1. Rubber Band Car Student Seminar Brad Nunn BSIE Purdue University Program Manager - Citrix Feb 25, 2006

2. Todays Activities Typical rubber band cars Typical rubber band cars Propeller based designs Propeller based designs Review competition rules Review competition rules Component design Component design Other designs Other designs Build a kit Build a kit

3. Typical Rubber Band Cars

7. Propeller Rubber Band Cars

8. Propeller Rubber Band Kit

9. Propeller Rubber Band Cars

11. Propeller Rubber Band Kit

12. Review Rules Refer to Go Cart Competition Construction and Operating Rules Refer to Go Cart Competition Construction and Operating Rules

13. Review Scoring F = 1 D 2 * W L W L Consider tradeoffs - (D+L squared)Consider tradeoffs - (D+L squared)

14. Terminology Potential to kinetic energy transfer Potential to kinetic energy transfer Torque Torque Acceleration Acceleration Speed Speed Momentum Momentum Friction Friction

15. Desired Outcomes A small car that travels 2500 cm and doesnt weigh much A small car that travels 2500 cm and doesnt weigh much A gradual transfer of energy that has just enough torque to establish motion A gradual transfer of energy that has just enough torque to establish motion A sustained transfer of energy that delivers sufficient momentum to cover the distance A sustained transfer of energy that delivers sufficient momentum to cover the distance

16. Competitive Benchmarks 2004-5:2004-5: 2003-4:2003-4:

17. Propeller Design Airscrew - push or pull Airscrew - push or pull Left hand or right hand when facing air flow Left hand or right hand when facing air flow Airfoil shape like a wing Airfoil shape like a wing

18. Rubber Bands All shapes and sizes All shapes and sizes Experiment! Experiment!

19. Component Design Low inertia and light weight Low inertia and light weight

20. Wheel and Axle Design Minimize friction loss Minimize friction loss

21. Lubrication Graphite powder Graphite powder Silicone spray (WD-40 is not recommended) Silicone spray (WD-40 is not recommended)

22. Creative thinking What advantage is there to winding a rubber band compared to stretching it? What advantage is there to winding a rubber band compared to stretching it? Are there other ways to use a rubber band that is wound up? Are there other ways to use a rubber band that is wound up?

23. KNEX Kit – Rubber Band Roller

24. Dixie Roller

25. Dixie cup Axles Dixie cup Axles Rubber Band Rubber Band Construction tool – fishing line Construction tool – fishing line CD Wheels CD Wheels Washer, grommet, bead bearing Washer, grommet, bead bearing Drive Lever Drive Lever Driven nail or paper clip Driven nail or paper clip Tape Tape

26. Design Challenges How do you make one wheel drive and the other one follow? How do you make one wheel drive and the other one follow? How do you nest the rubber band inside the axle so it doesnt rub? How do you nest the rubber band inside the axle so it doesnt rub? Little torque so the friction in the bearing must be kept to a minimum Little torque so the friction in the bearing must be kept to a minimum Little torque so the car must be light Little torque so the car must be light Construction tool Construction tool

27. Iterative Design Prototype Prototype Measure and record performance Measure and record performance Tweak the design (farther, shorter, lighter) Tweak the design (farther, shorter, lighter) Iterate Iterate Replicate Replicate Calculate Calculate Celebrate Celebrate

28. Design optimization Frictionless bearing Frictionless bearing Frictionless unwinding of the rubber band Frictionless unwinding of the rubber band Thick or thin rubber band Thick or thin rubber band Length of the lever arm Length of the lever arm How many wheels How many wheels Wheel materials for low inertia Wheel materials for low inertia

29. Todays Kit

30. Tools for cutting, drilling, and assembly

31. Aligning the Frame Align the axle holes before gluing railsAlign the axle holes before gluing rails Not the ends of the side railsNot the ends of the side rails

32. Gluing the Frame Use Gel Control Super Glue - NOT the Liquid (too watery)Use Gel Control Super Glue - NOT the Liquid (too watery) Less is more…Less is more…

33. Problems / Solutions What problems were encountered? What problems were encountered? What solutions were effective? What solutions were effective? What can be done for further improvement? What can be done for further improvement?

34. Optimization Enough torque to get moving? Enough torque to get moving? Multiple propellers? Multiple propellers? Travel straight? Travel straight? How many winds? How many winds? Too many winds? Too many winds? Smaller? Smaller? Farther? Farther? Lighter? Lighter?

35. Most important Have Fun! Have Fun!