A Twin Stick Conversion for the Flysky Fsi-6X Radio Control Transmitter

by Kurt Greiner (seaphoto@aol.com)

For years I have wanted a modern radio with the features of the old Ace Nautical Commander - the twin throttle sticks to control multi-motor models. With this project, I believe I have succeeded.

For the tools and supplies needed, I have included affiliate links to Amazon for them. I get a small commission off of each purchase.

The converted radio (right) next to a stock Flysky radio (Left)

About me

I am not a professional CAD artist or radio technician. This project was the result of a lot of iteration, and trial and error. I am making it available for free, including the
associated files, which can be found on Thingaverse for download.

https://www.thingiverse.com/thing:7160423/files

I spent a fair amount of time, and used a couple of radios and materials tinkering with this. If it works for you, and you want to help out, you can send me 10 dollars via PayPal at my email address at the top of this article. If not, that's OK too :-)

About this conversion

Skills - this project requires 3D printed parts, a small amount of soldering on 26 gauge wire, and cutting a hole in the back of the case for clearance.

Tools:

You will need a # 1 Screwdriver
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iFixit Jimmy, or similar thin tool (like a guitar pick) to pry
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#51, 1/8". 3/16" and 7/32" drill bits
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A drill bit holder
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A soldering iron (I love my Hakko FX88DX, but any small soldering iron will do)
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A razor saw or some other way to cut metal bar and tubing. A cheap aluminum miter box is helpful
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A 3d Printer or access to one. I used a Bambu Mini-A1 which has been rock solid for me. (Not an affiliate link, I just recommend this printer)

Optional
Low temperature hot melt glue gun and glue.

Supplies

It's probably cheaper to get these items locally, but I'm including links if you can't find them.

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You will need a Flysky Fs-i6X radio or equivalent. This conversion my fit other Flysky radio in that series, but has not been tested.
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K&S brass tubing 7/32"
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3/16 diameter solid brass or stainless steel round bar
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3/16 diameter solid aluminum round bar
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Thin solder (I like .032 diameter 63/37 flux core solder if you can find it)
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Soldering flux - highly recommended for better flow, even if you are using flux core solder
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Thin heat shrink tubing
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9 inches of 24 gauge or similar stranded (flexible) wire
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Small Screws; 6 1.7mm x 8mm self tapping screws, and 4 2.3mm x 10mm self tapping screws (this is the assortment I purchased for this project that has them)
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Small amount of Vaseline
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Black RTV sealant
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Filament for the printer. I recommend PETG, which is what I used. The color is up to you, but I found that black looks nice with this radio, a contrasting center support will look sharp, perhaps in red.
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Medium viscosity CA glue. I use Zap-A- Gap.
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Thin CA glue.
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Sanding stick or metal file to chamfer the edges of the metal parts as indicated
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A Fine point Sharpie felt pen
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A pencil

Optional

Two 1/8" x 1/4" long rare earth magnets. This will let the throttles snap together when not using them individually.

Low Temperature holt melt glue gun - to reinforce the delicate wire connections at the pots.

Small light hammer, block of wood

Dremel tool with rotary saw attachment.

Syringe and blunt needle to apply the RTV sealant.

Instructions

Note: In these instructions, I will use the terms "potentiometer" and "pot" interchangeably. You can enlarge any photo by clicking on it.

Step One, Print all the files.

https://www.thingiverse.com/thing:7160423/files

There is also an option drill guide for the Middle support if you don't have access to a drill press

You will need two of the following

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Quadrants

Throttle handle

One each of the following

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Bezel

Marking Template
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Shaft cutting Guide
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Middle Support with Hole
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Drill guide
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Back Cover

Step Two - Disassembly

Remove the batteries to the transmitter

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Take the back of the radio off by removing 4 screws and gently prying the radio halves away from each other. A guitar pick or other thin flat tool is useful for this, as is a dedicated pry tool, like the iFixit Jimmy

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After you separate the two halves, put them apart slowly - there are two wire you will need to disconnect, one for the trainer cord and the other from the battery compartment. These wiggle out, though a pair of small needle nose surgical pliers can be helpful. Avoid pulling the plugs out by their wires.

