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Knight Gear

Knight Gear. Group 6 Rene A. Gajardo Do Kim Jorge L. Morales Siddharth Padhi. Motivation. Heavy course work would require more materials. Posture is affected by the larger amount of things that a student carries. Knight Gear would allow for easier moving of school materials and more.

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Knight Gear

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  1. Knight Gear Group 6 Rene A. Gajardo Do Kim Jorge L. Morales SiddharthPadhi

  2. Motivation • Heavy course work would require more materials. • Posture is affected by the larger amount of things that a student carries. • Knight Gear would allow for easier moving of school materials and more.

  3. Goals and Objectives • Easy to use robot that follows the user using tracking algorithm. • Carry a limited load of materials for the user. • Onboard ultrasound sensors

  4. Specifications

  5. Micro controllers • One central microcontroller • All the heavy computing • Sensors • Motors, and accessories. • Does not need to be very powerful, but enough to be able to handle and process all incoming data • Data is simplified by the smaller, weaker, outer microcontrollers which handle the analog I/O from the devices.

  6. Micro Controller Comparison

  7. Why ATMega 2560 ? • Popular option amongst hobbyist with a large community for assistance • Programmable in C using Arduino • Enough memory for our needs • Allows Knight Gear to fully use all the Pulse Wave Modulation lines that it required for all of the ultrasound sensors and for the motor drivers. • With a 3.3 volt operating voltage, 54 digital I/O pins, 15 of them being PWM, 16 analog inputs, and a large amount of documentation

  8. Pin connections of Mega Pro 3.3

  9. Ultrasonic Proximity Sensor • It engenders high frequency sound waves (above 20,000 Hz), which is incorporated in these sensors, to measure the echo encountered by the detector, and is then received after reflecting back from the target. • This is the basic concept of how Knight Gear will detect and follow its user.

  10. Why PING))) 28015 ? • Precise, non-contact distance measurements. It is relatively easy to connect to microcontrollers • PING))) 28015 measures distance from about 2 cm (0.8 inches) to 3 meters (3.3 yards). • Robot side only receive signals, so cover the transmitter • User side only send signals, so cover the receiver Sensors from Maxbotix Parallax Ping Sensor

  11. Wireless Communication • Wireless communication is needed for localization of the user (which is the main feature of Knight Gear and its top priority). • Some wireless communications looked at were: • Wi-Fi • Bluetooth, and • ZigBee • ZigBee turns out to be the final choice for wireless communication in Knight Gear.

  12. Zigbee • Low cost, low power, wireless mesh network. • The following are the parameters of Zigbee

  13. Zigbeecontd… • Zigbee comes in 2 series. The following is the comparison table between Series 1 and Series 2:

  14. PNP Inverter • We needed to invert a serial signal from low to high using a PNP inverter. • Using the serial out on the XBee and inverting it, we can get a high pulse trigger for the PING sensor

  15. Solar Panel • Increasingly popular • No environmental pollution • No need of burning fossil to generate the electricity • Solar energy is no harm to our environment • Generates electricity with no cost.

  16. Solar Panel contd… • The material of the panel was important due to the different efficiencies of different materials in transforming solar energy into electricity. • There are several different types of solar panel in used today. Some of the solar panels suitable for Knight Gear were the following: • Monocrystalline • Polycrystalline • Amorphous

  17. Solar Panel contd… • Monocrystalline • Most efficient (13-17%) • These are one of the oldest and most sturdy ones • Expensive, require extra time and energy • Polycrystalline • Efficiency (11-15%) • One generally needs a larger polycrystalline solar panel to match the power output of a monocrystalline solar panel. • Less expensive than monocrystalline

  18. Solar Panel contd… • Amorphous • Non-crystalline silicon • Amorphous solar panels are most found in calculators. • The efficiency of amorphous photovoltaic cell is only about 6-8%.

  19. So, which one ? • Polycrystalline solar panels • To build our battery recharger for Knight Gear • Even though this is less efficient than monocrystalline panels • It is very cost effective.

