Does your receiver have telemetry, requiring more power than small ESCs provide?
Are you running brushless drive whose ESCs have no 5V return line to the receiver?
This voltage regulator will supply 5V at up to 3A from any battery 5-23V.
 
Specifications:
Input: 5-23V
Output: 5V, up to 3A
Dimensions: 38.0 x 11.4 x 10.2mm (1.50 x 0.45 x 0.40in)
Servo wire length: 20cm (7.9in)
Weight: 6.3grams (0.22oz)
 
To hook up in your robot:
1) Run the regulator's IN+/- wires to your battery (after your Power Switch, possibly through a Terminal Block).
2) Plug the black output connector (red and black wires) into your receiver.
3) Pull the center red wire out of any other ESCs that have BECs built into them