RadioMaster TX15 review

Since their beginnings just five years ago, RadioMaster have built an enviable reputation for their well designed and reasonably priced transmitters for EdgeTX.

The TX15 is their latest radio and very interesting it is, too. Marrying a fast STM32 H7 processor with the latest EdgeTX 3.0, the TX15 provides a glimpse into the future of open source RC.

In this review, I'll explore the TX15’s features and take it for a test flight with an F3F sailplane. So read on!

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TX15 MAX with alternative shoulder switches

Just one thing before we start: the TX15 doesn’t have sliders (it is not a replacement for the TX16S!). If sliders are important to you, then look away now.

Still here? Great… let's go!

Full disclosure: RadioMaster provided me with a review unit to keep. However, they have not imposed any conditions or seen this review prior to publication. All views expressed are my own.

Top view of the TX15

Overview

The RadioMaster TX15 is a classically shaped, mid-sized transmitter for EdgeTX. The internal RF module supports single-band ELRS on 2.4GHz or 900Mz, and an external JR-style module bay allows the use of other protocols.

Standard and Max versions

The TX15 is offered in two versions. The basic version has standard gimbals and is available in a wide range of colours. The Max version has CNC gimbals, anodised switches and a carbon-effect finish. 

The review unit is a TX15 Max. I have to say, it does look rather cool!

Compared to the Boxer

The TX15 bears some resemblance to the RadioMaster Boxer. However, while they share a similar form factor there are several differences. In particular the TX15 has:

• New case design
• Colour touch screen (v. mono/non-touch on the Boxer)
• ELRS internal module (no MPM option)
• Faster STM32 H750 processor
• Function buttons are programmable
• Shoulder switches are interchangeable
• New AG02 gimbals (on MAX version only)
• Built-in flash memory, no SD required
• Robust T antenna

It should be clear that the TX15 is a brand new radio, rather than a just variant of the Boxer.

What's in the box

My TX15 Max arrived fully intact after its long journey from China. Inside the package was a white display box, and inside that was RadioMaster’s signature semi-rigid case. The case has a carry handle and an internal pocket for accessories. 

Nestling inside the case was the TX15:

Carry case. The lid has a zippered pocket for accessories.

Also included in the package are:

• Alternative shoulder switches: 1 x momentary, 1 x 2-pos
• Harder springs (15 coils v. 18 coils)
• Allen key for adjusting spring tension
• Grub screws for sticks
• Getting started guide
• Set of stickers

All the extra bits and pieces

Styling and ergonomics

I like the styling of the TX15 MAX - it’s clean and functional, yet also attractive. The panels are moulded form a mix of hard and rubberised plastic. Fit and finish are very good - the best yet on a RadioMaster transmitter.

The unit weighs in at 770 g including batteries, around 80 g lighter than a TX16S. Thanks to the sculpted grips, and the perfect placement of the neckstrap hook, it's comfortable to hold even over long periods. A neckstrap is not supplied, however.

Textures and panel lines

All in all, the designer has clearly taken a lot of care with the styling and ergonomics - a view shared by a couple of clubmates who have held the unit.

Layout and controls

All the controls, except for the shoulder switches SE and SF, are clearly labelled.

The pots work smoothly and have precise centre detents. The four switches near the top are all 3-position. 

Located on the shoulders are two pad-style switches, latching on the left and momentary on the right. These can be swapped for normal switches (more details later).

The programming buttons generate a satisfying 'click' when pressed. They follow the usual RadioMaster layout, so if you already have an RM transmitter you'll know your way around the menus.

The T-antenna can be rotated about the vertical axis:

And can be folded down:

The screen is low-mounted. Some may prefer a high mounted screen, however the low position does make best use of space. 

The distance between the stick centres is 100mm (identical to the TX16S).

AG02 gimbals

The Max features RadioMaster's latest AG02 CNC gimbals. Compared with the already excellent AG01 units, the new gimbals are said to have lower rotational inertia, for better response to rapid inputs.

The AG02 is supplied with two sets of springs (18-coil/soft, 15coil/hard). My units came with the soft springs pre-installed.

In practice, the AG02 is silky smooth and the centring is well defined.

Precision

Using the analogue monitor in EdgeTX, I was able to confirm excellent repeatability of both centre and end stop values. There's almost zero jitter from the sensor, so the ADC filter (EdgeTX system option) is disabled by default for minimal latency.

External adjustments

Adjustments to tension etc. can be made either from the front of the gimbal, or through holes in the case (after removing the grips). There's no actual necessity to open the case although I'd recommend doing so for the initial setup.

Throttle axis

My transmitter was supplied for mode 2. It's easy to change modes - just a question of engaging or disengaging the centring springs, friction strap and ratchet. Again, this can be done through holes in the case.

Some high viscosity oil was present under the friction strap, and this provides a nice smooth feel. Best not to get it on your skin, though, as the oil is super sticky and difficult to remove.

