Information about power transmission and uses for each type Robotics 101 Why do we need Gears and Pulleys Why do we have gears Why do we have pulleys Geek Easy Work Can Tow or Push Heavy Objects ID: 409878
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Slide1
Gears, Pulleys, Sprockets, and Bearings
Information about power transmission and uses for each type.
Robotics 101Slide2
Why do we need Gears and Pulleys?
Why do we have gears?
Why do we have pulleys?
Geek
Easy Work Can
Tow or Push
Heavy Objects!
Easy Work Can
Lift
Heavy Objects!
Nothing To It!
Geek
Wow, How Easy…Keep On Moving Titanic!
Muscles on a Geek?
Come On!Slide3
Torque, moment, or moment of force,
is the tendency of a force to rotate an object about an axis, fulcrum, or pivot. Just as a force is a push or a pull, a torque can be thought of as a twist to an object. Mathematically, torque is defined as the cross product of the lever-arm distance and force, which tends to produce rotation.
Torque = Radius X Force
Or Force = Torque / Radius
What is Torque
?Slide4
Gears
Spur Gears 1:1
Direction -X=Y (Opposite)
X Gear
Y Gear
X Teeth=30
Y Teeth=30
Speed- X=Y
Speed Ratio-
X Pitch Diameter/Y Pitch Diameter= 1
X Teeth/Y Teeth= 1
Teeth
X Gear
X Pitch Diameter
Y Gear
Y Pitch
DiameterSlide5
Gears
Speed Ratio- Compare either ratio of # of teeth or diameters as both have same proportion:
# of teeth/min = (X teeth * RPMx) = (Y teeth * RPMy)
=
X teeth
=
RPMy = 30
=1.875 Y teeth RPMx 16
Or RPMx/RPMy = 1/1.875 = .533 = 16/30X PitchDiameter = 1.875 * Y PitchDiameter
X Teeth/Y Teeth= 30/16- Y=1.875X Speed-
RPMy=(1.875)RPMx or RPMx=(.533)RPMyTorque Ratio- Ty/Tx=.533 (Note: It is the inverse of the speed ratio)Ty= Tx/1.875 = Tx(.533) Efficiency of Spur Gears: Approximately 95%
X Gear
X Pitch Diameter
X Teeth=30
Y Teeth=16
Y Pitch Diameter
Τ
x
Τ
ySlide6
Multiple Stage Gearing
Top View
d=x
d=x
d=3x
d=3x
Ratio Gear #1- 3:1
Ratio Gear #2- 3:1
Motor
d=x
Out
InSlide7
Test
Direction- In direction = Out direction
Speed- Output = Input/(3*3) = Input/9
Speed Ratio- 9:1
Torque Ratio- 1:9Output Torque= Input Torque X 9
If the motor input RPM (revolutions per minute) is 5400 and input torque is 2 ft.*lbs.1) What is the output speed in revolutions per second (60 seconds in 1 minute)?
2) What is the output torque in Newton*meters if 1 N-m=0.71ft-lbs.? Slide8
Answers
Answer #1: 5400/9= 600RPM/60= 10 revs per second
Answer #2: 2ft-lbs*9= 18 ft.-lbs.* 0.71= 12.78 N-mSlide9
Gear Types
Bevel (90° Angle)
Internal (Planetary)
Rack and Pinion (Linear Motion)
Spur (Normal)
For all Gears:
Higher Pitch= More Teeth
Larger Face Width= More Force
Must Match Pressure AngleSlide10
Gear Rules and Types
FIRST Rules:
Any gear
Any type
Any manufacturerPlastic (Lighter, Smaller Load)Brass (A Little Lighter (mainly due to small width), Good Load)
Steel (Heavy, Excellent Load, will need to trim down gear on lathe for weight)Slide11
Pulleys
The only difference is the belt connection method
12’’
3’’
Speed- Y= 4X
Speed Ratio-
XDiameter
=
12
= 4:1
YDiameter 3
Torque Ratio-
Y= X/4
Efficiency of Pulleys:
Approximately 90%
X Pulley
Y PulleySlide12
Pulley Belts & Uses
Pulley Belts
V-Belt
Timing Belt
Uses:
-Ball Chute (2012)
-Drivetrain (2014, 2015)
-Climbing Obstacles
Problems:
Slipping
Belts coming off pulleys
(No Sideways Torque)Slide13
Chain and Sprockets
Chain and SprocketsThe only difference is the connection method
I
nstead of Belts (Pulley)
Instead of Teeth (Gears)Types of ChainPlastic
Light loads, breaks easilySteelHeavy loads (drivetrain)Types of SprocketsNylonLight loadsAluminum
Heavy loads (drivetrain)
Plastic Chain Stretches-
Steel is the way to GO!
Nylon Sprockets Crack- Aluminum is the way to GO!Slide14
Chain and Sprockets
Bicycle ChainSlide15
Bearings
Bearings- What Are They?
Problem!Slide16
Bearing Types
Type 1: Softer Material like Bronze or Aluminum
Type 2: Ball Bearing
Type 3: Roller Bearing
ShaftSlide17
Bearing Types
Sintered Bronze Bearing with optional oil impregnation
Ball Bearings
Needle Roller Bearings
Clutch
One Direction
Also Available
Steel Balls
Steel
Cylindrical
Rollers
Can be sealed or unsealedSlide18
Bearing Types
Pillow Block
Bearings
Self
AligningUsed when you need some compliance in alignment.Slide19
Issues to be aware of with bearings
Misalignment
of bearing systems can over-restrict them, causing higher friction and unnecessary force on systems. Be careful of over-restricting things that want to be able to move.
Dirt, debris, and chips
can get into bearings, especially open bearings: it increases friction and resistance. (Therefore protect bearing services when machining on or near the robot)
Exceeding the recommended load for a bearing can shorten or even end its life and lead to need for replacement- or may add friction to the system causing overload on motors causing them to fail.Motors have internal bearings you don’t see, so avoid excessive loads on shafts- beware of pounding on motor shaft ends (installing or removing items on motor shafts). Use proper techniques to avoid damaging internal shaft supports in the motor, by not applying excessive loads.
Don’t stand or lean on the robot! No matter how sturdy it “seems”- we have had bent wheel shafts, and gotten frames out of square. In trying to make weight we lighten up areas where possible, but the robot may be less robust.