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Al Williams

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Propeller-Driven Robot

April 18, 2010

I mentioned earlier how I'd fashioned some very simple H-bridges for a robot platform I was building. I like to talk to middle school and high school kids about engineering and a robot usually gets their attention. This robot will replace an old one I used for this purpose. The propeller? Well, that's a long story.You can see the robot in action on DDJ TV. You'll notice it doesn't have an obvious propeller on it. That's because the Propeller it the CPU driving it. This CPU is from Parallax (the people who invented the Basic Stamp).

I'm a big fan of alternate CPU designs, although the Propeller is a bit strange. Its defining feature is that it has no interrupts. Instead it has 8 separate CPUs (cores, I guess) that share access to some resources. A central controller gives each CPU access to the shared resources in a round-robin fashion. Instead of depending on an interrupt to provide determinism, the propeller dedicates a CPU to any time-sensitive task.

For example, one CPU could be generating PWM pulses while another monitors a robot's bump sensor. A third could listen for commands from a remote data link. Polling is fine if all that CPU has to do is poll.

I plan to work on the robot some more soon. I'll keep you up to date on how it progresses.

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