  20. Wheels Configuration • Mechanisms to provide locomotion that is required for the Knight Gear • Differential Drive • Ackerman Drive • Synchronous Drive, and • Omnidirectional Drive

  21. Differential Drive • Wheels rotate at different speeds when turning around the corners • It controls the speed of individual wheels to provide directionality in robot • Correction Factor may be needed to fix the excess number of rotations

  22. Chassis • Custom made chassis designed out of High Density Polyethylene (HDPE). • Most chassis found where either too small or too big for our needs. • Withstands heat • Water-resistant

  23. Chassis contd…

  24. Control Algorithm • We implement a PI controller instead of a PID controller to save memory. • Runs only on current error and integral of previous errors. • Using small constant multipliers to lower the deviation on Knight Gear. • The error is determined by the time it takes for the signal in the users transmitter to reach both sensors on Knight Gear.

  25. Control Algorithm Contd… • The microcontroller pings the radio frequency antenna on the user side transmitter • The user side transmitter then makes its Ping))) sensor emit an ultrasound wave • The ultrasound sensors on the robot pick up on the ultrasonic wave • The sensors return how far away the user is according to each • The data is then sent to the PI Controller

  26. Class Diagram of Knight Gear’s Control Algorithm

  27. Overall code • The robot turns in the direction of the of the sensor which detected the signal first. • The magnitude of the turn and the speed of the robot is calculated by the difference in time in which the sensors detect the user.

  28. Motors • Geared DC Motors • Bigger, more powerful version of DC motor • Used in robotics and other control situations where a small motor with lots of power is needed. • The speed is generally controlled using pulse width modulation of the fixed input voltage. • Can operate in both clockwise and counter clockwise • Speed can be altered by varying the voltage applied to the motor.

  29. Motors cont… Spur DC geared motors (x4) • DC motor combined with a gearbox that work to decrease the motor’s speed but increase the torque • Pololu’s metal gear motor:

  30. Motor controller • Microcontroller can decide the speed and direction of the motor, but provide very limited and small output current. • Motor controller provides enough current and voltage to the motor • However, they cannot control how fast the motor should spin. Therefore motor controller and microcontroller need to work together to make the motors to move properly.

  31. Motor ControllerH Bridge H bridge circuit is commonly used in robotics and other applications to allow the DC motors to run forward and backward 0 1 1 0

  32. Why SN754410 motor controller ? • Quadruple-Half h-bridge circuit -> control up to two motors • Provides sufficient continuous current of 1.1A • Provides peak output current of 2A which is same as the stall current of the motors • No extra diodes are needed that makes easy to implement the circuit • Cost effective

  33. Power source Rechargeable battery selection

  34. Why Nickel Metal Hydride ? • High capacity • Environmentally friendly • NiMH batteries can be charged at any time without affecting battery life • Cost effective

  35. Power System • Motors draw too much of currents ! • Separate power source for motors (9.6V 2200 mAH) • 6V 2100 mAH battery pack is used for other electronic devices • Power Regulation required for other devices • Power dissipation of other electronic devices • (6V– 5V) * 330mA = 0.33W • (5V-3.3V)*55mA = 0.094W • Low dropout linear voltage regulators are used.

  36. Linear Voltage Regulators LM2940 LM3940 • LM2940 LDO regulator for 6V to 5V @ Io =1A • LM3940 LDO voltage regulator for 5V to 3.3V@ Io =1A

  37. Power systempower regulation cont. • Block diagram of power system 6V 2100mAH battery pack Switch 6V -> 5V LDO regulator (LM2940) 5V -> 3.3V LDO regulator (LM3940) Microcontroller Motor driver IC Ultrasonic sensors Xbee RF module (wireless antenna)

  38. Power systempower regulation cont. • Block diagram of power system cont.

  39. Battery life test • 6V battery pack (robot side) • 2100 mAH / 330 mA = 4.45 Hours • 9.6V battery pack (robot side) • Free run -> 2200 mAH/320 mA = 4.81 hours • With 10 lb -> 2200 mAH/1360 mA = • 1.13 hours • With 20 lb -> 2200 mAh/3360 mA =0.46hours

  40. Xbee Testing • This figure shows how Xbee is programmed to give us the ID, high and the low for the signal which is shared by the sender and receiver.

  41. Xbee Testing contd…. • This figure shows that the Xbee is communicating successfully.

  42. PI Controller Testing • The values of the ultrasound sensors are printed in the com • Components of the PI controller are then printed • Also the direction (left or right) of the turn is printed • Finally the adjusted speed of the motors is printed

  43. Technical Problems while building Knight Gear • Inconsistency in devices • Ultrasonic sensors • Faulty and burned out sensors • Weight sensor • Xbee Antennas

  44. Questions?

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