Problem with Battery

Hi I am new to Arduino and I would like to build a 17 DOF robot.

I started with one leg which has 3 servos attached to it.

Completed project should look like this:

The legs will look like this:

In my project I am using 4XAA NiMH 1.2v/2400 mAh batteries
I have Arduino Mega 2560 board.

On a breadboard I attached the +/- cabling which goes to the 4xAA bateries. Also I get a reading from ohm meter.

On another breadboard I build the signaling for each servo and that goes to Arduino.

When I run 2 servos everything works fine. When I run the 3rd servo I do not get enough juice. The ohm meter reading goes close to 4v. Less then 5-4.8v.

With this 17 DOF robot Of course I will not run all servos similtanously but to run the project smoothly, What do you suggest for power?

I would attach pictures of my project but I just dismantled everything. Sorry

Thanks in advance for the advice.



Ah by the way the servos I have are: Tower Pro MG-996R s


As you have discovered, 4xAA NiMH batteries will power just two servos.

You need a battery capable of delivering around 1 ampere per moving servo, for as many servos as will be moving at once. RC battery packs will work, but you will also need a high power switching voltage regulator to produce 5-6 volts, at whatever amperage is required.

Depending the weight limit you have for your project, there are many options out there.

Li-ion batteries are usually the longest living batteries out there, but you shouldn't discharge them completely, or else it won't be charged fully any more.

Ah by the way the servos I have are: Tower Pro MG-996R s



Using them myself. I couldn't find the data on them, so I had to measure.

They are counterclockwise, with 0 at .5 msec and 180 at 2.5 msec

Running a dozen off a 5200 mAH 7.2V NiMH with a 1 diode drop. Works but battery life (or maybe just crappy cheap batteries) is short.

On order a LiPo 3s (11.1V) with a 15A buck down converter.

The nature of permanent magnet servos is that they are most efficient at the lower end of the torque curve. They eat lots of amps and the useful power falls near stall torque. Max horsepower at half stall torque. With higher battery voltage you get higher EMF, more power and better efficiency. I plan on running them at 7.2V regulated. The circuitry in them has a max rating of 7.5 V.