IME 106 LEGO Design

1. IME 106LEGO Design SIUE School of Engineering Fall 2006

2. Robot Any software controlled mechanical device • Actuators and Effectors • Sensors • Controller

3. Industrial Robots Check out the Mitsubishi Robotic Arms in IME CIM lab (EB 1022) !

4. Mobile Robots: Remote control, autonomous, or a mixture of two Go To http://roboti.cs.siue.edu/ to control Elmer, Taz, or Marvin

5. Goals: • Build better robots • Minimize mechanical breakdowns • Build robots that are easy to control • Encourage good design strategy

6. Who Builds Robots? • ECE - designs “the brain”, sensors, actuators & wiring. • ME - designs body, gearing, actuators • IME - designs and integrates controls. • CS – designs robot software All disciplines listed above work together to design/build robots.

7. Robotics made easy? Design Problem - Design and build a robot to vacuum your house. What are some of the challenges?

8. Design Challenges for Mobile Robots • Position - How does robot know where it is (or has been)? • Navigation - How does it navigate around obstacles? • Object Recognition - How does it recognize money, toys, even cats?

9. NEW Design Approaches • "Top-down" design • the process of starting with the goal of the project and then developing a solution. • "Bottom-up" design • the process of first learning about the available materials and then determining what can be done with them. Add “Project Planning” and “Testing” phases to robot design process.

10. Lego RCX Brick

11. RCX Brick withsensors & Motors

12. Lego RCX Brick Display

13. Design Strategy • Incremental • Test components parts as you build them • Drivetrain • Sensors, sensor mounting • Structure • Don’t be afraid to redesign • Internet for design ideas

14. Design Strategy • Drive-train driven • Chassis/structure driven • Modular?

15. Geometry • Three plates = 1 brick in height • 1-stud brick dimensions: exactly5/16” x 5/16” x 3/8” (excluding stud height 1/16”), • This is the base geometry for all LEGO components

16. Structure • Common pitfall when trying to increase mechanical robustness:

17. Structure • The right way:

18. Structure • The right way:

19. A good robot starts with a good foundation. A robot whose body is not structurally sound will be fraught with problems for the designers. The first and most important is that the friction between stacked bricks should not be relied upon for structural strength. Use connector pegs to help create a "skeleton" like the one below. A design like this is both light and strong but usually requires a number of rebuilds to get perfect.

20. Structural supports like the ones shown below can be placed on almost any chassis design. Use this to your advantage. You can get by with fewer legos and have a stronger chassis this way

21. The picture below demonstrates a very structurally sound way of constructing a frame with Legos. The 3 wide connector peg can be used for one of the 3 join points, or an additional 4x1 brick can be used.

22. The structure below demonstrates a very strong design that will not come apart unless you take it apart.

23. Pins and axles • Many various kinds • Pin, friction pin, and long variants • Evil, super friction pin that looks very similar to the normal friction pin • Axles, come in various numbers of studs • Never bend axles! Axles holding wheels or gears should be closely supported on both sides

24. Connector pegs • Black pegs are tight-fitting for locking bricks together. • Grey pegs turn smoothly in bricks for making a pivot

25. Connector Pegs

26. Gears • Transfer rotation from one axle to another • Even number of gears reverses the direction of rotation • The radii determine gear spacing, transferred speed, and power • Inverse relationship between power and speed • There are lots of gear spacing issues beyond the scope of Lego design

27. Gears (continued) • Worm gears • Are effectively one tooth gears • Significant efficiency lost to friction • Since they can’t be back driven, they are great for arms that should hold their position • Some good gear info at • http://www.owlnet.rice.edu/%7Eelec201/Book/legos.html

28. Worm Gears 3 • Pull one tooth per revolution 1 2 • Result is a 24:1 gearbox 4

29. Wheels • Like pulleys and gears, the wheel dimension is key! • Think of the wheel as the final gear in the drive train • Larger wheels will make the robot move faster, with less power • With stability, traction, turning agility, and so on, there are lots of trade-offs in choosing wheels • See the LEGO tire traction tests at: • http://www.philohome.com/traction/traction.htm

30. Drivetrain 40T • LEGO Gears 8T 16T Bevel 1T Worm 24T 24T Crown

31. Robot Basics - Gears • Speed • Torque (climb over obstacles) • Turns Tips - Try different size gear combinations, different types of gears (worm), and different motor placement (rear wheel drive or 4 wheel drive).

32. Seesaw Physics

33. Radius, Torque, and Force on a Gear torque = r x F

35. 3 to 1 reduction

36. Since the forces between the teeth of the two gears are equal in magnitude but act opposite in directions, the torque exerted on the right axle is three times the torque exerted on the left axle (sincethe radii of thee gears differ by a factor of three). Thus this gear system as acts as a “torque converter”, increasing the torque at the expense of decreasing the rate at which the axle turns.

37. 9 to 1 reduction

38. The torque at the “output shaft” is 9 times the torque provided on the left(‘input”) axle. The output shaft will of course spin 9 times slower than the input shaft, but it will be much harder to stall. Have someone grab the output shaft and try to “stall” your fingers as you spin the input axle. It’s not that easy!

39. A three stage gear train with a gear ratio of 27:1

40. Sample Drive Train

41. Lego Axle

42. Gear Rack

43. Axle Joiner

44. Toggle Joint

45. Caster Design

46. Lego Legs

47. Grippers

48. Changing Rotational Axis

49. Changing Rotational Axis

50. Spin x-y-z See more examples at http://constructopedia.media.mit.edu/