Motor Shield R3 No Torque

I'm using a Duemilanove with a Motor Shield R3 to power 2 6V 300 RPM motors. I'm powering it with this battery. When I power the motors (at power=255) I get very little torque. However, when I power the motor with the battery directly, I can't even stop it with my fingers. Why could this be? I'm building this for a deadline in a few days so it's very important that I get this to work :slight_smile: Thanks in advance!

You should check the voltage at the shield output.

Check the datasheet for the L298 chip: it loses a minimum of 1.8V, rising to a loss of 3.2V at 1A and 4.9V at 2A. Your 7.4V battery will therefore at best be giving 5.6 which would be ok for the 6V motor I guess BUT it depends what the no load current of the motors are.

If you have an ammeter, hook the motor to the battery and measure the no load current… double that for two motors, and if you’re up in the vicinity of 1 amp you may well be shy of voltage at the motors. (Edit… or check the motor datasheet) (More edit… and of course the voltage loss will increase when the motor is under load and requires more current.)

The battery can put out lots of amps, the motor shield can put out a couple at best - which motors are you using?, you
don't mention the current / torque specs which are the ones of interest here.