RadioMaster have landed a surprise! It was only in January that they launched their new flagship radio, the TX16S Mk3 - yet here we have another up-market radio, the GX15.
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| The RadioMaster GX15 |
In fact, these radios target slightly different markets. While the TX16S Mk3 is a general purpose powerhouse, the GX15 is optimised for planes, helis, and gliders.
As a keen soarer, I'm pretty much the target audience for the GX15, so was delighted to review it. My test procedure included a flight sesssion with an F3F model.
Read on to see how the GX15 performs, and who it's for.
Overview of the GX15
The GX15 is a high-end radio, optimised for LoS (line-of-sight) use in typical club environments. To that end the RF output is capped at 250 mW, allowing for a simpler, lighter design.
The GX15 available in two versions
- Standard, with regular gimbals and plain finish in a choice of colours.
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MAX, with AG02 CNC gimbals, faux carbon finish, leatherette side cheeks and
anodised metalwork (five colours available).
Compared with...
There are some obvious comparisons with the TX15 and TX16S Mk3. So let's go compare!
... TX16S Mk3
In terms of functionality, the main difference between the GX15 and the TX16S Mk3 is the RF module.
The TX16S Mk3 supports dual band (900 MHz and 2.4 GHz) Gemini/Xrossband. By contrast, the GX15 is 2.4 GHz Gemini only.
Other differences include the GX15's smaller, top mounted screen, redesigned programming controls, and lighter weight.
... TX15
Despite the ‘15’ moniker, the GX15 is quite different from the TX15.
The TX15 supports regular ELRS on 900 MHz or 2.4 GHz (but not Gemini), while the GX15 supports 2.4 GHz only, but with Gemini support.
Other differences include the GX15's sliders, extra switches and top mounted screen.
LoS or FPV?
The TX15 and TX16S Mk3 are 1 W capable, making them better choices for long range FPV applications.
Unboxing
Open the display box, and you’re greeted by a rather smart carry case with the transmitter nestling inside.
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| Carry case |
The case is made of semi-rigid foam covered in a tough fabric. An internal zipper pocket has enough space for a neck strap and a few other small items. External dimensions are 245 x 245 x 115 mm.
Accessories include a neckstrap and alternative shoulder panels:
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| Accessories (not shown: stickers and leaflet) |
Build quality
The GX15 MAX feels well made, with good quality materials and good panel fit.
The MAX version has a faux carbon finish, with a gloss varnish coating. Compared with the satin finish of previous MAX models, the gloss is easier to clean, though it does suffer a little from reflections.
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| Gloss finish over faux carbon base |
The side cheeks are made of rubber with a leatherette finish. The decorative stitching is colour-matched with the CNC items.
Remove six screws, lift off the back and hey presto everything is readily accessible. Should you ever need to remove the PCB, there are even icons showing which screws to remove!
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| Easily accessible internals |
Styling and ergonomics
The GX15 feels solid in the hand yet is refreshingly light weight. All edges are rounded, and it's very comfortable to hold.
The top mounted touch panel blends smoothly into rest of the shell. Much nicer than the 'bolt-on' look of other radios (think FrSky X20 and Jeti).
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| Elegant blending of screen |
The stick spacing is 120 mm, that’s 10 mm wider than the TX16S. I had no problem adjusting.
The unit weighs in at 840 g including batteries. That's a significant weight saving over the TX16S Mk3 (965 g) and Mk1 (930 g).
Balance with a neckstrap is good (I was using 18650 batteries).
Antennas
What, no antennas!?? In fact there are two, mounted internally and at 90 degrees to each other (what RM call 'polarisation diversity').
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| Dual antennas |
The change to internal is very welcome. It offers greater convenience (no antennas to fold out) and avoids risk of damage.
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 are all 3-position.
- SE and SG are 3-position
- SF (left side) is 2-pos, SH (right side) is momentary.
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.
The sliders are rear mounted and have a vertical action. Location is a personal thing - I prefer shoulder-mounted sliders with a horizontal action as on the TX16S Mk1.
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| Rear mounted slider |
The levers themselves are a little short, so some pilots may wish to print some longer ones. Most sliders designed for the TX16S Mk3 will also fit the GX15.
And if you don't want sliders, RadioMaster provide spare shoulder panels with slider slots blanked out. These are easy to replace.
Trims
The trims for the main flight controls are well placed, if not quite as easy to reach as on the TX16S Mk3.
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| Primary trims |
There are also two auxiliary trims designated T5 and T6. These are programmable like regular controls, with the bonus of being flight mode aware. Like the main trims, they hold their position between power cycles.
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| Auxiliary trims |
Programming controls
In a departure for RadioMaster, the GX15 doesn't use discrete buttons or a roller for menu navigation. Instead, there's a 4-way navigation pad on the left side, and a circular scroll wheel on the right side.
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| Navigation pad |
The new scheme is a great improvement. It's intuitive and there's no more fumbling around for the right button. In fact, I found myself using the new controls instead of touch much of the time.
The controls are far enough from the edge not to be operated by accident.
Function switches
Above the pots is an array of six buttons with integral RGB LEDs. The buttons are programmable in the Model Setup menu:
- 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 configurable for each button.
The buttons are tricky to identify by feel, so are best suited for ground-based functions such as motor arming, enabling logging etc.
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| Function switches |
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 RadioMaster's AG02 Hall Effect CNC gimbals. These are well proven and generally excellent units.
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| AG02 gimbal internals |
There is just one issue with the friction strap, described below.
Configuring spring tension
Spring tension is adjustable from the front of the gimbal. The standard springs worked fine for me but for those who prefer a soft feel, a set of weaker springs is provided in a separate bag.
