required an updated Lua script to be installed. (ELRS 4 is highly recommended, as it avoids the need to reserve channel 5 for arming.)

EdgeTX operating system

The review unit came with EdgeTX 2.12.2 (factory version). Thanks to the speedy STM32 H7 processor, the user interface is quite snappy - certainly a lot snappier than previous F7 radios like the TX16S Mk1 and Mk2. There are however one or two issues with the EdgeTX 2.12 user interface, in particular navigation feels a little unfinished. 

If you like programming your setups on a PC then you'll also need to download the EdgeTX Companion app (at the time of writing the GX15 is not supported, but should be soon).

Flight tests

So far I've had three outings with the GX15, flying my Sting and Pike Precision 2 F3F gliders. Receivers used were RadioMaster ER6 and Matek R24-P6V.

Both models use my F3F template, ShowItAll and Adaptive trim widgets. As Companion did not (yet) support the GX15, I did some YAML editing before loading the setups into the GX15.

GX15 with author's Pike Precision 2 during flight tests

The following ELRS configuration was used for flight tests:

• Dynamic RF power: on
• Max power: 100 mW (capped in EU/UK firmware)
• Packet rate: 100 Hz 
• Switch mode: 8 ch / full
• Antenna mode: switched

The logs showed a max TPWR (transmitted power) of 10 mW, with very occasional brief spikes to 25 mW. 

Screenshot of GX15 flight log

Conclusion

RadioMaster have done a rather fine job with the GX15! It's comfortable to hold, lightweight, and the new programming controls are great. Plus, that high mounted screen is safe from accidental swipes.

In fact, I have struggled to find any real drawbacks!

There are a couple of caveats, though. If you're into long range FPV, there are other better choices out there due to the 250 mW cap. Plus, the usual warnings with EdgeTX apply: it’s super flexible but comes with a steep learning curve. If you’re new to EdgeTX then please do your research first - see links at the end. The same applies to ELRS.

To summarise: the GX15 is a fine choice for LoS pilots who are looking for a modern, full feature EdgeTX/ELRS system, or who want to upgrade from a TX16S Mk1 or Mk2. 

Postscript
After several more sessions, I have decided to retire my TX16S Mk1 in favour of the GX15. It's a big step as the Mk1 with MPM and OpenTX has been rock solid during five years of flying  - including dozens of F3F competitions. The GX15 looks to be a worthy successor, and I look foward to many more sessions with this radio.

Pros

• Light weight (for a full size radio)
• Comfortable grip
• Excellent AG02 gimbals (MAX version)
• Internal antennas 
• Elegant integration of high mounted screen
• Bright, clear touch panel
• Screen location is safe from hands while flying
• Excellent sound
• New programming controls are simple and intuitive
• Flexible battery options
• 250 mW cap is club-friendly
  
  

Cons

• Slider position may not suit some flyers 
• Gloss finish suffers from reflections
• Slight nose down balance
• AG02 gimbal friction strap issue
  
  

GX15 MAX Specifications

• Color: Black / Transparent Charcoal / Red / Gold / Blue
• Voltage Range: 6.6 - 8.4V DC
• Current: 850mA (at max output power)
• Frequency: 2.400GHz
• Internal RF: ExpressLRS 2.4GHz
• Channels: Max 16 channels (Receiver dependent)
• Radio Firmware: EdgeTX (Transmitter) (requires version 2.12.0 or higher)
• Built-in Flash Storage: 512MB
• Cooling Fan: Yes
• Built-in Microphone: Yes (Future expansion)
• Built-in Motion Sensor: Yes
• MicroSD card (Not included): 32GB/FAT32 (Inserting a MicroSD card will disable the onboard flash)
• Display: 3.5-inch IPS touchscreen (480 x 320 resolution)
• Battery: 7.4V 2-cell Lithium-Polymer / Two 3.7V 18650 Lithium-Ion cells / 21700 5000mAh Battery (batteries not included)
• Connectivity: USB-C
• Gimbals: AG02 CNC Hall sensor gimbals
• Gimbal Sticks: M4
• Upgrade Method: USB-C (UF2)
• Module Bay: JR-compatible module bay for additional modules
• Dimensions: 178*168*81mm
• Weight: 725g (without battery)
  
  

Included items

• Battery tray for 2 x 18650 LiIo cells (battery not included)
• 2 x Replacement shoulder panels
• Type-C cable
• Screen protector
• 1.5mm hex wrench
• Low tension gimbals springs
• Gimbal stick set
• Blanking grommets for switches
• Neck strap
• Sticker set
• Manual
  
  

Links

• RadioMaster
• EdgeTX Clinic - ETX tutorials and templates
• ELRS Gemini - what is Gemini?
• Introduction to ELRS - RC-Soar blog
• RadioMaster TX16S Mk3 review - RC-Soar blog
• RadioMaster TX15 Review - RC-Soar blog
• RC-Soar.com - author’s website