To do in class

1. To do in class • Mechanical design is an important component of this class – how it relates to your project • What you want to learn? • What you plan to do?

2. Kinematics • The study of motion without regard to the forces or mass of the things moving. • Kinematic diagrams are scaled drawings symbolizing how mechanisms work. • We studied robot kinematics in Fall but we did not take into account forces.

3. Gears • Pulleys • Chains • Cams • Bearings • Wheel and Axle • Inclined Plane • Wedge • Screw • Lever • Cranks and sliders • Ratcheting mechanisms • Clutches • Brakes Examples of machines

4. Machines and Tools • Machines and tools are mechanical devices that work by transmitting or converting energy. • Machines are made up of a variety of mechanisms. • What are some examples of machines?

5. Simple Machines Screw Inclined Plane Wedge Pulley Wheel and Axle Lever All of these are related to robotics. Think how?

6. Mechanisms • Mechanisms help extend human capability by creating some desired output or motion. • A mechanism takes an input motion or force and creates a desired output motion or force. MECHANISM Motion or force Motion or force

7. Types of Motion • Common types of motion: • Linear • Reciprocal • Rotary • Oscillating All these have applications in robotics

8. Definitions: Energy: Ability to do work Work= Force x Distance Force: A Push or a Pull

9. Linkages

10. counter weight motor Rotating Arms Torques are largeUse counterweights and gears to compensateAttach the gear to the armAttach the motor to the robot gear bolted to arm driven gear

11. Role of Linkages • Linkages transmit the motion or force to the desired output location. • Linkages: • change the direction of the force • Change the length of motion of the force • Split the motion and force over multiple paths

12. Levers

13. Lever Pivot point, fulcrum • Downward motion at one end results in upward motion at the other end. • Depending on where the pivot point is located, a lever can multiply either the force applied or the distance over which the force is applied http://www.csmate.colostate.edu/cltw/cohortpages/viney/balance.html

14. Explanation Simple Lever Machine • This simple machine is based on the position of the effort force, resistance force, and fulcrum. • First class lever • Fulcrum located between effort force and resistance force • Usually used to multiply a force • Example: Seesaw This kind changes the direction of force. R Resistance force Effort force E F length1 length2 R * length1 = E * lenght2

15. Engagement Simple Experiment: Balancing Act • Using only a meter stick and a wooden block, balance two masses in a seesaw kind of structure. • How did you get them to balance? • Could you do it in one try? • Compare your setup with other possible setups Do this by yourself, not in class This is useful in robot arm design

16. Exploration Simple Experiment: Balancing Act Lever Forces • Materials • Computer/calculator • Force Probe • 500g mass • String • Meter stick • Wooden Block High school robotics

17. Exploration Simple Experiment: Balancing Act Lever Forces • Measure the Weight of the 500g mass (in Newtons). • Balance the middle of the meter stick on the wooden block. • Place the 500g mass at the 90 cm line. • Attach the string to the meter stick at the 10 cm line. • Attach the string to the force meter and pull down on the sensor until the meter stick is balanced. • Record the force needed to balance the meter stick. • Repeat the above steps with the 500g mass at the 70 cm line and the 60 cm line.

18. Exploration Simple Experiment: Balancing Act Lever Forces • After recording your data in a table, perform the following calculations for the three trials: • Divide the weight of the 500g mass by the force required to balance the meter stick. • Divide the distance between the force meter and the wooden block by the distance between the 500g mass and the wooden block. • How do these numbers compare? • What do these numbers indicate about the lever system?

19. Explanation Why use a Simple Machine? • Simple Machines make work easier by giving the user a mechanical advantage. • How do we calculate the mechanical advantage for a lever system? • Ideal Mechanical Advantage (IMA) = Leffort / Lresistance • Why do we stipulate that the MA is ideal? Because we’ve assumed that the machine puts out exactly as much work as we put in. This implies 100% efficiency • This situation is never possible…why? Mechanical Advantage = MA Leffort is the distance between the effort force and the fulcrum Lresistance is the distance between the resistance force and the fulcrum 100% efficiency is never possible because of FRICTION.

20. Explanation Lever Example • A worker uses an iron bar to raise a manhole cover that weighs 90 Newtons. The effort arm of the bar is 60 cm long and the resistance arm is 10 cm long. • Draw a picture of this scenario • Calculate the IMA of the lever system IMA = Le/Lr = 60 cm/ 10cm = 6 • What force would the worker need to apply to lift the manhole? ? 90 N • We need 90 N of force to lift the manhole cover, but we have a mechanical advantage of 6. • Now we only need 15 N of force to lift the manhole.

21. Three Classes of Levers

22. Classes of Levers “First Class Lever” • A first-class lever is a lever in which the fulcrum is located between the input effort and the output load. • In operation, a force is applied (by pulling or pushing) to a section of the bar, which causes the lever to swing about the fulcrum, overcoming the resistance force on the opposite side. • The fulcrum may be at the center point of the lever as in a seesaw or at any point between the input and output. • This supports the effort arm and the load. Examples: • Seesaw • Scissors (double lever)

23. First Class Lever Fulcrum is between EF (effort) and RF (load)Effort moves farther than Resistance.Multiplies EF and changes its directionThe mechanical advantage of a lever is the ratio of the length of the lever on the applied force side of the fulcrum to the length of the lever on the resistance force side of the fulcrum. Effort fulcrum Resistance

24. Examples of first class levers Common examples of first-class levers include • crowbars, • scissors, • pliers, • tin snips • and seesaws.

