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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


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


Gear trains

A gear train is a set or system of gears arranged to transfer one part of a mechanical system to another


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


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


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


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


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


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


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


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


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


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 =


Calculating gear ratios


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


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


Non-compound gear train

When there is only one gear per axel, it is non-compound

Gear ratio is 60:12 or 5:1


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


The end

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available at: 2.2, construct a boom crane construct a boom crane graphic retrieved from, ...

Documents

driven gear

main gear

gear ratios

idler gear

curved gear

similar gear worm gear

driving gear slide

boom crane gear trains