11/8/ Collin County Boosting Engineering Science and Technology Workshop

11/8/ AGENDA Introduction Lessons Learned Design Process Engineering Mechanics

11/8/ Time Save time: 1.Complete any known tasks prior to kickoff. 2.Organize all tools, parts, and supplies. 3.Establish a secure work area. 4. Establish and enforce chain of command to prevent unnecessary rework.

11/8/ Strategy STRATEGY IS AS IMPORTANT AS A FUNCTIONAL MACHINE : 1.Complete machine early in order to get practice. 2. Participate in Mall Day but also visit other hubs Mall Day.

11/8/ Documentation DOCUMENTATION IS ESSENTIAL 1.If it isn’t documented, it didn’t happen – document everything. 2. Have team notebooks and an overall master notebook. 3. Complete engineering notebook in stages as they occur.

11/8/ Schedule WEEK 1: Concept Selected WEEK 2:Mock-up Complete Course Complete WEEK 3:Prototype Robot Complete WEEK 4:“Production” Robot Complete Begin Drawings WEEK 5:Drive Practice, Strategy Development WEEK 6:Drive Practice Complete Drawings

11/8/ BEST Design Process The four main phases of design are: PhaseWhat You GetExample Conceptual DesignConceptFour wheels, scoop, scissor arm Preliminary DesignModel or mockupCardboard model of concept Detailed DesignPrototypeRobot from kit parts Production DesignProductRefined robot from kit parts In the COCO BEST suggested schedule, you have 1 week for each phase.

11/8/ 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 Have high reach Easy to operate Pick up gamepieces

11/8/ Conceptual Design STEP 2:BREAK DOWN LIST INTO NEEDS AND WANTS Requirement Need or Want Meet weight requirementsNeed Meet size requirementsNeed Negotiate courseWant Have high reachWant Easy to operateWant Pick up gamepiecesNeed

11/8/ Conceptual Design STEP 3: SET DESIGN TARGETS FOR EACH REQUIREMENT: RequirementNeed or WantDesign Target Meet weight requirementsNeedLess than 24 lbs Meet size requirementsNeedLess than 23x23x23 Negotiate courseWantClimb 5 inch ledge Have high reachWantReach 50 inches Easy to operateWantOne function per motor Pick up gamepiecesNeedPick up soup can and lawn chair

11/8/ Conceptual Design STEP 4: SELECT THE RELATIVE IMPORTANCE FOR ALL WANTS USING PAIRWISE COMPARISON Negotiate Course High ReachEasy to Operate TotalWeight Negotiate Course1 22/3 High Reach0111/3 Easy to Operate 0000/3 Total3

11/8/ Conceptual Design STEP 5: LIST ALL ROBOT FUNCTIONS MOVE TO SCORING AREA OBTAIN GAME PIECE SECURE GAME PIECE LIFT GAME PIECE …

11/8/ Conceptual Design STEP 6: DEVELOP CONCEPTS FOR EACH FUNCTION FUNCTIONCONCEPT (MAKE SKETCH) AMOVE TO SCORING AREA Chassis with wheels, chassis with treads, frame with wheels BOBTAIN GAME PIECEJaw, scoop, velcro CSECURE GAME PIECESpring, lock, rubber band DLIFT GAME PIECELever arm, fork lift, scissor lift

11/8/ 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

11/8/ 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?

11/8/ Conceptual Design Feasibility ConceptFeasible? A1 – Chassis with wheelsYes A2 - Chassis with treadsYes A3 - Frame with wheelsYes B1 – JawYes B2 - ScoopYes B3 – VelcroNo C1 – SpringYes C2 – LockNo C3 – Rubber BandYes D1 – Level armYes D2 – Fork liftNo D3 – Scissor liftYes

11/8/ Conceptual Design Go – NoGo (needs only) RequirementA1A2A3 Meet weight requirementsYes Meet size requirementsYes Pick up gamepiecesYes RequirementB1B2B3 not feasible Meet weight requirementsYes Meet size requirementsYes Pick up gamepiecesYes Etc…

11/8/ 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 RequirementWeightA1A2A3 Negotiate course.66Datum-S Have high reach.33Datum+- Easy to operate0Datum+- Total Plus20 Total Minus12 Overall1-2 Weighted Plus.330 Weighted Minus Overall Weighted -.33 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.

11/8/ 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 in the 24x24x24 inch box. You now have a model of the robot.

11/8/ 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.

11/8/ Production Design STEP 1: After testing the prototype, make changes as required. STEP 2: Once the robot is in its final configuration, make detailed drawings of each part.

11/8/ BEST Engineering Mechanics Purpose: Introduce students to the theory of some simple machines. Apply the theory of simple machines to robotics design.

11/8/ 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.

11/8/ Simple Machines 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: 1.LEVERS 2.PULLEYS 3.GEARS We will also discuss the concepts of torque as related to robotics design

11/8/ 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

11/8/ Levers There are 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.

11/8/ Levers

11/8/ 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.

11/8/ Levers W1 D1 = W2 D2 THE LEVER BALANCE EQUATION FOR A FIRST CLASS LEVER IS :

11/8/ 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

11/8/ Levers How many levers can you find in the loader?

11/8/ Block and Tackle PULLEYS / BLOCK AND TACKLE A block and tackle is an arrangement of rope and pulleys that allows you to trade force for distance.

11/8/ 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.

11/8/ 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

11/8/ 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.

11/8/ Gears Gears are generally used for one of three different reasons: 1.To reverse the direction of rotation 2.To increase or decrease the speed of rotation 3.To move rotational motion to a different axis

11/8/ 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).

11/8/ Torque 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 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)

11/8/ 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

11/8/ Torque F = T/r r = T/F 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: If you want to know the radius needed for your motor shaft, the equation becomes:

11/8/ Design Example 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:

11/8/ 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 : ItemWeight (oz)Distance from fulcrum (in) W D (in-oz) Rocket Grabber Arm81080

11/8/ Design Example If we add we get 800 in-oz. This is the right side of the lever equation. The equation becomes: W1 x 5 inches = 800 in-oz Or 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.

11/8/ 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 =.283 inches. This means our shaft needs to have a radius of.283 inches or a diameter of.566 inches. What else could you do to improve things? A counterweight, but not too much or the arm will not lower.