A buddy box setup is clearly the best way to train a new RC pilot. If you simply stick to one brand of transmitters for everyone involved, that’s not too much of a problem. But most flying clubs have quite a variety of systems being used – most of which are not compatible with each other. What do you do in a situation like that?
This article is a start on solving this problem. Reading between the lines, that means I haven’t totally solved it yet! But, I thought I’d let you in on some of the challenges in pursuing what seems to be some obvious solutions. As we get additional system solutions in place and tested, we will add those along the way.
Our buddy box system goal
In our club, the majority of the newer flyers have Spektrum radios. A handful have Futaba systems, and a few of us have Radiomaster or other similar ones. If a person just starting has plenty of cash to burn, they will probably just use Spektrum, as it is good and a bit less complex than an EdgeTX radio (Such as Radiomaster). With me being a Radiomaster guy, but having a lot of planes with DSMX receivers (mainly Lemon RX), I want a system that’s going to work with what I’ve got. Along with my own transmitter, that involves both the student’s transmitter and the receiver in the plane that he is going to use. So, ideally, we would like to be able to use pretty well any transmitter for the student, and whatever receiver is compatible with that in the plane, and have both of those work with one instructor transmitter. It’s a rather tall order.
The perfect buddy box system
Unfortunately, it doesn’t exist. But let’s get as close as we can.
For me, the simplest solution, and the best, is a pair of Radiomaster 4 in 1 modules. One internal, and one external. In addition, I have an external ELRS module available, when needed.
I use the internal module as the receiver, and transmit from the external module (see footnote 1 if you want an explanation). When the plane has an ELRS receiver, I use the external ELRS module to transmit.
For the internal module, in Model Setup / Internal RF, select “MULTI.” You can then select whichever RX protocol suits the student transmitter:
- BayanRX – Bayan Toys protocol – mainly used in toy quads
- DSM_RX – DSMX protocol (Spektrum)
- FS2A_RX – AFHDS 2A protocol (FlySky)
- FrSkyRX – Unsure which FrSky protocol this is for. My guess would be D8, as the Radiomaster R81 receiver can receive that.
Unfortunately, this list of recievers is way shorter than the list of transmitter protocols. So, for example, it cannot receive a radio signal from a Futaba transmitter, yet it can transmit a signal to the lower end Futaba protocol, S-FHSS. But, the big one for me is DSMX. That means I can have either a Spektrum, or a radio with a 4 in 1 module, as the student radio. And with the external 4 in 1 module I can transmit to the vast majority of receivers.
A protocol that is rapidly gaining popularity is ExpressLRS (ELRS, Express Long Range System). I started with Spektrum, so when I moved to a Radiomaster transmitter, I bought one with the internal 4 in 1 module. Later I added the ELRS external module. So now, in training, I can receive a signal from either a Spektrum or a 4 in 1 radio, and transmit to the an ELRS receiver in the plane. Where the student radio has a option to use ELRS, it can later be bound to the plane and used directly.
It’s then a simple matter of swapping out the external 4 in 1 module with the ELRS one as needed. As they clip in an out, that’s quick and easy. Here’s a video showing that system:
The lowest cost wireless buddy box system
Given that being able to receive a DSMX signal is the key, there is a low cost way of doing that with Radiomaster. It involves using a radio with the internal 4 in 1 module along with their SBus trainer module plugged into the JR bay. Inside the external module you add in a DSMX SBus receiver, powered by 5 volts.
In keeping the cost low, the 5 volts is the key. Spektrum make an SBus receiver that operates on 5 volts, but it’s cost plus the cost of the module brings the total cost up to that of a 4 in 1 module. But I have found a cheap SBus receiver sold by Ali Express that operates on 3.5 volts, and an inexpensive voltage reduction chip that can bring 5 volts down to 3.5 volts. Being on the cheap side for the link between the student and instructor isn’t a big deal, in that, should it fail, the instructor will simply take over anyhow.
In my initial attempt in implementing this solution I wasn’t aware that the voltage was different, and I think I cooked my SBus receiver. I have tested the voltage reduction chip, and it is delivering the right voltage, so I have another receiver on order, and I will be testing it.
Note that Radiomaster recommends their R81-V2 receiver for use in the trainer module. I also bought one of those, but so far have been unable to get it to work. With it you need to solder wires onto a tiny circuit board, right next to a computer chip, and I think I cooked that one in my soldering attempt! Are you picking up on a theme? These low cost solutions are very fiddly, and you might end up spending just as much on them if you attempt them as many times as I am doing! Anyhow, for the sake of completeness, I’ve also got another R81 on order, and hopefully we will be able to evaluate both those solutions in due course – along with tips on how to do it without cooking things!
Another possibility that we are looking into is using the Lemon RX transmitter module. It fits in a JR bay and is potenially one of those ideal, low cost solutions. We will be testing it.
Programming your radios for buddy box training
There is a procedure that you need to go through in setting up the student and instructor radios for training purposes. The above video shows you how to do that for the system with the external ELRS transmitter. As we get the other systems in operation we will also produce videos showing how to set them up. See youtube.com/@rcjim
Footnotes
- That is because I might be working with a plane having an ELRS receiver or one of the main brands. The 4 in 1 module doesn’t include ELRS. If the student is going to use ELRS, then they already have a Radiomaster or similar radio, and they can use a 4 in 1 module to communicate with my Radio. Unfortunately, as I have an internal 4 in 1 module, I cannot both receive and transmit ELRS at the same time.
RC Jim 