Wireless Buddy Box

by HilldaFlyer | September 18, 2015 | (6 Ratings) Posted in Projects

Wireless buddy box

Directions for building wireless training system. Cordless Training Setup between DSM2/DSMX compatible slave transmitter and Taranis as the Master transmitter. This modification will work for any slave receiver that has a CPPM output.

Ever since purchasing a Taranis Plus X9D and transferring all of my models from my Spektrum DX6i, I’ve been wanted to repurpose the DX6i to a more useful item than being a paper weight. Using it as a trainer (buddy box or slave transmitter) is just the thing. Over the summer I was helping a beginner pilot take to the sky with one of my models using the DX6i as a slave controller to my Taranis X9D. He was doing great for a first flight and then all heck broke loose - the plane seemed have lost all control. By taking control, the plane was saved in the nick of time. Unfortunately, when I switched the control back to the slave transmitter, the plane went out of control again. Come to find out, in all of our twisting and turning, the buddy cord that connects the two transmitters, got pulled out just enough to lose the connection. Having a short tether between two people trying to fly is really a pain. The solution, of course, is to go wireless. This article shows how you can build a wireless buddy box a couple of different ways and resolve a couple of issues I discovered in the process.

Self-Contained External unit.

The self-contained unit has its own battery and used the mono plug to connect the signal to the Taranis. This is probably the best method for individuals who don’t want to crack the case modify (add wires) to the Taranis’ PCB.

Since this unit is completely separable from the master transmitter, it can be easily used on another master transmitter or bound to a different slave transmitter, besides, it can be removed and stored when not in use. Another plus is that it does not use any power from the master transmitter. However, the downside is that the additional battery adds weight and bulk to the master transmitter and it is yet another battery to charge or to forget to turn off.

For this configuration, I used a 1000 mAh 2S LiPo. The input power range for the R410X or R615X is 3.7 to 9.4 V DC, well within the range of a 2S LiPo (6.6 v to 8.4 v). I used a mono plug from that I had from some old electronic equipment.

I probably should have shortened it to about 5 cm, but I left the cord long incase I wanted to use it for something else or put the slave receiver far away from the master transmitter. It is my understanding that you can use a stereo plug from junked headphones - just make sure you wire the signal lead to the headphone jack tip. The battery is wired to a servo plug, positive to the middle and negative to the end, as normal. The plug tip is wired to the signal pin on the servo plug and the stalk is wired the the negative pin on the servo.

Here is a post thread that help me in this process. “Spektrum wireless module for radios without wireless trainer capabilityshows how to add OrangeRx R615X inside a RadioShack battery box with, and later in the thread, without switches and binding buttons.

External Slave Receiver Powered by the Master Transmitter

The following modifications will void the warranty on your radio, so best that you have a skill level that will support the modification - basically you need to be able to solder a wire to a PCB.

The difference from the previous modification is that the receiver is powered by the transmitter’s battery. The power wire can taken from an the transmitter's battery by adding a “Y” harness to the power cord or by soldering the power leads to either a post on the battery plug or an post that is controlled by the Taranis’ power switch.

There are two ways to get the signal into the master transmitter 1) use a mono plug and the plug socket on the Taranis or 2) solder a wire to the signal pin on the inside of the master transmitter. This modification requires the ability to crack open the case of your transmitter and solder wires to its PCB.

True to form, I plunge in with a screwdriver and a multimeter. Remove the battery. Use a small pair of needle nose pliers to loosen the switch securing rings which straddle the case joint. I marked the switch with a piece of tape so that I could be sure to replace them in the same orientation. Remove the 6 phillips screws on the rear case that hold the front and rear cases together and gently separate them.

Open the case of the Taranis and lay both sides flat on something soft. I used a continuity to locate the battery connector pins. They are located directly underneath one of the ribbon wires that connect the front PCB to the rear PCB.

To disengage the ribbon wire from the clamp, gently lift the clamp and the ribbon will release.

This photo has colored toothpicks pointing to the unswitched battery lead pins.

I used a mono plug and continuity meter to locate the pin that is connected to the plug tip (toothpick points to the spot).The CPPM signal pin is located here.

To connect the receiver to the Taranis, I used a 15 cm JR style servo wire that I removed from the last plastic gear 9 g servo that shattered its gears. Cut the wire to size, strip off the insulation, tin with solder and solder into place. I used a small piece of paper and hot glue to secure the wire and hold it out of the way of the ribbon wire.


Before you go and solder anything, let me share with you what I learned. There is a slight modification you should perform to make you life much easier. It turns out that if you connect the signal wire directly to the signal pin, as I had originally done, the receiver will go into bind mode when it is powered up. I thought this had to do with the timing sequence of turning the different parts on, but I could not find a sequence that worked every time. There is a fix, however, that is really simple. Internet searches revealed others have had this problem and solved it. RCGroups Wireless trainer port revised shows how to add an inline resistor to the signal wire to prevent going into binding mode when powering up the Taranis. Buffered CPPM with 22K also shows how to do this.

So - I did this too. I installed a 22k ohm resistor to the signal wire and

I covered it with a little shrink wrap and resoldered it to the PCB. I have disconnected and reconnected both the R410X and R615X several times and they stay bound to the DX6i transmitter and don’t go into bind mode like they did before this modification. Perfect!

The servo wire can be routed to the outside of the case in several ways. I choose not to damage or modify the Taranis case in any way by feeding the wire into the battery compartment. You may elect to cut a small notch in the side of the case where the front and back cases meet, or put a hole in the back case or battery compartment lid. Others have created a hole into the module bay and placed the receiver in it. I elected to feed my wire into the battery compartment and then out between the case and the battery compartment lid because my module bay is always used by the DSM2/DSMX module.

