Engineering Design Process for BEST Robotics JANNE ACKERMAN COLLIN COUNTY (COCO) BEST & BEST OF TEXAS ROBOTICS

Transcription

1 Engineering Design Process for BEST Robotics JANNE ACKERMAN COLLIN COUNTY (COCO) BEST & BEST OF TEXAS ROBOTICS

2 Agenda Getting Started Lessons Learned Design Process Engineering Mechanics 2

3 Save Time Complete any known tasks prior to kickoff Organize all tools, parts, and supplies Establish a secure work area Establish and enforce chain of command to prevent unnecessary rework 3

4 Strategy STRATEGY IS AS IMPORTANT AS A FUNCTIONAL MACHINE Complete machine early in order to get practice. Participate in Mall Day but also visit other hubs Mall Day. 4

5 Documentation DOCUMENTATION IS ESSENTIAL If it isn t documented, it didn t happen document everything Have team notebooks and an overall master notebook Complete engineering notebook in stages as they occur 5

6 Schedule Week 1 Week 2 Week 3 Week 4 Week 5 Week 6 WHEN TASK/ACTION Understand requirements Concept selected Mock up complete Course complete Prototype robot complete Production robot complete Begin drawings Drive practice Strategy development Drive practice Complete drawings 6

7 BEST Design Process The four main phases of design are: Phase What You Get Example Conceptual Design Concept Four wheels, scoop, scissor arm Preliminary Design Model or mockup Cardboard model of concept Detailed Design Prototype Robot from kit parts Production Design Product Refined robot from kit parts In the BEST suggested schedule, you have 1 week for each phase. 7

8 Conceptual Design STEP 1: LIST ALL REQUIREMENTS FOR THE ROBOT This list is generated after reviewing the rules and developing a general strategy Draw a picture of the playing field and sketch strategies Example of requirements: Meet weight requirements Meet size requirements Negotiate course fast Have high reach Easy to operate Pick up game pieces 8

9 Conceptual Design STEP 2: BREAK DOWN LIST INTO NEEDS AND WANTS Requirement Need or Want Meet weight requirements Need Meet size requirements Need Negotiate course Want Have high reach Want Easy to operate Want Pick up game pieces Need 9

10 Conceptual Design STEP 3: SET DESIGN TARGETS FOR EACH REQUIREMENT: Requirement Need or Want Design Target Meet weight requirements Need Less than 24 lbs Meet size requirements Need Less than 23 x23 x23 Negotiate course Want Climb 5 inch ledge Have high reach Want Reach 50 inches Easy to operate Want One function per motor Pick up game pieces Need Pick up soup can and lawn chair 10

11 Conceptual Design STEP 4: SELECT THE RELATIVE IMPORTANCE FOR ALL WANTS USING PAIRWISE COMPARISON Negotiate Course High Reach Easy to Operate Total Weight Negotiate Course 1, 1 2 2/3 High Reach /3 Easy to Operate /3 Total 3 11

12 Conceptual Design STEP 5: LIST ALL ROBOT FUNCTIONS Move to scoring area Obtain game piece Secure game piece Lift game piece 12

13 Conceptual Design STEP 6: DEVELOP CONCEPTS FOR EACH FUNCTION A FUNCTION MOVE TO SCORING AREA CONCEPT (MAKE SKETCH) Chassis with wheels, chassis with treads, frame with wheels B OBTAIN GAME PIECE Jaw, scoop, velcro C SECURE GAME PIECE Spring, lock, rubber band D LIFT GAME PIECE Lever arm, fork lift, scissor lift E F Etc. 13

14 Conceptual Design STEP 7: ASSIGN A LETTER AND NUMBER TO EACH CONCEPT (Make a sketch of each) A1 Chassis with wheels A2 Chassis with treads A3 Frame with wheels B1 Jaw B2 Scoop B3 Velcro C1 Spring C2 Lock C3 Rubber Band D1 Level arm D2 Fork lift D3 Scissor lift 14

15 Conceptual Design STEP 8: EVALUATE CONCEPTS USING Feasibility can this be done? Go / No Go does it meet all needs? Decision Matrix does it meet wants? 15

