# How to build a buddy box cable for FlySky FS-i6X RC transmitters?

I have a couple of FlySky FS-i6X RC transmitters that I'd like to use to teach my brother how to fly. I've seen other people use "buddy box" cables that connect two transmitters and allow one person to temporarily give the other control of the aircraft while in flight.

The back of the transmitter has a port that looks like an old S-video receptacle. Can I use that to make a buddy box cable?

Yes, on both counts! That is an S-video (aka. Mini-DIN-4) connector, and you can use it to make a buddy box cable. The port carries a 4-channel CPPM signal that can be used by cheap USB adapters as a joystick HID input to your computer or for buddy box mode, which FlySky calls "Trainer mode". I've made one for my own use, following the specifications laid out by the user gcartled on the RCGroups forum.

## Making the Cable

It appears that there are sellers with listings for ready-made FlySky trainer cables, like this one on eBay, but I haven't tested them to confirm that they work. Note that @JohnRix in the comments has mentioned that the adapter he purchased for the i6 was incompatible with the i6x.

After obtaining a spare S-video cable (or creating your own from Mini-DIN-4 male terminations), chop it somewhere in the middle and reorder the connections for the 4 internal wires such that the pins 1 and 2 are connected to the opposite number on the other end of the cable. i.e.:

• pin 1 → pin 2
• pin 2 → pin 1
• pin 3 → pin 3
• pin 4 → pin 4
• metal housing → metal housing

(cit.)

This creates a crossover cable that allows the CPPM signals from the "slave"/trainee transmitter to be received by the "master"/trainer transmitter.

## Configuring the Trainer Transmitter to Enable "Trainer Mode"

In order to use trainer/trainee functionality, the appropriate settings must be configured on the trainer's transmitter so that it knows what switch will be used to toggle on/off control inputs from the trainee's transmitter. In this setup, the trainer's radio is the only one bound to the aircraft.

These instructions are confirmed functional for the FS-i6X transmitter, but it is likely to also work with the FS-i6 and other derivatives:

1. Turn on the transmitter.
2. Hold the OK key to open up the menu.
3. Scroll to System Setup and select with the OK key.
4. Scroll down to Trainer mode and select with the OK key.
5. Scroll using the OK key so that the horizontal arrow points to Mode and then use the UP key to change from Off to On.
• If you want to disable buddy box functionality in the future, come back here and change the Mode back to Off.
6. Scroll using the OK key so that the horizontal arrow points to Switch and then use the UP and DOWN keys to select the switch that you'd like to use to enable/disable buddy box functionality.
• (WARNING: you shouldn't have this switch bound to anything on your aircraft, as this could cause issues inflight when something is accidentally triggered in the process of enabling/disabling the biddy box)
• Note the position of the switch you selected that changes the text Inactive to Active at the bottom of the screen. The Active position enables the buddy box and vice versa.
7. Hold the CANCEL key until you hear a beep to save the changes and then press CANCEL twice more to escape the menus all together.

Now, go and fly!

• Are pins 3 and 4 required? Is the above programming for the master or student transmitter? May 27 '20 at 8:21
• Also, it appears that you can just buy an offical Flysky buddy box cable for \$10-15, from multiple sellers. May 27 '20 at 8:25
• @RobinBennett I have not verified that to be the case. It appears you are correct about the ready-made cables, but I haven't tested them to confirm that they work.
– ifconfig
May 27 '20 at 15:15
• Also, my answer clarifies which transmitter's settings need to be changed, the trainer's/master transmitter
– ifconfig
May 27 '20 at 22:16
• Thanks, I'd missed that. Do you have to do anything to the student's transmitter? May 28 '20 at 9:26

Just wanted to confirm that this does work...but it's incredibly tedious work. For my particular generic s video cable. the wires are sheathed around each other, so you have to carefully unsheath the outer wire without cutting the inner wire. These wires are so fragile that I inevitably cut through several strands. That's one issue.

The other issue is once you get 4 discreet wires, getting them to connect correctly given how thin the strands are makes it also a difficult task. Even after you've soldered them, they can't be heat shrunk together. So, when you finally go to heat shrink the whole thing up, you also inevitably get a lose connection.

So, even if this were to work when you get to the flying field to teach someone how to fly, I wouldn't be surprised if the cable isn't reliable.

I'm scrapping this project. Not worth it.

• In response to your comment from the now-deleted post about not having enough rep to comment: Still don't post an answer here if it's not an answer. If you have questions about anything in this OP, you should then make a new question that references this one.
– ifconfig
Mar 9 at 17:44
• I'm glad you're coming to our forum site, so welcome! But please acknowledge and abide by the code of conduct we use.
– ifconfig
Mar 9 at 17:45
• @Alvin, I found an S-Video cable in the house shortly after my problem above. Mine was wired similar to yours. Swapping the two inner wires over was a little tricky as you say, but it can be done, and insulated properly with a few well placed strips of heat shrink. As for connecting the housings, I cut away a little of the plastic casing on each end to solder a wire to, but then found the cable seemed to work without it anyway. The cable is sadly a little unreliable, but because the plugs are not tight enough in the sockets, rather than because of the wiring. You can't win eh! Mar 24 at 22:58