25. Second Class Lever RF (load) is between fulcrum and EF Effort moves farther than Resistance.Multiplies EF, but does not change its directionThe mechanical advantage of a lever is the ratio of the distance from the applied force to the fulcrum to the distance from the resistance force to the fulcrum. Effort Resistance

26. Explanation Three Lever Classes • Second class lever • Resistance is located between the effort force and the fulcrum. • Always multiplies a force • Example: Wheelbarrow E R F Always multiplies a force.

27. Examples of Second class levers “Second Class Lever” In a second class lever the input effort is located at the end of the bar and the fulcrum is located at the other end of the bar, opposite to the input, with the output load at a point between these two forces. Examples: • Paddle • Wheelbarrow • Wrench

28. Examples of second-class levers • Examples of second-class levers include: • nut crackers, • wheel barrows, • doors, • and bottle openers.

29. Third Class Lever EF is between fulcrum and RF (load) Does not multiply force Resistance moves farther than Effort.Multiplies the distance the effort force travelsThe mechanical advantage of a lever is the ratio of the distance from the applied force to the fulcrum to the distance of the resistance force to the fulcrum

30. Classes of Levers “Third Class Lever” Examples: • Hockey Stick • Tweezers • Fishing Rod • For this class of levers, the input effort is higher than the output load, which is different from second-class levers and some first-class levers. • However, the distance moved by the resistance (load) is greater than the distance moved by the effort. • In third class levers, effort is applied between the output load on one end and the fulcrum on the opposite end.

31. Explanation Three Lever Classes • Third class lever • Effort force located between the resistance and the fulcrum. • Effort arm is always shorter than resistance arm • MA is always less than one • Example: Broom E R F There is an increase distance moved and speed at the other end. Other examples are baseball bat or hockey stick.

32. Examples of Third Class Levers • Examples of third-class levers include: • tweezers, • arm hammers, • and shovels. Third class lever in human body.

33. Natural Levers in Human Body

34. Elaboration Natural Levers • Identify an example of a 1st class lever in the human body Example of first class lever in human body Remember to relax the body and feel the muscle groups working to move the bones

35. Elaboration Natural Levers • Identify an example of a 2nd class lever in the human body Second class lever in human body Remember to relax the body and feel the muscle groups working to move the bones

36. Elaboration Natural Levers • Identify an example of a 3rd class lever in the human body Remember to relax the body and feel the muscle groups working to move the bones

37. Mechanical Advantage • Mechanical Advantage is the ratio between the load and effort. • Mechanical Advantage deals only with forces. • Mechanical Advantage > 1 means that the output force will be greater than the input force. • (But the input distance will need to be greater than the output distance.)

38. Mechanical Advantage • First and Second class levers have a positive mechanical advantage. • Third class levers have a mechanical disadvantage, meaning you use more force that the force of the load you lift.

39. Velocity Ratio • Velocity Ratio deals with the distance gained or lost due to a mechanical advantage. • Velocity Ration >1 means that the input distance (or effort) to move a load will be greater than the output distance of the load.

40. Mechanical Advantage: Example Mechanical Advantage = effort arm resistance arm Crazy Joe is moving bricks to build his cabin. With the use of his simple machine, a lever, he moves them easily. The “effort arm” of his wheel barrow is 4ft., while the resistance arm of his wheelbarrow is 1 ft. 4/1 is his mechanical advantage. MA= 4.

41. How the Lever changes the Force? One convenience of machines is that you can determine in advance the forces required for their operation, as well as the forces they will exert. “The length of the effort arm is the same number of times greater than the length of the resistance arm as the resistance to be overcome is greater than the effort you must apply.” Plugging these into an equation gives you the change in force by using a lever. where L = length of effort arm, l = length of resistance arm, R = resistance weight or force, and E= effort force.

42. F o r c e C h a n g e • Suppose you want to pry up the lid of a paint can with a 6-inch file scraper, and you know that the average force holding the lid is 50 pounds. • If the distance from the edge of the paint can to the edge of the cover is 1 inch, what force will you have to apply on the end of the file scraper? L = 5 inches l = 1 inch R = 50 pounds, and E is unknown. = 10 pounds • You will need to apply a force of only 10 pounds.

43. Where can I find levers? Compound machine: Can Opener Simple machines • lever • wheel and axel • gear • wedge There are as many as 4 simple machines in a stupid CAN OPENER!

44. Where can I find levers? Compound Machine: Stapler Simple Machines: -Lever -Wedge Every complex mechanism can be decomposed to a network of simple machines

45. Where can I find compound machines? Compound Machine: Wheelbarrow Simple Machines: -Lever -Inclined Plane -Wheel and Axel Wheelbarrow

46. Levers and Linkages: Conclusions • Fulcrum • Load • Effort • Classes • First • Second • Third Concepts discussed Understanding of levers and linkages is important for those who build robots, especially humanoids

47. Rotary Mechanisms

48. Rotary Mechanisms • Gears, Pulleys, Cams, Ratchets, Wheels, etc. • These rotary mechanisms transfer of change input rotational motion and force to output motion and force. • Output force can be either rotational or reciprocating. Rotary mechanism rotational motion and force rotational or reciprocating motion and force.

49. Belts/Pulleys & Chains/Sprockets • Use belts and chains to convert motion and force. • Uses same measures of Mechanical advantage and Velocity Ratio as gears.

50. Inclined Plane