Finish the modification by reconnecting the ribbon wires to the PCB by slipping it back into the ribbon socket and sliding the clamp back into place. Place the rear cover back onto the front ensuring that there are no wires hanging out and the ribbon wires lay flat. Screw the back cover onto the front and tighten the switch securing rings.

It’s alive! But wait a minute, something is wrong! What’s Going On?

When using the buddy cord, my Spektrum DX6i worked flawlessly with the Taranis. When I switched control over to the slave transmitter, the elevator went full up and the motor spun up. Using the wireless module the channels were all screwed up. It turns out that the CPPM out from the R410X and R615X are in a different order because the throttle stick controls the elevator, the aileron stick controls the throttle and the elevator stick controls the ailerons. I’m not the first to discover this. Sounds like Dave McDonald had the same issue.

I was surprised to see that the CPPM channel sequence on the R410X comes out as AETR instead of TAER.Changing the buddy box channel sequence and reversing the aileron input on the TRAINER screen of the Taranis quickly fixed the problem

This is no big deal with the Taranis because you can easily set which channels of the slave transmitter control what channels. Scott Page demonstrates how to setup the the Taranis Trainer in word and a video. Sean Cull also provides a great explanation on how to change the inputs on the Taranis. If you like a video Painless360 also provides the setup and calibrate. Note that this demonstrates the wired buddy box with stereo plug. The plug’s tip is the CPPM, so stereo plugs should works too. There, now that it’s all sorted out and works great.One reminder, when you use a buddy box, always ensure the channels are properly selected as a part of the pre-flight check using both radios, especially if you switch the slave receiver.

The last step is to secure the slave’s receiver to the Taranis. I used a little piece of velcro. Of course this is optional - the R410X is so small and light that you could just let it dangle on the wire when in use.

When not in use, the wire tucks neatly in the battery compartment and the buddy receiver velcros to the back of the slave DX6i. In this configuration you don’t have to remember to charge the trainer module; it is as ready as your transmitter. I like the attribute that being external, it is accessible for binding or troubleshooting and you can see the indicator light inside the receiver. The almost insignificant downside is that the slave receiver uses your transmitter's power. Unless you wire it to a switched power pin, you will always want to unplug it when you are done for the day or it will surely drain your transmitter battery.

Done! No more tripping over cords.


One Last Configuration to share - Completely Internal

This configuration is almost identical to the previous one except the slave receiver is secured to the inside of the Master Transmitter’s case and the power is derived from a switched power pin so it turns off when the master transmitter is turned off. This arrangement is very clean, you’ll never forget it, it will always be ready to go with your transmitter, you’ll never forget to unplug it, but it would be a real hassle to troubleshoot at the field if it doesn’t work. Additionally, with this modification, there are other things that should be done to improve functionality, like adding a bind button and power switch so that you can bind it to other slave transmitters and turn it off when not in use. See references below for more information.


A note of caution. I did not experience this, but I thought it would be good to share.

Post 29 comments on safety of non-connect motor issues. I wanted to add that I would recommend you put the trainer on 2 switches. One to "arm" it, and the momentary switch to activate it. If you just leave it on the momentary switch, and you flip that switch with the plane on the bench and on, then it could put the throttle up to 50%. The default is all channels centered when there is nothing bound to the RX. Not sure if this is default from the RX or from the Taranis ppm input, or if anyone else's will be different. Just something to keep in mind.

Post 29 I checked and yes, if no trainer input is being received, then all trainer inputs are set to 0 (50%). I adjusted my trainer mode switch so that if throttle, elevator, and aileron are all 0 then the trainer switch will not activate.

Post 30 actually that is a good idea... Only I'd probably just use the throttle. If throttle is at 0 or less, don't activate trainer. (this way trims on other channels don't mess with it and allow it to activate) especially if you don't have an extra switch. But be aware what it will do in the air, if you hit the switch by accident while flying (half throttle and center all channels)



RC Groups “Taranis wireless buddy box using lemon r”Using a Lemon Rx instead of OrangeRx to connect to the Taranis

Post 12 introduces OrangeRx as receiver since lemon discontinued CPPM support.

Post 39 shows the OrangeRx 615X installed in module bay.

Post 41 modification to avert the R615x from starting in bind mode when Taranis is turned on.

OpenRC Forums: Wireless Trainer Connection on Taranis.

RC Groups TARANIS wireless trainer mod

RC Groups: CPO Quick Tip : Wireless Sim or Buddy Box with DX6i and Lemon-RX DSM2 PPM and You Tube: CPO Quick Tip : Wireless Sim or Buddy Box with DX6i and Lemon-RX DSM2 PPM

HilldaFlyer - September 2015


The-One-Who-Never-Crashes on September 25, 2015
Awesome job--great method and presentation!
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Yogenh on October 1, 2015
Can the same be done with the DX-7?? I have the DX-7 and a DX-6 and would love to be able to do something like that with it. Mine are the older ones that are not made with the wireless trainer.
You have been doing good with this. Thanks

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HilldaFlyer on October 1, 2015
I don't see why not. I performed the reverse by using my Taranis as the slave. There were those channel issues I mention in the article, but since is not the configuration I would use I didn't take time to solve it. Let us know how it goes.
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LapinFou on October 11, 2016
Hi folks,
This mod is not working with OTX2.1 or higher.
Here is a solution which is working fine for me. :)

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djdazzy on April 27, 2017
If you are running OTX2.1 or higher, you can connect everything into the JR bay connections without soldering. Feed the CPPM signal into the heartbeat pin.
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