Introduction to Robot Subsystems

1. Presented By: Lynbrook Robotics, Team 846 John Chai, David Liu, Aashish Sreenharan, Michael Wachenschwanz, and Toshi Tochibana Available online at lynbrookrobotics.com Tech > Resources > “WRRF Presentations” Introduction toRobot Subsystems

2. Talk Outline • Pneumatics • Sensors and Electronics • Electrical Components • Robot Drive Train Design

3. Michael Wachenschwanz and Toshi Tachibana present… Pneumatics

4. Pneumatics • Can you feel the pressure • Pneumatics is the use of pressurized air to achieve mechanical movement. • Air tends to move from high pressure to low pressure • Important note: There is no such thing as a negative pressure

5. Compressor • Where it all starts • The compressor takes air from the surrounding atmosphere and compacts it via pistons. • Comes with a release valve attached to it

6. Pressure Switch • Better safe than sorry • Safety Mechanism • Turns the compressor off at 120 psi and turn it back on at 115 psi

7. Tubing and Fittings • Keeping connected

8. Tank • The more the merrier • Tanks allows more air in the system. • When air is lost, psi drop is mitigated by larger tanks

9. Plug Valves • Done for the day • Releases all the compressed air in the system. • Must be release manually • Be sure to release the stored air when done with the system

10. Regulator • Stay in control • Regulators regulate the pressure. • Uses air from input to maintain the pressure of the output • Usually kept at 60 psi for FIRST competitions

11. Electric Valves • Handling the pressure • Single and double solenoid valves are used • Controlled by the control board via electricity • Double solenoids exposes one port to pressure and the other to the surrounding atmosphere

12. Actuators • Use the force • Actuators convert the difference in air pressure to mechanical motion • Linear actuators, or cylinders, are the more common actuators. For the competition, they come in 3 bore sizes: ¾, 1 ½, and 2 inches • Rotary actuators are also allowed

13. Notes on Actuators • Force = Pressure x Area • Area= pi x squared radius • radius = diameter (bore) / 2 • Retracting force is less than extending force

14. Flow Rate Valve • Control the flow • Simply a fitting that widen or narrows the flow path of the air • Used to slow the air movement, thus slowing mechanical movement • Does not take away from the net force. • Must be adjusted manually

15. Aashish Sreendharan presents… Electrical Components

16. Motors - CIM • Used to drive robot

17. Motors – Van Door • Powers doors on mini-vans

18. Motors – Fisher Price Motors • Used on Fisher Price Toys • Made by Johnson Electric or Mabuchi.

19. Power Distribution Diagram

20. Power Distribution Explained • Battery (12V, Lead-Acid Battery)‏ • Main Circuit Breaker • Power Distribution Block • Components: • Victors (ESC)‏ • Spikes • Controller

21. Power Distribution Picture

22. Spikes Relays • Control direction. • Two single pole, double throw relays. • Forward = 12V to M+ and M- grounded. • Reverse = 12V to M- and M+ grounded. • Neutral = M+ and M- grounded, or 12V applied. • H-Bridge.

23. H - Bridge • 4 Switches. • Combination of switches on to drive motor.

24. Electronic Speed Controllers • Known as: Victors. • Use Victor 884's. • Control speed and direction. • Uses PWM.

25. Pulse Width Modulation • Two Types: • Power Delivery • Control Signal

26. David Liu presents… Sensors and Electronics

27. Pulse Width Modulation • Two types • Power transfer • Between speed controller and motor • Signaling • Between controller and speed controller

28. Potentiometers (Pots) • Sensor for measuring position: • Rotation, distance, etc.

29. Potentiometers Simplest type: Slider Acts as a Voltage Divider Slider is connected to output. +5V +5V +5V 0V 5V 2.5V 4.2V 3.3V Output 10 KΩ GND GND 9 KΩ 3 KΩ GND 3.5V 0.5V 7 KΩ 1 KΩ

30. Reading the Value • Analog voltage level • Analog-to-Digital Converter (ADC) • Converts to number • 0-1023 for 10-bit ADC

31. Pots: Uses • Sense position: e.g. lift • How to sense the lift position? • Travel length is 6 feet • No linear pot long enough • Rotary Pots

32. Pots • Multi-turn pot: • Screw with wiper resting on threads • Usually 3, 5, or 10 turns • Alignment is important! • Continuous rotation: use encoder

33. Optical Encoders to controller to controller Optical Sensor Optical Sensor

34. Optical Encoders to controller to controller Optical Sensor Optical Sensor

35. Optical Encoders • Determining Distance Travelled • Count pulses • Example: • Given: Encoder stripes = 128 • Given: Wheel diameter = 6” • Given: counted 85 pulses = 12.52 inches

36. Optical Encoders • Determining Speed • A. Count pulses per interval • Example: in 1 second, 256 pulses. Speed = 2 revolutions/second • Inaccurate and slow • Analogy: On a bicycle • Mark the wheel • Count passes in a minute

37. Optical Encoders • Determining Speed • B. Measure time between pulses • Example: time between two pulses = 3.9ms • Only requires observing two consecutive pulses

38. Ultrasonic Sensors • Determine distance • Send pulse of sound • Measure time until echo

39. Johnathan Chai presents… Robot Drive Train Design

40. Required Capabilities • Speed • Point-to-point Movement • Turning in place • Controllable

41. Skid/Tank Steering • Power left and right sides independently • Joystick control

42. Ackerman Steering • Limited turning due to geometry Team 34’s Design on Chief Delphi

43. 4 Wheels • Fast but slides on ground when turning • Wide vs. Long base

44. 6 Wheels • Center wheels dropped about a quarter inch • “Rock” on center when turning

45. Swerve Drive • Maneuverability • Time costs Craig Hickman’s Design on Chief Delphi

46. Wheels • Rubber • Roughtop • Mecanum • Omni-wheels • Tank Treads AndyMark Wheels

47. Conclusion

48. Conclusion • Covered major components of FIRST robots • Slides available at lynbrookrobotics.com • Tech > Resources > “WRRF Presentations”