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## PowerPoint Slideshow about ' LEGO Design' - analu

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Presentation Transcript

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

- 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

- Common pitfall when trying to increase mechanical robustness:

Structure

- The right way:

Structure

- The right way:

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.

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

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.

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

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 Pegs will not come apart unless

Seesaw Physics will not come apart unless

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

torque = r x F

3 to 1 reduction will not come apart unless

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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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

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 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 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 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 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 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

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

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

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

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

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

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

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

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

- Incremental
- Test components parts as you build them
- Drivetrain
- Sensors, sensor mounting
- Structure

- Test components parts as you build them
- Don’t be afraid to redesign
- Internet for design ideas

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

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

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 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!

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