AG02 gimbal (both axes self centring)

End point adjustment

Unusually, stick travel is adjustable in both the horizontal and vertical axes. Reducing the travel will negatively impact resolution, however, so if you want to shorten their travel a better option may be just to screw down the sticks. If you do adjust the end points, then remember to recalibrate the gimbals.

Stick ends

My only niggle is that the supplied stick ends could be a little shorter (even when screwed down to the minimum they stand proud of the stem by around 4 mm). I've swapped them for spare stick ends which - as luck would have it - are also anodised red and look perfect. Stick thread is 4mm.

All in all, the AG02 is an excellent gimbal.

RF module

The internal RF module supports single band ELRS on 2.4GHz or 900MHz and is compatible with popular receivers like the ER6G and ER8G. 

Drone flyers should note that Gemini and Xrossband/XGem are not supported - for that you'll need a  GX12 or a Nomad module. 

RF firmware

The review unit came with ELRS 3.5.5 firmware installed. UK and EU users should note that LBT firmware was not available at launch - RadioMaster advised that it's scheduled for ELRS 3.6. 

Cooling

To deal with the 1W maximum output the module is equipped with both a heat sink and a cooling fan. I doubt my fan will see any action, though - 250mW is the default fan threshold, and 100mW is more than sufficient for line-of-sight flying (it's also the limit with the LBT firmware).

Cooling fan and heatsink for RF module

Expansion bay

The TX15 is equipped with an external module bay. Perhaps surprisingly, it accepts JR style modules rather than more modern and compact Nano modules. 

My iRangeX MPM fits perfectly, allowing me to use my FrSky ACCST receivers.

External module fitted

Function switches

Beneath the sticks is an array of six function switches. These have built in colour LEDs. They look similar to the dumb switches on the Boxer, however the ones on the TX15 are configurable.

Configurable function switches

The switches are configured in the Model Setup menu:

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

Typical uses include: motor arming gestures, telemetry announcements, selecting rates etc. If you get stuck on configuring the switches, the programming menu incorporates a QR code which points to a help page.

Internal gyro

The TX15 features an internal 2-axis gyro whose signal can be used as the input to a mix. It appears in the source lists as TltX and TltY representing absolute tilt angles.

The feature was introduced in a last minute firmware update, so I've only had a brief play. Potential uses include triggering telemetry call-outs, however to be usable there needs to be some form of shake detection (rather than just tilt), and that will require some programming.

Batteries and charging

The TX15 is supplied with a battery box for two 18650 LiIon cells. Batteries are not provided. For those who need greater duration, there's lots of space for 21700 cells. 

The specifications mention a 'smart balance battery circuit'. My guess is that this keeps cells in balance during discharge, preventing either cell from being over-discharged.

The manual states that only LiIon cells with a nominal voltage of 3.7V should be used with the internal charger.

Battery bay. Note the reset button under the connector.

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

Screen

The TX15 incorporates a 3.5-inch IPS touch screen. Resolution is 480 x 320 pixels. The screen is bright and I had no trouble reading it outdoors. 

Compared with TX16S

Compared with the TX16S (4.3 inch, 480 x 272), the TX15’s screen is physically smaller. However  the horizontal pixel count is the same, and the vertical count is higher. 

The result is that the TX15 renders more crisply, and there's more information on each page which means less scrolling is needed.

Removing the ETX graphic

While the screen is very good, the experience is spoiled somewhat by the EdgeTX background graphic. Fortunately it's easy enough to remove it.

To do this yourself, open the System>File Manager menu, then navigate to the Themes/EdgeTX folder. Next, scroll down to the file 'background.png'. Rename the file to something else so that EdgeTX won't find it. 

Then cycle the power and voilá - a nice clean background!

Speaker

The speaker is sufficiently loud and clear at the default setting, though there is some distortion at maximum volume.

Storage for models and settings

The TX15 features 4GB of internal flash memory for models setups, sounds etc. This will be easily sufficient for normal use. 

The unit also accepts a micro SD card. However, using a card disables the flash memory. I can't see much use for a card, except to be able to switch quickly to a backup transmitter. The card slot is located in the battery compartment.

Programming with EdgeTX 3.0

My set came with a pre-release version of EdgeTX 3.0. Thanks to the new MCU it's quicker to start up and much more responsive - a big improvement on what ETX users have been accustomed to.

Disabling touch

For my complex glider setups, I disable touch and just use the button interface - this is to reduce the risk of accidental changes. With previous versions of EdgeTX the button interface was slow and clunky, but thanks to the snappy response of ETX 3.0 on the TX15, it's now entirely practical. 

Touch can be disabled on a per model basis, via the 'No touch' special function.

Transferring models

EdgeTX Companion is an essential tool for transferring setups to a new transmitter. At the time of writing there no Companion program available for EdgeTX 3.0, so some trickery was needed to import my F3F setup. [edit] Companion 3.0 is now available.

Ease of programming

If you've not used EdgeTX before, please do your research first (the Getting Starting guide provided with the set is not an EdgeTX tutorial!). 

