Radio control receiver voltage not same as max motor voltage

[obrien136]

I have a receiver for an RC car that has a 6V max voltage and the motor has a 9V max voltage. BY that I mean, the max supply voltage you can apply to the receiver is 6VDC, while the motor takes a 9V max input drive voltage. I don't get enough torque out of the motor with a 6V drive input so I was wondering if I cam use different voltages for the receiver and the motor controller as shown in the attached drawing.

George

 

[jiripolivka]

You can use two separate power supplies with a common ground. Or you can derive the lower (6V) voltage for the receiver from the higher (9V) source by a voltage regulator. This regulator also reduces a possible motor interference which may affect the receiver.

 

[jpanhalt]

@obrien136

Most motor controllers have the motor power connected directly to them. Receiver power is often provided by that controller by what is called a BEC (battery eliminator circuit). The BEC is a voltage regulator to reduce motor drive voltage to whatever voltage is needed for the receiver. Here is how I would re-draw your circuit to include the BEC concept. New connections are in BLUE.



Every motor controller I have seen can be divided into a signal or logic section and a motor control section. The motor control section operates at whatever voltage is being used. Today, those voltages can be quite high relative to the typical logic signal of +5V. One could certainly design a signal section that would operate at those higher voltages (as implied in your drawing), but then consider whether the 5-V signal from the receiver would be detected as a positive (asserted) logic signal? Assume for that question you are using 48 V for the motor supply. Now, with your 9-V supply, I don't think that would be a problem. So, as suggested just above, you could get by with a separate lower voltage supply for the receiver.

However, unless there is a reason not to use a BEC-type circuit, I would concur with the suggestion by jiripolivka and use a voltage regulator to provide power for both the logic of the motor controller and the receiver.

John