We’ve decided to ditch the MD03 motor controller and replace it with a pair of relays. The MD03 uses an I2C bus and we’ve had a lot of issues generally with I2C based motor controllers as they seem to cause noise on the bus lines. The noise seems to cause the gumstix I2C driver to crash and it doesn’t seem to good at recovering itself. On a good day you can recover by reloading the driver on a bad day you have to reboot the whole gumstix. So we’ve now just wired two relays (via transistors) to some of the Gumstix GPIO lines. This means we don’t get any of the speed control the gumstix gave us which reduces the accuracy of the sail movement a little but it should be good enough for what we need.