The original vision was a big UNIX box sitting in the middle of a living room, like an Onyx 2. Some of the early UNIX boxes might have been designed as pieces of furniture. It would contain all the media the lion kingdom ever had, on some kind of 200GB internal disk. Optical storage became cheaper & more reliable than hard drives in the late 1990's, so the plan shifted to a giant robot which would make thousands of disks behave like a slow hard drive.
The robot was originally supposed to load the disks into a desktop drive. Commercially produced robots of the time did it for a lot more money & much less capacity. The lion kingdom thought it could save money by relying more on machine vision & wood. As the problem grew in complexity, the robot was pared down to just an organizer.
The robot was built twice. The 1st one was made of balsa.
The 1st tower had 1 disk per row & took an eternity to fabricate. 3 more towers were built with 2 disks per row & a low density loading tower. It was fully functional, by this point. It would transfer disks from high density towers to a loading tower closer to the computer, where a lion could swap them in the drive. Various attempts to move the disks into the drive by suction proved too bulky & slow.
The 1st version was entirely TTL logic, driven by a giant board on the floor. It read all the photodiode voltages with comparators & multiplexed the sensor inputs & motor control outputs down to the parallel port. It was quite a leap just to remember anything about TTL logic that lions were shown in school, just 5 years earlier. It was controlled by a modern PC. Ancient TTL logic from the 1970's was the only way for all those feeds & speeds from the 2000's to access the real world.
The balsa robot had a short life, despite appearing to contain a lot of disks. The disks had no caddies & risked getting scratched. It was built & all the disks were loaded in place, but the moment it had to be moved, it fell apart. The balsa was too fragile. After the robot was built, disks also started coming up erased from exposure to ambient light.
Before the 1st robot was finished, lions started trying microcontrollers in late 2002.
There was no Arduino in 2002, just buying an MC68HC11 & soldering it. Without an oscilloscope & very little knowledge of how the serial port worked, the lion kingdom gave up on making it print hello world. 6 months later, in June 2003, the lion came back to it & it finally worked. It turned out in the microcontroller world, the serial port wasn't independent of the CPU speed. The serial port was locked to the speed of the crystal, which was 50% faster than what the datasheet was written to. The serial port was 1800 baud instead of 1200 baud.
Despite having only 512 bytes of RAM, it was way beyond TTL logic.
In mid 2004, a new robot was started, with all microcontrollers. It was made of MDF & steel, with the disks inside caddies. The microcontrollers made it so much lighter & faster. 3 high density towers & a low density loading tower were built. This worked as designed for many years, until the capacity was used up.
There was no effort in optimizing the microcontrollers or the serial communication. 12V RS232 lines went all the way from the computer to the robot, which limited them to 57600 baud. The firmware was loaded into RAM before every use, rather than learning the protocol required to write the flash.
Unlike 3D printing robots or quad copters, the DVD robot had to navigate a large area to below a millimeter or it would either scratch disks or load the wrong ones. The cheap solution was laser pointers with apertures outside the lenses, reducing the beam size to 1mm diameter.
There were 2 red lasers...Read more »