16 Conceptual Design Feasibility Concept A1 Chassis with wheels A2 Chassis with treads A3 Frame with wheels B1 Jaw B2 Scoop B3 Velcro C1 Spring C2 Lock C3 Rubber Band D1 Level arm D2 Fork lift D3 Scissor lift Feasible? Yes Yes Yes Yes Yes No Yes No Yes Yes No Yes 16

17 Conceptual Design Go NoGo (needs only) Requirement A1 A2 A3 Meet weight requirements Meet size requirements Pick up game pieces Yes Yes Yes Yes Yes Yes Yes Yes Yes Requirement B1 B2 Meet weight requirements Meet size requirements Pick up game pieces Yes Yes Yes Yes Yes Yes B3 not feasible And so on.. 17

18 Conceptual Design Decision Matrix (wants only) + means that concept is better at meeting the requirement than the datum - means that concept is worse at meeting the requirement than the datum S means that concept is the same at meeting the requirement as the datum The chart shows A1 to be the preferred concept for the A function (move to scoring area) Continue this for all functions. The end result will be an overall concept. Example: Chassis with wheels, jaw, rubber band lock and lever arm. Requirement Weight A1 A2 A3 Negotiate course 0.66 Datum - S Have high reach 0.33 Datum + - Easy to operate 0 Datum + - Total Plus 2 0 Total Minus 1 2 Overall 1-2 Weighted Plus Weighted Minus Overall Weighted

19 Preliminary Design STEP 1: Take the concept and sketch an overall configuration. Do not worry about the details at this point. Label the major components. STEP 2: Sketch each of the major components on a separate sheet. Put enough information on the sketch so that the component can be made from a piece of cardboard. Try to keep the overall size requirement in mind. STEP 3: Make cardboard pieces from the sketches and assemble. STEP 4: Evaluate the model and ensure it meets all of the requirements. Make modifications as needed. Try it on the course and ensure it fits inside the 24x24x24 inch box. You now have a model of the robot. 19

20 Detailed Design STEP 1: Disassemble the cardboard model and mark-up each sketch to show the final dimensions. Also indicate on the sketch the material that will be used to make the real part. STEP 2: Create sketches for parts that are not on the model such as wheel mounts, motor mounts, etc. Consider lifting requirements, torque available from motors, etc. STEP 3: Create an overall assembly sketch of all parts. Label each part. You now have a detailed design of the robot. STEP 4: Fabricate each part from the sketch and assemble the robot. You now have a prototype robot. 20

21 Production Design STEP 1: After testing the prototype, make changes as required. STEP 2: Once the robot is in its final configuration, finalize detailed drawings of each part. 21

22 BEST Engineering Mechanics PURPOSE Introduce students to the theory of some simple machines. Apply the theory of simple machines to robotics design. 22

23 Machines WHAT IS A MACHINE? A device that transmits, or changes, the application of energy. Allows for the multiplication of force at the expense of distance. A machine does work. Work is force applied through a distance. 23

24 Simple Machines Simple machines have existed and have been used for centuries. Each one makes work easier to do by providing some trade-off between the force applied and the distance over which the force is applied. We will discuss the following simple machines and relate them to robotics design: LEVERS PULLEYS GEARS We will also discuss the concepts of torque as related to robotics design 24

25 Levers A lever is a stiff bar that rotates about a pivot point called the fulcrum. 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 25

26 Three Classes of Levers First Class Levers The fulcrum is between the effort and the load. A seesaw is an example of a simple first class lever. A pair of scissors is an example of two connected first class levers. Second Class Levers The load is between the fulcrum and the effort. A wheelbarrow is an example of a simple second class lever. A nutcracker is an example of two connected second class levers. Third Class Levers The effort is between the fulcrum and the load. A stapler or a fishing rod is an example of a simple third class lever. A pair of tweezers is an example of two connected third class levers. 26

27 Levers 27

28 Levers Force and Effort To lift a load with the least effort: Place the load as close to the fulcrum as possible. Apply the effort as far from the fulcrum as possible. 28

