TX16S-servo-gauge-mod

This project adds, inside the TX16S MKII radio, a servo whose arm rotates according to any action you perform on your TX16S. It could be for instance:

• the vertical speed telemetry (vario): no noise for neighbour pilots, no difficulties to hear the vario bips when flying close to noisy engine planes... Moreover, feeling thermal bubbles at the tip of your fingers is a nice more immersive experience...
• the altitude telemetry and you will feel how high is flying your glider
• a voltage telemetry, and you get a rotating gauge "read" from fingers tips
• any stick, switch or pot action...

see it working: https://youtu.be/M6sp2K4ucxU

hardware

a RP2040 zero microcontroler is connected to TX16S AUX1 port (GND,+5V,Tx) pins the RP2040 drives a nano servo

pins used on RP2040 are:

• +5V
• GND
• 29 : connected to servo signal wire
• 1 : connected to AUX1 port Tx

software

radio:
from SYSTEM/HARDWARE menu of TX16S, select LUA on AUX1 and keep the AUX1 port unpowered. As you may have noticed, there is a red warning at the bottom telling you to connect only 3.3V logic to the ports... Don't worry, the RP2040 comes with a 3.3V regulator on the board and is fully compliant with the 3.3V logic level.

in the radio a very simple LUA script is placed inside the SCRIPTS/FUNCTIONS directory (in the pictures the script is servVa.lua).

• function "run" is activated by a switch (here SC-) from a SPECIAL FUNCTION in the radio (here SF7). It does the following tasks:
  • activate the AUX1 port (switch ON 5V) which in turn switches ON the RP and the servo
  • periodically (by the EDGETX system) get the required parameter used to move the servo (eg Vertical Speed value from telemetry), format it and push it on the serial port
  • The LUA script manages the transfer function you want to apply to your servo command (eg for the vario ("servVa.lua" a "dead zone" is programmed around low vertical speeds and the Vspd is multiplied by 100 to express it in cm/sec then by a gain (typicaly 5x) to give some range to the servo arm. (100 cm/sec with the gain of 5x is equivalent to 50% motion of the servo arm)
• function "background" is executed by the system when the switch associated to the SF is set to OFF. It does only:
  • switch OFF the AUX1 port which in turn switches OFF the RP and the servo

You will find here several lua scripts, just use one at a time on the same model otherwise the background function of one script will switch OFF AUX while the other script tries to switch it ON !
(note that the length of the name of script files shall be 6 character max)

• servVa.lua : is the haptic vario script, so cool to feel thermals from fingers tips
• servAl.lua : TO TEST :moves the servo according to the altitude telemetry field
• servVB.lua : TODO : moves the servo according to Vbat voltage (+/-100%)
• servTh.lua : is just an example to move the servo following the position of the throttle stick
• servS2.lua : TODO : a more complex script combining all the above scripts using the S2 pot to select which value to "display" between vario, altitude, voltage and a special function switch to activate the script

RP2040:
it is programmed in the arduino IDE but if you're not familiar with this, it is simpler to upload the binary : unplug the RP2040, press and hold the boot button, plug the USB to a PC. A directory will open in a window, just drag ad drop the .uf2 file which is the binary program.

The program itself is trivial, it just reads the order on the serialport and sends it to the servo. There is a watchdog which resets the RP if no exchange with TX16S occurs within 0.5 sec.

mechanical integration

• a DIY AUX1 connector

  I did not want to solder anything to the radio, I therefore had to tinker a connector able to be connected from inside. I use a 3 pins 2.54 mm pitch female connector housing. just enlarge the holes drilling them at 1.5 mm and trim the length so that the rubber door still closes... For the male part, I use a 2mm pitch, 3 pins connector, the pins are really thin they enter easily into the 2.54 mm female housing and they make spring due to the difference in pitch and a pretty good contact. Solder them at the tip of a servo wire. Insert the female connector housing to the end from the outside then slide the 3 pins male connector into the housing from inside... Et voilà !

The required servo shall be as small as possible. And buy one with at least 180° of rotation angle.This one is perfect (and cheap), it is given for 260° of rotation angle with a PWM pulse between 500µsec and 2500 µsec. By software I limit its amplitude to ~180° with a pulse of 1500µsec +/-700µsec.

I bought it on aliexpress here: https://fr.aliexpress.com/item/1005005192733613.html?spm=a2g0o.order_list.order_list_main.107.4b2f5e5bT9yK34&gatewayAdapt=glo2fra

Before connecting it to the AUX port I measured its current:

• 5 mA when idle
• 40 to 50 mA when rotating freely
• up to 200 mA when applying torque on the horn (strong torque...)

As the internal regulator driving both AUX ports is able to deliver up to 500mA, this is really safe.

To install it inside the radio I designed a 3D printed support : link to Thingiverse : https://www.thingiverse.com/thing:6208248

Just use the smallest servo horn... As you can see on the first pictures it fits right into the button's hole of the MKII

bottom line

This is a nice little project if you want to play with LUA, telemetry and some electronics. You can use the same concept to do what you want with your servo such as rotating an antenna to keep it in sight of your bird (a GPS would be needed but the same logics will apply...)

Obviously connecting electronics to your beloved TX16S shall be done with care. Even if it works really well for me, I cannot be taken for responsible if you end frying your radio, do it at your own risks and enjoy!