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The Manipulator

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General Construction Issues. Weight Efficiency. Materials used. Aluminum is relatively light ... http://en.wikipedia.org/wiki/Image:Gear_words.png. Picture ... – PowerPoint PPT presentation

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Title: The Manipulator


1
The Manipulator
  • (The part of the robot that isnt the chassis)

2
Sources of Power
3
Pneumatics
4
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

5
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6
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

7
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

8
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)

9
Motors
10
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

11
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12
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

13
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14
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

15
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

16
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

17
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

18
General Construction Issues
19
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

20
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?

21
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

22
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

23
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/

24
If you need parts
  • McMaster-Carr
  • http//www.mcmaster.com/
  • AndyMark
  • http//andymark.biz/

25
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
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