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number since June 17, 2001
Click on the image for a larger view
This small robot was designed to demonstrate
precise odometry with Mindstorms technology. Thus the name "ODObot.
I also wanted to see the issues with a drive belt system, since
my current project - VacBot uses belts to drive it. To achieve
repeatable precise increments in movement, a cam was used to
push a switch in every 1/5 rotation of the wheel. Thus by counting
the clicks, you can tell how far you've gone and thus navigate
to a goal destination within reason and tolerances of the system.
The goal was to start at one point in a maze that had been modeled
after dozens of competition mazes to include sharp turns and
long distances to travel straight.
My first issue
was the fact that the robot did not go straight because of speed
differences and wheel alignment with such a crude construction
method. This was solved by putting a friction coupling element
between both drive motors so the speeds were averaged out.
Second was resolution.
With only 1/5 wheel positional clicks, the turning was not exactly
90d. By holding one wheel stationary during a turn, the outer
wheel had twice the clicks it had to go to turn, and thus doubled
my resolution on turns to an acceptable level.
This was the first
robot programmed in Robolab, a superior interface to the bricks
processor, allowing you to do just about anything most of the
C based programs will do.
showing the pulley drive system to the small gear train on the
Both sides were built as separate identical parts that were mirror
images then combined later.|
caster wheel on the rear.|
view, showing the extensive use of locking struts to keep the
robot connected very rigidly. It easily passed the "throw
it on the carpet test" and didn't fall apart.|
here's the maze made from formica topped particle board bought
at Home Depot, and black and red tape. It was designed for a
much smaller robot, so was tight fitting in some areas!|
Movie Clip (1.4MB)
fairly long movie shows the typical and very repeatable performance
ODObot1 in the maze, and thus proves that precise navigation
with even crude Lego technology is possible. (with sound!)|