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[on:]

Hello,

I been working on a small project at home. I have a mobile robot with 2 servos operating the wheels and 6 others operating an arm, making it a total of 8 servos. I'm currently using Arduino Mega and an external power supply, a modified ATX power supply (5V 30A). I have a battery from a previous R/C car project, 7.2V 4500mAh. I would like to use this battery to power the robot. I've tried connecting it directly but the servos do not switch on. I get a big voltage drop and current drop, as many of you figured out already. I thought if I made a simple voltage follower it would work, but didn't. How else can I power these servos without buying a Servo Controller. I would like to make a circuit with parts that can easily be found locally. Any help that can be offered, would be great.

[Reply #1 on:]

How else can I power these servos without buying a Servo Controller.

A servo controller really doesn't play into powering servos. servos are usually powered from the battery +- leads with the ground wires all connected together.

[Reply #2 on:]

Understood but how can I power all 8 servos using a 7.2 V 4500mAh battery.

[Reply #3 on:]

Are your servos rated for 7.2v operation?  Many are not.  If not, you will need some type of voltage regulator.

I power 18 servos off of a higher voltage battery and use a voltage regulator from http://www.dimensionengineering.com/
I got the SWADJ3, which lets me cut select the output voltage, and it handles enough current for my needs.

As for the physical arrangement, I bought a prototyping shield and some pin headers.
http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1265626147/6#6

[Reply #4 on:]

Can you show how you currently have power wired to the Arduino and servos with the 7.2v battery?

[Reply #5 on:]

All my servos are connected in parallel with the battery.

[Reply #6 on:]

Vince, I like what you did with the voltage regulator. But can you give me a list of the parts you used, the voltage regulator, battery, and the small circuit board switch(what does this do? do I need it?). Also, the pictures are great but are a bit fuzzy to see the connections in detail. Could you give me a quick short summary how you connected these devices.

[Reply #7 on:]

I'll see if I can get better pictures.

Parts list for my setup:

Polulu

Pololu Pushbutton Power Switch SV
http://www.pololu.com/catalog/product/750
This is a power switch that replaces a mechanical switch.

Small breadboard
http://www.pololu.com/catalog/product/1490

Various headers
#1065 #966 #965

Power block
#830
Although this comes out of the bread board fairly easily.

I also got wire kits
#313 Elenco JW-350 350-Piece Wire Kit



Dimension Engineering
Voltage regulator
http://www.dimensionengineering.com/DE-SWADJ3.htm
They have many different models to choose from, with widely ranging capacities.  This model works for my 18 servos - 12 are standard sized analog, and 6 are standard sized digital.


NKC
Mega shield kit
http://www.nkcelectronics.com/megashield-kit.html


A bit of soldering (like a LOT!!)