Each of the 18 joints is based on a cheap standard size RC servo. The parts for the mechanical structure were machined from extruded aluminium stock (mostly 3mm thick flat and angle cross section). A small Delrin button was added to the back plate of each servo (opposite the spline) so that all joints have a two-point hinge. The controller board has 3 ATtiny26 AVR microcontrollers, each capable of driving 8 servos. Communication with the board is through a parallel port on a Linux host via a custom driver. Position data and control commands are all sent to the AVR's USI as single-byte messages. The controller board and host driver use interrupts for handshaking in the data communication process. Kernel timers are used within the driver to ensure that each step within each coordinated move of the legs is sent to the AVRs without significant latency. The joint positions that are required for the tip of a leg to trace out a path through space are calculated in a user-space application and passed to the device driver via the write system call. The total mass of the hexapod is around 1.5kg (just over half of this is the RC servos), and the length is 420mm. The project to date has taken many many months... really...
The movie [mpeg4(5.3MB)|QuickTime(13MB)] shows the basic walking gates in a 5/6 duty cycle. The servos have insufficient torque to support the weight of the hexapod on 3 legs. The total mass might be reduced in the future by machining holes and slots in the structural parts (after I work out the minimum cross section that support the load without bending...)