Build a Drift Chassis

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

2. 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

3. 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

4. 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

5. 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.

6. 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

7. 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

8. Gear ratio Number of teeth on driven sprocket Number of teeth on driving sprocket 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

9. 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

10. 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

11. Calculating gear ratios

12. 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

13. 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

14. The end Graphic retrieved from, http://blog.cold-comfort.org/wp-content/uploads/2009/08/grinds-my-gears1.jpg, on 05/26/2010