Monday, December 19, 2011

FlySky FS-TH9X Simulator/Resistor Mod

transmitter module on back or radio
I have about 2 months to build and fly a quadcopter for a project I am working on.  Unfortunately I have never flown any type of remote control aircraft before.  So I am relying heavily on flight simulator software to teach me what I need to know.  One of the first things I purchased along with the quadcopter parts was AeroSim flight simulator software.  It's pretty cool software and one of the few flight sims that simulates multicopter flight.  The first thing I did when my FlySky FS-TH9X radio arrived was plugged it into my laptop to start the multicopter training program.

Of course, it didn't work.  Neither my computer, nor the AeroSim program recognized my radio controller.  After some online searching, I discovered that because of a design flaw in the radio (what do you expect from a $60 radio) the flight simulator port will not work unless you unplug the transmitter module.  So I unplugged the transmitter module and it worked with the software!  No big deal, right?  Almost.  Turns out that although the transmitter can be removed from the radio case, it is still hard-wired to the antenna.  So even though the module is unplugged, it dangles off the back of the radio by a very small wire.  Not only do you risk breaking the wire that way, but every time you plug the module back in you risk pinching the wire.  I could see that sooner or later that wire was probably going to give out.  After some more online research I found a solution.  If you add a resistor to one of the circuit boards, the radio will work with the simulator software without removing the transmitter module.

circuit board on back of radio case

close-up of circuit board
Luckily this is an easy fix.  Open up your radio and unplug the wires connecting the front and back of the case.  There is a circuit board on the back of the case.  On the bottom left of that circuit board there are a number of traces.  That is where the resistor will go.

circuit trace cut

You need to cut the trace before you add the resistor.  Check the picture above to see where to make the cut.  Use a razor blade to cut through the trace then scrape out the copper between the cuts to make sure the circuit is broken.

resistor soldered to base

Next you solder a 1K ohm (brown black red)  resistor to the bottom pin of the trace you cut.  Add some heat shrink tubing to the resistor to protect it from shorts.  Then solder the other end of the resistor to the top pin of the trace you cut.  Put everything back together and you are done.  Now you can plug your radio into a computer and use your flight simulator software without unplugging the transmitter module.
completed resistor mod
A complete explanation of the problem and solution can be found here.  Of course, another solution would be to relocate the antenna to the transmitter module so you could detach it completely from the radio.  See how to do that here.

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