Got an even better power solution. While replacing the regulator with an LM323T did let me get enough current, the batteries kept dying in minutes. So I got a DC-DC convertor for $6.95 from a surplus place (18->36V in, 5V out at up to 6A) and hooked it up to a lithium ion cordless tool battery (DeWalt, 20V, 1.5 AH). I just now finished a test run with the RPi, the wifi, the USB hard drive and both motors running continuously for ½ hour. Total time on the battery is about 1 hour, with about 40 minutes motor time, and it still has plenty of juice.
If I did my math right, the battery has 27WH out which the convertor turns into 22WH. At 8 watts for the robot with both motors on, that turns into almost 3 hours continuous operation with both motors on. Of course, there’s the battery’s discharge curve, the convertor’s input threshold, etc. to consider, but even so there’s a good chunk of operating time available, especially if the motors are not running full time. And as I said, I just finished a ½ hour continuous run, so that much is empirically demonstrated.
Just for the fun of it, I’m writing this on the robot. I’m logged in through vnc and using the robot as a web browser. There’s something very amusing about that.
Anyway, the RaspiRobot board is a great toy once the power issues are fixed.
cheers