1. Construct a boom crane
Graphic retrieved from, on 05/19/2010

2. 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

3. Gear trains
A gear train is a set or system of gears arranged to transfer one part of a mechanical system to another

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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

10. 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

11. 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

12. 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

13. 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 =

14. Calculating gear ratios

15. 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

16. 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

17. Non-compound gear train
When there is only one gear per axel, it is non-compound
Gear ratio is 60:12 or 5:1

18. 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

19. The end
Graphic retrieved from, on 05/26/2010