Thursday, January 5, 2012

Pythagoras: New Calibration Method

A new, more accurate method of calibrating the stepper's initial position. Previously, I can calculate the arm's position at any position on the potentiometer. However, this requires quite a bit of measurement and interpolation and extrapolation.

Instead, I measure the potentiometer's value once, at a known angle. In this case, its 45 degrees up from horizontal. Upon startup, the arms each move until the potentiometers hit the set value, which means the arm is at (almost) exactly 45 degrees up from horizontal. Basically the potentiometers act like optical gates.

The improvement on calibration can be seen in the vertical traverses. Previously, the robot would deviate from a vertical line by around 1/3 of an inch. Now, the deviation is less than 1/32 of an inch.

4 comments:

  1. Hi, I see that your delta robot has become very precise. Have you ever thought to draw a PCB circuit board with a sharpie marker in order to etch it later? This would be a revolutionary idea. This would facilitate the PCB home production greatly.

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    1. Now that there is a genuinely good idea. There is a fellow who ported G-Code to the mbed (the Smoothie project, http://smoothieware.org/) and if I manage to get it working with Pythagoras...

      The possibilities!!!

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  2. Just a question. Have you tried drawing a text file?

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    1. I don't have as font rendering on the robot, so it would have to be first rendered as an image first. And if it comes out anything like that one time I tried to print a coupon, its nearly unreadable.

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