ukengineman

There have been some queries refering to the F&M Digital 5 Tx and its use with a modern Futaba AM Rx. As I have been working on this project the following may be of interest. Back in the 1960's I had a Digital 5 and I have recently aquired another identical system which I am restoring. grotto2 also has one and we have exchanged useful information. I have the Tx fully operational and have a jumper which enables choice between F&M mode and Futaba compatible. The frame rate is fixed at 35ms which is OK for the modern Rx. Although 5 channels, 7 are actually transmitted the first and last are fixed length guard pulses and are part of the F&M Rx failsafe system. The first pulse shifts all the others along one so as grotto2 has pointed out you would only get 3 channels from a Futaba R114. Also the first guard pulse on my Tx is very long and causes the Rx O/P's to jitter. In the F&M Tx all the pulses are diode OR'd together to the gap pulse generator. A good tip from grotto2 is to lift the first diode (I have a jumper here) in the chain which removes the first pulse. The R114 then works happily giving you motor, aileron, elevator and rudder - you just lose the aux channel. The Bonner Digimites worked on a 1.7ms centre so for use with modern gear you will need to make this 1.5ms. On the F&M Tx PCB there is a master trim pot for each channel and they can easily be adjusted to 1.5ms, these pots are quite fierce in their adjustment. I have attached (hopefully!) some waveforms of the Tx envelope, one shows a complete frame (about 35ms, display 5ms/div) another shows the 7 pulses in F&M mode (2ms/div) and the remaining one shows the first pulse suppressed for use with a Futaba Rx (2ms/div). The 5 channels are centred on 1.5ms. I hope to fly at some of the UK meetings next summer using the F&M Tx with a Futaba R114 or HPI RF-2 Rx.
Alan