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Is this a simple RC buddy box system ?? Answered

Hi Guys,

I have recently resurrected my interest in Radio Control Aircraft. When I was teaching I ran an after school club to build and fly RC aeroplanes - However it is very hard for youngsters to pick up the skills without excessive crashes.

There is a system to over come this - The buddy box system available on many of the high end RC transmitters. 2 compatible transmitters are linked with a cord one is the master and one the slave. The operation of the master slave is by a switch on the master system.

Now all of these radios are relatively expensive - £100s. where you can buy relatively cheap equipment without this facility for £30 or less.

As far as I can tell the signal on the buddy box cord is a PWM signal which is passed serially from the slave into the master processor to proved the stick position information from the slave.

My question is will the much simpler cct below work or have I missed something in my though process.

I propose to cut the 5 volt line to the sticks in the master and insert a DPST switch This switches the 5 volts to the slave system which is un-powered. With 6 lines - 4 signal 1 +5 volts and 1 ground line I can provide the necessary position signals to drive the master transmitter.

If necessary I can fit a DPDT switch and cut the ground line as well.

Flicking the switch back will give control back to the master by switching the +5 volts.

If this looks OK I will get another transmitter and do the modification - Have I missed something obvious here.


I can't see why it wouldn't work - The only 'gotcha' may be the trim adjusters but as long as they don't adjust the physical position of the pot, (I think some cheap TXs do) you should be OK.  Can't see a problem if trimming's done in the software. 

I learned to fly RC (to a fairly basic level) on my own and found time on a flight sim invaluable.  I used the free FMS which takes its input from the buddy port of most transmitters.  Takes a bit of configuring but good results once it's working.

If you've flown RC before you probably know this already, but for learners you should tune the control surface throws right down on the TX to reduce the responsiveness of the model.

How about putting together a couple of RET Nutballs? Easy to build and great fun to fly, indoors or out, as the designer says 'from mild to wild' depending on the throws. 

Just thinking on a bit, with the simple arrangement you would have parallel resistance paths from the pots which weren't being used  You may need changeover switches on the pot sliders too.  The neat way to do this would be with analogue switches (CD4066 etc).

My thought is that if I go into the wiper connection (and isolate the ground line as well) - Then the master pot is effectively isolated as there isn't a signal path through it.

I don't know with 100K pots this will be necessary. May only know on trial.

This just seems so simple I wonder why I can't find any reference to is on any RC forum etc.

An example - If you're switched to slave you'll have a path through the master rudder slider to the (isolated) master 5V and 0V lines via the upper and lower parts of the master rudder track, and then to the other master pot sliders via their pot tracks above and below the slider, then back to the slave unit via the other connected sliders.
Any manual change to a control would reflect back to a small change on all the other pots. How big?   Best to suck it and see.

Maplin used to do a 6 pole 2 way rotary switch which would allow you to switch 5V, 0V and the four sliders . . . but no longer.   I've just had a look in my spares boxes and found 1P12W, 3P4W, 4P3W but no 6P2W.  (Schrodinger's switches - They're all there until you go looking for a specific one #;¬)

:-) I have just completed a nutball - waiting for suitable weather to fly.

http://www.flitetest.com  have an interesting approach to building. Some good video and free plans on their site.

Thanks for the input. I think it may be one of those things I am going to have to try. I have a old 27 Mhz 4 ch somewhere I can strip for the slave. need to find it now.

FMS doesn't seem to like my win 7 set up - I will have to look for some solutions.

Great minds think alike eh, Rick? You'll have fun with the Nutball ;¬)

Have you tried THIS fix to get FMS working with Win7?  It worked for me,

Rather then spend that much on they system or try to cobble together a system of your own, invest in a training simulator. For about $30 US you can get an RC simulator that comes with 6 channel remote that plugs into your computers USB port and allows you to practice flying without endangering the real planes.


I have seen then although a bit more expensive here -and a lot easier to fly thsn the real thing.

I still need input on mh circuit idea please guys have i missed somdthing simple electrical or doez, it look like it might work.