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| Crayonbot Design and Construction |
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These were the first notes I made when I started thinking about building
a drawing robot. The pull/pull cable drawing in the middle and the
clamping gripper in the lower left made it into the final design.
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The crayon gripper works very well, but has a very narrow range of
pen diameters that it works with. It attaches and detaches from the
robot arm easily. It's covered in more detail on the next page.
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Connecting the servo motor shafts to the moving parts using peanut butter jar
lids and picture hanger wire converts angular shaft rotation to linear motion.
With this design, one degree of shaft rotation equals one unit of movement along
the X and Y axis at any point in the motor's travel. This greatly simplified the
motion control software.
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A spring with about 16 oz of pull on one of the wires keeps the wires taut,
which eliminates backlash and gives good repeatable positioning. A 180 degree
servo and jar lid diameters of 3.25" gave about 5" of travel with
positional resolution better than 1/32".
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| A larger diameter pulley on the drawing table and a smaller one on the
robot arm gives a rectangular drawing area of about 4.5"x6".
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| A tin can with a larger diameter than the turret shaft pulley sacrifices
positional resolution, but allows the turret to rotate fully 90 degrees
perpendicular to the X axis on both sides. I could add a 2nd rack of colors
on the other side if I wanted to.
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| The spindle motor from a dead hard drive made an excellent turret bearing.
Hard drive salvage!
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