Lesson 5: Gears and StrengthDRAFTDESIGN ACTIVITY 3:ANSWERS TO WORKSHEET QUESTIONS

1. What is the final gear ratio of your robot?

This depends on your robot design.

2. Label these different gears.

3. List 3 characteristics of a worm gear.

1. It produces a very large gear ratio (n to 1 where n is the number of spur gear teeth).2. The output axle is perpendicular to the input axle.3. You cannot back drive a worm gear.

4. What is special about a slip clutch.

The slip clutch allows the axle to continue to turn if the teeth of the gear get stuck.

slip clutch

worm gear

rack

40 tooth spur gear

bevel or crown gear2001 Robotics Academy. All Rights Reserved.DRAFT

Lesson 5: Gears and StrengthDRAFTDESIGN ACTIVITY 3:ANSWERS TO WORKSHEET QUESTIONS

5. Look around your house and make a list of all the things you can find that contain gears that you can see.

Ten speed bike Egg beaterCorkscrew Hand drillClock Hand can openerIce cream scoop Salad spinner

6. Compute the following compound gear ratios.

1st gear pair: 16 to 24 = 2 to 3

2nd gear pair: 24 to 40 = 3 to 5

2/3 x 3/5 = 2 to 5

1st gear pair: 40 to 8 = 5 to 1

2nd gear pair: 24 to 8 = 3 to 1

3rd gear pair: 24 to 8 = 3 to 1

5/1 x 3/1 x 3/1 = 45 to 1

input

input

input

output output

output

input

output

input

1st pair

2nd pair

1st pair2nd pair

3rd pair2001 Robotics Academy. All Rights Reserved.DRAFT

Lesson 5: Gears and StrengthDRAFTDESIGN ACTIVITY 3:ANSWERS TO WORKSHEET QUESTIONS

1st gear pair: 24 to 1

2nd gear pair: 40 to 40 = 1 to 1

3rd gear pair: 8 to 16 = 1 to 2

4th gear pair: 24 to 8 = 3 to 1

24/1 x 1/1 x 1/2 x 3/1 = 36 to 1

6. What is wrong with this picture?

The spur gear is on the input axle of the motor. That means if the motor is turned on, the spur gear will try to drive the worm gear. Remember that worm gears can only turn other gears, not the other way around. If the motor were turned on, the motor would most likely stall.

input

output

1st pair2nd pair

3rd pair

4th pair2001 Robotics Academy. All Rights Reserved.DRAFT

LESSON 5:GEARS AND STRENGTHOBJECTIVE Learn how gears can be used to increase the torque, or strength, of the motor. Understand the relationship between force and torque. Understand the relationship between power, force and speed. Learn how to use run multiple tasks in your programs. Modify your robot so that it can push a relatively large amount of weight.

TORQUECOOL ROBOTPROGRAMMING TIPPROGRAMMING TIP The first task turns on Motor A for 4.5 seconds, then turns if off. The second task plays a rising sweep sound, then waits for a random amount of time. It does thi... The third task turns on Motor C for 1 second, then turns it off and waits for 2 seconds. It doe...

GEARS AND TORQUEPOWERPOWER Using gears to increase the torque is a good idea, but dont increase it so much that your robo... A blade or wall on the front of the robot is good to use as a pushing surface. Use what you have learned about treads.

PROGRAMMING CHALLENGE