1. Presented by University of Miami
SECME Mousetrap Car
Presented by University of Miami
Originally prepared by: Brad Nunn
BSIE Purdue University Program Manager - Citrix
10/1/2005
UPDATED: September 2011

2. Performance Rules
Refer to Mousetrap Car Construction and Operation Rules
Bail
don’t cut or remove or add to it
OK to straighten

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

4. Desired Outcomes
A small car that travels 2500 cm quickly and doesn’t weigh much
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

5. Wheel Design
Wheel diameter

6. Wheel Design Wheel Construction
Rubber bands around wheels for traction

7. Axle Design Axle diameter and mechanical advantage
Simple ratio of diameters
For distance cars use the smallest axle that provides sufficient mechanical advantage to drive a large wheel
Glue at least one drive wheel to axle

8. Two Step Axle
At start, use the thick part of the axle for increased torque
Once rolling, use the thin part of the axle for more distance

9. Wheel and Axle Design Minimize friction loss
Lubrication – silicone or graphite powder – WD-40 not recommended

10. Construction Techniques
Releasing the drive string from an axle to allow coasting
Being able to disconnect drive strings on either end might make it easier to wind a car with a more complex pulley or gear drive

11. Construction Techniques
Creating an axle hook on a solid shaft

12. Construction Techniques
Simple, easy to tie knots
Surgeon’s Loop – useful for making a loop at the end of a string

13. Another Axle Hook
Plastic wire tie

14. Prepping the Trap Parts of the trap that are OK to remove
Don’t cut the bail!

15. Super Glue – Gel Control
Safety first! (immediate clean up with soap and water, goof-off, nail polish remover)
Gel Control formula isn’t runny – a little goes a long way (and dries faster)

16. Making the Frame
Align the axle holes
Not the ends of the side rails

17. Prototyping What problems were encountered?
What solutions were effective?
What can be done for further improvement?

18. Maximizing Axle Rotations
Options to control torque, acceleration, speed, and number of rotations
Levers
Pulleys
Gears

19. Use of Levers
Length of lever vs. torque

20. Use of Levers Where do they go?
Locate the pivot point of the lever as far as possible from the axle to maximize the string that is pulled from the axle
Additional lever length that extends beyond the axle reduces torque and only pulls marginally more string
Only 50% of the additional lever length will translate into pulling more string
The additional lever length will potentially extend the overall length of the car by 100% of the additional lever length

21. Use of Levers
Position of lever arm for max torque at startup

22. Use of Levers Torque (and acceleration) due to use of a lever
A simple demonstration of levers and torque

23. Use of Levers
A good distance car

24. Cars with Levers

25. Cars with Levers

26. Cars with Levers

27. Car with Pulleys

28. Car with Pulleys
A simple pulley demonstration…

29. Use of Gears Why are gears generally used?
Transmit torque from one shaft to another
Increase or decrease the speed of rotation
Reverse the direction of rotation
Why are gears useful in this application
Small
Lightweight
Significant multiplications possible
Enables unmodified mousetrap bail

30. Gears
Gears
A simple gear demonstration…

31. Gear Trains Compound gear trains using double spur gears
A simple gear train demonstration…

32. Cars with Gears

33. Cars with Gears

34. Cars with Gears

35. Cars with Gears

36. Cars with Gears

37. Discuss limitations What are the limitations with the use of a lever?
What are the limitations with the use of pulleys?
What are the limitations with the use of gears?

38. Optimization Use rubber bands on the wheel surface for traction?
Reduce size and weight?
Use axle bushings to reduce friction?
Use guides/bushings for string alignment?
Maintain alignment of axles and wheels?
Maintain alignment of shafts/pulleys/gears?
Use the space between the wheels?
Use the space above and below the trap?
Figure out a faster way to wind it up?
Lube the axles with powdered graphite?

39. Drawing Guidelines Views – Front, Top, Side (RH rule) Scale
Hidden lines
Center lines
Dimension lines
Identify components
Title Block
Engineering paper = Vellum

40. Most important
Have Fun!