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Problem: In a RC Helicopter the Speed regulator shuts off motor after 5-6 minutes due to over heating,
This is a serious problem that can course damage to heli or even people.

System spec:
Battery 10 Cells 3300 NiMh, 12 Volt.
Motor = Speed 600 current usage 16 A cont.
Reciever drives 4 servos and Gyro and Speed controller with BEC, current usage 500mA at 5 volt.
Regulator with overheating problem Kontronik Easy 3000 (30A with 1.5A BEC)

First we measured the input battery current usage opperating all servos but not the motor,
12 volt input and about 500mA avarage = 6 Watt input power.
The reciever and servos are driven by a LINEAR LM317 regulator inside the speed regulator, outputting 5 volt,
the rest (7 volts) are just generating heat inside the speed regulator, 7 x 0.5 = 3.5 Watts !

So we added a SWITCHMODE BEC regulator and left the BEC inside the speed regulator unconnected.

Here the new BEC is mounted just on top of the reciever. The Switchmode BEC regulator and convert any input voltage,
into a 5 volt output voltage at upto 3A load, with almost no heat loss at all.

After a lot of testing on the table we was happy nothing got hot, so we decided to test it in real life,
We could not repeat the cut-off problem, not even after 11 minutes in the air.
The regulator still gets a little bit hot, so we wanted to know exactly the power loss inside the regulator,
the speed regulator internal DC resistance was measured 4.72mOhm, so at 16A the power loss is 1.2Watts (75.5mV voltage drop),
excluding the switching loss that we could not measure using our simple millivoltmeter and amp meter,
RDSON for each FET must be about 4.72 x 3 = 14mOhm.

Here is the original HOT speed regulator.

We removed the covering plastic, and mounted (using epoxy) two small heatsinks normally designed for TO-220 Transistors.
Now after both modifications was made, we made our last test flight for that nite: now it is just as cold as we wanted..

Conclution:
1. Surprise, the powerloss added by a LINEAR BEC when using many cells and many servos, are 3 times higher than the power fet loss !
2. Maybe the added heatsink was enought to solve the cut-off problem, we dont know.
3. By using a Switchmode BEC the power loss saved will end up in 13.3 sec extra flying time.