Proper battery Freaduino / Servo motors

Using Arduino Motors, Mechanics, Power and CNC
1

Hi,

I would like to be sure if this battery could be used for feeding a Freaduino UNO & two servos.

Capacity : 1050mAh
Constant discharge: 20C
Burst rate: 30C (15sec)
Configuration : 3S 11.1v
Pack size: 73x18x35mm
Weight : 100.3g
Discharge plug: XT60

The shield and servos would be working for some hours (between 1 to 4). Im looking for some small battery, because baterry holder for 8/6 alkalines would make the robot bigger for what i need it for.

Thank you!

2

That's basically an 11V-AH battery.
A servo needs 5 volts (or 6V) for power typically, and figure it will draw 1A when moving so it will need a 5VAH battery.
Then with near perfect DC-DC conversion, that battery could likely power a servo for 2 hours, or 2 servos for 1 hour.
Look at converters like this:

And if you think about the batteries as I did, you can likely find one with enough capacity.

3

Thank you very much for your answer. :smiley:

So, if i understand it right, that Pololu voltage regulator, will regulate the input voltage of the battery providing up till 3 A (more duration for the servos).

I thought the battery above would be a good one because 6V x 2 servos =12V. But as you said, the problem is the amperage.

What about this? (Maybe 2, plus the regulator)
http://www.active-robots.com/12v-ultra-alkaline-battery

Again, thanks a lot.

4

6V x 2 servos =12V

No, 2 servos would be connected to the power source in parallel, so still 6V.

edit: pic attached

Many servos- small V2.jpg

5

HI!

One friend told me that Servomotors need too much energy, and maybe two connected straight to one shield would work but because their power needs the values will oscillate or start to fail.

Do you think thats wrong?

Thanks!!

Edit:

I didn´t see the picture you added. So with a 9v battery for the Arduino, and 6V battery for both Servos will be fine...

Thanks for your time!

6

Doubtful on the 12V cell. No current rating provided.
I think find one like your original, but with higher capacity, like 6000mAH.
Or, check the current draw on your servo, maybe they are less than 1A, or worse, more!

What shield? What servo? Post more specifics.

7

SpringRC SM-S4303R Continuous Rotation Servo

Freaduino UNO

I found this in Sparkfun comments for the servo:

"...120 mA at 5V for full speed unloaded. If you load it up, I got it up to about 250 mA before I decided not to break the thing."

So... 1050/120=8,75----- 8,75 hours ?

8

No clear rating then - current at Stall would be good to know.
So go with the 1A rule of thumb then, and find a bigger rechargeable battery if you want 4 hour operation.

9

2ndattempt:
So with a 9v battery for the Arduino, and 6V battery for both Servos will be fine...

  • If by 9V battery you mean a PP3, they are notorious for not lasting very long. You might be better with a bunch of AAs
  • 6V supply to servo needs to provide enough current remember: as CR says maybe allow 1A at stall. I got over 500mA on some tests I did a while back.
10

Servos are typically rated to run at 6 to 7.2V

Arduino Vin requires at least 6.5V, and 7V is preferred.

Therefore a 7.2V NiMH pack is ideal for running servos and the Arduino
together - but only it can supply plenty of current so that the servos
don't pull the voltage down and reset the Arduino. Also a 2S LiPo pack
is nominally 7.4V which is possible (a little high for the servos, but
I suspect people do this all the time).

Its better if possible to have separate power for the servos, in which
case 6V SLA or NiMH pack for servos, and perhaps a 9V rechargable
PP3-sized battery for the Arduino might be reasonable.