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LEGO Design. SIUE School of Engineering Fall, 2005. Goals:. Build better robots Minimize mechanical breakdowns Build robots that are easy to control Encourage good design strategy. Geometry. Three plates = 1 brick in height.

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Lego design

LEGO Design

SIUE

School of Engineering

Fall, 2005


Goals
Goals:

  • Build better robots

    • Minimize mechanical breakdowns

    • Build robots that are easy to control

    • Encourage good design strategy


Geometry
Geometry

  • Three plates = 1 brick in height

  • 1-stud brick dimensions: exactly5/16” x 5/16” x 3/8” (excluding stud height 1/16”),

  • This is the base geometry for all LEGO components


Structure
Structure

  • Common pitfall when trying to increase mechanical robustness:


Structure1
Structure

  • The right way:


Structure2
Structure

  • The right way:


Lego design

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.


Lego design

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


Lego design

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.


Lego design
The structure below demonstrates a very strong design that will not come apart unless you take it apart.


Connector pegs
Connector pegs will not come apart unless

  • Black pegs are tight-fitting for locking bricks together.

  • Grey pegs turn smoothly in bricks for making a pivot


Connector pegs1
Connector Pegs will not come apart unless


Drivetrain
Drivetrain will not come apart unless

40T

  • LEGO Gears

8T

16T

Bevel

1T Worm

24T

24T

Crown


Seesaw physics
Seesaw Physics will not come apart unless


Radius torque and force on a gear
Radius, Torque, and Force on a Gear will not come apart unless

torque = r x F


3 to 1 reduction
3 to 1 reduction will not come apart unless


Lego design

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 (sincethe 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.


9 to 1 reduction
9 to 1 reduction 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


Lego design

The torque at the “output shaft” is 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 (since9 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. It’s not that easy!


A three stage gear train with a gear ratio of 27 1
A three stage gear train with a gear ratio of 27:1 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


Lego drive trains
Lego Drive Trains 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


Lego axle
Lego Axle 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


Sample drive train
Sample Drive Train 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


Gear rack
Gear Rack 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


Worm gears
Worm Gears 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

3

  • Pull one tooth per revolution

1

2

• Result is a 24:1 gearbox

4


Axle joiner
Axle Joiner 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


Toggle joint
Toggle Joint 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


Caster design
Caster Design 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


Lego legs
Lego Legs 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


Grippers
Grippers 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


Car turn problem
Car Turn Problem 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


Lego differential gear
Lego Differential Gear 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


Differential drive
Differential Drive 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 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.


Motors
Motors 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

  • 9V Gear Motor

  • ~ 150 mA

  • 300 RPM (no load)

  • Polarity


Motors1
Motors 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

  • 9V Micro Motor

  • 20-30 RPM


Mounting motors
Mounting Motors 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

Note Bulge under motor


Mounting motors1
Mounting Motors 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

  • Add a gear:


Mounting the motor
Mounting the Motor 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


Lego sensors
Lego Sensors 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


Light sensor mount
Light Sensor Mount 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


Lego design
This shows an interesting way to mount a photoresistor, as well as how to sheild it from a dedicated light source.


Touch sensor mount
Touch Sensor Mount well as how to sheild it from a dedicated light source.


Changing rotational axis
Changing Rotational Axis well as how to sheild it from a dedicated light source.


Changing rotational axis1
Changing Rotational Axis well as how to sheild it from a dedicated light source.


Spin x y z
Spin x-y-z well as how to sheild it from a dedicated light source.

See more examples at http://constructopedia.media.mit.edu/


Lego rcx brick
Lego RCX Brick well as how to sheild it from a dedicated light source.


Rcx brick with sensors motors
RCX Brick with well as how to sheild it from a dedicated light source.sensors & Motors


Lego rcx brick display
Lego RCX Brick Display well as how to sheild it from a dedicated light source.


Build for good control
Build for good control well as how to sheild it from a dedicated light source.

  • Slow vs. fast?

  • Gear backlash

  • Stability

  • Skidding (Tank-tracks vs. wheels)

  • Differential Steering !!!


Design strategy
Design Strategy well as how to sheild it from a dedicated light source.

  • Incremental

    • Test components parts as you build them

      • Drivetrain

      • Sensors, sensor mounting

      • Structure

  • Don’t be afraid to redesign

  • Internet for design ideas


Design strategy1
Design Strategy well as how to sheild it from a dedicated light source.

  • Drive-train driven

  • Chassis/structure driven

  • Modular?


Testing
Testing well as how to sheild it from a dedicated light source.

  • Don’t wait until you have a final robot to test

    • Interaction of systems

    • Work division (work concurrently)

  • Develop test methods

  • Repeatability


Competition philosophy
Competition Philosophy well as how to sheild it from a dedicated light source.

  • Have fun

  • Be creative, unique

  • Strive for cool solutions, that work!

  • Aesthetics: it’s fun to make beautiful robots!