Hello! + a BEC Question.


Junior Member
Hi everyone,
I really like what you guys have going here, it's a great source of information for someone fairly new like me! I'm from Canada near Vancouver. I fly for a living in the real world in search and rescue, and fly a drone and a small quadcopter in my spare time.

I recently built a FT mustang mini, and it all went together very well. The final product looks awesome, the only problem is the ESC stopped working. For the life of me I can't figure out why. Everything was working perfectly and then all of a sudden I plugged in the BEC wires into the receiver and the ESC shut down. I pulled the BEC wires out of the receiver and the ESC booted up again (lights and motor beeps), plugged it back in and it shut off again. I used a multimeter and checked the voltage across the BEC lead 5v, but when it's plugged into the receiver it drops below 2v. In my mind I blew the BEC somehow, but the thing is there is no sign of physical damage, heat, I never saw smoke or heard any sparks. Anyway, I ordered a new ESC and an external UBEC just in case. The original setup I had used an afro 12a ESC and an orangeRx with 4 9g servos powered from a 3s 850 mah lipo.

My question now is was I pushing the BEC too hard with a 3s and 4 servos? It heated up (on servos only, no motor movement), but never too hot to handle, or melt plastic. I figured I would design some kind of air cooling flap for the ESC in flight because of the heat.

If you're reading thanks for putting up with the text wall! I could use some help and would really appreciate your insights.

I look forward to more FT model building in the future!



Posted a thousand or more times
Some thoughts...

Depending on the BEC in the ESC it's possible that 4 9g servos is too much. You need at least 2A and most likely 3A BEC. For example HXT900 servos can draw up to 750mA peak according to various measurements people have made. Quite a bit more than than you might expect.

However they draw much less when idle so just plugging the ESC in should not pull down the BEC voltage to 2v unless it is very under spec'ed. Instead you will see intermittent operation if you try to exercise all the servos at once.

If you have this ESC

then it has a 0.5A BEC which is far too low for your build.

However problem could be the weak BEC but if it's being pulled down to 2v when you plug it into the receiver without doing anything it may be you also have something wired wrong.

First I would remove the servo plugs from the receiver and see if it still happens. Even a .5A BEC should be able to power an RX.

If it doesn't work then maybe there is something wrong with your receiver or the ESC wiring. Loose connection or perhaps even a short somewhere. Possibly you have the ESC servo plug backwards in the RX. That should not be harmful but it could cause strange things.

If it works not then it's probably one of the servos. Plug them in one at a time and see if the problem correlates. A .5 amp BEC should be able to power 1 idle servo and probably move it without trouble too.

To eliminate the receiver you really need a servo tester which will allow you to exercise the servos and the ESC without the RX in the picture.

In any case, a .5 BEC is not enough for 4 servos so if that is what you have you will need to get a 3A or more external BEC or a different ESC with a 3A or more BEC.


New member
Your idea about cooling the BEC and the ESC is good. On multirotors the ESC get lots of air and cooling from the propwash but on most planes they are boxed in and heat can be a problem. I ither make a naca duckt or i make a hole to the outside in the plane and glue my ESC i the Hole


Build another!
Is anything getting warm with the battery connected? I'm thinking current draw is pulling down the voltage. That could mean motor issue, not ESC. Does the motor spin freely? Is there a possibility connecting another?

x2 on the BEC amperage. BTDT. But it was in flight while deploying flaps and not sitting idle.

Could just be defective ESC too. Happens. :(



Junior Member
Thanks for your help!

Edit: I forgot to mention I finally checked, and realised that you're right, the BEC on the afro is only .5A so I definitely fried it. It's weird how there weren't any signs though. Usually when I fry electonics there's more of a show.

I ordered a 3A externel BEC with a new ESC so I think that'll work when it finally gets here. I do have a servo tester and I was able to hook up an arduino to put 5v into the receiver and everything was working without the ESC. So I've narrowed it down to the ESC.

The BEC I got is switching, have any of you guys had problems with RF interference with these on park flyers like the mini series? I got this one:


it says it has shielding but it's cheap so I dont trust it.

Thanks again everyone!
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