If you’ve ever wanted to build a model on your MakerBot without a PC attached at all (or perhaps you just never have a USB cable quite long enough to reach…) there’s an easy solution!

This is a quick one-line addition to the V2 MakerBot motherboard firmware. With this change, your MakerBot will start up normally unless there’s an “autoexec.s3g” file on the SD card. If there is such a file, it will immediately start building from that file. This way, after you’ve got your MakerBot set up, you can do builds simply by copying a file to SD card and turning it on.

// Excerpt from G3Firmware/v2/src/Motherboard/Main.cc
int main() {
        steppers::init(Motherboard::getBoard());
        reset(true);
        sei();
        // Try to start playing back autoexec.s3g. If there
        // is no SD card or this file does not exist, this
        // function call silently fails and your MakerBot
        // will start normally.
        sdcard::startPlayback("autoexec.s3g");
        while (1) {
                // Toolhead interaction thread.
                tool::runToolSlice();
                // Host interaction thread.
                runHostSlice();
                // Command handling thread.
                command::runCommandSlice();
        }
        return 0;
}

If you need help compiling and installing new MakerBot firmware, check out the V2 Firmware page on the MakerBot wiki.