Technical, Techniques, Hints, and Tips > Radio Equipment
Digifleet FM Tx service manual
scimitarjohn:
Most 'IT pros' I dealt with would have a job changing your screen saver! Pretty sure my service manual came with the set but if not I dread to think of the hours I'd have to work for that £2.50 back in the day.
roycv:
Another memory has surfaced! I used to do my own repairs and bought several Fleet servo electronic kits to replace the electronic kits in older servos, they all worked fine and there were no problems. At the time the government decreed that there should be a circuit diagram of the electronics in all items, radios etc, that was when we had more discreet components in use.
I noted that the electronics chip in the kit had the description scraped away, there is a notch in the chip to orientate it in the circuit and I am prettty sure the components in the circuit were not identified either. I knew which chip he was using and anyone else could have worked it out from the component placement.
Make what you will of it but it seemed a bit 'cheap' to me.
Maybe around that time Acoms brought out an esc with a full speed over ride. Back then there was a 0.7 volt drop across the power transistor (OC29 or OC 35 etc,) and if you were using 10 amps (I never did) then there was a significant power loss in heat and hence the large heat sinks at the time.
I had an idea how to make a circuit that did an over ride but wondered how Acoms did it. I borrowed one and traced the circuit out for my own benefit. It was a straight copy of a published circuit I had also found.
If anyone wonders what I mean, you take a sample of the output current which is via a resistor in the emmitter / gate circuit of a transistor with a relay as its load. When the current hits the maximum it is enough to trigger the transistor to call the relay which then switches the battery direct to the electric motor, so eliminating the esc and power losses from the operation. I know it seems a bit cheap on my part but the equivalent cost then was more like £100+ for an ESC.
The first esc I made was the Pompey esc published in one of the magazines. This had the motor across the bar in the H with 4 power transistors at the corners of the H, so the total voltage drop was double the above at 1.4 volts and with 10 amps flowing that is 14 watts of heat that could be going to the motor!
I do not know how it is done now as I have tiny esc's that take 10 amps with no heat problems at all. I stopped my electronics when the surface mount technology came in!
Everything is so cheap now there is no incentive to diy your electronics.
Roy
scimitarjohn:
I know what you mean, it's a cost benefit thing but I still play, my last was variable voltage/current power supply for the Lions etc. My first set all valve, non het outfit, 27 Tx with twin triode for variable mark space, relayed output on the Rx to drive a leadscrew rudder positioner. All homemade, still have the Rx ! how I wish I'd have kept the whole thing. When I'd saved up enough for the Digifleet, I'm not even sure esc's were available, were they? anyway built my own using the Ferranti SRC419 chip with a bank 2N3055s on a big copper heat sink to drive. Still use it in a Sea Viper I built when I was about 12.
Circlip:
Now that looks like a hairykits Sea Hornet?
Regards Ian.
scimitarjohn:
I'm afraid it was over 60 years ago Ian so only remember the name as someone on here told me a while ago. It ran with single channel radio and a 6v lantern battery for the motor so a very leisurely pace, perhaps a good thing with no speed control? I played on a lovely pond at Blackheath, no boating there now thanks to the killjoys.
Navigation
[0] Message Index
[*] Previous page
Go to full version