Robogames California holds many different competitions, one of which is Mech Warfare. With a passion for robotics, and a little time to spare during my first two years at college, I decided that I would build an entry robot for when I had the ability to attend Robogames. Thus, I began working on designing a robot around components that I can afford, hobby servos and scrap stainless steel that I happened to be able to get my hands on.
Having started this project at the end of high school, I figured that I could get away with some simplifications to the legs of a biped, and make a relatively simple walking robot. I planned on keeping the working mechanism as simple as possible so that the programming (my weak point) would be kept relatively simple. Turns out, making a bipedal robot is actually a rather in depth and complex process, especially if it needs to be responsive, and controlled by simple inputs. As such, the robot has been through 3 revisions, each of which is described a little bit below. Keep in mind, this was a project that I did in my spare time during my first few years of college.
Revision 3 Robot:
Revision 3 robot, carries over a lot of features from previous revisions, while taking the better qualities, and adding new features. The primary difference being the order of the degrees of freedom in the legs. The rotation of the leg now takes place in the foot, allowing the robot to balance over one foot and pivot in place over it. Still using 6 degrees of freedom for each leg, and a pan/tilt system. Kinematics for foot placement has been implemented.
Remote control using a PS2 controller and Xbee radios have been implemented. Thanks to the PS2X Library, the controller can use the analog inputs of the buttons, triggers and the analog sticks. These will be used to control walking, and thus the gait control will be done through software, which is the part of the project taking the most time.
Rev. 03 Robot remote control demo:
Revision 2 Robot:
This revision robot used 6 degrees of freedom on each leg, and featured a pan/tilt setup for the weapons. Kinematics for this configuration of leg proved to be very difficult to calculate. The rotation of the leg was implemented after the horizontal swing of the hip, making for some strange angles. The rotation at the hip was carried over from revision one. This revision did not make it very far, as moving the rotation of the legs proved a much easier method for calculating the kinematics. Certain design features were carried over such as the pan/tilt setup for the weapons systems.
Revision 1 Robot:
This robot was the simplest revision, and attempted to replicate the wind-up toys, with 4 degrees of freedom per leg, and a pan servo. 3 degrees of freedom replicated the ankle, knee and hip movements, and the fourth allowed for rotation of the leg at the hip. The intention of this design was to keep the kinematics simple, while allowing the robot to pivot about one leg.
Complications arose when the robot needed to be able to pivot about a leg. The legs used tongs to allow the robot to balance on one foot, and these needed to extend past the center of gravity of the robot in order to allow it to stand up on one leg. But, pivoting about one leg made this very difficult to implement without the balancing tongs of each leg hitting each other. Thus, more degrees of freedom were needed. However, implementing basic kinematic calls and structuring a basic gait was completed on this revision.
Rev. 01 Robot gait demo: