I became interested in hexapods after seeing Matt Denton's MSR-01 and Zenta's A-pod and Phoenix. I'm studying engineering so I decided to put some of the maths to use and write my own hexapod control program. To help with testing this out I built a hexapod using just about the cheapest servos I could find (HXT900, which were $3.60 at the time, they're now $2.99).
I'm redesigning this to solve some issues I had. On the original, the coxa joint did not have enough movement and the legs were too flexible, which was also because of the coxa joint - it pivoted only on the servo shafts without support on the other end of the servo.
Now my coxa and femur servo's are joined by a coxa part cut from a 4mm plastic chopping board. The coxa has pivot opposite the coxa servo's shaft. The femur, tibia and body plates are cut from 4mm plywood.
The servo's are controlled by an SD21 I2C controller. A Picaxe 18x takes commands over bluetooth serial from the program running on my laptop or phone and sends them to the SD21. This is proving a bit slow, which leads to jerky servo movement. I'm probably going to get a Pololu Maestro servo controller which is serially controlled and has some other cool features like using pins and inputs and running scripts and sequences. I just need to assemble the parts and update the leg parameters and servo directions in the program and hopefully I can get a video of it walking. So far this has cost me about £100 to build.