UH Lego Mindstorms Structural Tutorial

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UH Lego Mindstorms Structural Tutorial

• By H. Bartels
• Date 8/6/2007

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Primary Construction Styles
Stud Style
Pin Style
Axle Style
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Basic Block dimensions
(3) Small Blocks (1) Regular Block
Height 1.2 Stud spaces
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Stud Type Construction

• Classic Lego Construction

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Diagonal Bracing Guide Chart
7 Stud Spaces (8 studs) required to span 3 bricks
high x 6 stud spaces long
Single Regular Brick
Brick Height in terms of Stud Spacing
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Pin Style Construction
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Pin Style Properties

• Dual Purpose
• Hinge - Allows Rotation (grey pins)
• Single pin
• Pin - Structural Component (black pins)
• Requires at least 2 pins to prevent rotation

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Axle Style Construction
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Axle Type Properties

• Dual Purpose
• Transmit rotation
• Gears
• Rotary motion from motors
• Structural Element
• Requires (1) axle to lock motion
• Can be used to create compact structures
• Especially useful for tying together multiple
  sensors in close proximity

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90 deg style connections
Combined pin and axle connector
Compound connectors (mixed construction)
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Gearing

• Transmit rotation from motor to axle not aligned
  with motor output
• Modify Motor Output Speed
• Alternately motor speed can be reduced
  programmatically
• Rotate Multiple Wheels with one Motor
• Transmit rotation through 90 deg angle

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Spur Gears
0.5
1.0
1.5 spaces
2.5 spaces
40 tooth
24 tooth
16 tooth
8 tooth
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Spur Gear Engagement
4 spaces
2 spaces
Overall Ratio 5
Ratio 24/8 3
Ratio 40/24 5/3
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Gear Spacing Requirements
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Bevel Gears

• allow 90 deg transformation of rotation

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Worm Gears

• High Gear Ratios
• 1 Rev per tooth
• with 40 tooth spur gear can obtain 401 ratio
• Worm gears are prime mover- mating spur gear
  cannot rotated (Worm gear locks the spur gear)
• Automatic locking mechanism

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Use Web Links for Building

• www.lego.com/eng/create/designschool/lesson.asp
• mindstorms.lego.com/MeetMDP
• neuron.eng.wayne.edu/LEGO_ROBOTICS/lego_building_t
  utorial.pdf
• www.philohome.com/nxt.htm

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Some Mindstorms NXT Books

• "LEGO MINDSTORMS NXT The Mayan Adventure" by
  James Floyd Kelly
• "Building Robots with LEGO Mindstorms NXT" by
  Mario Ferrari and Guilio Ferrari
• "LEGO MINDSTORMS NXT-G Programming Guide" by
  James Floyd Kelly

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Vehicle Topology

• No. of wheels
• 3 wheel
• 4 wheel
• Steering
• Relative wheel motion (Skid Steer)
• Single steering front wheel for 3 wheel
  construction
• Automotive style Ackerman steering
• Not practical for Lego construction since
  accuracy is inadequate

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Vehicle Stability Considerations

• Always consider attachments when determining
  center of gravity location
• For 3 wheelers keep CG close to base of triangle

Keep CG within shape formed by contact points
Triangle Base
Ratio 40/24 5/3
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Links to example robots on the web

• Like A Rock
• www.teamhassenplug.org/robots/LikeARock
• Tribot and accessories instruction manuals
• www.legoeducation.info/nxt/resources/building-guid
  es
• Spider Bot
• www.sorosy.com/lego/spider1/dls/spider1_instructio
  ns.pdf
• Cool Car
• mindstorms.lego.com/NXTLOG/ProjectDisplay.aspx?id
  8ebaef69-9fdd-46d1-98b8-c7cc585ce304
• NXTWay
• www.philohome.com/nxtway/nxtway.htm

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Robot Build for Programming Task
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Robot Build Requirements

• Skid steer type vehicle with (2) drive motors
• One accessory Arm able to be rotated using a
  motor
• (2) sensors
• (1) Touch Sensor
• (1) Light Sensor

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Accessory Arm
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Sensor Configuration
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Touch Sensor Integration