RC Model Reviews

Hi all,

I have a turnigy 9x and I want to help my girlfriend with her flying. She fly's good but sometimes makes a (for her) unrecoverable mistake. She has her own model with her own rx, a HK-T4a.

My questions are:
- which one is master and which is slave?
- How do I have to connect them and how do I have to setup the switches.

Thanks very much!

Anyone? Is it posseble at all?

Ok back to basics, Does the HK-T4a have a trainer port and do you have a cable?

(ok I found a "manual" and see that it has a ps2 style trainer port.) http://www.rcgroups.com/forums/showthread.php?t=1051701

In most cases the master will be the transmitter that normally controls the aircraft.

Personally though I would go for a trainer transmitter with a momentary switch that the trainer holds to relinquish control to the student. When panic sets in they release the switch and recover.

Maybe convert her to a 9x as well, which makes buddy boxing a piece of cake. Or swap receiver with a 9x one and use your 9x as the trainer and her rx as the student.

I thought the trainer had control over the panic switch...

I don't know anything about "buddyboxing" but my preference would be to have her controlling her plane with her Tx (HK T4a). If I see her getting in to trouble I let go of my trainer switch and have control. The reason for this setup would be a panicing GF forgetting to release the switch (I know her to well ). It doesn't matter witch Tx is bound to the Rx because they both can bind to the same Rx's.

So in a nutshell:
GF flying with HK T4a
Me holding 9x trainer-switch and taking over if nessesary
Receiver doesn't matter

Would this be possible?

Edit: I have the skills to make my own cable

Buddy Box definition from Wikipedia

In short this system uses the master tx to send control signals to rx. Student tx does not transmit but sends signals to teacher tx for transmission. Teacher tx decides what to do with signals depending on setup (trainer switch etc).
As far as who controls what, technically it is going to be easier for the 9x to be the tx to the aircraft and passing through the student control signals. I cannot see a trainer switch on the HK unit so using that is out of the question.

Jim's suggestion is another good idea, but does require the aircraft to have receivers from both tx units installed. So you will need room in the aircraft to fit it.

This is 4 channel version. Check the files section for how to wire it in.


If you are going to go down the traditional buddy box system, your next issue is going to be creating a cable with a s-video (not ps2 as I originally said) style connector at one end and a mono 3.5mm at the other. From what I can work out pin 1 goes to centre and the shell/ground goes to ground.

Otherwise pickup one of the suggested aircraft based units and install that with the two rx. Setup the 5th channel on the 9x to be controlled from the trainer switch, test and double check all works correctly, and off you go.

Frazzy wrote:I thought the trainer had control over the panic switch...

To reiterate: As I understand it (and this is how I set it up) the preferred method of a buddy box setup is that the trainer tx is set-up so the trainer pulls and HOLDS the trainer switch to relinquish control TO the student tx. Releasing the switch reverts control back to the trainer tx.

So the trainer has to actively hand control over to the student and continues to hold the trainer switch until such time that they need to regain control.

The trainer switch is usually a momentary switch i.e. the switch is spring loaded so it always returns to the same position, unlike an on/off switch.

I'm going to make the cable and see what happens. Although the AXN has lots of room, I don't think I can fit two receivers in it.

Oh and BTW Trainer mode under Er9x firmware waaaay better than stock firmware.

I use Er9x and have upgraded another club members radio to Er9x. He was struggling to get a working Buddy Box with his 9x. Flashed it and all his difficulties setting up trainer mode vanished.

were the difficulty's setting up for master or for slave? I'm going to use mine as a master so it shouldn't be a problem.