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.
Changing stick mode
Swapping between mode 1 and mode 2 can be done from the front of the gimbal.
Adjusting the throttle ratchet/friction
The AG02 features separately adjustable friction and ratchet.
- For mode 2, the adjustment screws are accessible after removing the left hand side cheek.
- For mode 1, the adjustment screws may be accessed after removing the right hand switch panel.
There is a known issue with the friction strap - when tightening for maximum tension, a screw can interfere slightly with the strap. The effect is to reduce the travel at one end. I dealt with this by relaxing the friction, and relying more on the ratchet.
Adjusting travel limits
Both the horizontal and vertical travel limits are adjustable externally. The sticks must be recalibrated after adjustment (via System>Hardware).
Sight, sound and tilts
RadioMaster have finally listened! Yes, the screen on the GX15 is located at the top of the unit. Not only is it easier to read, but it's out of the way of wandering hands (an issue that affects the TX16S Mk3)
The panel itself is a 3.5-inch panel IPS device with a resolution of 480 x 320. It's the same spec as the TX15 but rather smaller than the massive screen on the TX16S Mk3 (5-inch, 800 x 480).
The screen is readable even in bright sunlight.
- Open the System>File Manager menu
- Navigate to the Themes/EdgeTX folder.
- Scroll down to the file background.png
- Rename the file to, say, 'background_xxx.png'
- Cycle the power
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. These appear in the source lists as TltX and TltY and return the tilt angle. However, 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 cells or a 6200 mAh LiPo pack.
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| Battery compartment |
Charging is via the USB port at the top of the unit. RadioMaster claim 'intelligent battery management' but there are no further details.
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| Sockets L-R: headphone, USB charge+data, pupil/trainer |
RF module
The GX15 comes with an internal ELRS module which supports the following ELRS transmission modes:
- 'Standard' ELRS (2.4 GHz, single transmission)
- ELRS Gemini (2.4 GHz, simultaneous dual path transmission)
XGem/Xrossband (dual-band) is not supported.
The review unit came with ELRS v3.6 FCC firmware. I since now flashed v4.1 EU, and this required an updated Lua script to be installed.
Maximum output is 250 mW. The module is equipped with a heatsink and fan, though the fan didn't cut in during tests (the EU firmware which I'm using is limited to 100 mW - still more than enough for line of sight flying).
'Standard' ELRS mode
Most sailplane pilots will be using 2.4 GHz receivers such as the RadioMaster ER6G, ER8G etc. For these, only a single transmit path is used.
In this mode the module can transmit using Antenna 1, Antenna 2, or it can switch alternately 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 should be appearing soon.
External modules
The GX15 also accepts JR-style external modules, for example the iRangeX 4-in-1 MPM (in short supply), or the RM Nomad micro (for those who want Xrossband for FPV). Note that some modules, like the Nomad, can interfere with the folding handle, so check first.
EdgeTX operating system
The review unit came with EdgeTX 2.12.2 (factory version). This is a pretty stable version. If you like programming your setups on a PC then you'll also need to download the EdgeTX Companion app.
User interface
The GX15 is equipped with an STM32 H7 processor. This makes for a snappy EdgeTX experience. There are however one or two issues with the EdgeTX 2.12 user interface, in particular navigation feels a little unfinished.
Programming EdgeTX
EdgeTX offers immense flexibility, however, the learning curve is steep. If you haven't used EdgeTX before, then please do your research first (the leaflet provided with the set is not an EdgeTX tutorial!). See links at end for EdgeTX resources.
ELRS protocol
ELRS is a robust protocol which offers excellent range, and the hardware is very competitively priced.
However ELRS is not 'fit and forget' like some other systems - some knowledge is required in order to configure it correctly. If this is your first experience with ELRS, then please do your research first - see links at the end.
Flight tests
My first outing with the GX15 was at Ivinghoe Beacon, flying a Sting F3F model.
The setup was based on my F3F v6.2 template, with ShowItAll and Adaptive trim widgets. As the GX15 was not supported in Companion some YAML splicing was needed to get it up and running.
The session went very well. The transmitter was a delight to hold, thanks to its low weight and splendid ergonomics... and that out-of-the way screen provided peace of mind against accidental operation.
It seems I'm not the only one to like the GX15, as other club mates were also suitably impressed.
Conclusion
RadioMaster have done a rather fine job with the GX15.
With its high mounted screen and new programming controls, it fixes almost all of the ergonomic issues of the TX16S - including the Mk3.
The RF specification is well chosen for LoS applications. 250 mW is more than adequate for LoS, and capping the output has allowed for a simpler, lighter transmitter design.
In short, the GX15 is an excellent choice for plane/heli/glider pilots who fly line of sight (rather than FPV) and who are looking to upgrade to a modern, full feature ELRS system.
Pros
- Light weight (for a full feature radio)
- Comfortable grip
- Internal antennas for convenience
- 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
- RF options are well suited for line of sight applications
- Flexible battery options
Cons
- Slider position may not suit some flyers
- Gloss finish may not be to everyone's taste
- AG02 friction strap issue
GX15 Specifications
- Item: GX15 Radio
- Color: White / Yellow / Red / Green / Blue
- Voltage Range: 6.6 - 8.4V DC
- Current: 850mA (at max output power)
- Frequency: 2.400GHz
- Internal RF: ExpressLRS 2.4GHz with Gemini support
- Channels: Max 16 channels (Receiver dependent)
- Radio Firmware: EdgeTX (Transmitter) (requires version 2.12.0 or higher)
- Built-in Flash Storage: Yes
- 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: V6 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: 681g (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
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