Buddy box or buddy boxing is a colloquialism referring to two R/C aircraft radios joined together for pilot training purposes.
Buddy boxing is accomplished by joining the student and master transmitters via a cable. The instructor gives the student control of the aircraft via a spring-loaded switch (or button) on the top left corner of most transmitters. When the switch is held on by the instructor, control of the aircraft is at the student's transmitter. Should the student encounter difficulty in flight, the instructor can regain control at the master transmitter merely by releasing the switch.
This has the twin advantages that it eliminates the time delay of physically passing a transmitter between student and instructor (allowing training at a much lower level), and it gives the instructor the power to regain control when he wants.
It should be noted that the two transmitters need not be on the same frequency. The master transmitter is the one that actually flies the plane; buddy boxing turns the student transmitter into a "dummy" remote control of the master. The student transmitter is operated with power switched off and the crystal removed as power for both is provided by the master. The student transmitter will power up via the buddy box lead despite being switched off.
It is important to make sure that the servo reversing switches, trim, rates, mixes, etc. are set the same way on both transmitters.
Some buddy box leads do not provide power, making it necessary to switch on the slave transmitter with the crystal removed to prevent it from transmitting.
Some advanced radios allow the master to switch only some channels over to the slave and to retain control of the others. Others allow the signal from the slave to be mixed by the master transmitter, so one does not have to duplicate potentially complicated mixer settings on the slave transmitter.
This training system is universal among the five major R/C radio manufacturers (Futaba, JR, Hitec, Airtronics and KO Propo) which means that transmitters do not have to be the same brand in order to be joined via an umbilical cable. There are, however, many incompatible different types of cable connectors (plugs). Futaba even has 'old' and 'new' style plugs. Manufacturers do not sell leads to connect to other brands but it is possible to build one from different plugs.
There are also two incompatible modulation schemes, positive and negative
- JR and Sanwa/Airtronics operate with positive pulse code modulation
- Futaba, Hitec and Multiplex operate with a negative pulse code modulation
- Graupner radios are either positive or negative modulation depending on model
It is possible to use some simple electronics to convert between these.
- Buddy Box compatibility between different brands of transmitters.