Biollante is my own personal attempt to build a
Replicating Rapid Prototyper, of a
design radically different from their present "Darwin" design. At
present, I have a frame, and some
motor firmware for the PIC16f628a.
Why name it Biollante? Well, at the time, the Reprap Builder's Blog was awash with Godzilla-inspired names. I decided to be a rebel and a lemming simultaneously, picking the lamest Godzilla monster I knew -- an incorporeal mutant rosebush that can cough radioactive spores and fly through spaaaace! It's also a reminder to me to not take this too seriously; after all, just because I'm a reprap builder doesn't make me a good reprap builder. ;)
Instead of designing the structure around a rigid platform like a milling machine, or an "arm" like actuator, I decided to build a Stewart platform. My hope is that such a symmetrical and intrinsically stable platform will be easier to build than a top-heavy structure with few load-bearing points. The electronics and software will become more complicated, of course -- twice as many motors to control -- but this mechanical numbskull considers it more than a good tradeoff for a simpler and stabler mechanism.
Since it is only intended to have plastic laid down on it, not to push metal into a milling bit, it can also be much lighter than I think I could build for a rigid linear axis system. So light, in fact, that I have used needle joints for the universal joints, held together by worryingly strong magnets scavenged from dead hard drives.
The linear actuators are simply 12cc Monoject® medical syringes. They are convenient since they are cheap, seal well, and calibrated to millimeters. Yes, millimeters -- 0.2ml of fluid is exactly 1mm of motion. Their motion will be driven by a fluid pump, probably another syringe.
I'm borrowing a lot of design on the electronics from the RepRap "universal" controller; each module, designed around a PIC16f628a microcontroller, performs one function, communicates serially, and is connected in a ring. The computer sends to the first module, the first to the second module, etc, and the last module sends back to the computer. But there are some important differences:
- Seperate power and data connectors to avoid disaster
- Individual voltage regulators for each module to avoid motor noise
- Modified pin allocation to take advantage of more PIC hardware features
- Discrete transistors instead of expensive, hard-to-find stepper chips
- Human-readable and writable ASCII packet format -- talk to the chip from any serial terminal
- Chip does not busyloop while waiting for a packet to become complete
- Firmware written in nearly 100% pure ANSI C, inline assembler used only for device-specific functions
- Constant values placed in EEPROM memory to conserve code space -- can be updated at runtime
Now, onto the fun stuff.
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