Feedback and Sensors Oakwood FLL #44267 Robot, Lesson 2 Michael - - PowerPoint PPT Presentation

Feedback and Sensors

Oakwood FLL #44267 Robot, Lesson 2 Michael Lyle

Agenda

3:15 - Robot presentation 3:30 - Core values discussion & video 3:40 - Snack & discuss team names 3:50 - LEGO group work 4:25 - Cleanup 4:30 - Helen Rhee – Environmental engineering and watershed

What we’d like to happen

“Spin both motors at speed 50 for 2.5 seconds”

Even if robot is mechanically “perfect”...

Solid, carefully chosen wheels

x

Good center of gravity Rigid, heavy robot

What actually happens

“Spin both motors at speed 50 for 2.5 seconds”

Things change every run

• Dust on playfjeld/wheels
• Bumps under mat
• Battery charge level
• Robot starting position
• How compacted the pieces are
• Variation in tire surface
• Gear periodic error
• T

emperature

• Etc, etc, etc.

Demonstration

Just doing a series of motions… and hoping for the best… is not enough. We need some way to fjx errors and variation: feedback.

Odometry

• Means “measurement of distances”
• LEGO motors can measure how far they’ve turned
• Reduces some kinds of errors
• Still not very good
• Fooled by wheels slipping
• Wheels have to slip some to start/stop/turn

Mechanical feedback

WALL

Mechanical feedback

WALL

Color sensors

• Measures how much light is refmected (has other modes)
• Most useful with black lines on fjeld
• Can be used to follow lines
• T

wo can be used to “align” on a line

• Can be fooled by similar colors on playfjeld—
• nly use once “close”

Line following

This is a “bang-bang” line follower. It is always turning on and off the line. There are smoother ways to do this, but this is a good start.

Other sensors

• Ultrasonic rangefjnder
• T
• uch sensor
• Gyro sensor

Robot design rubric

Summary

• Make robot as mechanically precise as possible
• Choose strategy & make attachments able to tolerate errors
• Fix as much error as possible with feedback

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Mechanical

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Line-following

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Aligning

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Other, creative solutions