FWIW, the original source is available on the forums, posted to a comment when the V2 source was released. I have not seen any information on how to build or package the firmware though. The V2 community was able to reverse the process by taking a V2 firmware package, stripping out the firmware binary, and replacing it with their new build. I didn’t keep up with development much after that, but there were a lot of posts and utilities posted to the forums.
I no longer have access to the sort of embedded systems hardware that I’d need to unbrick the controller after a mistake, so it’s not a project that I’m personally willing to work on.
A long time ago, users did reverse engineer the pin connectors on the print heads, allowing them to build their own custom print heads. My search-fu is not working today. I’ll keep looking, and add some links if I find them. IIRC, that works was done before the V2 was announced, but my memory could be off.
After reading the firmware, I believe you can use the larger 220mm axis for all 3 axis (handwaving around the size of the base plate). You’ll have to switch to a different slicer that lets you set the build volume. The M1025 command takes 2 different arguments:
M1025 M[0|1]M1025 [X|Y|Z]<length_in_mm>
Some experimentation will be needed, because the axises have slightly different lengths:
#define X_MAX_POS 131
#define Y_MAX_POS 129 // Move +2mm after hitting the endstop @whimsycwd Caution!, if we don't set this, it will cause the Y125 hit module in specific situat
#define Z_MAX_POS 128
#define Z_LONG_MODULE_POS 221
The M1025 M[0|1] commands switch between Z_MAX_POS and Z_LONG_MODULE_POS, so if I was attempting to use a long module in the X or Y, I would try the X/Y MAX_POS +93 rather than just using 221. But that’s where I’d start, not something I’ve tried.
A few people even did a bit of reverse engineering on the controller, but I think it was only enough to replace burnt out stepper motors and transitors. I remember seeing some posts many years ago, but I’m having a hard time even remembering what terms I’d use to search for them. I’ll update if I find anything.