The Manipulator

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The Manipulator

• (The part of the robot that isnt the chassis)

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Sources of Power
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Pneumatics
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Components

• Compressor
• Pumps air into the airtanks
• Air tanks
• Holds air for later use and compression
• Cylinder
• Powered by air
• Interacts with something outside the system
• Tubing
• Connects elements of the system, stores some air
• Solenoid (gates)
• Directs where the air can go, releases exhaust
• Pressure Gauge
• Indicates pressure in system
• Safety valve
• Opens if pressure is at an unsafe level

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Cylinder

• Stroke
• Difference in distance between the cylinders
  piston while retracted and while extended
• Smaller strokeless air needed
• Diameter
• Smaller diameterless air needed
• Smaller diameterless weight

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Advantages

• Good at performing infrequent action
• (action performed once or twice per match)
• Low power usage
• Good for push/pull actions
• Other types of action require simple machines for
  changes in direction
• Difficult to turn the pistons linear motion into
  rotational motion
• Simple
• Conceptually
• In terms of programming (on/off function)
• Multiple pistons w/ a single compressor
• More pistons mean more possible tasks to perform
• Reliable
• Easy to tell when something is wrong

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Disadvantages

• On/off limit
• Difficult to make it so the piston is between
  fully extended and retracted
• Weight of system
• Many air tanks and many pistons are weighty
• No redundancy
• If one part of the system breaks down, the rest
  of the system will be affected
• Compressor refilling speed
• If air lostgtair pumped into air tanks, there will
  soon not be enough air to power the system
• Capacity
• If a compressor is not on board, the system will
  be less and less effective as the action of
  extending/retracting is repeated (air lost and no
  air gained)

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Motors
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Components

• Motor
• Hooked up to an electrical power source
• Gear
• The motors axis spins must have a gear
• To interface with said gear you need a gear with
  the same pitch
• Chain/Sprocket system
• On motors axes, instead of a gear, a sprocket is
  attached to the axis
• The sprocket interfaces with a chain which
  interfaces with another sprocket in order to spin
  something

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Interface

• Gears must fit each other
• Pitch should be considered before purchasing any
  gears
• Chains must fit sprockets
• Also need matching pitch in order to interface
• Pitch(number of teeth)/(pitch diameter)
• There are other ways to find pitch, this method
  has less room for error
• Usually an approximation is fine

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Programming

• The motor is either on or off
• Gear tooth sensors are valuable
• Senses how many revolutions have occurred, can be
  used to calculate change in distance
• Can be used to prevent a motor from overshooting
  a set target

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Motor Power Transmission
Worm gear

• Torquetwist
• Measured in ft-lbs or N m
• A higher value means more twisting power
• A high speed motor can be geared down to produce
  higher torque at a lower speed
• A motor powering a worm gear usually produce a
  lot of torque

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Advantages

• Control
• Degrees of movement, not just extended/retracted
• Functional flexibility
• Many different tasks can be performed
• The spinning motion is fairly easy to turn into
  linear motion
• Reliant on battery power
• During a match, it is highly unlikely that a
  robots battery will run out, even if it is
  running several motors
• Light-weight gears, sprockets, and chains
• Many websites sell plastic gears
• The sprocket/chain system replaced by a
  pulley/belt system
• Sprockets analogous to pulleys, chains analogous
  to belts
• Also classified by pitch
• Pulleys can be made out of plastic
• Belts can be made out of rubber or similar
  material

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Disadvantages

• Programming is slightly harder
• Mostly because of gear tooth sensors
• Still very manageable
• Torque/speed tradeoff
• This is usually fine, since there are not many
  actions that require high levels of torque and
  speed

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General Construction Issues
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Weight Efficiency

• Materials used
• Aluminum is relatively light
• Unnecessary items
• Dont let your robot do too much
• Use CAD
• With the density of all the materials you plan to
  use, CAD can predict how much your robot will
  weigh
• Leave room for error
• Swiss cheesing
• Drilling holes reduces weight
• Can be used as a last-minute fix

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Weight distribution

• Center of gravity
• Should be kept over points of support, such as
  wheels
• Height
• Taller robots have a higher center of gravity
• To balance this out, the base of the robot should
  heavy in comparison to the tallest part
• Acceleration
• Combined with height can cause a robot to topple
• Consider the robot in the background
• When it lifts the ball, how does the center of
  gravity change?

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Durability

• Fragility of materials
• Pneumatics/motors should be protected in some way
• This is especially true of pneumatic tubing
• Exposure
• The parts of the robot that extend beyond the
  base are most likely to get broken
• Test!
• Find out what it takes to tip your robot over
• At high speed, drive your robot into walls
• Replacement parts
• Make replacements for every part that is very
  likely to get broken
• More is better when it comes to replacement parts

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Specialization

• Rule-defined roles
• In 2008 there were 2 roles
• Hurdler
• Racer
• In 2007 there were 2 roles
• Defender
• Placer
• Fulfill one roll very well
• Teams chosen in the draft will be chosen for role
  diversity
• The ability to score points matters less during
  the drafts
• A low-scoring robot is fine if its fulfilling
  some sort of defensive role

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Resources

• Chief Delphi
• http//www.chiefdelphi.com
• FIRST Robotics website
• http//www.usfirst.org/
• http//first.wpi.edu/Workshops/index.html
• The Blue Alliance
• http//www.thebluealliance.net/

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If you need parts

• McMaster-Carr
• http//www.mcmaster.com/
• AndyMark
• http//andymark.biz/

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Picture sources (in order of appearance

• http//www.teamdavinci.com/flashfiles/pneumaticdia
  gram.jpg
• http//www.chiefdelphi.com/forums/portal.php
• http//en.wikipedia.org/wiki/ImageGear_words.png