Separate power supply for Arduino Motor Shield ?

Hi

I am planning to build a two-wheeled robot with Arduino UNO R3 and Arduino Motor Shield R3.

For the two wheels I am using 2 motors, each with 4.5V DC and no load current of 190mA (250 mA MAX) as per the datasheet.

The above is just a basic to start of.
In future I will be adding range finders and bluetooth or wireless modules to control it. And also 16x2 LCD to output information.

Based on the above I have a couple of queries:

  1. Do I need to power the Arduino Motor Shield separately for the motors? If yes should I use a 9V single battery or 4 AA batteries or 8 AA batteries for the motors?
  2. As for the Arduino UNO board, how much power supply should be required? Again, will a 9V single battery be enough?

Thanks

  1. Do I need to power the Arduino Motor Shield separately for the motors? If yes should I use a 9V single battery or 4 AA batteries or 8 AA batteries for the motors?
  2. As for the Arduino UNO board, how much power supply should be required? Again, will a 9V single battery be enough?

Use 6AA batteries. They can supply both motors and the Arduino. Remember that the motor power comes BEFORE the Arduino. NOT from the Arduino board!

A seperate Arduino battery helps to cure serious noise problems but is often not necessary.

Do not forget the battery off switch. The robot will draw some power even if not moving.

I would't bother with 9V PP3-sized alkaline batteries, they are pretty pathetic, and useless for motors.

Rechargable AA packs are going to be a better bet.

First find out the current your motor needs under load - the no-load current is uninteresting
at best. If the motor shield is up to the real load currents then you also need to consider the
voltage drop across the driver (if its a L298 or L293 based driver), and probably use a NiMH AA pack
sufficient for your 4.5V plus driver losses (probably 7 or 8 volts in practice).

The Arduino needs perhaps 30mA, but if you share with the motor supply you are likely to suffer from
random resets as the motors pull high currents under stall conditions. A DC-DC converter from motor
battery to 5V is one solution, a separate battery pack (4 or 5 AA's or AAA's) is another. A 9V PP3 might
hold out for this too, a rechargable one would be best.

MarkT. You may have a point. I am indeed using a crappy 9v battery. However, the battery is fully capable of running both motors simultaneously. Although it might be possible that a sudden change in direction can cause such a power surge that I get crowbarred. I've got a Li-Po. I'll try that bad boy tomorrow.

Thanks for your help.