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I finally built my plane and started testing it on my workbench. If I moved the servos a lot (using my transmitter), the motor would cut out, the ESC would play a tone similar to when I first turn it on, and after 3-5 seconds the motor would restart. During the reset, the servos still responded. I flew the plane with issue as I knew the extreme control inputs I had given in testing wouldn't be needed in flight.

I think the problem is probably that my BEC is too small, but I'd just like your confirmation.

Details about my setup:

  • I am using a 3 cell battery
  • The ESC has a 1-amp BEC.
  • I am using a Spektrum AR410 receiver (although I don't think this is relevant)
  • I have 2x 6 gram servos on extensions.
  • Depending on which direction you rotate the control surfaces, they do need quite a bit of force.
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I think it's a combination of the BEC and stiff controls.

1 amp BECs are often just linear regulators, effectively a transistor that acts like a variable resistor. It takes in battery voltage and turns some of the power into heat so that the remainder is 5v. If you were running a 2 cell battery, it would have to dissipate 7-5=2v but with a 3 cell battery it's 11-5=6v. That's three times as much, so it can only manage a third of the current.

2 servos are normally fine with that set up, but if the stiff control surfaces cause the servos to draw more power than normal they could cause the BEC output voltage to drop to the point where the receiver or ESC shuts down. Or maybe it overheats and there's a thermal cut off - I'm not really sure of the failure mode, but at least it didn't catch fire!

If you're curious, you could check to see how hot it gets, and measure the voltage at the receiver when the motor cuts. There are also servo power meters, or you could, HobbyKing seem to have discontinued theirs.

You may be able to solve the problem by freeing up the hinges and pushrods, but a better BEC is cheap and it's not a good idea to fly with a set up that you know could fail.

The better BECs are known as 'switching' because they switch the power on and off rapidly and then smooth the output, so there's much less power wasted as heat. Sometimes these are known as UBECs, because some early ones were sold under the name 'Ultimate-BEC'.

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  • $\begingroup$ Thanks, this is very helpful. However, I have not noticed any overheating of the ESC. I spent 30 mins testing it as a glider in which this happened nearly every flight (because it was flying very slow so I needed max deflection to control), and the ESC was not noticeably warmer than ambient temperature. It was a warm day and the ESC had no cooling. I won't buy a new ESC yet, but if the problem becomes annoying or the ESC burns out I will upgrade. I'm afraid I can't loosen the hinges as they are made out of paper/tape/hot glue (as done by FliteTest). $\endgroup$
    – ThatCoolCoder
    Commented Jan 19, 2021 at 20:09
  • $\begingroup$ I've made a few FT models - if the hinges are stiff, you may have to much hot glue in there. You might be able to use the nozzle of the hot glue gun to smear it a bit thinner. $\endgroup$
    – Robin Bennett
    Commented Jan 20, 2021 at 9:10
  • $\begingroup$ Okay, I will try that. $\endgroup$
    – ThatCoolCoder
    Commented Jan 20, 2021 at 20:09
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    $\begingroup$ I tried your tip and it worked a bit, but the problem is still there. I've flown it a few times since and the motor kept cutting out at high control loads (it also doesn't help that I put an extra servo for a bomb drop). I will buy a new esc next time I can go to my hobby shop. $\endgroup$
    – ThatCoolCoder
    Commented Jan 25, 2021 at 21:28

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