RadioMaster GX15 review

In January I reviewed RadioMaster's new flagship radio, the TX16S Mk3. It's a powerhouse of a radio for both line of sight (LoS) and long range FPV. However, its dual band capability and huge screen come at the cost of extra weight and usability.

Enter the GX15, a new high end radio specifically for LoS pilots. It's lighter, more compact, and with a different RF section.

RadioMaster GX15

I've been in possession of a unit for several weeks now. During that time I've used it to control a high value F3F model over several flying sessions. (Yes, I do actually flight test radios which I review!)

So, is the GX15 really the answer to glider/electric flyers' prayers? Read on and find out!

Full disclosure: RadioMaster provided me with a review unit for me 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. The RF module supports ELRS and Gemini on 2.4 GHz.

Physically, the set is characterised by a 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 and, unlike the others, it sports a top-mounted screen and internal antennas. In terms of switch gear, the GX15 is the equal of the TX16S Mk3:

• GX15 and TX16S Mk3: 8 switches (+2 optional), 2 pots, 2 sliders, 6 programmable buttons.
• TX15: 6 switches, 2 pots, 6 programmable buttons

All three support regular ELRS (single path/single band). However, due to their different chipsets, they differ in their support for Gemini (dual path/single band) and Xrossbland/XGem (dual path/dual band).

• GX15 (2 x SX1281). 2.4 GHz only. Supports ELRS and Gemini. 250 mW max.
• TX16S Mk3 (2 x LR1121). 900 MHz and/or 2.4 GHz. Supports ELRS, Gemini  and Xrossband. 1 W max.
• TX15: (1 x LR1121). 900 MHz or 2.4 GHz. ELRS only. 1 W max.

For long range FPV, the TX15 and TX16S Mk3, with their support for 900 MHz and 1 W output, are better options than the GX15.

Weight is a consideration when flying for long periods. The weights below are for the MAX versions without batteries. For the standard (non-Max) versions, subtract around 60 g.

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

As can be seen, the GX15 is 140 g lighter than the TX16S Mk3 - a noticeable saving.

Unboxing the GX15

First impressions are positive - the GX15 arrives in a smart, lightweight carry case with a stout handle. There's an internal zipper pocket for storing a neck strap and other small items. 

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

Carry case

The set comes with a neck strap, alternative shoulder panels, USB-C cable, screen protector, gimbal screws, switch blanking plugs, and a set of softer springs. Plus an Allen key for gimbal adjustments.

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 feels like solid with good fit and finish. It passed the squeeze and twist test, with no sign of creaking. Just one little hiccup: the 4-way navigation pad is a bit rattley on my unit.

The side grips are made of leatherette. They feel nice and add a touch of class. A thoughtful detail: the stitching is the same colour as the CNC items.

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

Easily accessible internals

Styling and ergonomics

The review unit features a faux carbon pattern with a high gloss finish. It’s easy to wipe clean, but I find it a bit too reflective, and not as classy looking as the matt finish on the TX15 MAX.

Glossy surface

The screen blends smoothly into rest of the shell, giving it a compact, understated look.

Elegant treatment of screen surround

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

With its short/wide form factor, and rounded edges, the GX15 feels quite different from my TX16S Mk1. The main adjustment was getting used to the slight lower position of the gimbals. However, after a couple of flights, I felt comfortable with the new radio.

One nice detail is the little recess around each slider - this forms a home for the middle finger and provides some useful stability. 

When hanging from a strap, the top wants to tip down a little more than I'd like. The balance will of course be more neutral if larger batteries are used. (If you're really picky RadioMaster offer a balance bar as an accessory, although this will partially obscure the on/off switch as well as putting extra strain on the attachment point.)

Antennas

The GX15 features two 2.4 GHz antennas. These are located internally, and oriented at 90 degrees to each other.

