BUILDING A COMPETITIVE ROBOT - Mastering Lego … Robot/Building a Competitive... · , copyright...

www.masteringlegorobot.com, copyright 2012

BUILDING A COMPETITIVE ROBOT

01 September 2012 www.masteringlegorobot.com, copyright 2012 1


SEA MONSTER ROBOT HISTORY

• Serious competitor. Last six VA/DC FLL championship tournament (2006-2011) results:

– Two first-place robot performance awards

– Three second-place robot performance awards

– One first-place robot design (mechanical) award

• Began as a modified tribot and evolved season by season.

• Scored perfect 400* in 2007 regional.

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*Team jumped up and down celebrating before buzzer, causing object to fall and resulting in 385 score.

01 September 2012


KEY SEA MONSTER ROBOT FEATURES

• Compact size

• Large double wheels for speed and traction

• Center of mass between wheels and skid

• Two light sensors, placement optimized for following lines

• Touch sensor for fast mission transitions

• Back bumper for fast alignment to wall

• Bottom skid to go straight & climb ½” wall

• Strong mounting points for attachments

• Arm motor & mounting points won’t pull off

• Easy access to battery charging port

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LEGO DIGITAL DESIGNER

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• The building instructions for the Lego competitive robot were developed with Lego’s Digital Designer software.

• The good news is that the Lego software is free and can be downloaded at http://ldd.lego.com/en-us/download/.

• The bad news is that it has some limitations:

– Some common Lego parts like the wheels used in our robot aren’t available for designing.

– Parts that fit together in actuality sometimes can’t in Digital Designer.

– Complex assemblies can’t always be rotated to fit.

– The generated building instructions may be out of order or the pictures may block viewing how some pieces come together.

• The file Competitive Robot.lxf has the Lego design. It can be used to gain understanding of how to put the robot together. It can also be modified to document enhancements.

01 September 2012


BUILD BOTTOM PORTION OF ROBOT

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• Instructions are in Competitive robot (bottom) building

instructions.pdf.

01 September 2012


ADJUSTMENTS TO BUILDING INSTRUCTIONS (page 11 of bottom instructions)

Insert 3M peg here to mate three beams.

6 01 September 2012


ADJUSTMENTS TO BUILDING INSTRUCTIONS (page 37 of bottom instructions)

Replace yellow beam with second light sensor so that it is back-to-back with the first light sensor.

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BUILD TOP PORTION OF ROBOT

Instructions are in Competitive robot (top) building instructions.pdf.

Note: Remember to attach rechargeable battery to NXT brick first.

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WIRE TOP

• Connect 16 cm cable (or

longer) to motor.

• Connect 20 cm cable (or longer) to touch sensor.

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WIRE FRONT

• Connect two 12 cm cables*

(or longer) to motors.

• Cables go under cross-beams, around pegs and then back under beams.

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*Note: The Mindstorms Education NXT Base Set does not come with many really short cables. Order lots of NXT Extended Connector Cables Sets (W991534).

01 September 2012


JOIN TOP AND BOTTOM

• Lay touch sensor cable flat

under NXT brick.

• Snap lowest portion of beams of top section to two pegs (each side) of bottom section.

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JOIN SENSOR CABLES TO PORTS

• Snap touch sensor cable to

port #1.

• Snap right light sensor cable to port #2.

• Snap left light sensor cable to port #3.



CONNECT MOTOR CABLES TO NXT BRICK

• Connect arm motor cable to port A.

• Connect 20 cm cable to port B. Thread it behind top two axles. Connect to right motor.

• Repeat for second 20 cm cable from port C to left motor.



ADD BEAMS TO LINK TOP AND BOTTOM

• Snap 13M beams to three pegs at top of NXT brick.

• Fit three axles through holes in beams and then fit ½ bushings onto axles.



MAKE WHEELS

• Start with 81.6 x 15 motorcycle tire and wheel.

• Insert four 3M pegs, avoiding holes aligned with long center line.

• Snap second wheel onto first wheel.



MAKE WHEELS (continued)

• Insert four 2M pegs in 7M beam.

• Snap onto wheel.

• Insert 7M axle so that it is flushed on other side of wheel.

• Attach to motor.

• Repeat for second wheel.



FIND MATCHING LIGHT SENSORS

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• After building the robot, verify that the two light sensors match performance.

• Why? Line following requires calibrating the robot, which takes the black and white light measurements of one light sensor and applies the calibration to both sensors.

• How? On the NXT brick, go to View -> Reflected Light. Select Port 2. Put robot over white and black lines on mat and record values. Repeat with Port 3. Mount the pair of sensors that best match.

01 September 2012


BALANCE WEIGHT OF ARM MOTOR

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• When the robot runs above 50% power, the robot will pull to the left. This becomes progressively worse as power approaches 100%. This can be tested with the programs test 50.rbt – test 100.rbt.

• Why does it pull to the left? The arm motor weighs 3 ounces and puts additional downward pressure on the right wheel, giving it better traction. The left wheel with less traction will slip more as power increases.

• Solutions?

– Ideally, put a counterweight over the left wheel.

– Move the arm motor closer to the front middle of the robot.

– Don’t run the motors at maximum power.

– Take into account how far the robot will pull to the left or right when routing the robot.

01 September 2012


BALANCE WEIGHT OF ARM MOTOR (continued)

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• If you can, get hold of the 2 x 6 x 2 “heavy crane” brick from the 2006 Nano Quest challenge (part no. 73843). It weighs 2 ounces.

01 September 2012


BALANCE WEIGHT OF ARM MOTOR (continued)

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• Modify the left side of the robot to hold the counterweight. Instructions can be found in Competitive robot top w battery instructions.pdf.

01 September 2012


OTHER ENHANCEMENTS TO CONSIDER

• Move arm motor location based on mission locations:

– Left or right side

– Higher or lower

• Shade light sensors to minimize effects of ambient light.

• Widen distance between wheels. The base on the bottom can be widen by two beams and still fit underneath the NXT brick. Widening the robot can help it go straighter.

• Add front touch or ultrasonic sensor to detect walls or mission objects.

• Try other tires, though the double motorcycle tire assembly should be the best combination of size and grip.



ANOTHER ENHANCEMENT TO CONSIDER

• Replace bottom skid with smooth wheels in back.


BUILDING A COMPETITIVE ROBOT - Mastering Lego … Robot/Building a Competitive... · , copyright...

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