Tapping power from unused receiver battery port.

[redboat219]

I have a 3v mini airpump that i want to use. Problem is how to power it. Can't use power right off the 7.4 lipo pack as it'll fry the motor over time. Although I can power it with it's own battery pack, it will take up extra space inside the wtc. As most esc nowadays come with built in BECs to power the receiver and servos the battery port is unused.

Question is, Can i connect the pump to the receiver battery port and power the motor directly off the receiver? Speed control isn't necessary, just want the motor to run. On and off will by through a servo operated switch.

Esc i plan to use is an Mtroniks Micro Viper 10. The pump motor is a Mabuchi F130.

Here are its specs.
Typical operating voltage: 3 V
Free-run motor shaft speed @ 3V: 12300 rpm
Free-run current @ 3V: 150 mA
Stall current @ 3V: 2100 mA
Motor shaft stall torque @ 3V: 0.5 oz·in

[KevinMc]

I wouldn't think this will do any harm to your receiver, but I think there's a good chance you'll overload the BEC in your micro Viper. From the numbers you've provided the pump could be expected to pull anything from 0.5A to 1A (ballpark guess) which on the high end will tax the BEC capability on its own.

Why not power from the battery pack and use a series resistor to limit the current through the motor? Some experimentation will be required, but something around 2 ohms to 10 ohms of resistance in a package that's rated for 5 Watts should do you.

[redboat219]

Ok. Guess using the receiver battery port to power a motor isn't advisable. How about powering a leveler connected to a servo?

[KevinMc]

As a general statement using receiver bus power is fine as long as you have a BEC that can support the current draw, but the motor you propose to use seems as though it will pull a considerable current. Typically electronics that do not have motors attached (like automatic leveling devices, depth controlling devices, and even LEDs) put a nearly negligible additional load on the system so powering them from the receiver bus is fine. As soon as motors/servos come into play you need to pay very careful attention. You could still do as you propose and power the motor from the receiver bus if you also put in a larger BEC in to support the load. I don't know if that's a "better" solution for you than powering from the battery bus and limiting the current with a resistor, each solution has pros and cons.

[redboat219]

Thanks Kevin.

I asked about plugging the leveler into the Rx battery slot because I only have a 4 channel Futaba 27mhz radio for the Kilo. Plan to connect the leveler to the RX in "stand alone" mode to control the stern planes.

[KevinMc]

No worries.

If you happen to be using an ADF or ADF2 as your pitch controller you don't even need to plug the pitch lead in to operate it in "stand alone" mode. Power for the pitch side and the pitch servo will be pulled from the failsafe side of the device. ;)

[redboat219]

Got a microgyros unit.o

[Subculture]

The microgyros unit will operate in standalone mode, in fact pretty much all levellers work this way.

The leveller itself draws close to nothing in power terms, but it does need power to work. The servo is the current sucker, and f you use a digital model, some of those can be very thirsty, so make sure your BEC is adequate.

[redboat219]

The microgyros unit will operate in standalone mode, in fact pretty much all levellers work this way.

The leveller itself draws close to nothing in power terms, but it does need power to work. The servo is the current sucker, and f you use a digital model, some of those can be very thirsty, so make sure your BEC is adequate.

Not sure of it's specs but it's the 9 gm micro servo that's in the standard 2" subdriver.

Rx battery slot -> microgyros angle keeper -> micro servo ->stern planes