build a drift chassis

Available at: www.etcurr.com Lesson 2.3, Build a Drift Chassis

Build a Drift Chassis

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Build a Drift Chassis Performance 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 train explain the purpose of a chain and sprocket set explain the relationship between gear ratios, speed, and

torque calculate gear ratios


Chassis

The chassis is the under part of a motor vehicle, consisting of the frame with the wheels and motors

The chassis can be thought of as the base for the robot

In VEX, the parts of a robot that perform the tasks of collecting or moving items rests on top of the chassis


Sprocket and chain

A sprocket is a profiled wheel with teeth that meshes with a chain, track or other perforated or indented material

A sprocket is distinguished from a gear in that sprockets are never meshed together directly

A sprocket is distinguished from a pulley in that sprockets have teeth and pulleys are smooth


Sprocket and chain

Sprockets are used in bicycles, motorcycles, cars, tanks, and other machinery

The 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.


Drive train

To perform this function, two sprockets must be connected with a chain

The chain and sprockets together are referred to as a drive train (chain drive) system


Advantages of sprocket and chain over gears

A 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 gears

This is particularly advantageous when the space through which you’re trying to transfer that mechanical power is small or restricted


Gear ratio The gear ratio can be thought as a multiplier on torque

and a divider on speed To gain torque you must give up speed To gain speed you must give up torque

The gear ratio is the relationship between the number of teeth on two sprockets that are connected by a chain

To 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 =


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


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 sprocket driving a larger sprocket If you need to increase the speed of a

motor Increase the speed with a small gear ratio

• Big sprocket driving a smaller sprocket


Calculating gear ratios


Idler sprocket

In 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 sprocket

If the chain is too tight, the chain drive may not rotate because of too much friction


Idler sprocket

It may be necessary to insert an idler sprocket An idler sprocket can be inserted in between

the two main sprockets, causing the chain to tighten


The end

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build a drift chassis

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