Question on Operating Voltage

Hi,

I have just started on a project on constructing a mini robot. My robot consists of the following items:

  1. Arduino UNO
  2. Adafruit Motor Driver (v1)
  3. 2 DC Motor 48:1

When i apply a 9V battery source, the robot will work perfectly fine. However, when i apply a 6V battery source (4 AA batteries in series), the robot will not work. Can anyone explain to me why is this so? Is this because of the operating voltage on some of the components?

Please realize that 4AA batteries only theoretically provide 6 Volts. They may do that if they are brand new. They will definitely never do that if they are rechargable.

Measure the voltage you assume to be 6 Volts. How many Volts do you truly measure?

The recommended Input voltage for a Arduino Uno is 7-12 Volts according to https://www.arduino.cc/en/Main/ArduinoBoardUno

If you are powering the Arduino with less than 7V via the Japan Jack the internal voltage regulator won't work correctly or not at all. Thus your sketch won't run and can't control the motor shield.

You COULD feed an external power supply directly into the 5V pin of the Arduino, but only if you would power it with regulated 5V!

But: As a general rule this is not recommended as you will bypass all internal protection mechanism!

If possible, I would use 6 x AAA, if you can live with the limited battery life due to the capacity.

Have a look at this information about powering Arduinos; http://www.open-electronics.org/the-power-of-arduino-this-unknown/

The DC Motor that i had has operating voltage from 3V to 6V. How come it can still be driven when i use a 9V battery source? How do i know how much voltage is being applied to the DC motors?

Most probably the 9V battery voltage breaks down to 6V when you connect the motors. Such a battery is not really usable with motors and other current-hungry devices. You can try 3 AA cells to power the Arduino directly (5V pin), and also the motor driver. But then add a big capacitor to stabilize the operating voltage of the Arduino board - again the motor currents will result in ripple on the power line.

The motor current is the critical parameter, not the voltage. If you use PWM, the voltage is switched at 480Hz or 960Hz, what should be taken into account when measuring the current or voltage. Does the motor driver board have a current sense output? Then you can add a RC low pass filter to that output, and monitor the average current on the cap.

That retired/old V1 motorshield from Adafruit uses inefficient L293 chips with a voltdrop of 2-4volt.
A 9volt motor supply could be 6volt left for the motors.

Use a supply that is 3volt higher than the motors need. With the right current capability.
That excludes a smoke alarm battery.
Leo…

Hi, Do you have a DMM, a Digital Multi Meter?

Tom... :)

I think we need a diagram of how you are wiring things up and some code. Dwight