29 Levers The lever balance equation for a first class lever is: W1 D1 = W2 D2 29

30 Levers If more weights are to be added, simply add them to the required side of the equation. For example, to add an additional weight (W3), a distance (D3) to the right of the fulcrum makes the equation W1 D1 = W2 D2 + W3 D3 This can be demonstrated using a ruler as a lever and coins as weights 30

31 Levers How many levers can you find in the loader? 31

32 Block and Tackle A block and tackle is an arrangement of rope and pulleys that allows you to trade force for distance. 32

33 Block and Tackle Imagine that you have the arrangement of a 100 pound weight suspended from a rope, as shown. If you are going to suspend the weight in the air then you have to apply an upward force of 100 pounds to the rope. If the rope is 100 feet long and you want to lift the weight up 100 feet, you have to pull in 100 feet of rope to do it. 33

34 Block and Tackle Now imagine that you add a pulley. Does this change anything? Not really. The only thing that changes is the direction of the force you have to apply to lift the weight. You still have to apply 100 pounds of force to keep the weight suspended, and you still have to reel in 100 feet of rope to lift the weight 100 feet 34

35 Block and Tackle Now add another pulley. This actually does change things in an important way. You can see that the weight is now suspended by two ropes rather than one. That means the weight is split equally between the two ropes, so each one holds only half the weight, or 50 pounds. That means that if you want to hold the weight suspended in the air, you only have to apply 50 pounds of force (the ceiling exerts the other 50 pounds of force on the other end of the rope). If you want to lift the weight 100 feet higher, then you have to reel in twice as much rope feet of rope must be pulled in. This demonstrates a force-distance tradeoff. The force has been cut in half but the distance the rope must be pulled has doubled. 35

36 Gears Gears are generally used for one of three different reasons: To reverse the direction of rotation To increase or decrease the speed of rotation To move rotational motion to a different axis 36

37 Gears You can see effects 1, 2 and 3 in the figure The two gears are rotating in opposite directions. The smaller gear spins twice as fast as the larger gear because the diameter of the gear on the left is twice that of the gear on the right. The gear ratio is therefore 2:1 (pronounced two to one"). The axis of rotation of the smaller gear is to the right of the axis of rotation for the larger gear. If D is the motor and 2D is being driven, 2D has twice the torque. (Same effect can be accomplished with a belt). 37

38 Torque A force applied to a body that causes it to rotate creates torque. The motors supplied in your kits are designed for a specific torque and are listed as: Large motors 216 in-oz at 56 rpm (a little less than 1 revolution per second) Small motors 34 in-oz at 113 rpm (a little less than 2 revolutions per second) 38

39 Torque The equation for torque for the motors is: T = r F Where: T = torque of the motor r = radius of the motor shaft, pulley or whatever is attached to the motor shaft F = the force created by the motor 39

40 Torque Since the torque is pretty much a constant (you are stuck with the motors provided in the kit), and you probably want to know the force your motor can produce, the equation can be written as: F = T/r If you want to know the radius needed for your motor shaft, the equation becomes: r = T/F 40

41 Design Example Let s take the concepts we have learned and design an arm that will lift a 1 lb game piece. Let s assume that our mockup resulted in the following: 41

42 Design Example Since the arm is a lever, let s use the lever equation to figure out how much force is on the string. The weights and distances from the fulcrum for everything on the right is: Item Weight (oz) Distance from fulcrum (in) W D (in-oz) Rocket Grabber Arm

43 Design Example If we add we get 800 in-oz. This is the right side of the lever equation. The equation becomes: W1 * 5 in = 800 in-oz W1 = 160 oz This means that the force in the string is 160 oz except, we have two strings sharing the load because of the pulley arrangement so therefore the force in the string is only 80 oz. Let s put in a safety factor of 1.5 so that the force in the string is now 80 * 1.5 = 120 oz. This will ensure that the motor will lift the required weight even on low batteries, etc. 43

44 Design Example Now we need to calculate the motor shaft size that will create a 120 oz force. The equation for the shaft radius is r = T/F or r = 34/120 = This means our shaft needs to have a radius of inches or a diameter of inches. What else could you do to improve things? A counterweight, but not too much or the arm will not lower. 44