Powering a servo externally through a voltage divider

Other Hardware General Electronics
1

Hello, I am trying to control a Power HD-1440A Micro Server with my Arduino Uno and power it from an external 9V battery.

To get the correct voltage which is between 3.7V and 6V I have created a voltage divider with a 10k resistor and 2 10k resistors (to give a 20k resistor). This gives me 4.9V with the load attached. However the servo doesn't move at all. I am using the default servo sweep example and have tested the servo by powering from the arduino. I have a feeling it's something to do with my wiring.

You will have to forgive my rather crude diagram, it is my first attempt at creating one.

I would appreciate any suggestions as I am still rather new to all of this!

Thanks

servo-divider_bb.png
servo-divider_bb.png1057×815 40 KB

2

WHile you may see 4.9 V there, not much current can flow and the servo won't work. AND if the servo could do anything it would be unreliable because the loading from the servo would change the voltage as it would be part of the voltage divider.

A voltage divider works as a reference, or for something that is a constant load, otherwise...

You need to supply the servo 5V from a source with sufficient current for the servo.

3

Put another way you use a voltage regulator to provide constant voltage power to a device, never a voltage divider.
Note that most small 9V batts cannot supply enough current for a servo.

4

See the links in my signature for an alternative using AA batteries.

Duane B

5

Thanks for the advice. I have some 3.7 Lipos I can use instead, but even if I use 2 of these I will still have more than the 6V, what's the best way for me to limit the supply to 6V? Some sort of diode?

6

what's the best way for me to limit the supply to 6V

A low drop out voltage regulator.

7

A diode will give you approx 0.7V drop so that would work.

8

kf2qd:
A diode will give you approx 0.7V drop so 2 in series would probably work.

9

Hi,

I don't think diodes are the way to go, My 2s lipos output 8.4 volts from a full charge dropping to 7.2 as they discharge. A voltage regulator will give you a constant output voltage where as two diodes will simply drop a constant voltage from the input voltage. As the input drops, the diodes output will also drop giving you a voltage range of 7 volts to 5.8 volts which could damage your servos.

One quick and easy option is a ready made rc regulator, I have seen 6 amp 6 volt regulators for about 10 dollars.

EDIT: first result returned by google - not a recommendation, just an example -

http://www.rcpitstop.co.uk/lipo-receiver-battery-pack-regulator-60-volt-5-amp-1962-p.asp

Duane B

rcarduino.blogspot.com