I made my own redundant BEC module for RC models. It takes full battery voltage (usually 4 or 6 lithium cells in my case) and regulates it down to around 5 volts to power servos and other electronics.
My design uses two separate LM2576 switching regulators that power the output through diodes to isolate them. I also have an extra output filter to minimize ripple and voltage spikes. My goal with this project was to create something that is more heavy-duty and reliable than most cheap BEC modules for RC models you can buy.
EasyEDA Schematic and PCB design: https://easyeda.com/Axbri/rc-model-redundant-bec-v2