Your input voltage to the controllers, in this case I think you are referring to the EZB and Iotiny,  is indeed variable.  IoTiny Voltage input (Vin) range: Minimum: 4.5 volts Maximum: 16 Volts. I didn't look up the EZ-B but I think it's pretty much the same. So you are correct considering the voltage range they except then 7.5 volts will work to power them. Just remember,  The power output pin on the EZ-B and Iotiny digital port will also output the 7.5 volts.

@dave

"The power output pin on the EZ-B and Iotiny digital port will also output the 7.5 volts."

i will only use the white pin on ezbv4 for the signal. averything els positieve and negatif , for the servo's on terminals .4.98 volts.