EdgeTX is much more flexible - and fun - than programming a Spektrum or Futaba radio... but the learning curve is a little steeper. Fortunately there are good resources to help you get on board. See links at the end of this review.

Replacing the shoulder switches

Like the Boxer, the TX15 comes fitted with 'pad' style shoulder switches. Unlike the Boxer, however, RadioMaster have thoughtfully included a pack of alternative switches, together with new panels. One is a momentary switch and the other a 2-position switch. 

RadioMaster also offer a twin-pack of 3-position switches, as an optional extra.

Alternative switches and firmer gimbal springs

Most sailplane pilots will want to install the alternative switches, so let's look at the procedure.

Opening the case

The first step is to open the case, easily accomplished by removing the rubber grips and undoing four hex-head self tapping screws. The back lifts off cleanly, after which everything is beautifully accessible. In fact, the TX15 is the easiest transmitter to maintain that I've come across. 

TX15 with the back cover removed

Latching connectors

The shoulder switches are soldered to small daughter boards with flying leads. So the next step is to remove the boards (by unscrewing a couple of self-tapping screws) then disconnect the flying leads from the main board.

The leads use JST-GH locking connectors - the first time I've seen these inside a transmitter. They offer a more secure connection, however you have to remember to release the locking tabs before pulling on the cable.

Shoulder switch after replacement. Note orientation of board.

Switch orientation

With the old switches removed, it's time to install the new assemblies. They can fit either way, but only one way is correct - the flying leads should emerge from inside the shell (see photo). If there's any doubt, you can use the System/Hardware menu to check for correct orientation.

Test flights

In spite of the wind being a little uncooperative recently, I managed a session with my 'hack' F3F model, a Sting equipped with an ER6 receiver and RM GPS sensor.

The TX15 was loaded with my F3F template, as well as these scripts: F3F tracker, crow aware trim and ShowItAll. (Incidentally, I've just updated ShowItAll to work with the TX15.)

Using the TX15 was a pleasure - both the tx and the operating system felt solid and I gelled with it quickly. I also found myself enjoying the softer feel of the AG02 compared to the AG01 on my TX16S, so will keep the softer springs.

The session lasted approximately one hour and inspection of the logs showed a VFR figure of almost constant 100%, with only occasional brief dips to 95%. No complaints!

During flight tests

Conclusions

It's clear that a lot of care and experience has gone into design of the TX15 MAX. The ergonomics are  good. The replaceable switches are a great idea. The AG02 gimbals are top notch. Last but not least, the H7 processor transforms the responsiveness of EdgeTX. 

Niggles? Well it's a minor one - the supplied stick ends could be a little shorter. If you like your sticks short, then get yourself a pair of 4mm aftermarket stick ends.

A couple of things to bear in mind: EU and UK users will have to wait a little for EU/LBT firmware. Also, ETX 3.0 is a major upgrade, so we can expect a couple of point upgrades while it beds down. 

Ultimately the TX15 should appeal to the following sailplane/electric flyers:

• Boxer users who’ve worn out their gimbals(!)
• F3F/slope pilots looking for something smaller and lighter than a TX16S.
• F5J pilots looking for a smaller tx (though motor and camber will need to be assigned to switches). 
• Anyone in the market for a mid size touch-enabled ELRS transmitter, and who doesn't require sliders.

As for me, I do actually need sliders and many of my models use legacy protocols, so the TX16S will remain my primary transmitter. However, the TX15 will be my first choice for my ELRS equipped slope models.

One things is for sure: the TX15 Max deserves to be a winner for RadioMaster.

Specification

• Size: 178*168*81mm
• Weight: 672g (without battery)
• Color: Red/ Black/ Gold
• Frequency: 2.400GHz OR Sub-G 900MHz
• Internal RF: ELRS 2.4GHz / Sub-G 900MHz
• Supported Protocols: Express-LRS
• Cooling Fan: Yes
• Transmitter Module: Built-in ELRS
• Built-in Flash Size: 4GB
• MicroSD card* (Not included): 32GB/FAT32 (Inserting a MicroSD card will disable the onboard flash)
• Antenna Gain: 2dB (transmit power adjustable)
• Current: 875mA at max power output
• Voltage Range: 6.6 - 8.4V DC
• Radio Firmware: EdgeTX (Transmitter) (requires version 3.0.0 or later)
• Module Firmware: ExpressLRS
• Channels: Max 16 channels (Receiver dependent)
• 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: V5.0 Hall sensor gimbals (standard) AG02 CNC Hall sensor gimbals (Max)
• Gimbal Sticks: M4
• Upgrade Method: USB-C (UF2)
• Module Bay: JR-compatible module bay for additional modules

Links

Manufacturer/developer sites

• RadioMaster - RadioMaster 
• EdgeTX.org - open source R/C operating system
• ExpressLRS - open source R/C protocol
• RC Groups / TX15 - community support for TX15
• RC Groups / EdgeTX - community support for EdgeTX

Author's sites

• RC-Soar.com - for all things soaring
• EdgeTX Clinic - tutorials and templates for EdgeTX