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Monday, December 21, 2009

Phase 1: Collect underpants.

In the absence of a robot capable of supporting it's own weight, I've started planning my next move.

The purpose of writing my own firmware for this robot is purely academic. I don't have a specific goal in mind for this project, even though I'm sure we would all enjoy a robot which could clean our house, bring you drinks, or make us coffee.

As I develop more and more features, I can share them as code snippets which will help other people with their projects. Of course, when I decide I want to revolutionize the coffee robot industry, I will be adequately prepared.

Now that I have figured out how to use the servos as sensors to get feedback about the robot's position, I plan to implement an inverse kinodynamics engine to enable balance without an accelerometer.

For those who aren't down with the lingo, kinodynamics is a contraction of kinematics and dynamics.

Kinematics is concerned with modelling the behaviour of a system given a physical and geometric configuration. In the case of the humanoid robot, this means calculating the relative location of the arms, legs, feet, etc, simply given the angular position of each of the 16 servos. This can be calculated (relatively) simply using basic (again, not something you'd find next to the funny pages) vector mathematics and trigonometry.

Now, dynamics. Kinematics merely describes the geometry and structure of an object. It's velocity, mass, angular momentum and behaviour when subjected to a force are all in the domain of dynamics. When your robot falls down the stairs in a hilarious but tragic accident, his dynamic behaviour determines how long you will watch in abject horror.

So, a kinodynamic model of a humanoid robot can be used to generate a fairly reliable prediction of the state of a robot at a future instant, given the current state and control space.

Put more simply, this model can be used to calculate "safe" actions, which will result in the robot performing a motion while keeping it's centre of mass over it's feet - in other words, balancing.

These are all quite lofty goals, and right now it looks complex, but I'll outline more details in future posts.

Stay tuned for Phase 2: "???"

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