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Transcript of Available at: 2.2, Construct a Boom Crane Construct a boom crane Graphic retrieved from, ...
Available at: www.etcurr.com Lesson 2.2, Construct a Boom Crane
Construct a boom crane
Graphic retrieved from, http://www.crane-spare-parts.com/images/manitowoc-crane.jpg, on 05/19/2010
Available at: www.etcurr.com Lesson 2.2, Construct a Boom Crane
Construct a Boom Crane Performance Objective: Given provided VEX components,
construct a boom crane that extends a minimum of twelve inches and can lift a weight ( > 5 lbs) one foot off the ground in less than thirty seconds.
Enabling Objectives: define the following terms: spur gear, worm gear, rack gear,
pinion gear, bevel gear, driving gear, driven gear, gear ratio, idler gear, compound gear train, non-compound gear train, speed, torque
explain the characteristics of a gear train explain the relationship between gear ratios, speed, and torque calculate gear ratios
Available at: www.etcurr.com Lesson 2.2, Construct a Boom Crane
Gear trains
A gear train is a set or system of gears arranged to transfer one part of a mechanical system to another
Available at: www.etcurr.com Lesson 2.2, Construct a Boom Crane
Gears
A gear is a rotating machine part having cut teeth, which mesh with another toothed part in order to transmit torque or power
The four main VEX gears
Available at: www.etcurr.com Lesson 2.2, Construct a Boom Crane
Why gears
Gears have four main purposes To increase or decrease the speed or torque
of a rotating part To synchronize the rotation of two axis To reverse the direction of a rotating part To move rotational motion to a different
axis
Available at: www.etcurr.com Lesson 2.2, Construct a Boom Crane
Spur gears The main gear used in
building a robot will be a spur gear
They consist of a cylinder with teeth projecting radially
These gears can be meshed together correctly only if they are fitted to parallel axles.
Spur gears are described by the number of teeth they have
36 tooth spur gear
84 tooth spur gear
Available at: www.etcurr.com Lesson 2.2, Construct a Boom Crane
Worm gear
A worm is used to create a greater gear reduction (discussed later)
The worm gear is the driving gear
A worm is used to turn another gear, usually a spur or similar gear
worm gear
Worm and spur gear
Available at: www.etcurr.com Lesson 2.2, Construct a Boom Crane
Rack and pinion
A rack gear is a straight, not curved gear A rack gear is used with a pinion gear A rack and pinion are used to transfer
motion in a linear direction
Pinion gear
Rack gear
Available at: www.etcurr.com Lesson 2.2, Construct a Boom Crane
Bevel gear Bevel gears have teeth at an angle Bevel gears are used to transfer rotation
by 90 degrees
Single bevel gear Two bevel gears transferring rotation
Vertical rotation
Horizontal rotation
Available at: www.etcurr.com Lesson 2.2, Construct a Boom Crane
Driving and driven gear
The driving gear is attached to the source of power, usually a motor
The driven gear is being rotated by the driving gear
Available at: www.etcurr.com Lesson 2.2, Construct a Boom Crane
Speed vs. Torque
Speed is the magnitude of an objects velocity, or the rate of change of its position
Torque is the tendency of a force to rotate an object about an axis Just as a force is a push or a pull, a torque
can be thought of as a twist
Available at: www.etcurr.com Lesson 2.2, Construct a Boom Crane
Gear ratio
The gear ratio can be thought as a multiplier on torque and a divider on speed or vise versa To gain torque you must give up speed To gain speed you must give up torque
Available at: www.etcurr.com Lesson 2.2, Construct a Boom Crane
Gear ratio
The gear ratio is the relationship between the number of teeth on two gears that are meshed
To calculate the gear ratio, you count the number of teeth on the driven gear, divide that number by the number of teeth on the driving gear
Number of teeth on driven gearNumber of teeth on driving gearGear ratio =
Available at: www.etcurr.com Lesson 2.2, Construct a Boom Crane
Calculating gear ratios
Available at: www.etcurr.com Lesson 2.2, Construct a Boom Crane
Big or small ratio?
If a motor needs to lift a heavy object you will need to increase torque Increase the torque with a large gear ratio
• Small gear driving a larger gear If you need to increase the speed of a
motor Increase the speed with a small gear ratio
• Big gear driving a smaller gear
Available at: www.etcurr.com Lesson 2.2, Construct a Boom Crane
Idler gears
Gears that are inserted between driving and driven gears
Have no effect on the gear ratio (it cancels itself out)
Idler gears reverse the direction of the driven wheel
Available at: www.etcurr.com Lesson 2.2, Construct a Boom Crane
Non-compound gear train
When there is only one gear per axel, it is non-compound
Gear ratio is 60:12 or 5:1
Available at: www.etcurr.com Lesson 2.2, Construct a Boom Crane
Compound gear train
When a pair of gears is on a single axel, it is a compound gear train
There are two sets of gear ratios
Multiply the two ratios to get total system gear ratio
Available at: www.etcurr.com Lesson 2.2, Construct a Boom Crane
The end
Graphic retrieved from, http://blog.cold-comfort.org/wp-content/uploads/2009/08/grinds-my-gears1.jpg, on 05/26/2010