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# Powering Servo motors?

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#### Echelon 01

##### New Member
I have two possible power sources: either two 9v batteries (in series or parallel) or 8 C-cell batteries configured to produce 6 volts. These are design constraints and I can not get power any other way but these.

Now, I want to power two servo motors at once they are for the right and left treads of the robot. They both draw 680mA max, and less than 10mA idle. They will not always be on at the same time, but will be on at the same time when the robot is going straight. I only need the robot on for 2 minutes so draining the batteries after this time is more than acceptable. The minimum voltage that needs to supplied to the motors is 4.9 volts and the max is 6.1 volts. Any kind of voltage regulator or current limiting device can be used.

Anyone have an idea of what is the optimal configuration of the batteries - or what kind of regulation i can use to get 5-6 volts with enough current for both motors (1.33 Amps im assuming but that is the max they would ever need combined) ? Any comments or ideas whatso ever appreciated.

Apologize for double posting this message in the robotics topic section but Need to find some responses :lol:

This answer is for a practical application.
Connecting batteries in parallel is never a good idea. They simply cannot be made to have *exactly* the same internal resistances and so one battery will always supply more current than the other.
Since you run that robot for such a short time why not just use 4 x 1.5V 'C' cells in series? You get a little above 6V when they are new, using alkaline cells, you should get enough current until the voltage drops too low for your servo motor. Or use 5 NiCad C cells in series and run that machine for much longer.

Now, if you are making a theoretical question (such as an assignment) and you *must* use an impractical number of batteries, choose the 8 x C-cell ones.
There is not enough grunt in the little 9V batteries.
Use a voltage regulator that can handle at least 1 Amp of current. You could use a variable type or a fixed 5V one, the latter padded up with 2 diodes to output 6V.
Klaus

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