Hobbywing - 1S - DC/DC-BEC - Booster (Allows a 2S ESC to run 1S - giving 3A 6v to the receiver - HW30600400001

Or use 2S (7.4v) 8.4V ESC, remove voltage protection, then use 1S (3.2v) 4.2V lipo instead via this module, still giving 6v to the receiver. Or in applications where the ESC has no 6V BEC output. 

1S DC-DC BOOSTERs, DC-DC power booster modules which can draw power from the 1S LiPo battery then boost it to the voltage level (6V) suits the receiver & servo and provide the continuous output current up to 3A, are mainly applied in 1/12 RC vehicles. Nowaday 1/12 cars usually use 1S LiPo batteries, and BECs in ordinary ESCs are step-down. In that case, the BEC output voltage will be lower than 4.2 V that cannot meet the power demand of the receiver & servo. Therefore, 1/12 cars have to run with purpose-built 1S ESCs installed in or external receiver batteries connected if speed controllers are common. No other solutions. However, things will be different after adopted this booster. Then the receiver battery can be abandoned and users can be free from charging and maintaining batteries.