Long-term Memory

When learning to fly a remote controlled model, getting a good teacher is worth a lot. But if all the teacher can do is watch the plane crash, he/she is of not much use…

Most transmitters have a “trainer” connection. This allows two remotes to be connected together. One is preforming the master-role and is actually controlling the model. The other remote is the slave and sends signals to the master. The teacher can program his master-transmitter to copy some of the slave’s signals, thereby letting the student control the plane. A simple toggle of the switch returns the control to the teacher.

Obviously, each brand of transmitters has its own “standard” of doing things. Some use a DIN6 contact, others use a mono- or stereo 3.5mm jack and there is the obligatory “proprietary connector”. Here are my notes of the expedition into the trainer-cable jungle.

Most transmitters give out the unmodulated signal on one of their pins. For compatibility reasons, you should always make sure the slave sends out PPM signals and not the brand-specific PCM signal. My Futaba FF9 has a 6-pin connector which I’ve never seen before:

This is the male plug; the transmitter obviously has the corresponding female socket.

Following the numbering scheme on the right picture, I measured the following:

• Pin 1 does not seem to be connected
• Pin 3 – Pin 2: gives the unmodulated signal. High is approximately 1.8V; low is 0V
• Shorting pin 4 and 5 (as shown in the picture) activates “simulator mode”: the transmitter switches on, but the RF module is disabled.
• Pin 6: signal input from slave

The signal is either PPM or PCM, depending on the selected transmission mode. It seems to be negative: long pulse high, shorter pulses low. The picture on the right shows a slave or simulator cable: the RF is deactivated and the output of the remote is carried across the cable, either to the computer or the master remote.