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Build a Drift ChassisGraphic retrieved from, http://sports.espn.go.com/espn/gallery/enlargePhoto?id=3571481&story=3571491, on 08/12/2010

Available at: www.etcurr.comLesson 2.3, Build a Drift ChassisBuild a Drift ChassisPerformance Objective: Given provided VEX components, build a drift chassis that can complete five laps around the room in less than 80 seconds.Enabling Objectives:define the following terms: chassis, chain and sprocket, driving sprocket, driven sprocket, idler sprocket, drive trainexplain the purpose of a chain and sprocket set explain the relationship between gear ratios, speed, and torquecalculate gear ratiosAvailable at: www.etcurr.comLesson 2.3, Build a Drift ChassisChassisThe chassis is the under part of a motor vehicle, consisting of the frame with the wheels and motorsThe chassis can be thought of as the base for the robotIn VEX, the parts of a robot that perform the tasks of collecting or moving items rests on top of the chassisAvailable at: www.etcurr.comLesson 2.3, Build a Drift ChassisSprocket and chainAsprocketis a profiledwheelwith teeth that meshes with achain,trackor other perforated or indented materialA sprocket is distinguished from agear in that sprockets are never meshed together directlyA sprocket is distinguished from apulleyin that sprockets have teeth and pulleys are smooth

Available at: www.etcurr.comLesson 2.3, Build a Drift ChassisSprocket and chainSprockets are used in bicycles, motorcycles, cars, tanks, and other machineryThe purpose of sprockets is either to transmit rotary motion between two shafts where gears are unsuitable or to impart linear motion to a track, tape etc.

Available at: www.etcurr.comLesson 2.3, Build a Drift ChassisDrive trainTo perform this function, two sprockets must be connected with a chainThe chain and sprockets together are referred to as a drive train (chain drive) system

Available at: www.etcurr.comLesson 2.3, Build a Drift ChassisAdvantages of sprocket and chain over gearsA drive chain is an efficient system, transferring up to 95% of the power from the drive shaft, where a gear drive only transfers 85% of the power from the drive shaft, at best A drive chain also allows you to transfer power from the drive shaft over a longer distance than would be possible or feasible solely with gearsThis is particularly advantageous when the space through which youre trying to transfer that mechanical power is small or restrictedAvailable at: www.etcurr.comLesson 2.3, Build a Drift ChassisGear ratioThe gear ratio can be thought as a multiplier on torque and a divider on speed To gain torque you must give up speedTo gain speed you must give up torqueThe gear ratio is the relationship between the number of teeth on two sprockets that are connected by a chainTo calculate the gear ratio, you count the number of teeth on the driven sprocket, divide that number by the number of teeth on the driving sprocket

Number of teeth on driven sprocketNumber of teeth on driving sprocketGear ratio = Available at: www.etcurr.comLesson 2.3, Build a Drift ChassisSpeed vs. TorqueSpeed is the magnitude of an objects velocity, or the rate of change of its positionTorque is the tendency of a force to rotate an object about an axisJust as a force is a push or a pull, a torque can be thought of as a twist

Available at: www.etcurr.comLesson 2.3, Build a Drift ChassisBig or small ratio?If a motor needs to lift a heavy object you will need to increase torqueIncrease the torque with a large gear ratioSmall sprocket driving a larger sprocketIf you need to increase the speed of a motorIncrease the speed with a small gear ratioBig sprocket driving a smaller sprocketAvailable at: www.etcurr.comLesson 2.3, Build a Drift ChassisCalculating gear ratios

Available at: www.etcurr.comLesson 2.3, Build a Drift ChassisIdler sprocketIn some chain drives it is difficult to have the exact number of chain links to have the chain fit around the two sprockets with the right fit (tightness)If the chain is too lose, it can slip and cause the driven sprocket to not rotate in sync with the driving sprocketIf the chain is too tight, the chain drive may not rotate because of too much frictionAvailable at: www.etcurr.comLesson 2.3, Build a Drift ChassisIdler sprocketIt may be necessary to insert an idler sprocketAn idler sprocket can be inserted in between the two main sprockets, causing the chain to tighten

Available at: www.etcurr.comLesson 2.3, Build a Drift ChassisThe end

Graphic retrieved from, http://blog.cold-comfort.org/wp-content/uploads/2009/08/grinds-my-gears1.jpg, on 05/26/2010Available at: www.etcurr.comLesson 2.3, Build a Drift Chassis