There are a dozen different ways to tackle this problem, but this solution is brain dead easy to execute, highly reliable, and can be used on any size airframe--big or small.
This example uses discreet BECs for power, but anything can be used from Dual BECs to Receiver Batteries, to a straight tap from the flight battery so long as the voltage is appropriate for the receiver.
The parts are about a dollar. No Kidding. Source information is in the video.
T-Shirts: https://teespring.com/stores/rcvideoreviews
RCVR Amazon Basics List
Solder Station Heavy Duty Helping Hands: https://amzn.to/32WInJN
ToolkitRC WM150 Watt Meter https://amzn.to/2A13Ogu
Generic Watt Meter https://amzn.to/377epmg
10 Pack XT60 Connectors with shrink tube: https://amzn.to/2zVBWdB
50 Pack 3.5mm Bullet Connectors: https://amzn.to/3dw8pot
10 Pack 300mm Servo Extensions: https://amzn.to/3dVBRoi
Heat Shrink Tubing: https://amzn.to/3ezjIxB
ZTW 10a peak/6a cont BEC 6v/5.5v/5v: https://amzn.to/2ZdAA6S
ZTW 40a ESC with XT60 Installed: https://amzn.to/3fPu2ll
ZTW 60a ESC with XT60 Installed: https://amzn.to/2CqrNGH
ZTW 80a ESC with XT60 Installed: https://amzn.to/2ZLIUuS
ZTW Programming Card: https://amzn.to/2BuHZqb
MG90s 9g Servo 5 Pack: https://amzn.to/315Kmuh
ISDT LiPo Balance Checker: https://amzn.to/2Z0HOee
Generic LiPo Balance Checker: https://amzn.to/3drCO7B
FrSky S6R Rx with Stabilizer: https://amzn.to/320IrHU