From a practical perspective, the change to internal is very 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 switch gear:

Switches

The switches follow the format of the TX16S:

Switches

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

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

There is also provision for two user-fitted switches or pots SI and SJ.  These plug into the 'EX1' and 'EX2' sockets on the PCB. [edit] The pin ordering on the EX1 and EX2 sockets is reversed compared with the TX16S Mk2.

Pots and sliders

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

S1, S2 pots

The sliders (LS, RS) are mounted at the rear of the shell. They have a vertical action which I find a little awkward compared with the TX16S Mk1. Also, the stock levers are rather short. Fortunately the latter can be dealt with by printing longer levers (levers designed for the TX16S Mk3 will also fit the GX15).  

Rear mounted slider

For pilots who don't need sliders, RadioMaster provide spare shoulder panels with the slots blanked out - a nice little detail.

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

The new scheme is quick and intuitive, and there's no more fumbling for the right button. Also switching between widgets is a lot easier, just a click left or right on the pad. 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 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 in the TX15 and TX16S Mk3. 

Each axis has adjustable spring tension, and you can also reduce the movement and each end. These adjustments can be accessed from the front of the gimbal, using an Allen key - great for tweaking on the field.

AG02 gimbal internals

Hard/soft springs

The gimbals come with regular springs installed. For those who prefer a soft feel, a set of weaker springs is provided. Personally I found the standard springs fine.

Tip: changing the springs requires some care. Don't try to do it in situ, as they can get bent. Instead, remove the rocker first, then it's easy to unhook the spring from the rocker.

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. The friction is adjustable for each, however the adjusters are hidden as follows:

• 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. 

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. 

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

Battery compartment

Charging is via the USB port which is located at the top of the unit. RadioMaster advise that the charger is rated for LiPo chemistry, in other words charge terminates at 4.2 V per cell. This means that if using LiIon cells, only batteries with 3.7 V  (not 3.6 V) nominal voltage should be charged through the transmitter. 

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

RF module

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

• ELRS
• Gemini 
  
  

RF module with heatsink and fan

Let's take a deeper dive:

ELRS mode

This mode is compatible with popular  receivers like the ERx, ERxG and ERxGV.  A single transmit path is employed using Antenna 1 or Antenna 2, or alternating between the two.

Gemini mode

In Gemini mode, each packet is transmitted simultaneously over parallel 2.4 GHz transmission paths. 

RadioMaster have recently released the ER3, ER12 and ER16 Gemini-capable receivers. These are large units, best suited for large model applications.

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 strongly recommended, as it avoids the need to reserve channel 5 for arming.)

EdgeTX operating system

The review unit came with EdgeTX 2.12.2. Thanks to the speedy STM32 H7 processor, the user interface is a lot snappier compared with F7 radios like the TX16S Mk1 and Mk2. 

EdgeTX is open source and wonderfully flexible, but it comes with a learning curve. 

If you like programming your setups on a PC then you'll also need to download the EdgeTX Companion application, available for Windows, Mac and Linux.

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. 

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, relatively lightweight, and the new programming controls are simple to use. Plus, the screen is in the ideal location. 

As with any radio there were one or two niggles, but I struggled to find any significant drawbacks. 

(Of course, the usual caveats apply with EdgeTX and ELRS: they're super flexible but come with a steep learning curve. If you’re new to either then please do your research first - see links at the end.)

In conclusion: if you're into long range FPV then look elsewhere. Otherwise, the GX15 is an excellent choice for anyone looking for a modern, full feature EdgeTX/ELRS system. It also makes a fine upgrade option for users of the TX16S Mk1/2. 

Postscript
After several more test sessions, I have decided to retire my TX16S Mk1 in favour of the GX15. It's a big step - my Mk1/MPM/OpenTX combo has been rock solid in dozens of F3F competitions, for over five years. 

The GX15 looks to be a worthy successor, and I look forward to many hours of competition flying with this radio.

Pros

• Comfortable to hold
• Light weight (for a full size radio)
• 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 when hanging from strap
• 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