Simple Machines Gears Velocity Ratios and Mechanical Advantage

Simple Machines: Gears, Velocity Ratios and Mechanical Advantage

What is a simple machine? § A device which uses basic mechanisms to make work easier for the user. § Example: Lifting a heavy box with a rope and pulley system § Simple machines are found in many transportation devices such as the following: § Cars § Bicycles § Trains

What are gears and why are they so useful? § Gears are toothed wheels which interlock to form simple machines. § The tighter the joint, the less chance of slipping § Gears range in size but the important number is how many teeth a gear has.

What is a gear ratio? § A gear ratio is the ratio between the driver gear (the one being powered) and the driven gear (the one connected to the driver) § Gear Ratios are expressed as fractions and can be written a number of ways. § § § 1 to 3 1/3 1: 3 § Always remember that the driven gear will turn in the opposite direction of the driver gear

What is a pulley? § A wheel with a grove carved around its circumference in which a rope or belt is placed to drive the wheel. § Pulleys are used in a number of applications including: § Elevators § Cranes § Automobiles

A Pulley System

Drawbacks of Pulleys § Pulleys work great as long as the belt which connects them is tight and both pulleys are aligned. § Pulleys tend to slip when too much strain is placed on the system.

How do I calculate my gear ratio? § A simple equation is used to find the ratio of your gearing system § Number of Teeth on the Driven Gear / Number of Teeth on the Driver Gear. § Size of the driver pulley/ Size of the driven pulley

What is Velocity Ratio (VR)? § When calculating for velocity or speed, it is best to have a ratio in which the driver gear is larger than the driven gear. § For maximum speed you should always have a larger driver gear/pulley paired with a smaller driven gear/pulley.

What is Mechanical Advantage (MA)? § Reciprocal of velocity ratio. § Mechanical advantage describes how much work can be done based on the input. § If my system required me to apply 50 pounds of force into the system to lift 100 pounds of weight, I have used MA.

So which do I want? § Higher velocity ratios are better when working on straight and level surfaces which are smooth. § Always remember that with a high VR your system will have very low power. § Higher mechanical advantage systems are better with inclines surfaces that are bumpy. § With a high MA your system will produce more power, but will move slower.