Mechanisms Automation and Robotics VEX © 2011 Project Lead The Way, Inc.
What is a Mechanism? A mechanism is the part of a machine which contains two or more pieces arranged so that the motion of one compels the motion of the others. Generally used to: – Change the direction of movement – Change the type of movement – Change the speed of movement – Change the amount of torque or force available to do work
Mechanisms - Change Direction • Meshed gears in a gear train always turn in opposite directions • The flow of power is reversible only if you can make the input shaft turn by turning the output shaft
Mechanisms - Change Movement Rotary Oscillating Linear Reciprocating
Mechanisms - Change Speed • Gear ratios compare the output (or driven/follower gear) to the input (or drive gear) • If the output gear is larger than the input gear the speed will decrease • If the output gear is smaller than the input gear the speed will increase.
Mechanisms – Change Force or Torque A force is a push or pull in a straight line. Torque is a push or pull in a circular direction.
Simple Gear Train A. Driven Drive B. Driven Drive
Where Do You Find a Simple Gear Train? Found in: – Watch – Sewing Machine – Motor Watch gears Two meshed gears will rotate in opposite directions.
Cool Simple Gear Train • https: //www. youtube. com/watch? v=Vo. BGa u 9623 I&list=PLE 539743 FE 2 BE 696 B&inde x=18
Simple Gear Train with Idler Driven Idler Drive
Where Do You Find a Simple Gear Train with Idler? Two meshed gears will rotate in opposite directions. An Idler Gear allows the drive and driven gears to rotate in the same direction. 8. Found in – Vehicles, to place into reverse. https: //www. youtube. com/watch? v=67 u. Dj. Mz 6 Ep. A
Where Can You Find a Bevel Gear? Found in: • Hand drill/Drill Presssee in action! • Car differential • Shaft-driven bicycle • The bevel gear is used to change rotational motion at a 90˚ angle. • Using gears with differing numbers of teeth will change the speed and torque.
Differential Gear 1. 2. 3. 4. Gears used – Bevel Axles turn – Same direction Used in – Vehicles Purpose – Wheels spin at different speeds when turning Howstuffworks. com/differential
Worm and Wheel Worm
Where Do You Find a Worm and Wheel? Found in: • Tuning mechanism on string instruments • A worm is used to • Electric motors reduce speed and increase torque. • Winch • The motion is not reversible; a gear cannot drive a worm.
Leadscrew 1. Input Movement rotary 2. Output Movement linear
Where Do You Find a Lead Screw? • Jack • Vice • Changes rotary movement into linear movement • Significantly increases force • A person can put a little force into turning the handle to move a heavy car.
Rack and Pinion 1. Input Movement rotary 2. Output Movement linear Rack
Where Do You Find a Rack and Pinion? Used in steering systems of • Used to convert cars to convert rotary motion between rotary of steering wheel to the side and linear to side motion in the wheels. motion. • Provides gear • Rack and pinion reduction to steering make it easier to Pinion turn the wheels. Rack
Universal Joint Angular Range: > 90˚ and < 270˚
Where Can You Find a Universal Joint? • Drive shaft of vehicles • Power take-off Universal joints are used to transmit rotary movement at an angle that is not 90°. www. rqriley. com/imagespln/pattersn_ujoint. jpg
Chain Driven Larger drive gear: • Speed is increased • Torque is decreased Drive Smaller drive gear: • Speed is decreased • Torque is increased Driven
Where Do You Find a Chain and Sprocket? Found in: • Bicycle • Motorcycle Advantage of Chain and Sprocket over spur gears: Transfer torque and speed over long distances
Belt Driven https: //www. youtube. com/watch? v=Syp 3 CW 9 s. Fbk&list=PLE 5397 43 FE 2 BE 696 B&index=29
Where Do You Find a Pulley and Belt? Found in: • Lawn mower • Car engine BELTS Belts instead of chains: • Quieter • Less expensive
Crank and Slider Crank Slider
Where Do You Find a Crank and Slider? Found in: • Steam train • Internal combustion engine https: //www. youtube. com/watc h? v=RFa. LPu. Kky. AE
Cam and Follower FOLLOWER CAM
Where Do You Find a Cam and Follower? Found in: Cam shaft • As a cam rotates, the flat follower is raised and lowered, converting rotary motion to reciprocating (back and forth) motion. https: //www. youtube. com/w atch? v=ESRsd 1 Te. OSg
Cool Mechanisms • • https: //www. youtube. com/watch? v=r 0 y_u. No. Yq. WM&list=PLE 539743 FE 2 BE 696 B&index=15 https: //www. youtube. com/watch? v=WR 931 mt. C 3 l 4&list=PLE 539743 FE 2 BE 6 96 B&index=17 https: //www. youtube. com/watch? v=w. Ddm. X 6 y. GCu. Y&list=PLE 539743 FE 2 B E 696 B&index=28 https: //www. youtube. com/watch? v=u 9 Bh 7 Jq. Vwo&index=30&list=PLE 539743 FE 2 BE 696 B
Infinite Mechanisms • An infinite mechanism can move in one direction forever- it doesn’t have an end point and thus need to reverse direction. These infinite mechanisms are the only mechanisms you’ll be able to use for the pull toy. • • • Bevel Cam and Follower Crank and Slider Simple Gear Train with Idler Worm and Wheel
VEX Robotics Tip #1 Simple Gears can be used so that the rod used for the input (wheels) does not need to be the same rod used for the output.
VEX Robotics Tip #2 These can be bent (if necessary, ask Mr. Melville first). These rods can be cut to length (if necessary, ask Mr. Melville first).
VEX Robotics Tip #3 Rods work best when they go through at least 2 walls and when they’re anchored by as many black plastic anchors as possible (4 in this example).
VEX Robotics Tip #4 • Cam pivot example- add pic
Mechanisms We’re Building Wall Assembly (required for some mechanisms) - Wall Assembly Required - MODIFIED Wall Assembly Required 1. Open Autodesk Inventor. - Wall Assembly Required T: Middle SchoolMelvilleStudent Technology FilesVexParts 2. Open the file 00 Wall Asembly from here: T: Middle SchoolMelvilleStudent Technology FilesVexParts Wall Assembly