I have at times subdivided the power supply, that is had one battery supply power to, say rx and tail surface servos and another only powering ailerons, or whatever you need. The way to do it on a two-servo aircraft is to cut the positive lead from the rx to the elevator (being normally more used than the rudder) and solder a male connector to the servo lead, connecting the red (positive) lead and making a Y-junktion (if that is the word) to the black (negative lead). Now, you just insert one battery in the rx as ususal, check the function - rudder OK? Now you insert the other in the connector on the elevator servo lead. OK? Both should work very well by now, if you haven't made a mistake! It doesn't work if you cut the negative lead instead! You could make a Y-lead harness that duplicates this function, of course, but the more connectors, the more weight wasted! This arrangement is especially good if you have a wing with lots of extras in it, like flaps, dive brakes, spoilers, electric landing gear, et cetera, things that are not 100% essential for flight, but heavy power drainers, with high peak demand. Use a hefty power pack for those, with low internal resistance, say SCR1700s, while the essential functions could be serviced by a BEC, if the model is electrically powered, or a big 3000mAh NiMH pack, if it some kind of long-edurance sloper. I used this system when I installed a failsafe on one of the channels and as the normal reason for the rx to die is battery failure, the failsafe would be unable to do anything about the situation when the power failed if it hadn't the ability to power itself and the servo (a throttle servo) after the rx quit. It worked flawlessly when tested on the ground (I just turned off the rx power switch and the throttle closed and the engine stopped, just as I wanted it). It never was tested in earnest, but it could equally well be used to switch batteries automatically in flight - if the main fails the servo could push a switch to change main battery, so to speak - but be careful so the servo can't flip the switch back - as it then would cut the power from the 'new' main battery as soon as the rx goes on line again! A much simpler way, and MUCH cheaper and lighter, is to install low voltage drop diodes in series with both your packs, that way they can't recharge/dis- charge each other. if you normally use four cells I would recommend five cells and normal silicone diode - if you're not extremely weight concious, that is. Then you need a better diode with less voltage drop - ask the retailer! Air raid alarms going off outside - I better get going :-)! Tord, Sweden *'`'*.,.*'`'*.,.*'`'*.,.*'`'*.,.*'`'*.,.*'`'*.,.*'`'*.,.*'`'*.,.* -- If reply difficulties - use [EMAIL PROTECTED] Tord S. Eriksson, Ovralidsg.25:5, S-422 47 Hisings Backa, Sweden RCSE-List facilities provided by Model Airplane News. Send "subscribe" and "unsubscribe" requests to [EMAIL PROTECTED]
