Hi Steve,
Thanks for your reply. I added the lines
pinMode(APWM, OUTPUT);
pinMode(BPWM, OUTPUT);
to the setup() section but sadly it still didn't work - nothing happened.
One thing I did notice is that there only seemed to be 3.5v between the 5V pin and ground on the motor driver. Also, according to this page it actually needs 7 to 24v in order to work. It seems your idea of a higher voltage is the right way to go!
Originally, the Bigtrak only had three batteries supplying 4.5v in total. I don't want to go over this voltage in case the motors don't like it.
So the problem now is that I need to supply 7v without outputting more than 4.5v. Even with the 2v drop, it's still too high - what would you recommend? Do you think I should add a voltage divider between the motors and the driver?
Also, what power supply would you recommend? USB power packs obviously aren't an option now as they supply 5V.
Thanks for all the help,
Brychan