LEGO Design

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LEGO Design

• SIUE
• School of Engineering
• Fall, 2005

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Goals

• Build better robots
• Minimize mechanical breakdowns
• Build robots that are easy to control
• Encourage good design strategy

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Geometry

• Three plates 1 brick in height

• 1-stud brick dimensions exactly 5/16 x 5/16 x
  3/8 (excluding stud height 1/16),
• This is the base geometry for all LEGO
  components

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Structure

• Common pitfall when trying to increase mechanical
  robustness

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Structure

• The right way

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Structure

• The right way

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A good robot starts with a good foundation. A
robot whose body is not structurally sound will
be fraught with problems for the designers. The
first and most important is that the friction
between stacked bricks should not be relied upon
for structural strength. We recommend using
connector pegs to help create a "skeleton" like
the one below. A design like this is both light
and strong but usually requires a number of
rebuilds to get perfect.
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Structural supports like the ones shown below can
be placed on almost any chassis design. Use this
to your advantage. You can get by with fewer
legos and have a stronger chassis this way
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The picture below demonstrates a very
structurally sound way of constructing a frame
with legos. The 3 wide connector peg can be used
for one of the 3 join points, or an additional
4x1 brick can be used.
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The structure below demonstrates a very strong
design that will not come apart unless you take
it apart.
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Connector pegs

• Black pegs are tight-fitting for locking bricks
  together.
• Grey pegs turn smoothly in bricks for making a
  pivot

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Connector Pegs
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Drivetrain

• LEGO Gears

40T
8T
16T
Bevel
1T Worm
24T
24T Crown
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Seesaw Physics
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Radius, Torque, and Force on a Gear
torque r x F
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(No Transcript)
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3 to 1 reduction
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Since the forces between the teeth of the two
gears are equal in magnitude but act opposite in
directions, the torque exerted on the right axle
is three times the torque exerted on the left
axle (since the radii of thee gears differ by a
factor of three). Thus this gear system as acts
as a torque converter, increasing the torque at
the expense of decreasing the rate at which the
axle turns.
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9 to 1 reduction
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The torque at the output shaft is 9 times
the torque provided on the left(input) axle.
The output shaft will of course spin 9 times
slower than the input shaft, but it will be much
harder to stall. Have someone grab the output
shaft and try to stall your fingers as you spin
the input axle. Its not that easy!
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A three stage gear train with a gear ratio of
271
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Lego Drive Trains
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Lego Axle
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Sample Drive Train
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Gear Rack
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Worm Gears

• Pull one tooth per revolution

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1
2
Result is a 241 gearbox
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Axle Joiner
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Toggle Joint
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Caster Design
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Lego Legs
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Grippers
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Car Turn Problem
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Lego Differential Gear
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Differential Drive
The differential gear is used to help cars turn
corners. The differential gear (placed midway
between the two wheels) allows one wheel to turn
at a greater speed than the other. Even though
the wheels may be turning at different speeds,
the action of the differential means that the
torque generated by the motor is distributed
equally between the half-axles upon which the
wheels are mounted. Assuming the robot's weight
is sufficient and distributed properly, the robot
should be able to turn with its drive motors at
full power without causing either wheel to slip.
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Motors

• 9V Gear Motor
• 150 mA
• 300 RPM (no load)
• Polarity

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Motors

• 9V Micro Motor
• 20-30 RPM

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Mounting Motors
Note Bulge under motor
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Mounting Motors

• Add a gear

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Mounting the Motor
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Lego Sensors
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Light Sensor Mount
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This shows an interesting way to mount a
photoresistor, as well as how to sheild it from a
dedicated light source.
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Touch Sensor Mount
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Changing Rotational Axis
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Changing Rotational Axis
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Spin x-y-z
See more examples at http//constructopedia.medi
a.mit.edu/
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Lego RCX Brick
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RCX Brick withsensors Motors
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Lego RCX Brick Display
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Build for good control

• Slow vs. fast?
• Gear backlash
• Stability
• Skidding (Tank-tracks vs. wheels)
• Differential Steering !!!

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Design Strategy

• Incremental
• Test components parts as you build them
• Drivetrain
• Sensors, sensor mounting
• Structure
• Dont be afraid to redesign
• Internet for design ideas

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Design Strategy

• Drive-train driven
• Chassis/structure driven
• Modular?

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Testing

• Dont wait until you have a final robot to test
• Interaction of systems
• Work division (work concurrently)
• Develop test methods
• Repeatability

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Competition Philosophy

• Have fun
• Be creative, unique
• Strive for cool solutions, that work!
• Aesthetics its fun to make beautiful robots!