Volvo 240

Playing with Robots

Legged Robots

Just before the summer of 2002 I took on a project at the NTUA which was to be my undergraduate degree thesis. The work was on the energy consumption of a one-legged hopping robot. I completed my thesis in late 2003.

Here there is a little information about the project.

The area I worked in is that of legged robots. The particular project was to do with the (relatively) simple system, of a one-legged robot. Specifically, how best to regulate the parameters of the robot so that it may move using the least energy possible. This involves making use of the natural dynamics of the robot, so that all the motors of the robot have to do is compensate friction.

In the beginning I studied the case of an actuated pendulum as a first model. Later, I moved on to study the robot more realistically, using a SLIP model. The SLIP models a one-legged robot as a concentrated mass for the body (larger yellow sphere in figure at the right), a massless springy leg (red component), a massless foot (small yellow sphere). The body is joined to the leg with a hip, so the leg may rotate freely.

Although the SLIP is the simplest realistic model of the robot, it has been used extensively to correctly predict the behavior of the real one-legged robot, at least qualitatively. Also, the SLIP model may be used to assist in the study and control of multi-legged robots.

When the robot is on the ground, its in the stance phase, while the flight phase is when its in the air. Below the various stages of the motion are shown. At the left the robot is just about to touch down, then it executes the stance pahse. The fourth snapshot shows the moment of liftoff and then the flight phase follows. During the flight phase the leg will swing forward (with a motor for example) and the robot will be ready for the next stance phase.