Unplug the four pin connector from left side of the existing gimbal assembly

Remove the four screws holding the gimbal assembly to the transmitter.

Remove the gimbal from the transmitter.

Place transmitter and rear cover away from the workbench to protect it from metal filings and powder from future steps.

Remove all the screws from the gimbal chassis. There should be 11 screws. It's important to remove them all, as you will need the potentiometers from the existing gimbal, and they are retained by circular saddles.

At this point I have found it helpful to reinforce the wires where they exit the pots with a drop of hot melt glue on each pot circuit board, encapsulating those wires. Let it cool

Remove the two potentiometers. Be careful to not stress the solder connections to the small circuit boards.

Step 3 Preparation

There are three 26 guage wires that connect the two potentiometers together. Cut them, one at a time, and insert a 3 1/2" extension between each. Make sure you have a good connection and cover them with heat shrink tubing. Don't forget to slide the heat shrink on before you solder! Use a heat gun and shrink both ends before proceeding.

(Tip, a small ring of larger diamter heat shrink can be slid on to each connection as you make them, giving you a way to bind them all neatly together at the end. While not neccesary this gives you a neater job) On my prototype, you can see that I used a blue ring of heat shrink to do this)

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Complete extending the wires for the other two pot wires.

Using the # 51 drill bit, open the holes in the potentiometer sadles. Also open the holes in the bezel mounting holes, and the Center support with Hole mounting holes at either end of the support. You don't have to open any holes on the inside face of the bezel, just the four that on the side that will face out towards you when the transmitter is assembled.

Using a 7/32" bit, clean out the round hole on the inside of the two quadrants. It should be pretty close to size, but I like to bore out to the final dimension due to variations in printing. Make sure you bore from the large hole side, not the narrow, smaller side.

Using the 3/16" drill bit, clean out the hole in the middle support with hole part. If you have a drill press, use that, otherwise use the drill guide that is included in the printing files. Take your time, if the hole is not perpendicular the shaft will be out of alignment, which can cause your quadrants to bind upon assembly. If you need to, print a couple to make sure you get thiis correct.

Step 4 Bushings and shafts

Slightly ease or chamer the end of the 7/32" tubing and insert it into one of the quadrants. Insert into the quadrant until it bottoms out. If you need to use a hammer to tap it in, rest the other end of the tubing on a block of wood, and light strike the top of the quadrant; avoid distoring the narrow opening that the potentiometer will be inserted into. It should require a moderate amount ot of force to seat the tube.

Using a razor saw, trim any tubing flush with the inner face of the quadrant; sand or file as needed. Repeat this with the other quadrant. Run the tip of a hobby knife around the inside of the tube to de-burr it as needed.

Sand or file the cut end of the tube flush with the face of the quadrant

Ream the inside of the tube to remove any burr

Use the Shaft cutting guide to mark out the length of the 3/16" solid metal shaft. Mark it with a Sharpie, and trim to this line with a razor saw (if brass) or whatever you have to cut stainless. An alumimum miter box is handy for this step. Lightly sand or chamfer the ends to remove any burrs. The shaft should slide and rotate into the quadrant bushings without binding.

Insert the shaft into the Middle Support with Hole. It may need to be tapped into place. The center of the support should be in the midde of the shaft, with both ends projecting out equally. If the fit is loose, use a small amount of thin CA glue to hold it in place. Be sure to let it fully cure and remove any trace of the glue on the outsde of the shafts before proceeding. Once the glue is dry, apply a small amount of Vaseline to the exposed portions of the shafts. A microbrush is handy for this.

While you have the 3/16" drill out, clean out the holes on the side of the quadrants where the throttle handle supports are attached to the quadrants. Also clean out the holes in the throttle handles. Use your 1/8" drill to clean out the holes on the side of the throttle handles if you will be using the optional magnets.

Assembly

Note, there is no need to apply excess torque to any of the screws during assembly, as you are driving metal into plastic.

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Put both quadrants on either side of the Middle Support with Hole. The hole for the throttle handle supports should be on the radiused side of the support

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Check for any binding, the quadrants should rotate smoothly.

