(18-06-2012, 06:26 PM)wingtipper Wrote: i'm a bit of a novice here , but i scrutinized one of jasons bigger models with this very thing in mind . his UBECS , are soldered into the 6s battery deans plug , that also plugs into the ESC . i thought 2 things here . #1 wow thats great for power energy supply , and # not so good if your battery cokmpletely fails in the air . but really your servoes will draw what they require , not what the U'BEC SAYS . so the higher i would think the better , 6 i would think would be ok . of course i'm only theorizing , and i'm glad you found the problem . i'm sure with your 6s 5000mah battery , it would supply heaps of current to the servos ,
even when the motor starts to drop off .
good luck , i havent done this yet , but its on my mind also , for safety . look forward to reading others opinions on your questions , and finding out the correct answer , but you seem already on track to the fix .
I do solder the BEC inputs on to the Terminals of the plug for the ESC on some of my smaller models but these are only 3S and 4S setups. On every model that I run 6S the ESC has it's own internal 5A BEC. Except for my Ugly stick which uses a 4S nicad pack for the radio link, it also has a nicad voltage monitor/alarm on it, as it's the only 6S powered model I run with out telemetry to monitor the battery voltage.
Frank you may have mistook the voltage divider I use to provide the signal voltage to the FRSky RX, for a BEC on one of the 6S models when you were looking at it. It's also soldered to the ESC's plug terminals.
The FRsky telemetry uses an A to D converter that accepts a signal voltage between 0 and 3.2 Volts. I use this to monitor the battery voltage, Actually it can monitor 2 independant voltages, I measure one from the main power pack and one from the radio link pack or BEC/liniar reg.
Now the voltage it measures must be between those limits, 0 and 3.2 Volts, you can set an alarm to go off at any point you like with in that range. There are two sets of alarms for each channel, stage one, basic warning, stage two more urgent, Set them at some point between 0 and 3.2V and then use a voltage divider to bring the Pack voltage sample down to the right ratio to match the alarm points. It may sound complicated but it's not that hard to do and wellworth it. I reckon Samste will be looking to do something like this with his New TX and FRsky Telemetry recievers.
On the bigger models that run 12S I use dual 8A liniar regulators with two seperate 800Mah 2S lipos. That provides nice clean noise free power to the Reciever that is totally independant of the (often noisy) motor supply. Also because there are two supplies if one fails I have a second to keep the RC link up. You need to use diodes if you going to connect two liniar regs together or you can use a twin one that's ready made from dual sky. About $30
It's worth remembering that tha greater the voltage difference across the BEC the harder it has to work. You may well find a BEC that provides 5A with 3S could only provide 3A with 4S.
There are different types of BEC some are little switch mode supplies and can be noisy, but handel the voltage difference better than liniar regulator type BECs. Liniar regs are very low noise, better for your reciever and servos but work very hard if there is a big voltage difference between their input and out put.
Those big servos do use quite a bit of current. You can measure it but if you do, use a 10A multi meter not a 100A curent meter that you use for measuring your main motors current draw. Big current meters are not very accurate down in the lower ranges. Don't just take my word for it check it your self.
Those big servos need a burst of curent to get them moving that's where you see the high draw it's a pulse when the servo's motor spools up then the current drops a little. If there's big enough capasitors in the BEC then it's not such a problem as they kind of act like a flywheel and smooth things out a bit.
If you have a current or noise problem a seperate Nicad pack will be a great solution if your not too worried about the weight. It can provide 20A if need be and is not very expencive. I think it's a good idea to have a low voltage monitor or alarm for a seperate pack if you use one for the RC link.
Hope this is of some help.
X9 & DX8
paaaaaatience 
paaaaaaatieeence 
dooooohhhh !!! 
