 ## Presentation on theme: "Construct a boom crane Graphic retrieved from, http://www.crane-spare-parts.com/images/manitowoc-crane.jpg, on 05/19/2010."— Presentation transcript:

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

Two bevel gears transferring rotation
Bevel gears have teeth at an angle Bevel gears are used to transfer rotation by 90 degrees Vertical rotation Horizontal rotation Single bevel gear Two bevel gears transferring 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 gear Number of teeth on driving gear Gear 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