Check the fit of this assembly in opening of the bezel. It should take a small amount of effort to push them in, and they should stay in place through a friction fit. This will give the throttles the right amount of resistance so they stay where you want while running your model.

Take your two potentitomers, and center their shafts by rotating them one way and other until you find the center of rotation. They should have about 100 degrees of swing, give or take, on either side to work properly. When you have their shafts centered, posistion the circuit boards to face inside the radio case (and away from the throttle handle support holes)

Insert the potentiometer with the larger circuit board on the left side of the quadrant assembly. Insert the other on the right side. Run the wires abovc the assembly, which will be the top of the radio case. Note that it will seat full on the first step of the potentiometer shaft, but there will be two steps exposed.

Put the assembly into the bezel, making sure that the potentiometers seat into the slots provided in the bezel

gimball assembly right

Put the Saddles over the potentiometers, making sure you clear the wires. I found on the left side it is good to put the small 1.7mm x 8mm screw in the upper hole first, and then place it into place, as the wiring harness can get in the way. Be very careful not to trap or damage the wiring harness when screwing the saddles into place.

Note that these should be 1.7mm x 8mm Screws!

Depending on the tolerances of you printer, the saddles may not fully seat, and that is Ok. They just have to prevent the potentiomers from moving.

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Insert the solid aluminum throttle sticks into the quadrants. These should be a tight fit, so you may have to press a bit. If it is loose, you can use a small drop of medium viscosity CA cement to lock them into place

This is a good place to check to make sure your potentiometer shafts were properly oriented. You should be able to push the sticks up and down to their full travel. If you cannot, you will need to disassemble and re-orient the pot shafts.

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Prepare the throttle handles. If you want to have rare earth magents installed so the sticks can move together, insert a 1/8" diamter by 1/4" long rare earth magnet into the hole at the end of one handle. It should be a press fit. Then take the other magnet and let it attack to the first; this ensures that you don't have the polarization reversed. Then insert this into the second throttle handle and seat it. The magnets will project slightly from each throttle handle. If you find that they require more force that you want to disengage, then you can use shorter magnets and set them flush with the end of the handle. You can experiment to find the best amount for your needs.

Insert the throttle handles onto the stick shafts. Your Gimbal is now assembled

Now insert the bezel assembly into the radio. You can feed in one of the throttle handles first; it will fit when completly assembled. If you find it easier to do so, you can remove one or both of the throttle handles. When the gimbal is seated on the four posts inside the radio case, you should feel it seat into place.

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Use 4 2.3mm x 10mm screws to attach the gimbal to the case. Again, no need to over-torque these screws.

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Plug the gimbal plug back into place.

Step 5 back clearance

Use the template to mark out the location of the hole needed for clearance. The template lip should be touching the side of the case, and the bottom should just touch the top of the radio compartment. A standard pencil will show up just fine on the plastic. Cut out the hole using a razor saw and sand to the mark.

Cut the hole slightly inside the markings. You can use a variety of ways to cut the cover; razor saw, chain drill a series of holes, a dremel tool equiped with a saw blade, whatever is safe and comfortable for you to do, With the undersized rough hole cut, sand to fit. Check with the printed cover often; you are aiming for a nice friction fit. the back cover will sit on the two "ears" and the lip at the rear.

Once you are satisfied with the fit, use medium CA on the side lip and the two mounting ears to hold the cover in place. Apply a small bead of black RTV around the perimeter to seal the cover and add strength. You can use masking tape as a mask on either side of the bead for a neater application, or put the RTV into a syringe with a needle tip and smooth it with a handy tool, like a pencil eraser.

Once the RTV has dried, plug the two plugs for both the trainer socket and the batteries back into place. You will find it is easier if you put the corner of the tranmitter inside the lip of the back so you get enough slack in the cords. Snap the cover back on, and replace the four screws you removed. Replace the batteries

Step 6 setting up the model.

On Flyskys, the throttle most be down before the radio will turn on. The right side throttle will be the one the radio recognizes for this, though if you put them both down it will work just fine too.

Chanel one is for your steering servo
Chanel three is for your port side motor
Channel four is for your starboard side motor.

You will need to program your individual speed controls per the manufactuer's directions.

And that's it! You now have a twin throttle radio! I hope you have fun with it.

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