So I inherited a plane with twin 70mm motors. Everything seems in order except there seems to be no BEC. When I hook up the LiPO, the motors beep, but no respinse from the surfaces, and I just get a sporadic beep that separates progressively further between the two motors. No problem, I hooked up a separate battery to the receiver, and everything works the way it should. Which told me there is a missing link. Normally you get a plane that's ready to go, and the ESC/BEC is a combo. Yes there are setups where the BEC and ESC are separate, which seems to be the case here.

My question is, in the experience of seasoned electric powered pilots, would there be a problem with using the LiPo for the fans and a small LiFE for the controls together? I hooked it up this way and it works, but if over time it will cause problems (at some point they are both sharing a common ground, and are different voltages -- 6S Lipo vs 6.6v Life)? From the stock setup, it looks like each motor has an esc, but it looks like the previous owner removed the BEC, or maybe I'm just missing something.

Any ideas?

kinda depends on the esc themselves.
if they are opto esc, then no problem with the lipo 6s for motivation, and the life 6.6v for rx/servos. could also use a bec with the 6s lipo as well, if you want to not buy a 6.6 life pack, or with another pack of greater than 6v.

and you want everything to share ground.

if the esc are not opto, then, you need to be finding out why their internal bec is not functioning.

$50 on a battery or $5 on a BEC? No brainer. Not even considering the weight difference.

Cost is not an issue given that, as I said, I already have the battery. Weight is moot because this little life battery weighs next to nothing. I'm just more concerned about any possible conflicts in voltage.

Thanks, makes sense. I did figure out that the plane is missing the BEC. Right now, just for setting it up, I have the BEC lead going to a voltage sensor input on the receiver. Using the 6s lipo for motor, and the 6v life for receiver. The life battery is a tiny 1300 mah, so it weighs almost nothing. Do you think this setup will cause any voltage conflicts? I've been thinking it thru, going over the connections, and everything seems to make sense, but figured I'd run it by someone with more experience in this area in case I'm missing something?

Or true, I could just buy a BEC and be done, lol

This will only be a problem if the ESC's do actually have a BEC. A simple fix is to remove the red (+) wire from the connector of the ESC where it goes into the Rx. The ESC will function fine with a Signal and Neg wire only. That way no power to the Rx can come from the ESC. Run a separate Rx pack and you are done.

what low said.

just use a straight pin to unlock the red wire connector in each esc rx lead and pull it out.then shrink wrap over the connector so it can not short out on anything, and tape it back along the lead to keep i out of the way.

we pull and isolate the connector, just in case we ever want to re use this esc and need to have that power connector active.

Gotcha. As there is no apparent BEC, I'm guessing the connector your talking about is the lead that's labelled "throttle"? BTW, Even though there's a throttle lead, the escs just sit there and beep when i plug in the lipo, and nothing happens, theres no power ti the receiver unless I power up the receiver with a separate battery, which is why I believe the BEC is missing. I wish there was a manual, but as the plane is discontinued, no joy.

Just wanna make sure I understand you guys fully. Thanks again!

for 70-90 ( 6S - 8 S Lipo) mm fan ..all the brand use BEC and its no problem ..in a bigger EDF jet when its more expensive hardware ..maybe beyyret to use a separate 6.6 v or higher if HV servo

Right, but this one doesn't have a bec so I was just wondering if it was fine to use the two battery setup or should I go ahead and buy an external bec

Just a regular switch and a RX battery and its fine . Or a good quality BEC from Castle Creation .

Gotcha, that's how it's set up now, and it seems to work just fine.

Thanks!