Propeller DCM





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Uploaded on Apr 13, 2011

This is a Parallax Propeller chip running a partial implementation of Premerlani and Bizard's work on Direction Cosine Matrix computation for orientation sensing. I'm hoping to use this in a quad-rotor without a GPS or magnetometer - I wanted to see how good the algorithm was at stabilizing pitch and roll. So far it looks very promising.

All the work is done on the Propeller itself. It reads the gyro and accelerometer values on one core, and computes the DCM from those readings on another core. At this point the code is still written in the high-level language, Spin. Since all the math is fixed point, there's a strong chance I won't actually have to write an assembly version - I've timed it at 400 updates per second.

The visualization app was a quickie written in C#. The DCM algorithm was initially written on the PC side for ease of debugging - the Prop just sent sensor readings. Once it was all working, porting to the Prop only took a couple hours.

The Propeller chip makes this kind of thing remarkably easy. Since the chip has multiple hardware cores running in parallel you don't have to deal with interrupts. When I get this running in my flight controller, it'll have the following hardware cores running:

1) Receive signals from remote control
2) Read gyro and accelerometer
3) Run DCM algorithm, handle flight logic
4) Control servos and motors
5) Blinky lights (gotta have 'em)
6) Talk to the PC / XBee

... and I'll still have two left.


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